The paradigm of materials science and engineering is on the verge of a significant transition in this early 21st century. 
The characteristics of the new trend can be summarized as the increased importance of interdisciplinary research and the convergence of multiple areas. Our research group focuses on the creation of new biomaterials by the hybridization of bio-organic and inorganic materials. In the past decades, biomaterials have been extensively studied mostly for medical applications, such as implantation and drug delivery, due to their excellent biocompatibilities. Nowadays, biomaterials further expand their boundaries to various functionalities, including electronics and energy devices. In particular, we are interested in the development of functional biomaterials through the inspiration from nature. Biological systems in nature have solved the problem of designing and synthesizing functional materials with novel nanostructures through the evolution over millions of years. The coupling of biological inspiration with nano-scale design can lead to enhanced performance and properties of materials for evermore demanding applications to energy conversion/storage (e.g., artificial photosynthesis, plastic batteries) and healthcare (e.g., peptide self-assembly, amyloid theranostics, wearable bioelectronics). 


Photobiocatalytic Materials and Platforms for Artificial Photosynthesis

Green plants operate elaborate photosystems in a beautiful harmony to convert sunlight into chemical energy through photoinduced electron transfer. In the context of solar chemical synthesis, natural photosynthesis that converts solar energy into reduced organic chemicals remains a target model for researchers to realize artificial photosynthesis. Natural photosystems hint at the design of solar energy conversion in connection to redox enzymatic catalysis. Biocatalytic artificial photosynthesis grafts solar energy conversion with redox enzymatic catalysis by mimicking natural photosynthesis through an integral coupling of photocatalysis and biocatalysis cycles with the ultimate goal of utilizing solar energy for the synthesis of value-added chemicals and fuels. We aim for the development of sustainable and efficient photobiocatalytic platforms through direct and indirect transfer of photo-induced electrons to redox enzymes.


Nature-Inspired Design of Carbo-Organic Materials for Plastic Batteries

In human history, interdisciplinary research on fundamental processes occurring in nature has provided insights into technology innovation. For example, highly optimized light-harvesting systems in nature inspired the development of efficient and cost-effective organic solar cells. Biological metabolism comprises energy transduction machineries that operate by a series of redox-active components for storing energies from nutrients, which are transduced into high energy intermediates for cellular works such as chemical synthesis, transport, and movement. The natural redox reactions in biological metabolism have inspired us to design high performance energy storage materials towards the development of plastic batteries. Naturally occurring redox chemicals are promising alternatives to conventional inorganic electrode materials based on transition metal oxides. The minimal environmental footprint as well as distinctive material properties, such as light weight, flexibility, and chemical tunability, make them beneficial as a green electrode material in rechargeable batteries.


Self-Assembled Biomaterials and Photodynamic Modulation of Amyloidosis

Self-assembly is centrally important in life and has a great potential for fabricating novel materials as well. The self-assembly of peptides into amyloid aggregates is a pathological hallmark of many neurodegenerative diseases. Recently, we have succeeded in the modulation of Alzheimer’s beta-amyloid peptide aggregation and toxicity by using excited electrons generated from photosensitizing materials. Considering that medical use of light is considered as an attractive therapeutic strategy due to the temporal and spatial controllability and reduced side effects, we envision that our unique approach may provide a potential and alternative therapeutic solution for treating Alzheimer's and other protein misfolding-related diseases using light. From an engineering point of view, the self-assembly of peptide-based building blocks into nanostructures is an attractive route for fabricating novel bio-inspired materials because of their capacity for molecular recognition and functional flexibility as well as environmental compatibility. Our research group focuses on the fabrication, characterization, and applications of peptide nanostructures.



Design of Biosensing Platforms for Alzheimer's Disease Theranostics

The development of an efficient biosensing platform has attracted high interests in recent years due to its importance for healthcare, environmental monitoring, defense, and many other areas. We are interested in the application of nanomaterials (e.g., nanoparticles, nanowires, nanogels, carbon nanotubes, graphene) as a sensing platform to the development of biocatalytic and bioaffinity sensors, in particular for the diagnostics of amyloid diseases. When materials become small in size (typically less than 100 nm), they exhibit unique electronic, photonic, and catalytic properties that are different from those of bulk materials. The integration of nanomaterials with biological recognition components (e.g., enzymes, antibodies, DNA) that display unique recognition, catalytic, and inhibition properties is expected to yield novel hybrid nanobiomaterials for biosensors and bioelectronics. Currently, we are developing electrochemical and photoelectrochemical sensing platforms for rapid detection of Alzheimer's disease markers such as beta-amyloid and tau proteins in human plasma.


J. Kim, S. H. Lee, F. Tieves, C. E. Paul, F. Hollmann, and C. B. Park* "TBA (under embargo)" Science Advances, vol. ( ), pp. ( ), 2019
S. K. Kuk, K. Gopinath, R. K. Singh, T-D. Kim, Y. Lee, W. S. Choi, J-K. Lee, and C. B. Park "NADH-free electroenzymatic reduction of carbon dioxide by conductive hydrogel-conjugated formate dehydrogenase" ACS Catalysis, vol. ( ), pp. ( ), 2019
S. K. Kuk, Y. Ham, K. Gopinath, P. Boonmongkolras, Y. Lee, Y. W. Lee, S. Kondaveeti, C. Ahn, B. Shin, J-K. Lee, S. Jeon, C. B. Park "Continuous 3D titanium nitride nanoshell structure for solar-driven unbiased biocatalytic CO2 reduction" Advanced Energy Materials, vol. ( ), pp. ( ), 2019
S. Willot, E. Fernandez-Fueyo, F. Tieves, M. Pesic, M. Alcalde, I. Arends, C. B. Park, F. Hollmann "Expanding the spectrum of light-driven peroxygenase reactions" ACS Catalysis, vol. 9, pp. 890–894, 2019 [Link]
Y. W. Lee, P. Boonmongkolras, E. J. Son, J. Kim, S. H. Lee, S. K. Kuk, J. W. Ko, B. Shin, and C. B. Park "Unbiased biocatalytic solar-to-chemical conversion by FeOOH/BiVO4/perovskite tandem structure" Nature Communications, vol. 9, pp. 4208, 2018 [Link]
J. Kim, S. H. Lee, F. Tieves, D. S. Choi, F. Hollmann, C. E. Paul, and C. B. Park "Biocatalytic C=C bond reduction through carbon nanodot-sensitized regeneration of NADH analogues" Angewandte Chemie International Edition, vol. 57, pp. 13825-13828, 2018 [Link]
K. Kim, S. H. Lee, D. S. Choi, and C. B. Park* "Photoactive bismuth vanadate structure for light-triggered dissociation of Alzheimer β-amyloid aggregates" Advanced Functional Materials, vol. 28, pp. 1802813, 2018 [Link]
D. H. Nam, J. Z. Zhang, V. Andrei, N. Kornienko, N. Heidary, A. Wagner, K. Nakanishi, K. P. Sokol, B. Slater, I. Zebger, S. Hofmann, J. C. Fontecilla-Camps, C. B. Park, and E. Reisner "Solar water splitting with a hydrogenase integrated in photoelectrochemical tandem cells" Angewandte Chemie International Edition, vol. 57, pp. 10595-10599, 2018 [Link]
S. H. Lee, D. S. Choi, S. K. Kuk, C. B. Park "Photobiocatalysis: Activating redox enzymes by direct or indirect transfer of photoinduced electrons" Angewandte Chemie International Edition, vol. 57, pp. 7958-7985, 2018 [Link]
E. J. Son, S. H. Lee, S. K. Kuk, M. Pesic, D. S. Choi, J. W. Ko, K. Kim, F. Hollmann, C. B. Park "Carbon nanotube-graphitic carbon nitride hybrid film for flavoenzyme-catalyzed photoelectrochemical cell" Advanced Functional Materials, vol. 28, pp. 1705232, 2018 [Link]
C. B. Park "Author profile: Chan Beum Park" Angewandte Chemie International Edition, vol. 57, pp. 382, 2018 [Link]
D. S. Choi, Y. Ni, E. Fernandez-Fueyo, M. Lee, F. Hollmann, C. B. Park "Photoelectroenzymatic oxyfunctionalization on flavin-hybridized carbon nanotube electrode platform " ACS Catalysis, vol. 7, pp. 1563-1567, 2017 [Link]
S. H. Lee, D. S. Choi, M. Pesic, Y. W. Lee, C. E. Paul, F. Hollmann, C. B. Park "Cofactor-free, direct photoactivation of enoate reductases for asymmetric reduction of C=C bonds" Angewandte Chemie International Edition, vol. 56, pp. 8681-8685, 2017 [Link]
S. K. Kuk, R. K. Singh, D. H. Nam, R. Singh, J-K. Lee, C. B. Park "Photoelectrochemical reduction of carbon dioxide to methanol via a highly efficient enzyme cascade" Angewandte Chemie International Edition, vol. 56, pp. 3827–3832, 2017 [Link]
J. H. Park, S. H. Lee, G. S. Cha, D. S Choi, D. H. Nam, J. H Lee, J-K Lee, C-H Yun, K. J. Jeong, C. B. Park "Cofactor-free light-driven whole-cell cytochrome P450 catalysis" Angewandte Chemie International Edition, vol. 54, pp. 969-973, 2015 [Link]
M. Lee, J. U. Kim, K. J. Lee, S. Ahn, Y-B. Shin, J. Shin, C. B. Park "Aluminum nanoarrays for plasmon-enhanced light-harvesting" ACS Nano, vol. 9, pp. 6206-6213, 2015 [Link]
B. I. Lee, S. Lee, Y. S. Suh, J. S. Lee, A-K Kim, O-Y Kwon, K. Yu, C. B. Park. "Photo-excited porphyrins as a strong suppressor of beta-amyloid aggregation and synaptic toxicity" Angewandte Chemie International Edition, vol. 54, pp. 11472-11475, 2015 [Link]
J. H. Kim, M. Lee, C. B. Park*. "Polydopamine as a biomimetic electron gate for artificial photosynthesis" Angewandte Chemie International Edition, vol. 53, pp. 6364-6368, 2014 [Link]
M. Lee, J. U. Kim, J. S. Lee, B. I. Lee, J. Shin, C. B. Park*. "Mussel-inspired plasmonic nanohybrids for light harvesting" Advanced Materials, vol. 26, pp. 4463-4468, 2014 [Link]
J. Hong, M. Lee, B. Lee, D-H. Seo, C. B. Park*, K. Kang* "Biologically inspired pteridine redox centers for rechargeable batteries" Nature Communications, vol. 5, pp. 5335, 2014 [Link]
M. Lee, J. Hong, D-H. Seo, D. H. Nam, K. T. Nam, K. Kang*, C. B. Park*. "Redox cofactor from biological energy transduction as energy-storage chemical" Angewandte Chemie International Edition, vol. 52, pp. 8322-8328, 2013 [Link]
M. Lee, J. Hong, H. Kim, H. Lim, S. B. Cho, K. Kang*, and C. B. Park*. "Organic nanohybrids for fast and sustainable energy storage" Advanced Materials, vol. 26, pp. 2558-2565, 2013 [Link]
J. S. Lee, H-A. Joung, M-G. Kim, C. B. Park "Graphene-based chemiluminescence resonance energy transfer for homogeneous immunoassay " ACS Nano, vol. 6, pp. 2978-2983, 2012 [Link]
J. H. Kim, M. Lee, J. S. Lee, C. B. Park*. "Self-assembled light-harvesting peptide nanotubes for mimicking natural photosynthesis" Angewandte Chemie International Edition, vol. 51, pp. 517-520, 2012 [Link]
J. S. Lee, K. H. You, C. B. Park*. "Highly photoactive, low band-gap titanium dioxide nanoparticles wrapped by graphene" Advanced Materials, vol. 24, pp. 1084-1088, 2012 [Link]
S. Kim, C. B. Park*. "Bio-inspired synthesis of minerals for energy, environment, and medicinal applications" Advanced Functional Materials, vol. 23, pp. 10-25, 2012 [Link]
J. S. Lee, I. Yoon, J. Kim, H. Ihee, B. Kim, C. B. Park*. "Semiconducting peptide nanowires self-assembled in vapor phase" Angewandte Chemie International Edition, vol. 50, pp. 1164-1167, 2011 [Link]
S. Kim, S. H. Ku, S. Y. Lim, J. H. Kim, and C. B. Park*. "Graphene-biomineral hybrid materials" Advanced Materials, vol. 23, pp. 2009-2014, 2011 [Link]
J. Ryu, S. H. Lee, D. H. Nam, and C. B. Park* "Rational design and engineering of quantum-dot sensitized titanium dioxide nanotube arrays for artificial photosynthesis" Advanced Materials, vol. 23, pp. 1883-1888, 2011 [Link]
J. Ryu, S.-W. Kim, K. Kang, C. B. Park "Synthesis of diphenylalanine/cobalt oxide hybrid nanowires and their application to energy storage" ACS Nano, vol. 4, pp. 159-164, 2010 [Link]
J. Ryu, S-W. Kim, K. Kang, C. B. Park*. "Mineralization of self-assembled peptide nanofibers for rechargeable Li-ion batteries" Advanced Materials, vol. 22, pp. 5537-5541, 2010 [Link]
J. Ryu, S. H. Ku, H. Lee, C. B. Park*. "Mussel-inspired polydopamine coating as a universal route to hydroxyapatite crystallization" Advanced Functional Materials, vol. 20, pp. 2132-2139, 2010 [Link]
J. Ryu, C. B. Park*. "Synthesis of diphenylalanine/polyaniline core/shell conducting nanowires by peptide self-assembly" Angewandte Chemie International Edition, vol. 48, pp. 4820-4823, 2009 [Link]
J. Ryu, S. Y. Lim, C. B. Park*. "Photoluminescent peptide nanotubes" Advanced Materials, vol. 21, pp. 1577-1581, 2009 [Link]
H-K Song, S. H. Lee, K. Won, J. H. Park, J. K. Kim, H. Lee, S-J Moon, D. K. Kim, C. B. Park*. "Electrochemical regeneration of NADH enhanced by platinum nanoparticles" Angewandte Chemie International Edition, vol. 47, pp. 1749-1752, 2008 [Link]
J. Ryu, C. B. Park*. "High-temperature self-assembly of peptides into vertically well-aligned nanowires by aniline vapor" Advanced Materials, vol. 20, pp. 3754-3758, 2008 [Link]
T. H. Han, J. Kim, J. S. Park, C. B. Park, H. Ihee*, S. O. Kim*. "Liquid crystalline peptide nanowires" Advanced Materials, vol. 19, pp. 3924-3927, 2007 [Link]
M. Y. Lee, C. B. Park, J. S. Dordick*, D. S. Clark*. "Metabolizing enzyme toxicology assay chip (MetaChip) for high-throughput microscale toxicity analyses" Proc. Natl. Acad. Sci. USA, vol. 102, pp. 983-987, 2005 [Link]
Q. Li, J-S. Lee, C. Ha, C. B. Park, G. Yang, W. B. Gan, Y-T. Chang*. "Solid phase synthesis of styryl dye library and its application to amyloid sensors" Angewandte Chemie International Edition, vol. 43, pp. 6331-6315, 2004 [Link]

J. Kim, C. B. Park*. "Shedding light on biocatalysis: photoelectrochemical platforms for solar-driven biotransformation" Current Opinion in Chemical Biology, vol. 49, pp. 122-129, 2019 [Link]
B. I. Lee, Y. J. Chung, C. B. Park*. "Photosensitizing materials and platforms for light-triggered modulation of Alzheimers beta-amyloid self-assembly" Biomaterials, vol. 190-191, pp. 121-132, 2019 [Link]
S. H. Lee, D. S. Choi, S. K. Kuk, C. B. Park*. "Photobiocatalysis: Activating redox enzymes by direct or indirect transfer of photoinduced electrons" Angewandte Chemie International Edition, vol. 57, pp. 7958-7985, 2018 [Link]
E. J. Son, J. H. Kim, K. Kim, C. B. Park*. "Quinone and its derivatives for energy harvesting and storage materials" Journal of Materials Chemistry A, vol. 4, pp. 11179-11202, 2016 [Link]
S. Kim, J. H. Kim, J. S. Lee, C. B. Park*. "Beta-sheet-forming, self-assembled peptide nanomaterials towards optical, energy, and healthcare applications" Small, vol. 11, pp. 3623-3640, 2015 [Link]
J. H. Kim, D. H. Nam, C. B. Park*. "Nanobiocatalytic assemblies for artificial photosynthesis" Current Opinion in Biotechnology, vol. 28, pp. 1-9, 2014 [Link]
S. H. Lee, J. H. Kim, C. B. Park*. "Coupling photocatalysis and redox biocatalysis toward biocatalyzed artificial photosynthesis" Chemistry - A European Journal, vol. 19, pp. 4392-4406, 2013 [Link]
S. H. Ku, M. Lee, C. B. Park*. "Carbon-based nanomaterials for tissue engineering" Advanced Healthcare Materials, vol. 2, pp. 244-260, 2013 [Link]
S. Kim, C. B. Park*. "Bio-inspired synthesis of minerals for energy, environment, and medicinal applications" Advanced Functional Materials, vol. 23, pp. 10-25, 2013 [Link]
B. Boonyaratanakornkit, C. B. Park, D. S. Clark*. "Pressure effects on intra- and inter-molecular interactions within proteins" Biochimica et Biophysica Acta, vol. 1595, pp. 235-249, 2002 [Link]
[162] J. Kim, S. H. Lee, F. Tieves, C. E. Paul, F. Hollmann, and C. B. Park*
TBA (under embargo)

Science Advances, vol.( ), pp.( ), 2019

[161] D. Wang, J. Jang, K. Kim, J. Kim, and C. B. Park
“Tree to bone”: Lignin-polycaprolactone nanofibers for hydroxyapatite biomineralization

Biomacromolecules , vol.( ), pp.( ), 2019


Bone contains an organic matrix composed of aligned collagen fibers embedded with nano-sized inorganic hydroxyapatite (HAp). Many efforts are being made to mimic the natural mineralization process and create artificial bone scaffolds that show elaborate morphologies, excellent mechanical properties, and vital biological functions. This study reports a newly discovered function of lignin mediating the formation of human bone-like HAp. Lignin is the second most abundant organic material in nature, and it exhibits many attractive properties for medical applications, such as high durability, stability, antioxidant and antibacterial activities, and biocompatibility. Numerous phenolic and aliphatic hydroxyl moieties exist in the side chains of lignin, which donate adequate reactive sites for chelation with Ca2+ and the subsequent nucleation of HAp through co-precipitation of Ca2+ and PO43-. Our results underpin the expectations for lignin-based biomaterials towards future biointerfaces and hard tissue engineering.

[160] S. K. Kuk, K. Gopinath, R. K. Singh, T-D. Kim, Y. Lee, W. S. Choi, J-K. Lee, and C. B. Park
NADH-free electroenzymatic reduction of carbon dioxide by conductive hydrogel-conjugated formate dehydrogenase

ACS Catalysis, vol.( ), pp.( ), 2019


The electrocatalytic reduction of CO2 under low overpotential and mild conditions using redox enzyme is a propitious route for carbon capture and conversion. Here, we report bioelectrocatalytic CO2 conversion to formate by conjugating a strongly CO2-reductive, W-containing formate dehydrogenase from Clostridium ljungdahlii (ClFDH) to conductive polyaniline (PANi) hydrogel. The ClFDH in the hybrid electrode successfully gained electrons directly from PANi and exhibited high capability for electroenzymatic conversion of CO2 to formate at low overpotential without NADH. We describe a potential electron transfer pathway in the PANi-ClFDH bioelectrode based on multiple spectroscopic analyses and a QM/MM-based computational study. The 3D-nanostructured PANi hydrogel facilitated rapid electron injection to the active site of ClFDH. In the absence of NADH, the PANi-ClFDH electrode showed stable CO2-to-formate transformation at overpotential as low as 40 mV, with 1.42 μmol h-1 cm-2 conversion rate, 92.7% faradaic efficiency, and 976 h-1 turnover frequency.

[159] S. K. Kuk, Y. Ham, K. Gopinath, P. Boonmongkolras, Y. Lee, Y. W. Lee, S. Kondaveeti, C. Ahn, B. Shin, J-K. Lee, S. Jeon, and C. B. Park
Continuous 3D titanium nitride nanoshell structure for solar-driven unbiased biocatalytic CO2 reduction

Advanced Energy Materials, vol.( ), pp.( ), 2019


The Z-scheme-inspired tandem photoelectrochemical (PEC) cells have received attention as a sustainable platform for solar-driven CO2 reduction. Here, we report on continuously 3D-structured, electrically conductive titanium nitride nanoshells (3D TiN) for biocatalytic CO2-to-formate conversion in a bias-free tandem PEC system. The 3D TiN exhibited a periodically porous network with high porosity (92.1%) and conductivity (6.72 × 104 S m-1), which allowed for high enzyme loading and direct electron transfer (DET) to the immobilized enzyme. We found that the W-containing formate dehydrogenase from Clostridium ljungdahlii (ClFDH) on the 3D TiN nanoshell was electrically activated through DET for CO2 reduction. At a low overpotential of 40 mV, the 3D TiN-ClFDH stably converted CO2 to formate at a rate of 0.34 μmol h-1 cm-2 and a faradaic efficiency (FE) of 93.5%. Compared to a flat TiN-ClFDH, the 3D TiN-ClFDH showed a 58 times higher formate production rate (1.74 μmol h-1 cm-2) at 240 mV of overpotential. Lastly, we succeeded in assembling a bias-free biocatalytic tandem PEC cell that converted CO2 to formate at an average rate of 0.78 μmol h-1 and a FE of 77.3% only using solar energy and water.

[158] S. K. Kuk, J. Jang, H. J. Han, E. Lee, H. Oh, H. Y. Kim, J. Jang, K. T. Lee, H. Lee, Y. S. Jung, C. B. Park*, and B. Bae*
Siloxane-encapsulated upconversion nanoparticles hybrid composite with highly stable photoluminescence against heat and moisture

ACS Applied Materials & Interfaces, vol.( ), pp.( ), 2019


We report a siloxane-encapsulated upconversion nanoparticle hybrid composite (SEUCNP) that exhibits excellent photoluminescence (PL) stability for over 40 days even at elevated temperature, in high humidity, and in harsh chemicals. The SE-UCNP is synthesized through UV-induced free-radical polymerization of sol-gel derived UCNP-containingoligosiloxane resin (UCNP-Oligosiloxane). The siloxane matrix with random network structure by Si-O-Si bonds successfully encapsulates the UCNPs with chemical linkages between the siloxane matrix and organic ligands on UCNPs. This encapsulation results in surface passivation retaining intrinsic fluorescent properties of UCNPs under severe conditions (e.g., 85 °C, 85% relative humidity) and a wide range of pH (from 1 to 14). As an application example, we fabricate a two-color binary micro-barcode based on SE-UCNP via a low-cost transfer printing process. Under near-infrared irradiation, the binary-sequences in our barcode are readable enough to identify objects using a mobile phone camera. The hybridization of UCNPs with a siloxane matrix provides the capacity for highly stable UCNP-based applications in real environments.

[157] Y. J. Chung, B. I. Lee, and C. B. Park*
Multifunctional carbon dots as a therapeutic nanoagent for modulating Cu(II)-mediated β-amyloid aggregation

Nanoscale, vol.11, pp.6297-6306, 2019 [Link]


The abnormal self-assembly of cerebral β-amyloid (Aβ) peptides into toxic aggregates is a hallmark of Alzheimer’s disease (AD). Here, we report on multifunctional carbon dots that can chelate Cu(II) ions, suppress Aβ aggregation, and photooxygenate Aβ peptides. Copper ions have high relevance to AD pathogenesis, causing Cu(II)-mediated Aβ aggregation and oxidative damage to neuronal cells. For effective conjugation with Cu(II)-bound Aβ complexes, we have designed carbon dots that possess nitrogen (N)-containing polyaromatic functionalities on their surface by employing o-phenylenediamine (OPD) as a polymerization precursor. We demonstrate that the pOPD-derived carbon dots exhibit multiple capabilities against Cu(II)-mediated Aβ aggregation. Furthermore, the pOPD-derived carbon dots exhibited dramatically enhanced absorption and fluorescence upon coordination with Cu(II) ions and effectively photooxygenated Aβ peptides. The photodynamically modulated Aβ residues lost the propensity to coordinate with Cu(II) and to assemble into toxic aggregates. This work demonstrates the potential of carbon dots as a multifunctional β-sheet breaker and provides a promising anti-amyloidogenic strategy for future Aβ-targeted AD treatments.

[156] J. Yoon, S. H. Lee, F. Tieves, M. Rauch, F. Hollmann, and C. B. Park*
Light-harvesting dye-alginate hydrogel for solar-driven, sustainable biocatalysis of asymmetric hydrogenation

ACS Sustainable Chemistry & Engineering, vol.7, pp.5632–5637, 2019 [Link]


We report visible light-driven, asymmetric hydrogenation of C=C bonds using an ene-reductase from Thermus scotoductus SA-01 (TsOYE) and a light-harvesting dye (rose bengal, RB) co-immobilized in alginate hydrogel. Highly efficient encapsulation of RB in alginate hydrogel was achieved using the intrinsic affinity between TsOYE and RB, which allowed for the construction of robust RB-TsOYE-loaded alginate capsules. In the absence of NADH, the photobiocatalytic system facilitated asymmetric reduction of 2-methylcyclohexenone to an enantiopure (R)-2-methylcyclohexanone (ee>99%, max. conversion: 70.4%, turnover frequency: 1.54 min-1, turnover number: 300.2) under illumination. A series of stability tests revealed a significant enhancement of TsOYEs robustness in alginate hydrogel against heat and chemical denaturants. This study provides insight into a greener and sustainable approach of cofactor-free OYE catalysis for producing value-added chemicals using light energy.

[155] E. J. Son, Y. W. Lee, J. W. Ko, and C. B. Park*
Amorphous carbon nitride as a robust photocatalyst for biocatalytic solar-to-chemical conversion

ACS Sustainable Chemistry & Engineering, vol.7, pp.2545–2552, 2019 [Link]


Graphitic carbon nitride (GCN) is a two-dimensional, metal-free conjugate polymer that exhibits exceptional thermal and chemical stabilities, tempting electronic band structure, photosensitivity, and earth-abundance. Despite the potential of GCN as a photocatalyst, it suffers from a limited range of visible-light absorption with an edge wavelength of around 470 nm. Here, we report that amorphous carbon nitride (ACN) is a promising photocatalyst in comparison to GCN for solar-driven biotransformation via regeneration of nicotinamide cofactor (NADH). Under visible light (λ > 420 nm), NADH regeneration yields by ACN reached 62.3% within an hour whereas GCN hardly reduced NAD+ to NADH. The in-situ regenerated cofactor was consumed by redox enzymes to convert substrates into value-added chemicals. The remarkable photocatalytic activity of ACN originated from its unique microstructure that lacks hydrogen bonds linking polymeric melon units, leading to extended visible light absorption and less charge recombination. Our results suggest that ACN efficiently drives biocatalytic photosynthesis, simultaneously achieving exceptionally durable reusability and long-term catalytic stability.

[154] M. Ahn, B. I. Lee, S. Chia, J. Habchi, J. R. Kumita, M. Vendruscolo, C. M. Dobson, and C. B. Park*
Chemical and mechanistic analysis of photodynamic inhibition of Alzheimer’s β-amyloid aggregation

Chemical Communications, vol.55, pp.1152-1155, 2019 [Link]


The aberrant self-assembly of polypeptides into misfolded β-sheet-rich amyloid aggregates is closely associated with the pathogenesis of a variety of neurodegenerative disorders including Alzheimer’s, Parkinson’s, and Creutzfeldt-Jakob diseases. Central to monitoring amyloid formation in vitro has been thioflavin-T (ThT), which has been the most extensively utilized fluorescent probe. Here, we report the inhibition of the aggregation of Aβ42, the major isoform of β-amyloid found in disease-related amyloid deposits, by photosensitized ThT. Our data from 2D NMR and mass spectrometry and quantitative analysis from chemical kinetics give residue-specific information on how photosensitized ThT affects the chemical behavior of Aβ42 monomers and how such changes affect the kinetics and mechanism of aggregation. These results provide a detailed molecular understanding of the effects of photosensitizers on the aggregation behavior of Aβ42, and might facilitate the potential development of light-mediated therapeutic agents for Alzheimer’s disease.

[153] S. Willot, E. Fernandez-Fueyo, F. Tieves, M. Pesic, M. Alcalde, I. Arends, C. B. Park, F. Hollmann
Expanding the spectrum of light-driven peroxygenase reactions

ACS Catalysis, vol.9, pp.890–894, 2019 [Link]


Peroxygenases are receiving tremendous interest as catalysts for selective oxyfunctionalisation reactions, which require controlled supply of H2O2 to operate efficiently. They are rapidly inactivated in the presence of even small concentrations of H2O2. Here, we propose a photocatalytic system for the reductive activation of ambient O2 to produce H2O2 which uses the energy provided by visible light more efficiently based on the combination of wavelength-complementary photosensitizers. This approach was coupled to an enzymatic system to make formate available as sacrificial electron donor. The scope and current limitations of this approach are reported and discussed.

[152] J. Kim and C. B. Park
Shedding light on biocatalysis: photoelectrochemical platforms for solar-driven biotransformation

Current Opinion in Chemical Biology, vol.49, pp.122-129, 2019 [Link]


Redox biocatalysis has come to the forefront due to its excellent catalytic efficiency, stereoselectivity, and environmental benignity. The green and sustainable biotransformation can be driven by photoelectrochemical (PEC) platforms where redox biocatalysis is coupled with photoelectrocatalysis. The main challenge is how to transfer photoexcited electrons to (or from) the enzyme redox centers for effective biotransformation using solar energy. This review commences with a conceptual discussion of biocatalytic PEC platforms and highlights recent advances in PEC-based biotransformation through cofactor regeneration or direct transfer of charge carriers to (or from) oxidoreductases on enzyme-conjugated electrodes. Finally, we address future perspectives and potential next steps in the vibrant field of biocatalytic photosynthesis.

[151] T-K. Lee, J. H. Park, D. S. Choi, G-Y. Lee, W. S. Choi, K. J. Jeong, C. B. Park*, and C-H. Yun*
Solar-driven biocatalytic C-hydroxylation through direct transfer of photoinduced electrons

Green Chemistry, vol.21, pp.515-525, 2019 [Link]


Cytochrome P450s are multifunctional redox enzymes that have high potential in drug development and fine chemical industry for the synthesis of steroids, lipids, vitamins, and natural products. Despite the immense potential of P450s, the dependence on nicotinamide cofactor (NADPH) and NADPH-P450 reductase (CPR) limits their employment in the chemical industry. Here, we present a visible light-driven platform for biocatalytic C-hydroxylation reactions using natural flavin molecules, especially flavin mononucleotide, as a photosensitizer. Employing visible light as a source of energy instead of nicotinamide cofactor, the bacterial CYP102A1 heme domain was successfully applied for photobiocatalytic C-hydroxylation of 4-nitrophenol and lauric acid in the absence of NADPH and CPR. We present a proof of concept that the photoactivation of flavins is productively coupled with the direct transfer of photoinduced electrons to the P450 heme iron, achieving photobiocatalytic C-hydroxylation reactions.

[150] B. I. Lee, Y. J. Chung, and C. B. Park*
Photosensitizing materials and platforms for light-triggered modulation of Alzheimers beta-amyloid self-assembly

Biomaterials, vol.190-191, pp.121-132, 2019 [Link]


The abnormal aggregation of β-amyloid (Aβ) peptides is a hallmark of Alzheimer’s disease (AD) that affects more than 10% of the people over the age 60 world-wide. While the exact mechanism of neuronal loss and cognitive decline has not been elucidated yet, the amyloid hypothesis about the causative role of Aβ aggregation in AD pathology has been widely supported by the numerous in vivo and in vitro data. In this respect, many efforts have been made to explore therapeutic agents that can modulate the aggregation of Aβ, but none of the efforts succeeded in producing effective anti-Ab drugs for treating AD. This article provides an overview of recent attempts that have employed light energy to intervene with the self-assembly process of Aβ peptides via the generation of oxidative stress by photosensitizers, such as natural or synthetic dyes, light-responsive nanomaterials, and photoelectrochemical platforms. The underlying mechanism of photodynamic reactions suppressing Aβ aggregation and the dilemma in generating long-been-blamed oxidative stress are discussed by addressing the positive role of oxidative stress produced by the photosensitizers in the light-induced suppression of Aβ-mediated neurotoxicity. We have summarized current challenges and strategies to advance photo-induced inhibition and modulation of Aβ aggregation as a therapeutic option for treating AD in the future.

[149] Y. W. Lee, P. Boonmongkolras, E. J. Son, J. Kim, S. H. Lee, S. K. Kuk, J. W. Ko, B. Shin, and C. B. Park
Unbiased biocatalytic solar-to-chemical conversion by FeOOH/BiVO4/perovskite tandem structure

Nature Communications, vol.9, pp.4208, 2018 [Link]


Redox enzymes catalyze fascinating chemical reactions with excellent regio- and stereo-specificity. Nicotinamide adenine dinucleotide cofactor is essential in numerous redox biocatalytic reactions and needs to be regenerated because it is consumed as an equivalent during the enzymatic turnover. Here we report on unbiased photoelectrochemical tandem assembly of a photoanode (FeOOH/BiVO4) and a perovskite photovoltaic to provide sufficient potential for cofactor-dependent biocatalytic reactions. We obtain a high faradaic efficiency of 96.2% and an initial conversion rate of 2.4 mM h-1 without an external applied bias for the photoelectrochemical enzymatic conversion of a-ketoglutarate to L-glutamate via L-glutamate dehydrogenase. In addition, we achieve a total turnover number and a turnover frequency of the enzyme as high as 108,800 and 6,200 h-1, respectively, demonstrating that the tandem configuration facilitates redox biocatalysis using light as the only energy source.

[148] G. Son, S. H. Lee, D. Wang, and C. B. Park
Thioflavin T-amyloid hybrid nanostructure for biocatalytic photosynthesis

Small, vol.14, pp.1801396, 2018 [Link]


Amyloidogenic peptides can self-assemble into highly ordered nanostructures consisting of cross beta-sheet-rich networks that exhibit unique physicochemical properties and high stability. We have constructed light-harvesting amyloid nanofibrils by employing insulin as a building block and thioflavin T (ThT) as a amyloid-specific photosensitizer. The ability of the self-assembled amyloid scaffold to accommodate and align ThT in high density on its surface allowed for efficient energy transfer from the chromophores to the catalytic units in a similar way to natural photosystems. Insulin nanofibrils significantly enhanced the photoactivity of ThT by inhibiting non-radiative conformational relaxation around the central C-C bonds and narrowing the distance between ThT molecules that were bound to the beta-sheet-rich amyloid structure. We demonstrated that the ThT-amyloid hybrid nanostructure is suitable for biocatalytic solar-to-chemical conversion by integrating the light-harvesting amyloid module (for nicotinamide cofactor regeneration) with a redox biocatalytic module (for enzymatic reduction).

[147] J. Kim, S. H. Lee, F. Tieves, D. S. Choi, F. Hollmann, C. E. Paul, and C. B. Park
Biocatalytic C=C bond reduction through carbon nanodot-sensitized regeneration of NADH analogues

Angewandte Chemie International Edition, vol.57, pp.13825-13828, 2018 [Link]


Light-driven activation of redox enzymes is an emerging route for sustainable chemical synthesis. Among redox enzymes, the family of old yellow enzymes (OYEs) dependent on the nicotinamide adenine dinucleotide cofactor (NADH) catalyzes the stereoselective reduction of α,β-unsaturated hydrocarbons. Here, we report OYE-catalyzed asymmetric hydrogenation through light-driven regeneration of NADH and its analogues (mNADHs) by N-doped carbon nanodots (N-CDs), a zero-dimensional photocatalyst. Our spectroscopic and photoelectrochemical analyses verified the transfer of photo-induced electrons from N-CDs to an organometallic electron mediator (M) for highly regioselective regeneration of cofactors. Light triggered the reduction of NAD+ and mNAD+s with the cooperation of N-CDs and M, and the reduction behaviors of cofactors were dependent on their own reduction peak potentials. The regenerated cofactors subsequently delivered hydrides to OYE for stereoselective conversions of a broad range of substrates with excellent biocatalytic efficiencies.

[146] K. Kim, S. H. Lee, D. S. Choi, and C. B. Park*
Photoactive bismuth vanadate structure for light-triggered dissociation of Alzheimer β-amyloid aggregates

Advanced Functional Materials, vol.28, pp.1802813, 2018 [Link]


Bismuth vanadate (BiVO4) is an attractive, low-cost n-type semiconductor that exhibits excellent photoelectrocatalytic properties, chemical stability, and biocompatibility. This study reports a newly discovered function of BiVO4 dissociating highly stable, self-assembled amyloid aggregates associated with Alzheimer’s disease. We have developed a visible light-active, nanoporous BiVO4 photoelectrode-based platform for dissociating β-amyloid (Aβ) assemblies and alleviating Aβ aggregate-induced toxicity. Our multiple photochemical and microscopic analyses revealed that β-sheet-rich, long Aβ fibrils were effectively destabilized and broken into small-sized, soluble species by BiVO4 photoelectrode under illumination of a white light-emitting diode and an anodic bias. The photo-activated BiVO4 under anodic bias generated oxidative stress, such as superoxide ions and hole-derived hydrogen peroxide, which caused photooxidation of Aβ residues and irreversible disassembly of Aβ aggregates. The efficacy of photoelectrocatalytic dissociation of Aβ aggregates was enhanced by Mo-doped BiVO4, which facilitated the separation of electron-hole pairs by improving electron-transport properties of BiVO4. Furthermore, we verified that both pristine and Mo-doped BiVO4 photoelectrodes were nontoxic and effective in reducing Aβ-associated cytotoxicity. Our work shows the potential of BiVO4-based photoelectrode platforms for the dissociation of neurotoxic, highly stable Aβ assemblies using light energy.

[145] D. H. Nam, J. Z. Zhang, V. Andrei, N. Kornienko, N. Heidary, A. Wagner, K. Nakanishi, K. P. Sokol, B. Slater, I. Zebger, S. Hofmann, J. C. Fontecilla-Camps, C. B. Park, and E. Reisner
Solar water splitting with a hydrogenase integrated in photoelectrochemical tandem cells

Angewandte Chemie International Edition, vol.57, pp.10595-10599, 2018 [Link]


Hydrogenases (H2ases) are benchmark electrocatalysts in H2 production, both in biology and (photo)catalysis in vitro. We report the tailoring of a p-type Si photocathode for optimal loading and integration of H2ase by employing a hierarchical inverse opal (IO) TiO2 interlayer. This proton reducing Si|IO-TiO2|H2ase photocathode is capable to drive overall water splitting in combination with a complementary photoanode. We demonstrate unassisted water-splitting by wiring Si|IO-TiO2|H2ase to a modified BiVO4 photoanode in a photoelectrochemical (PEC) cell during several hours of irradiation. Connecting the Si|IO-TiO2|H2ase to a photosystem II (PSII) photoanode provides proof-of-concept for an engineered Z-scheme that replaces the non-complementary, natural light absorber photosystem I by a complementary abiotic silicon photocathode.

[144] D. Sohn, J. W. Ko, E. J. Son, S. H. Ko, T-H. Kim, H. Kwon, and C. B. Park*
Cellulose-templated, dual-carbonized Na3V2(PO4)3 for energy storage with high rate capability

ChemeElectroChem, vol.5, pp.2186-2191, 2018 [Link]


Sodium-ion rechargeable batteries are a promising candidate for large-scale electrical energy storage systems due to the abundance of sodium resources. Herein, we report the development of carbon-incorporated NASICON-Na3V2(PO4)3 (NVP) as a cathode active material for Na-ion batteries using carboxymethyl cellulose (CMC) and sucrose as dual carbon sources. The interaction between CMC and sucrose resulted in the formation of a highly porous structure (surface area: 58.998 m2 g-1) with increased sp2 carbon species, facilitating mass and charge transportation. The specific capacity (104.99 mAh g-1) of dual-carbonized CMC/sucrose-NVP (CS-NVP) was close to the theoretical capacity (117.6 mAh g-1). Furthermore, the dual-carbonized NVP exhibited stable cyclability, showing a specific capacity of 75.04 mA g-1 even at a high rate of 20 C.

[143] ⁠S. H. Lee, D. S. Choi, S. K. Kuk, and C. B. Park*
Photobiocatalysis: Activating redox enzymes by direct or indirect transfer of photoinduced electrons

Angewandte Chemie International Edition, vol.57, pp.7958-7985, 2018 [Link]


Biocatalytic transformation has received increasing attention in green synthesis of chemicals because of the diversity of enzymes, their superior catalytic activities and specificities, and mild reaction conditions. The idea of solar energy utilization in chemical synthesis through the combination of photocatalysis and biocatalysis provides an opportunity to make the "green" process greener. Oxidoreductases catalyze redox transformation of substrates by exchanging electrons at the enzyme active site, often with the aid of electron mediator(s) as a counterpart. Recent progress indicates that photoinduced electron transfer using organic (or inorganic) photosensitizers can activate a wide spectrum of redox enzymes to catalyze fuel-forming reactions (e.g., H2 evolution, CO2 reduction) and synthetically useful reductions (e.g., asymmetric reduction, oxygenation, hydroxylation, epoxidation, Baeyer-Villiger oxidation). This review provides an overview of recent advances in light-driven activation of redox enzymes through direct or indirect transfer of photoinduced electrons. The approaches and understanding in the construction of catalytic assemblies to activate different redox enzymes using organic dyes, carbon-based nanomaterials, semiconductors, and photoelectrochemical platforms are outlined. We discuss current technical challenges and strategies to advance photobiocatalytic transformation as a synthetic tool that meets an ever-increasing demand for sustainable chemistry.

[142] E. J. Son, S. H. Lee, S. K. Kuk, M. Pesic, D. S. Choi, J. W. Ko, K. Kim, F. Hollmann, and C. B. Park*
Carbon nanotube-graphitic carbon nitride hybrid film for flavoenzyme-catalyzed photoelectrochemical cell

Advanced Functional Materials, vol.28, pp.1705232, 2018 [Link]


In green plants, solar-powered electrons are transferred through sophistically arranged photosystems and are subsequently channelled into the Calvin cycle to generate chemical energy. Inspired by the natural photosynthetic scheme, we have constructed a photoelectrochemical cell (PEC) configured with protonated graphitic carbon nitride (p-g-C3N4) and carbon nanotube hybrid (CNT/p-g-C3N4) film cathode and FeOOH-deposited bismuth vanadate (FeOOH/BiVO4) photoanode for the production of industrially useful chiral alkanes using an old yellow enzyme homologue from Thermus scotoductus (TsOYE). In the biocatalytic PEC platform, photoexcited electrons provided by the FeOOH/BiVO4 photoanode are transferred to the robust and self-standing CNT/p-g-C3N4 hybrid film that electrocatalytically reduces flavin mononucleotide (FMN) mediator. The p-g-C3N4 promoted a two-electron reduction of FMN coupled with an accelerated electron transfer by the conductive CNT network. The reduced FMN subsequently delivered the electrons to TsOYE for the highly enantioselective conversion of ketoisophorone to (R)-levodione. Under light illumination (> 420 nm) and external bias, (R)-levodione was synthesized with the enantiomeric excess value of above 83%, not influenced by the scale of applied bias, simultaneously exhibiting stable and high current efficiency. Our results suggest that the biocatalytic PEC made up of economical materials can selectively synthesize high-value organic chemicals using water as an electron donor.

[141] G. Son, B. I. Lee, Y. J. Chung, and C. B. Park*
Light-triggered dissociation of self-assembled beta-amyloid aggregates into small, nontoxic fragments by Ru (II) complex

Acta Biomaterialia, vol.67, pp.147-155, 2018 [Link]


The self-assembly of beta-amyloid (Abeta) peptides into highly stable plaques is a major hallmark of Alzheimers disease. Here, we report visible light-driven dissociation of beta-sheet-rich Abeta aggregates into small, nontoxic fragments using ruthenium (II) complex {[Ru(bpy)3]2+} that functions as a highly sensitive, biocompatible, photoresponsive anti-Abeta agent. According to our multiple analyses using thioflavin T, bicinchoninic acid, dynamic light scattering, atomic force microscopy, circular dichroism, and Fourier transform infrared spectroscopy, [Ru(bpy)3]2+ successfully disassembled Abeta aggregates by destabilizing the beta-sheet secondary structure under illumination of white light-emitting diode light. We validated that photoexcited [Ru(bpy)3]2+ causes oxidative damages of Abeta peptides, resulting in the dissociation of Abeta aggregates. The efficacy of [Ru(bpy)3]2+ is attributed to reactive oxygen species, such as singlet oxygen, generated from [Ru(bpy)3]2+ that absorbed photon energy in the visible range. Furthermore, photoexcited [Ru(bpy)3]2+ strongly inhibited the self-assembly of Abeta monomers even at concentrations as low as 1 nM and reduced the cytotoxicity of Abeta aggregates.

[140] J. W. Ko, W. S. Choi, J. Kim, S. K. Kuk, S. H. Lee, and C. B. Park
Self-assembled peptide-carbon nitride hydrogel as a light-responsive scaffold material

Biomacromolecules, vol.18, pp.3551–3556, 2017 [Link]


Peptide self-assembly is a facile route to the development of bioorganic hybrid materials that have sophisticated nanostructures towards diverse applications. Here, we report the synthesis of self-assembled peptide (Fmoc-diphenylalanine, Fmoc-FF)/graphitic carbon nitride (g-C3N4) hydrogels for light harvesting and biomimetic photosynthesis through non-covalent interactions between aromatic rings in Fmoc-FF nanofibers and tris-s-triazine in g-C3N4 nanosheets. According to our analysis, the photocurrent density of the Fmoc-FF/g-C3N4 hydrogel was 1.8 times higher (0.82 μA cm-1) than that of the pristine g-C3N4. This is attributed to effective exfoliation of g-C3N4 nanosheets in the Fmoc-FF/g-C3N4 network, facilitating photo-induced electron transfers. The Fmoc-FF/g-C3N4 hydrogel reduced NAD+ to enzymatically active NADH under light illumination at a high rate of 0.130 mole g-1 h-1 and drove light-responsive redox biocatalysis. Moreover, the Fmoc-FF/g-C3N4 scaffold could well-encapsulate key photosynthetic components, such as electron mediators, cofactors, and enzymes, without noticeable leakage, while retaining their functions within the hydrogel. The prominent activity of the Fmoc-FF/g-C3N4 hydrogel for biomimetic photosynthesis resulted from the easy transfer of photo-excited electrons from electron donors to NAD+ via g-C3N4 and electron mediators as well as the hybridization of key photosynthetic components in a confined space of the nanofiber network.

[139] B. I. Lee, Y. S. Suh, Y. J. Chung, K. Yu, and C. B. Park
Shedding light on Alzheimers β-amyloidosis: Photosensitized methylene blue inhibits self-assembly of β-amyloid peptides and disintegrates their aggregates

Scientific Reports, vol.7, pp.7523, 2017 [Link]


Abnormal aggregation of β-amyloid (Aβ) peptides is a major hallmark of Alzheimer’s disease (AD). In spite of numerous attempts to prevent the β-amyloidosis, no effective drugs for treating AD have been developed to date. Among many candidate chemicals, methylene blue (MB) has proved its therapeutic potential for AD in a number of in vitro and in vivo studies; but the result of recent clinical trials performed with MB and its derivative was negative. Here, with the aid of multiple photochemical analyses, we first report that photoexcited MB molecules can block Aβ42 aggregation in vitro. Furthermore, our in vivo study using Drosophila AD model demonstrates that photoexcited MB is highly effective in suppressing synaptic toxicity, resulting in a reduced damage to the neuromuscular junction (NMJ), an enhanced locomotion, and decreased vacuole in the brain. The hindrance effect is attributed to Aβ42 oxidation by singlet oxygen (1O2) generated from photoexcited MB. Finally, we show that photoexcited MB possess a capability to disaggregate the pre-existing Aβ42 aggregates and reduce Aβ-induced cytotoxicity. Our work suggests that light illumination can provide an opportunity to boost the efficacies of MB toward photodynamic therapy of AD in future.

[138] Y. J. Chung, K. Kim, B. I. Lee, and C. B. Park*
Carbon nanodot-sensitized modulation of Alzheimers β-amyloid self-assembly, disassembly, and toxicity

Small, vol.13, pp.1700983, 2017 [Link]


The self-assembly of amyloidogenic peptides into β-sheet-rich aggregates is a general feature of many neurodegenerative diseases, including Alzheimers disease, which signifies the need for the effective attenuation of amyloid aggregation toward alleviating amyloid-associated neurotoxicity. In the present study, we report that photoluminescent carbon nanodots (CDs) can effectively suppress Alzheimers β-amyloid (Aβ) self-assembly and function as a β-sheet breaker disintegrating preformed Aβ aggregates. We synthesized CDs using ammonium citrate through one-pot hydrothermal treatment and passivated their surface with branched polyethylenimine (bPEI). The bPEI-coated CDs (bPEI@CDs) exhibited hydrophilic and cationic surface characteristics, which interacted with the negatively charged residues of Aβ peptides, suppressing the aggregation of Aβ peptides. Under light illumination, bPEI@CDs displayed a more pronounced effect on Aβ aggregation and on the dissociation of β-sheet-rich assemblies through the generation of reactive oxygen species from photoactivated bPEI@CDs. We verified the light-triggered attenuation effect of Aβ aggregation using a series of experiments, including photochemical and microscopic analysis. Furthermore, our cell viability test confirmed the ability of photoactivated bPEI@CDs for the suppression of Aβ-mediated cytotoxicity, indicating bPEI@CDs’ potency as an effective anti-Aβ neurotoxin agent.

[137] S. H. Lee, D. S. Choi, M. Pesic, Y. W. Lee, C. E. Paul, F. Hollmann, and C. B. Park
Cofactor-free, direct photoactivation of enoate reductases for asymmetric reduction of C=C bonds

Angewandte Chemie International Edition, vol.56, pp.8681–8685, 2017 [Link]


Enoate reductases from the family of Old Yellow Enzymes (OYEs) can catalyze stereoselective trans-hydrogenation of activated C=C bonds. Despite their potential, however, their application is limited by the necessity for continuous supply of redox equivalents such as nicotinamide cofactors [NAD(P)H]. Here, we report visible light-driven activation of OYEs through NAD(P)H-free, direct transfer of photoexcited electrons from xanthene dyes to the prosthetic flavin moiety. Our spectroscopic and electrochemical analyses verified spontaneous association of rose bengal and its derivatives with OYEs. Illumination of a white light-emitting-diode triggered photoreduction of OYEs by xanthene dyes, which facilitated the enantioselective reduction of C=C bonds in the absence of NADH. The photoenzymatic conversion of 2-methylcyclohexenone resulted in enantiopure (ee >99%) (R)-2-methylcyclohenanone with conversion yields as high as 80-90%. The turnover frequency was significantly affected by the substitution of halogen atoms in xanthene dyes. The NADH-free, xanthene-sensitized photobiocatalytic platform was successfully applied to different homologues of OYEs from Thermus scotoductus and Bacillus subtilis. This work demonstrates a simple and versatile way of activating OYEs by direct coupling of OYE-catalysis with molecular photocatalysis.

[136] J. W. Ko, E. J. Son, and C. B. Park
Nature-inspired synthesis of nanostructured electrocatalysts through mineralization of calcium carbonate

ChemSusChem, vol.10, pp.2585-2591, 2017 [Link]


Biomineralization is a biogenic process that produces elaborate inorganic and organic hybrid materials in nature. Inspired by the natural process, this study explores novel mineralization approach to create nanostructured CaCO3 films composed of amorphous CaCO3 hemispheres using catechol-rich polydopamine (PDA) as a biomimetic mediator. We successfully transformed thus-synthesized biomimetic CaCO3 to nanostructured films of metal oxide minerals, such as FeOOH, CoCO3, NiCO3, and MnOOH, via a simple procedure. CaCO3-templated metal oxide minerals functioned as an efficient electrocatalyst; CaCO3-templated CoPi (nanoCoPi) film exhibited high stability as a water oxidation electrocatalyst with a current density of 1.5 mA cm-2. The nanostructure of nanoCoPi consisting of individual nanoparticles (~70 nm) and numerous internal pores (BET surface area: 3.17 m2g-1) facilitated an additional charge transfer pathway from the electrode to individual active sites of catalysts. This work demonstrates a plausible strategy for facile and green synthesis of nanostructured electrocatalysts through biomimetic CaCO3 mineralization.

[135] M. Lee, J. Hong, B. Lee, K. Ku, S. Lee, C. B. Park*, K. Kang*
Multi-electron redox phenazine for ready-to-charge organic batteries

Green Chemistry, vol.19, pp.2980-2985, 2017 [Link]


Organic redox compounds represent an emerging class of cathode materials in rechargeable batteries for low-cost and sustainable energy storage. However, the low operating voltage (< 3 V) and necessity of using lithium-containing anodes have significantly limited their practical applicability to battery systems. Here, we introduce a new class of p-type organic redox centers based on N, N’-substituted phenazine (NSPZ) to build ready-to-charge organic batteries. In the absence of lithium-containing anodes, NSPZ cathodes facilitate reversible two-electron transfer at 3.7 and 3.1 V accompanying anion association, which results in a specific energy of 622 Wh kg-1 in dual-ion batteries.

[134] S. K. Kuk, R. K. Singh, D. H. Nam, R. Singh, J-K. Lee, and C. B. Park
Photoelectrochemical reduction of carbon dioxide to methanol via a highly efficient enzyme cascade

Angewandte Chemie International Edition, vol.56, pp.3827-3832, 2017 [Link]


Natural photosynthesis is an effective route for clean and sustainable conversion of CO2 to high-energy chemicals. Inspired by the natural scheme, we designed a tandem-photoelectrochemical (PEC)-cell-integrated-with-enzyme-cascade (TPIEC) system, which transfers photogenerated electrons to a multi-enzyme cascade for biocatalyzed reduction of CO2 to methanol. We applied a hematite photoanode and a bismuth ferrite photocathode to fabricate the iron oxide-based tandem PEC cell for visible light-assisted regeneration of nicotinamide cofactor (NADH). The cell utilized water as an electron donor and spontaneously regenerated NADH. To complete the TPIEC system, a superior three-dehydrogenase cascade system was employed in the cathodic part of the PEC cell. Using applied bias, the TPIEC system achieved high methanol conversion output, providing a PEC platform for highly selective synthesis of hydrocarbon fuel using readily-available solar energy and water.

[133] D. S. Choi, Y. Ni, E. Fernandez-Fueyo, M. Lee, F. Hollmann, and C. B. Park
Photoelectroenzymatic oxyfunctionalization on flavin-hybridized carbon nanotube electrode platform

ACS Catalysis, vol.7, pp.1563-1567, 2017 [Link]


Peroxygenases are very promising catalysts for oxyfunctionalization reactions. Their practical applicability, however, is hampered by their sensitivity against the oxidant (H2O2), therefore necessitating in situ generation of H2O2. Here, we report a photoelectrochemical approach to provide peroxygenases with suitable amounts of H2O2 while reducing the electrochemical overpotential needed for the reduction of molecular oxygen to H2O2. When tethered on single-walled carbon nanotubes (SWNT) under illumination, flavins allowed for a marked anodic shift of the oxygen reduction potential in comparison to pristine-SWNT and/or non-illuminated electrodes. This flavin-SWNT-based photoelectrochemical platform enabled peroxygenases-catalyzed, selective hydroxylation reactions.

[132] K. Kim, B. I. Lee, Y. J. Chung, W. S. Choi, and C. B. Park*
Hematite-based photoelectrode materials for photoelectrocatalytic inhibition of Alzheimers beta-amyloid self-assembly.

Advanced Healthcare Materials, vol.6, pp.1601133, 2017 [Link]


We report a photoelectrocatalytic way for suppressing beta-amyloid (Abeta) self-assembly using a visible light-active, hematite-based photoelectrode platform. Upon illumination of a light-emitting diode with anodic bias, we found that hematite photoanodes generate reactive radical species such as superoxide ions and hydroxyl radical via the photoelectrocatalytic process. According to our analyses, the hole-derived radicals, in particular the hydroxyl radical, played a significant role of oxidizing Abeta peptides, which effectively blocked further fibrillation. The efficacy of photoelectrocatalytic inhibition on Abeta aggregation was enhanced by introducing cobalt phosphate (Co-Pi) as a co-catalyst on the hematite photoanode, which facilitated the separation of electron-hole pairs. We verified that both bare and Co-Pi@hematite photoanodes are biocompatible and effective in reducing Abeta aggregation-induced cytotoxicity.

[131] S. K. Kuk+, B. I. Lee+, J. S. Lee, and C. B. Park*
Rattle-structured upconversion nanoparticles for near IR-induced suppression of Alzheimers beta-amyloid aggregation.

Small, vol.13, pp.1603139, 2017 [Link]


The abnormal aggregation of extracellular beta-amyloid (Abeta) peptides is a major pathological event of Alzheimers disease. Recently, photodynamic suppression of the assembly of Abeta peptides into beta-sheet-rich aggregates and the resulting neurotoxicity were suggested; however, its application has been limited by the low tissue penetration-depth of UV or visible light. Herein, we report rose bengal (RB)-loaded upconverting nanocomposites as a NIR-responsive inhibitor of Abeta aggregation. Rattle-structured, organosilica shell (ROS) deposited on NaYF4:Yb,Er nanocrystals (UCNPs) was adopted as an efficient photosensitizer carrier with high loading capacity and disaggregation effect of RB. We demonstrated that the UCNP@ROS exhibited high energy transfer efficiency to the loaded RB under the irradiation of 980 nm NIR light and generated singlet oxygen efficiently inhibiting Abeta self-assembly. Furthermore, RB-loaded UCNP@ROS is not only biocompatible, but also effective in suppressing Abeta-induced cytotoxicity under NIR light, suggesting its potential towards photodynamic treatment of of Alzheimers disease in future.

[130] E. J. Son, J. H. Kim, J. W. Ko, and C. B. Park*
Catecholamine-functionalized graphene as a biomimetic redox shuttle for solar water oxidation

Faraday Discussions, vol.198, pp.135-145, 2017 [Link]


In natural photosynthesis, solar energy is converted to chemical energy through a cascaded, photoinduced charge transfer chain that consists of primary and secondary acceptor quinones (i.e., QA and QB), which leads to exceptionally high quantum yield near unity. Inspired by the unique multistep charge transfer architecture in nature, we have synthesized catecholamine-functionalized, reduced graphene oxide (RGO) film as a redox mediator that can mimic quinone acceptors in the photosystem II. We utilized polynorepinephrine (PNE) as a redox-shuttling chemical, as well as to coat graphene oxide (GO) and to reduce GO to RGO. The two-electrons-and-two-protons-involving charge transfer characteristic of quinone ligands in PNE acted as an electron acceptor that facilitated charge transfer in photocatalytic water oxidation. Furthermore, PNE-coated RGO film promoted fast charge separation in [Ru(bpy)3]2+ and over two-fold increased the activity of cobalt phosphate on photocatalytic water oxidation. The results suggest that our bio-inspired strategy for the construction of forward charge transfer pathway can provide more opportunities to realize efficient artificial photosynthesis.

[129] D. H. Nam, S. K. Kuk, H. Choe, S. Lee, J. W. Ko, E. J. Son, E-G. Choi, Y. H. Kim, and C. B. Park*
Enzymatic photosynthesis of formate from carbon dioxide coupled with highly efficient photoelectrochemical regeneration of nicotinamide cofactors

Green Chemistry, vol.18, pp.5989-5993, 2016 [Link]


Green conversion of carbon dioxide to fuels has attracted high interest recently due to the global issues of environmental sustainability and renewable energy sources. In this study, we present photoelectrochemical (PEC) regeneration of nicotinamide cofactors (NADH) coupled with enzymatic synthesis of formate from CO2 towads mimicking natural photosynthesis. The water oxidation-driven PEC platform exhibited high yield and rate of NADH regeneration compared to many other homogeneous, photochemical systems. We successfully coupled solar-assisted NADH reduction with enzymatic CO2 reduction to formate under continuous CO2 injection.

[128] D. H. Nam, G. M. Ryu, S. K. Kuk, D. S. Choi, E. J. Son, and C. B. Park*
Water oxidation-coupled, photoelectrochemical redox biocatalysis toward mimicking natural photosynthesis.

Applied Catalysis B: Environmental, vol.198, pp.311-317, 2016 [Link]


Redox enzymes are industrially important for catalyzing highly complex reactions because of their excellent regio- and stereo-selectivity; however, broad application of redox enzymes has been often limited by the requirement of stoichiometric supply of cofactors such as β-nicotinamide adenine dinucleotide (NADH). Here, we report light-driven cofactor regeneration coupled with water oxidation by employing a photoelectrochemical cell platform consisted of a FeOOH/Fe2O3 photoanode and a black silicon photocathode. The FeOOH layer deposited on Fe2O3 surface decreased reaction barriers for water oxidation. The black silicon photocathode exhibited high photocurrent response and superior capacity to drive cofactor reduction. The cofactor regeneration yield in the photoelectrochemical cell was almost two-fold higher than that obtained in homogenous system, which demonstrates that photoelectrochemical cell is a promising platform for redox biocatalytic reactions using water as an electron donor.

[127] E. J. Son, J. W. Ko, S. K. Kuk, H. Choe, S. Lee, J. H. Kim, D. H. Nam, G. M. Ryu, Y. H. Kim, and C. B. Park*
Sunlight-assisted, biocatalytic formate synthesis from CO2 and water using silicon-based photoelectrochemical cells.

Chemical Communications, vol.52, pp.9723-9726, 2016 [Link]


We report on a silicon-based photoelectrochemical cell that integrates a formate dehydrogenase from Thiobacillus sp. (TsFDH) to convert CO2 to formate using water as an electron donor under visible light irradiation and an applied bias. Our results revealed that sequential transfer of electrons, extracted via a water oxidation reaction at a npp+ triple-junction silicon on ITO (3-jn-Si/ITO/CoPi) photoanode, to a a hydrogen-terminated silicon nanowire (H-SiNW) photocathode, and further to TsFDH, leads to effective formate production with a faradaic efficiency of 16.18% under the applied bias of 1.8 V, while no formate was synthesized directly at the H-SiNW photocathode alone. The formate yield increased significantly through the integrated PEC system, which continuously regenerated NADH for TsFDH-catalyzed CO2 reduction. Moreover, we demonstrated that our silicon-based biocatalytic system could be operated under natural sunlight using a solar tracking module, which is a highly desirable result for the practical utility of the PEC as a sustainable solar energy harvesting system. The current study suggests that the deliberate integration of biocatalysis to a PEC platform can provide an opportunity to synthesize valuable chemicals with the use of earth-abundant materials and sustainable resources. With our biocatalysis-integrated PEC platform, further engineering of enzymes and photoelectrode materials would provide more opportunity to improve efficiency of the system.

[126] E. J. Son, J. H. Kim, K. Kim, and C. B. Park*
Quinone and its derivatives for energy harvesting and storage materials.

Journal of Materials Chemistry A, vol.4, pp.11179-11202, 2016 [Link]


In nature, quinone plays a vital role in numerous electrochemical reactions for energy transduction and storage; such processes include respiration and photosynthesis. For example, fast proton-coupled electron transfer between primary and secondary quinones in green plants triggers the rapid charge separation of chlorophyll molecules, achieving unparalleled photosynthesis with near-unity quantum yield. In addition, quinone-rich polymers such as eumelanin and polydopamine show unique optical and electrical properties (e.g., strong broadband absorbance or a switching response to external stimuli), mostly arising from their chemically disordered structures. Understanding the unique features of quinone and its derivatives can provide solutions to the construction of bio-inspired systems for energy harvesting and conversion. This paper reviews recent advances in the design of quinone-functionalized hybrid materials based on quinones redox, electrical, optical, and metal chelating/reducing properties to determine these materials applications in energy-harvesting and -storage systems, such as artificial photosynthetic platforms, rechargeable batteries, pseudocapacitors, phototransistors, plasmonic light harvesting platforms, and dye-sensitized solar cells.

[125] W. S. Choi, S. H. Lee, J. W. Ko, and C. B. Park*
Human urine-fueled, light-driven NADH regeneration for redox biocatalysis.

ChemSusChem, vol.9, pp.1559-1564, 2016 [Link]


FROM WASTE TO VALUABLES: Human urine is studied as a potential source of energy for light-driven redox biocatalytic reactions. The urea-rich human urine functions as an efficient chemical fuel in a photoelectrochemical cell regenerating nicotinamide cofactor (NADH), an essential hydride mediator that is required for numerous redox biocatalytic reactions. We demonstrate the utility of human urine as a chemical fuel for driving redox biocatalysis in a photoelectrochemical cell. Ni(OH)2-modified alpha-Fe2O3 is selected as a photoanode for the oxidation of urea in human urine and black silicon (bSi) is used as a photocathode material for NADH regeneration. The electrons extracted from human urine are used for the regeneration of NADH. The catalytic reactions at both the photoanode and the photocathode were significantly enhanced by light energy that lowered the overpotential and generated high currents in the full cell system.

[124] Y. J. Chung, B. I. Lee, J. W. Ko, and C. B. Park*
Photo-active g-C3N4 nanosheets for light-induced suppression of Alzheimers beta-amyloid aggregation and toxicity.

Advanced Healthcare Materials, vol.5, pp.1560-1565, 2016 [Link]


Graphitic carbon nitride (g-C3N4) is a metal-free material of only carbon and nitrogen-based structure called tri-s-triazine, which is non-toxic, abundant, and cost-effective. While there are only a few studies about biomedical applications of g-C3N4, good biocompatibility of g-C3N4 has been confirmed recently through its use in cancer diagnosis, drug delivery, and cell imaging. Here we report that g-C3N4 has a suppressive ability toward Alzheimers beta-amyloid (Abeta) aggregation under light illumination. Under commercial white light emitting diode light, photo-induced electrons of g-C3N4 with a 2.6 eV bandgap generated reactive oxygen species (ROS), such as superoxide anion and singlet oxygen; then, the ROS blocked further Abeta aggregation as a way of photo-oxidation, impacting the conformational structure of Abeta. Through metal doping into a g-C3N4 framework, we further demonstrated that Fe-doped g-C3N4 showed enhanced optical properties and stronger inhibition on Abeta aggregation than bare g-C3N4. Both g-C3N4 and Fe-doped g-C3N4 had negligible cytotoxicity and exhibited significant reduction in Abeta-induced cell death.

[123] K. R. Yoon+, J. W. Ko+, D-Y. Youn, C. B. Park*, and I-D. Kim*
Synthesis of Ni-based co-catalyst functionalized W:BiVO4 nanofibers for solar water oxidation.

Green Chemistry, vol.18, pp.944-950, 2016 [Link]


Harnessing solar energy has recently attracted much attention due to the increased importance of environmental and energy issues. In particular, the photolysis of water using photocatalysts, so called artificial photosynthesis, has been receiving great attention in terms of the direct and efficient solar energy conversion system to produce O2 and H2 as chemical fuels. The effectiveness of water splitting using photocatalysts is determined by the utilization of visible light of the solar spectrum, capacity of the harvested light to generate charge carriers, and the extent of charge separation and transfer. Thus, the selection of semiconducting photocatalyst materials with proper band position, bandgap energy, and long-lived stability is critical for the viable water splitting system. Herein we report on the synthesis of highly porous, 1-D tungsten-doped BiVO4 nanofibers (W:BiVO4 NFs). To facilitate photocatalysis, we introduced nickel nanoparticles (NiOx NPs) as co-catalysts on the surface of the W:BiVO4 NFs. The outstanding water oxidation performance of the NiOx NPs-functionalized W:BiVO4 NFs were obtained through (i) the control of polymer/precursor to achieve porous W:BiVO4 NFs (for higly increased surface area), (ii) the control of tungsten-doping level (for fast charge transfer), and (iii) the optimization of the loading amounts of NiOx NPs (for efficient charge pathway suppression of charge recombination).

[122] J. H. Lee, D. H. Nam, S. H. Lee, J. H. Park, S. J. Park, S. H. Lee, C. B Park*, and K. J. Jeong*
Solar-to-chemical conversion platform by robust cytochrome P450-P(3HB) complex.

Journal of Industrial and Engineering Chemistry, vol.33, pp.28-32, 2016 [Link]


In the past 50 years, cytochrome P450 monooxygenases (P450s) have been given significant attention for the synthesis of natural products (e.g., vitamins, steroids, lipids) and pharmaceuticals. Despite their potential, however, costly nicotinamide cofactors such as NAD(P)H are required as reducing equivalents; thus, in situ regeneration of NAD(P)H is essential to sustaining P450-catalyzed reactions. Furthermore, poor stability of P450s has been considered as a hurdle, hampering industrial implementations of P450-catalyzed reactions. Herein we describe the development of an economic and robust process of P450-catalyzed reactions by the combination of P450 immobilization and solar-induced NADPH regeneration. The P450 monooxygenase could be efficiently immobilized on a P(3HB) biopolymer, which enabled simple purification from the E. coli host. We clearly demonstrated that the P450-P(3HB) complex exhibited much higher enzymatic yield and stability than free P450 did against changes of pH, temperature, and concentrations of urea and ions. Using the robust P450-P(3HB) complex and solar-tracking module, we successfully conducted P450-catalyzed artificial photosynthesis under the irradiation of natural sunlight in a preparative scale (500 mL) for multiple days. To the best of our knowledge, this is the largest reactor volume in P450-catalyzed reactions reported so far. We believe that our robust platform using simple immobilization and abundant solar energy promises a significant breakthrough for the broad applications of cytochrome P450 monooxygenases.

[121] J. W. Ko, B. I. Lee, Y. J. Chung, and C. B. Park*
Carboxymethyl cellulose-templated synthesis of hierarchically structured metal oxides.

Green Chemistry, vol.17, pp.4167-4172, 2015 [Link]


Cellulose, a main component of green plants, is the most abundant organic chemical on Earth, produced 1011 tons per year in the biosphere. The polysaccharide consists of D-glucose units linked by beta-1,4-glycosidic bonds and has been widely utilized in diverse engineering fields because of its biocompatibility, abundance, and high chemical stability. In this work, we have demonstrated the utility of carboxymethyl cellulose (CMC) fibers as a sacrificial template to produce binary and tertiary metal oxides fibers. The electrostatic interaction between metal ions and the carboxyl groups in CMC fibers induced a hierarchical structure of metal oxides. The morphologies of synthesized metal oxides (e.g., CeO2, ZnO, and CaMn2O4) could be controlled according to synthetic conditions, such as metal precursor concentration, calcination temperature, and the amount of CMC fibers. Thus-synthesized CMC-templated metal oxide fibers exhibited enhanced performances for photocatalytic, photochemical, and electrocatalytic reactions. The CeO2 fibers showed much higher photocatalytic activity than CeO2 nanoparticles due to superior ability to generate reactive oxygen species which can degrade organic pollutants. We also demonstrated that hierarchical ZnO fibers hybridized with g-C3N4 could provide directional charge transfer pathway and showed their utility for biocatalyzed artificial photosynthesis through visible light-driven chemical NADH regeneration coupled with redox enzymatic reaction. The electrochemical properties of CaMn2O4 fibers enabled bi-functional reactions of oxygen reduction and evolution reactions. We expect that the economical and environmentally friend approach could be extended to green synthesis of hierarchically structured materials of other metal oxides.

[120] B. I. Lee+, S. Lee+, Y. S. Suh, J. S. Lee, A-K Kim, O-Y Kwon, K. Yu, and C. B. Park
Photo-excited porphyrins as a strong suppressor of beta-amyloid aggregation and synaptic toxicity

Angewandte Chemie, vol.54, pp.11472-11475, 2015 [Link]


The abnormal assembly of beta-amyloid (Abeta) peptides into neurotoxic, beta-sheet rich amyloid aggregates is a major pathological hallmark of Alzheimers disease (AD). Photodynamic therapy (PDT) is a promising strategy for treating various diseases due to its temporal and spatial controllability and reduced side effects. However, PDT for neurodegenerative diseases has not been explored yet. Here, we show that light-induced photosensitizing molecules can regulate Abeta amyloidogenesis. Our multiple photochemical analyses using circular dichroism, atomic force microscopy, dot blot, and native gel electrophoresis verified that photo-activated meso-tetra(4-sulfonatophenyl) porphyrin (TPPS) successfully inhibits Abeta aggregation in vitro. Furthermore, we demonstrate that Abeta toxicity was relieved in the photoexicited-TPPS-treated Drosophila AD model. TPPS suppresses neural cell death, synaptic toxicity, and behavioral defects in the Drosophila AD model under blue light illumination. Behavioral phenotypes, including larval locomotion defect and short lifespan caused by Abeta overexpression, were also rescued by blue light-excited TPPS.

[119] M. Lee, J. U. Kim, K. J. Lee, S. Ahn, Y-B. Shin, J. Shin, and C. B. Park
Aluminum nanoarrays for plasmon-enhanced light-harvesting.

ACS Nano, vol.9, pp.6206-6213, 2015 [Link]


The practical limits of coinage metal-based plasmonic materials demand sustainable, abundant alternatives with a wide plasmonic range of the solar energy spectrum. Aluminum (Al) is an emerging alternative, but its instability in aqueous environments critically limits its applicability to various light-harvesting systems. Here, we present a novel design strategy to achieve a robust platform for plasmon-enhanced light-harvesting using Al nanostructures. The incorporation of mussel-inspired polydopamine nano-layers in the Al nanoarrays allows for the reliable use of Al plasmonic resonances in a highly corrosive photocatalytic redox solution, and provides nanoscale arrangement of organic photosensitizers on Al surfaces. Resulting Al-photosensitizer core-shell assemblies exhibit plasmon-enhanced light absorption, which enables a 300% increase in photo-to-chemical conversion. Our strategy opens a path to realizing the stable and advanced use of aluminum for plasmonic light-harvesting.

[118] G. M. Ryu, M. Lee, D. S. Choi, and C. B. Park*
Hematite-based photoelectrochemical platform for visible light-induced biosensing.

Journal of Materials Chemistry B, vol.3, pp.4483-4486, 2015 [Link]


Photoelectrochemical (PEC) detection is an attractive biosensing strategy because it inherits the benefits of electrochemical sensors, such as low cost, simple instrumentation and high sensitivity. Furthermore, PEC sensing can reduce undesired background noise and enhance sensitivity by using two separate forms of signals: light (for excitation) and electricity (for detection). Hematite is a promising photoanode material because of its strong absorption of visible light (Eg ~2.1 eV), high stability, low price, and environmentally benign characteristics. Here, we report the first hematite-based PEC biosensor platform to detect NADH under visible light. To enhance the electrical signal of photoanodes, we employed mussel-inspired polydopamine which immobilize redox mediators on hematite. The enzymatic PEC biosensor enabled the detection of glucose, ethanol, and lactate, and even showed successful detection of glucose in human plasma suggesting the practical usefulness of our platform.

[117] S. Kim, J. H. Kim, J. S. Lee, and C. B. Park*
Beta-sheet-forming, self-assembled peptide nanomaterials towards optical, energy, and healthcare applications.

Small, vol.11, pp.3623-3640, 2015 [Link]


Peptide self-assembly is an attractive route to the synthesis of intricate organic nanostructures that possess remarkable structural variety and biocompatibility. Recent studies on peptide-based, self-assembled materials have been expanding beyond the construction of high-order architectures; they are now reporting new functional materials that have applications in the emerging fields, such as artificial photosynthesis and rechargeable batteries. Nevertheless, there have been rather scarce reviews particularly concentrating on such versatile, emerging applications. Herein we selectively review recent advances in the synthesis of self-assembled peptide nanomaterials (e.g., cross beta-sheet-based amyloid nanostructures, peptide amphiphiles, etc.) and describe their new applications in diverse, interdisciplinary fields ranging from optics, energy storage/conversion to healthcare. We highlight the applications of peptide-based self-assembled materials in unconventional fields, such as photoluminescent peptide nanostructures, artificial photosynthetic peptide nanomaterials, and lithium-ion battery components. We also discuss relation of such functional materials to the rapidly progressing biomedical applications of peptide self-assembly, which include biosensors/chips and regenerative medicine. The combination of strategies shown in respective applications would further promote the discovery of novel, functional small materials.

[116] E. J. Son, J. S. Lee, M. Lee, H. C. Vu, H. Lee, K. Won*, and C. B. Park*
Self-adhesive graphene oxide-wrapped TiO2 nanoparticles for UV-activated colorimetric oxygen detection.

Sensors and Actuators B: Chemical, vol.213, pp.322-328, 2015 [Link]


Titanium dioxide has long been pursued as a promising material for many photocatalytic applications because of its chemical activity and stability as well as low cost. On the other hand, graphene oxide (GO) can serve as a scaffold for functional hybrid materials by interacting with various organic and inorganic chemicals. Herein, we synthesized graphene oxide-wrapped anatase TiO2 nanoparticles (GO-TiO2 NPs) as a self-adhesive photocatalyst for UV-activated colorimetric oxygen indicators. Our multiple analyses with zeta potential, UV-Vis spectrophotometry, and cyclic voltammetry revealed that methylene blue (MB), a widely used redox dye for colorimetric oxygen indication, strongly adsorbs onto GO-TiO2 NPs by both electrostatic and pi-pi stacking interactions. We successfully fabricated UV-activated visual oxygen indicator films using MB, GO-TiO2 NPs, glycerol, and hydroxyethyl cellulose (HEC) as a redox dye, a UV-absorbing self-adhesive photocatalyst, a sacrificial electron donor, and an encapsulation polymer, respectively. The chemical attraction between GO and MB significantly reduced dye leakage problem, a major drawback of conventional oxygen indicators; MB leaching from GO-TiO2-based film was 4.8 times lower than that from TiO2-based film. This novel MB/GO-TiO2/glycerol/HEC film was photobleached by UV irradiation within 6 min and regained its blue color in the air within 20 min, demonstrating its useful functionality as a UV-activated colorimetric oxygen indicator.

[115] J. H. Park, S. H. Lee, G. S. Cha, D. S Choi, D. H. Nam, J. H Lee, J-K Lee, C-H Yun, K. J. Jeong, and C. B. Park
Cofactor-free light-driven whole-cell cytochrome P450 catalysis.

Angewandte Chemie, vol.54, pp.969-973, 2015 [Link]


Cytochromes P450 (P450 or CYP) belong to a superfamily of multifunctional monooxygenases that contain heme molecules (i.e., Fe-porphyrin) as a prosthetic group. They can catalyze various oxidative metabolic reactions of endogenous and exogenous compounds in living organisms. Their catalytic diversity and vast substrate range with regio- and stereo-specificity have high potential in applications to drug metabolism as well as in the fine chemical synthesis of steroids, lipids, vitamins, and natural products. Here, we have designed a novel visible light-driven platform for cofactor-free, whole-cell P450 photo-biocatalysis using eosin Y (EY) as a photosensitizer. EY can easily enter into the cytoplasm of Escherichia coli and bind specifically to the heme domain of P450. The catalytic turnover of P450 was mediated through the direct transfer of photo-induced electrons from the photosensitized EY to the P450 heme domain under visible light illumination. The photoactivation of the P450 catalytic cycle in the absence of cofactors and redox partners is successfully conducted using many bacterial P450s (variants of P450 BM3) and human P450s (CYPs 1A1, 1A2, 1B1, 2A6, 2E1, and 3A4) for the bioconversion of different substrates, including marketed drugs (simvastatin, lovastatin, and omeprazole) and a steroid (17beta-estradiol), to demonstrate general applicability of the light-driven, cofactor-free system.

[114] J. S. Lee, B. I. Lee, and C. B. Park*
Photo-induced inhibition of Alzheimers beta-amyloid aggregation in vitro by rose bengal.

Biomaterials, vol.38, pp.43-49, 2015 [Link]


The abnormal aggregation of beta-amyloid (Abeta) peptides in the brain is a major pathological hallmark of Alzheimers disease (AD). The suppression (or alteration) of Abeta aggregation is considered to be an attractive therapeutic intervention for treating AD. We report on visible light-induced inhibition of Abeta aggregation by xanthene dyes, which are widely used as biomolecule tracers and imaging markers for live cells. Among many xanthene dyes, rose bengal (RB) under green LED illumination exhibited a much stronger inhibition effect upon photo-excitation on Abeta aggregation than RB under dark conditions. We found that RB possesses high binding affinity to Abeta; it exhibits a remarkable red shift and a strong enhancement of fluorescence emission in the presence of Abeta. Photo-excited RB interfered with an early step in the pathway of Abeta self-assembly and suppressed the conformational transition of Abeta monomers into beta-sheet-rich structures. Photo-excited RB is not only effective in the inhibition of Abeta aggregation, but also in the reduction of Abeta-induced cytotoxicity.

[113] J. H. Lee, D. H. Nam, S. H. Lee, J. H. Park, S. J. Park, S. H. Lee, C. B. Park*, K. J. Jeong*
New platform for cytochrome P450 reaction by in situ immobilization on biopolymer.

Bioconjugate Chemistry, vol.25, pp.2101-2104, 2014 [Link]


Cytochrome P450 monooxygenases that catalyze a remarkable variety of oxidative transformation are of exceptional interest for the synthesis of fine chemicals. However, due to their instability and the requirment of expensive cofactors, P450s have not been used extensively for industry yet. Here, we developed new platform of P450-catalyzed reaction toward preparative scale process by the immobilization of P450s on polyhydroxybutyrate granules. Using the fusion with phasin, P450s could be efficiently immobilized on P(3HB) granules in the cytoplasm of Escherichia coli, and the complex was simply purified by centrifugation after cell disruption. Under various harsh environmental conditions (pH, temperature, urea, and ionic strength), the immobilized P450s exhibited much higher stability and activity compared to those of non-immobilized P450s.

[112] J. Hong+, M. Lee+, B. Lee, D-H. Seo, C. B. Park*, K. Kang*
Biologically inspired pteridine redox centers for rechargeable batteries

Nature Communications, vol.5, pp.5335, 2014 [Link]


The use of biologically occurring redox centers holds a great potential in designing sustainable energy storage systems. Yet, to become practically feasible, it is critical to explore optimization strategies of biological redox compounds, along with in-depth studies regarding their underlying energy storage mechanisms. Here, we report a molecular simplification strategy to tailor the redox unit of pteridine derivatives, which are essential components of ubiquitous electron transfer proteins in nature. We first apply pteridine systems of alloxazinic structure in lithium/sodium rechargeable batteries, and unveil their reversible tautomerism during energy storage. Through the molecular tailoring, the pteridine electrodes can show outstanding performance, delivering 533 Wh kg-1 within 1 hour and 348 Wh kg-1 within 1 minute, as well as high cyclability retaining 96% of the initial capacity after 500 cycles at 10 A g-1. Our strategy combined with experimental and theoretical studies suggests guidance for the rational design of organic redox centers.

[111] S. H. Lee+, G. M. Ryu+, D. H. Nam, J. H. Kim, and C. B. Park*
Silicon nanowire photocathodes for light-driven electroenzymatic synthesis.

ChemSusChem, vol.7, pp.3007-3011, 2014 [Link]


In this report, photoelectroenzymatic synthesis of chemical compounds employing platinum nanoparticle-decorated silicon nanowire (Pt-SiNW) is presented. Pt-SiNW was proved to be an efficient material for photoelectrochemical cofactor regeneration because silicon nanowire absorbs a wide range of solar spectrum and platinum nanoparticle serves as an excellent catalyst for electron and proton transfer. By integrating the platform with redox enzymatic reaction, visible light-driven electroenzymatic synthesis of L-glutamate was achieved. Compared to electrochemical and photochemical methods, this approach is free from side reactions caused by sacrificial electron donor and has advantages of applying low potential to realize energy-efficient and sustainable synthesis of chemicals by photoelectroenzymatic system.

[110] J. Ryu, D. H. Nam, S. H. Lee, and C. B. Park*
Biocatalytic photosynthesis with water as an electron donor.

Chemistry - A European Journal, vol.20, pp.12020-12025, 2014 [Link]


Efficient harvesting of unlimited solar energy and its conversion into valuable chemicals is one of the ultimate goals of scientists. With the ever-increasing concerns about sustainable growth and environmental issues, numerous efforts have been made to develop artificial photosynthetic process for the production of fuels and fine chemicals mimicking natural photosynthesis. Despite the research progresses made over the decades, the technology is still in its infancy because of the difficulties in kinetic coupling of whole photocatalytic cycles. Here, we report a new type of artificial photosynthesis system that can avoid such problems by integrally coupling biocatalytic redox reactions with photocatalytic water-splitting. We found that photocatalytic water-splitting reaction can be efficiently coupled with biocatalytic redox reactions by using tetra-cobalt polyoxometalate and Rh-based organometallic compound as hole and electron scavengers, respectively, for photoexcited Ru(bpy)32+ dye. Based on these results, we could successfully photosynthesize a model chiral compound (L-glutamate) using a model redox enzyme (glutamate dehydrogenase) upon in-situ photo-regeneration of cofactors.

[109] J. H. Kim, M. Lee, and C. B. Park*
Polydopamine as a biomimetic electron gate for artificial photosynthesis.

Angewandte Chemie Intl. Ed., vol.53, pp.6364-6368, 2014 [Link]


We report on the capability of polydopamine (PDA), a mimic of mussel adhesion proteins, as an electron gate as well as a versatile adhesive for mimicking natural photosynthesis. This work demonstrates that PDA accelerates the rate of photoinduced electron transfer from light-harvesting molecules through two-electron and two-proton redox-coupling mechanism. The introduction of PDA as a charge separator significantly increased the efficiency of photochemical water oxidation. Furthermore, simple incorporation of PDA ad-layer on the surface of conducting materials (such as carbon nanotubes) facilitated fast charge separation and oxygen evolution through the synergistic effect of PDA-mediated, proton-coupled electron transfer and substrate materials high conductivity. Our work shows that PDA is an excellent electron acceptor as well as a versatile adhesive; thus, it opens a new electron gate for harvesting photoinduced electrons and designing artificial photosynthetic systems.

[108] J. S. Lee+, D. H. Nam+, S. K. Kuk, and C. B. Park*
Near-infrared-light-driven artificial photosynthesis by nanobiocatalytic assemblies.

Chemistry - A European Journal, vol.20, pp.3852-3857, 2014 [Link]


Solar energy has attracted much attention because of the huge amount of energy continuously transferred from the sun to the Earth. While numerous photosensitizing systems had been studied over the decades for light harvesting, most photosensitizers possess a large bandgap (> 1.7 eV) requiring ultraviolet and visible light for their activation. Considering that over 46% of solar energy is in the near-infrared (NIR) range, almost half of overall solar spectrum cannot be utilized to activate those photosensitizers. Herein, we first report on NIR light-driven biocatalytic artificial photosynthesis using upconversion nanoparticles. Upconversion refers to nonlinear optical processes that occur through anti-Stokes emission, in which an emitted photon has more energy than the absorbed photon by sequential absorption of photons. For NIR light-driven photoenzymatic synthesis, we synthesized silica-coated upconversion nanoparticles, such as Si-NaYF4:Yb,Er and Si-NaYF4:Yb,Tm, for efficient photon-conversion through Forster resonance energy transfer (FRET) with rose bengal (RB), a photosensitizer. We observed NIR-induced electron transfer using linear sweep voltammetric analysis, which indicated photoexcited electrons of RB/Si-NaYF4:Yb,Er were transferred to NAD+ through a Rh-based electron mediator. RB/Si-NaYF4:Yb,Er nanoparticles, which exhibited higher FRET efficiency due to more spectral overlap than RB/Si-NaYF4:Yb, resulted in much better performance for photoenzymatic conversion. Our work shows that upconversion nanoparticles with anti-Stokes emission are promising light harvesters for versatile usage of NIR light in solar-to-chemical conversion processes.

[107] M. Lee, J. U. Kim, J. S. Lee, B. I. Lee, J. Shin*, and C. B. Park*
Mussel-inspired plasmonic nanohybrids for light harvesting.

Advanced Materials, vol.26, pp.4463-4468, 2014 [Link]


We present a simple and versatile approach for the construction of plasmonic metal/ photosensitizer core-shell nanohybrids for efficient light harvesting by adopting multi-purpose polydopamine (PDA) nanolayers inspired by mussel adhesion. In our plasmonic core-shell assembly, PDA coating plays multiple roles: (1) a reducing agent for the synthesis of metal nanoparticles, (2) a scaffold for the encapsulation of photosensitizing dye molecules, and (3) an adhesive layer between the nanohybrid and the substrate. In contrast to nanolithography processes, the entire synthetic procedure can be handled in an aqueous solution under mild conditions and requires no intricate equipment, which confers advantages in large-scale production. Also, by virtue of the remarkable adhesive versatility of PDA coating, this approach can be applied to the development of elaborate core-shell nanostructures regardless of material type and morphology of substrates. We found that the resulting plasmonic nanohybrids exhibit strongly enhanced photocatalytic activity during visible light-induced artificial photosynthesis as a result of amplified light absorption by molecular photosensitizers through LSPR from the plasmonic metal nanoparticles. We expect that a diverse range of metal core (e.g., gold and silver) and dye molecule combinations are possible through the use of our strategy to facilitate the synthesis of assorted sets of nanohybrids with desired optical properties, allowing design flexibility in solar energy conversion applications.

[106] M. Lee+, J. Hong+, H. Lim, S. B. Cho, K. Kang*, and C. B. Park*
Organic nanohybrids for fast and sustainable energy storage.

Advanced Materials, vol.26, pp.2558-2565, 2014 [Link]


Bio-inspired organic electrodes that imitate natural energy metabolisms, such as respiration and photosynthesis, can facilitate the design of sustainable batteries. For example, the electro-active carbonyl compounds mimicking biological quinone cofactors that can be obtained from biomass through eco-friendly processes are intriguing candidates for such electrode materials. Also, flavin-based electrodes that function through the imitation of the cellular energy transduction mechanism are promising candidates. The practical use of organic-based electrodes, however, suffers from sluggish kinetics and poor capacity retention, which originate from low electronic conductivity and dissolution of electroactive compounds into electrolytes. Here, we report a novel and facile design strategy for organic electrodes to achieve high energy and power densities combined with excellent cyclic stability. Non-covalent nanohybridization of electroactive aromatic molecules with single-walled carbon nanotubes (SWNTs) by exploiting pi-pi interactions leads to a rearrangement of electroactive molecules from bulk crystalline particles into molecular layers on conductive scaffolds. The nanohybrid electrode in the form of a flexible, free-standing paper (free of binder/additive and current collector) results in ultrafast kinetics delivering 510 Wh/kg within 30 minutes (204 mAh/g ~ 98% of theoretical capacity) and 272 Wh/kg of energy even within 46 seconds. Moreover, the stable anchorage of electroactive molecules on SWNTs enables above 99% capacity retention upon 100 cycles, which was hardly achieved for organic electrodes. Our approach can be extended to other aromatic organic electrode systems, bringing organic redox chemicals a step closer to practical cathodes in rechargeable batteries.

[105] W-H. Ryu+, Y. W. Lee+, Y. S. Nam, D-Y. Youn, C. B. Park*, and I-D. Kim*
Crystalline IrO2-decorated TiO2 nanofiber scaffolds for robust and sustainable solar water oxidation.

Journal of Materials Chemistry A, vol.2, pp.5610-5615, 2014 [Link]


Solar-driven water oxidation is an essential way to provide electrons for artificial photosynthesis. IrO2 colloids have been used as one of highly-efficient water oxidation catalysts due to their distinguished catalytic activity for water oxidation. However, IrO2 nanoparticles (NPs), which posses a hydrous nature, often suffer from corrosive surface degradation and enter into unstable Ir oxidation states, thereby limiting their cycling characteristics. In this work, we propose a new water oxidation catalyst for enhanced oxygen evolution and long-term recyclability through the functionalization of highly crystalline IrO2 NPs on semiconducting TiO2 nanofibers (NFs). The effects of IrO2 NPs immobilized on TiO2 NFs were investigated in terms of decoration position (inner and outer layers of NFs), crystallite size (10 nm and 30 nm), and loading amount (0 - 5.17 wt %). IrO2 (10 nm)-decorated TiO2 NFs exhibited a high turnover number (TON: 322) and superior recyclability for repeated water oxidation (90% O2 evolving capability after 10 cycles). X-ray photoelectron spectroscopy analysis verified that TiO2 NFs anchored to discrete IrO2 NPs can maintain the oxidation state of IrO2 by self-reduction of TiO2 scaffold. Our synthetic strategy offer a promising route for fabricating efficient and robust catalyst via immobilization of crystalline water oxidation catalysts on semiconducting metal-oxide scaffold.

[104] J. Y. Lee, D. H. Nam, M. W. Oh, Y. Kim, H. S. Choi, D. Y. Jeon, C. B. Park, Y. S. Nam
Serum-stable quantum dot-protein hybrid nanocapsules for optical bio-imaging.

Nanotechnology, vol.25, pp.175702-175711, 2014 [Link]


We introduce shell cross-linked nanocapsules as an efficient tumor-targeted systemic delivery nanocarrier for highly luminescent, heavy-metal-free Cu0.3InS2/ZnS (CIS/ZnS) core-shell quantum dots (QDs). The CIS/ZnS QDs are synthesized by using a hot injection method with copper iodide, indium acetate, zinc stearate, and dodecanethiol. A mixture of the prepared QDs and amine-reactive six-armed poly(ethylene glycol) (PEG) in dichloromethane was emulsified into an aqueous solution containing human serum albumin (HSA). The resulting shell cross-linked nanocapsules show excellent dispersion stability in a serum-containing medium and high luminescence comparable to QDs in a non-polar organic solvent. Folic acid is introduced as a tumor-targeting ligand. In vivo tumor targeted delivery is demonstrated by measuring the fluorescence intensity of several major organs and tumor tissue after an intravenous tail vein injection of the nanocapsules into nude mice. The cytotoxicity of the QD-loaded HSA-PEG nanocapsules is also examined in several 32 types of cells. Our results show that the cellular uptake of the QDs is critical for cytotoxicity. Moreover, a significantly lower level of cell death is observed in the CIS/ZnS QDs compared to nanocapsules loaded with cadmium-based QDs. This study suggests that the systemic tumor targeting of heavy metal-free QDs using shell cross-linked HSA-PEG hybrid nanocapsules is a promising route for in vivo tumor diagnosis with reduced non-specific toxicity

[103] J. H. Kim, D. H. Nam, and C. B. Park*
Nanobiocatalytic assemblies for artificial photosynthesis.

Current Opinion in Biotechnology, vol.28, pp.1-9, 2014 [Link]


Natural photosynthesis, a solar-to-chemical energy conversion process, occurs through a series of photo-induced electron transfer reactions in nanoscale architectures that contain light-harvesting complexes, protein-metal clusters, and many redox biocatalysts. Artificial photosynthesis in nanobiocatalytic assemblies aims to reconstruct man-made photosensitizers, electron mediators, electron donors, and redox enzymes for solar synthesis of valuable chemicals through visible light-driven cofactor regeneration. The key requirement in the design of biocatalyzed artificial photosynthetic process is an efficient and forward electron transfer between each photosynthetic component. This review introduces recent research outcomes in the development of nanobiocatalytic assemblies that can mimic natural photosystems I and II, respectively. Current issues in biocatalytic artificial photosynthesis and future perspectives are discussed.

[102] J. H. Kim, D. H. Nam, Y. W. Lee, Y. S. Nam*, and C. B. Park*
Self-assembly of metalloporphyrins into light-harvesting peptide nanofiber hydrogels for solar water oxidation

Small, vol.10, pp.1272-1277, 2014 [Link]


The self-assembly of peptide-based building blocks is an attractive route for fabricating functional materials due to their unique features, such as functional flexibility and molecular recognition as well as environmental compatibility. Here, we report on the development of artificial light-harvesting hydrogel generated by the self-assembly of Fmoc-FF peptides and metalloporphyrins. We utilized the self-assembled peptide nanostructure of Fmoc-FF as a template to assemble metalloporphyrins into efficient light- harvesting antenna. The metalloporphyrins were placed in close enough proximity to each other to enable excited energy transfer, increasing the photosensitization efficiency, as observed in natural light-harvesting complexes in green plants. The metalloporphyrins in the light-harvesting hydrogel increased the efficiency of photocatalytic water oxidation by iridium oxide nanoparticles up to about 3.7 times compared to their physical mixture. The peptide-based platform could further extend possible sets of functional molecules simply by adding or modifying amino acids in the motif peptides. Scientific insights into the effects of nanoscale-assembled structures of photosensitizers on excited energy transfer can broaden the potential application of biomimetic approaches for light-driven energy systems and photosensitive sensor devices.

[101] J. W. Ko+, W-H. Ryu+, I-D. Kim*, and C. B. Park*
Bi-functional RuO2/Co3O4 core/shell nanofibers as a multi-component 1-D water oxidation catalyst

Chemical Communications, vol.49, pp.9725-9727, 2013 [Link]


Artificial photosynthesis is an attractive way to utilize solar energy through inspiration from natural photosynthesis in green plants. Water-splitting is critically required to establish an artificial photosynthetic system that consists of sequential charge-obtaining and transferring reactions. The oxidation of water is a limiting step to achieving water-splitting because of its multi-hole-related characteristics. A key to the development of effective water oxidation catalysts is the optimized control of material structure and composition through a facile synthetic method. This work synthesized polycrystalline RuO2/Co3O4 core/shell nanofibers by electrospinning and evaluated their photocatalytic water oxidation performance using a Ru(bpy)32+/persulfate system under visible light illumination. Our results show that RuO2/Co3O4 nanofibers exhibit significantly enhanced efficiency of photocatalytic water oxidation with a higher number of turnover frequency than those of pristine Co3O4 nanoparticles, Co3O4 nanofibers, and RuO2 nanofibers, respectively. The unique core-shell structure of RuO2/Co3O4 nanofibers comprising the inner region of highly conductive RuO2 and the outer region of catalytic Co3O4 provided a fast and effective transport highway for holes to O2-evolving sites. This work highlights the potential of tailored 1D binary composite nanofibers for the development of efficient oxygen-evolving catalysts and offers a new viewpoint for exploring multi-component catalysts through electrospinning.

[100] M. Lee+, J. Hong+, D-H. Seo, D. H. Nam, K. T. Nam, K. Kang*, and C. B. Park*
Redox cofactor from biological energy transduction as energy-storage chemical

Angewandte Chemie Int. Ed, vol.52, pp.8322-8328, 2013 [Link]


Cellular metabolism comprises energy transduction machineries that operate by a series of redox-active components to store energies from nutrients, which are transduced into high-energy intermediates for cellular works such as chemical synthesis, transport, and movement. Biological energy transduction mechanism hints at the construction of a man-made energy storage system. Herein, we present a bio-inspired strategy to design high-performance energy devices based on the analogy between energy storage phenomena of mitochondria and lithium rechargeable batteries. Flavins, a key redox element in respiration and photosynthesis, facilitate either one- or two-electron-transfer redox processes accompanying proton transfer at nitrogen atoms of diazabutadiene motif during cellular metabolism. We have successfully demonstrated flavins as a molecularly tunable cathode material that exhibits reversible reactivity with two lithium ions and electrons per formula unit. Analysis of both the ex situ characterizations and density-functional theory (DFT)-based calculations revealed that the redox reaction occurs via two successive single-electron transfer steps, which is analogous to the proton-coupled electron transfer mechanism of flavoenzymes. Tailored flavin analogues obtained via chemical substitution on the isoalloxazine ring showed fine tunability of electrochemical properties, exhibiting a gravimetric capacity of 174 mAh/g and an average redox potential of 2.65 V, and its expected energy density is comparable to that of LiFePO4.

[99] S. H. Ku and C. B. Park*
Combined effect of mussel-inspired surface modification and topographical cues on the behavior of skeletal myoblasts

Advanced Healthcare Materials, vol.2, pp.1445-1450, 2013 [Link]


The control of cell-material interaction is a key issue in the design of suitable scaffold materials for tissue engineering because the physicochemical properties (e.g., surface chemistry, topography) of substrate materials significantly influence cell behaviors. We studied the effect of mussel-inspired polydopamine (PDA) functionalization of the substrate surface in combination with topographical cues on the behavior of skeletal myoblasts. The formation of the PDA ad-layer on the scaffold surface was analyzed using multiple tools including atomic force microscopy, scanning electron microscopy, and Raman spectroscopy. When myoblasts were grown on planar glass substrates, the PDA ad-layer well-supported the adhesion and proliferation of myoblasts, and enhanced the differentiation of myoblasts into multinucleate myotubes. We further developed well-aligned nanofibrous scaffolds to resemble the highly ordered architectures of skeletal muscle tissues, followed by PDA-based surface functionalization. On PDA-modified nanofibers, myogenic protein expression and the fusion of myoblasts were increased significantly compared with those on unmodified nanofibers. The multinucleate myotubes on the aligned nanofibers were oriented in a direction parallel to the nanofibers. Our results suggest that the combination of mussel-inspired surface functionalization and uniaxial topography is a useful strategy for scaffold design in skeletal tissue engineering.

[98] S. H. Lee, J. H. Kim, and C. B. Park*
Coupling photocatalysis and redox biocatalysis toward biocatalyzed artificial photosynthesis

Chemistry - A European Journal, vol.19, pp.4392-4406, 2013 [Link]


Solar energy utilization is accomplished in green plants through a cascade of photo-induced electron transfer, which remains a target model for realizing artificial photosynthesis. In this article, we introduce the concept of about how to design biocatalyzed artificial photosynthesis through coupling redox biocatalysis and photocatalysis to mimic natural photosynthesis. Key design principles for reaction components, such as electron donors, photosensitizers, and electron mediators, are described for artificial photosynthesis involving biocatalytic assemblies. Recent research outcomes that serve as a proof of the concept are summarized and current issues are discussed to provide a future perspective.

[97] J. S. Lee, S. H. Lee, J. Kim, and C. B. Park*
Graphene/Rh-complex hydrogel for boosting redox biocatalysis

Journal of Materials Chemistry A, vol.1, pp.1040-1044, 2013 [Link]


We report the synthesis of a 3D-structured graphene/Rh-complex hydrogel that works as a robust catalyst for electroenzymatic reactions. Pyridine nucleotide cofactors [NAD(P)H] are critically required as a reducing power for many reactions catalyzed by redox enzymes. Thus, in-situ regeneration of reduced cofactors is essential to ensuring redox enzymes continue their turnover. We successfully designed the graphene/Rh-complex hydrogel by immobilizing Rh complex, an organometallic mediator, in the network of graphene hydrogel having large surface area and high conductivity. The pi-electron system in the aromatic heterocyclic region of Rh complex played a critical role in the immobilization and stabilization of Rh complex in the graphene hydrogel for electrochemical NADH regeneration. The catalytic activity of graphene/Rh-complex that has phenanthroline as a ligand remained almost the same through repeated tests. When a-ketoglutarate was electroenzymatically converted to L-glutamate in the presence of graphene/Rh-complex hydrogel, L-glutamate yield increased more than 10 times than that of free Rh complex. This work demonstrates that graphene hydrogel can boost industrially important reactions catalyzed by redox enzymes.

[96] S. H. Ku and C. B. Park*
Myoblast differentiation on graphene oxide

Biomaterials, vol.34, pp.2017-2023, 2013 [Link]


Graphene-based nanomaterials have received much attention in biomedical applications for drug/gene delivery, cancer therapy, imaging, and tissue engineering. Despite the capacity of 2D carbon materials as a nontoxic and implantable platform, their effect on myogenic differentiation has been rarely studied. We investigated the myotube formation on graphene-based nanomaterials, particularly graphene oxide (GO) and reduced graphene oxide (rGO). GO sheets were immobilized on amine-modified glass to prepare GO-modified glass, which was further reduced by hydrazine treatment for the synthesis of rGO-modified substrate. We studied the behavior, including adhesion, proliferation, and differentiation, of mouse myoblast C2C12 on unmodified, GO-, and rGO-modified glass substrates. According to our analyses of myogenic protein expression, multi-nucleated myotube formation, and expression of differentiation-specific genes (MyoD, Myogenin, Troponin T, and MHC), myogenic differentiation was remarkably enhanced on GO, which resulted from serum protein adsorption and nanotopographical cues. Our results demonstrate the ability of GO to stimulate myogenic differentiation, showing a potential for skeletal tissue engineering applications.

[95] J. W. Ko, J. H. Kim, and C. B. Park
Synthesis of visible light-active CeO2 sheets via mussel-inspired CaCO3 mineralization

Journal of Materials Chemistry A, vol.1, pp.241-245, 2013 [Link]


Ceria attracted much attention due to its unique redox properties and high reactivity, which has been widely applied for solid oxide fuel cells, catalysis, and sensors. However, the use of ceria as a photocatalyst is limited due to its large optical bandgap (3.19 eV). In this study, we successfully synthesized ceria sheets that exhibited distinct polycrystalline sheet-like structure with grains, the size of which varied with calcination temperatures. The grain size of ceria sheets influenced the concentration of cerium ions on their surface, thus affecting their bandgap. The nano-grained ceria sheets exhibited a red-shift in the UV-visible absorption spectrum and a much narrower bandgap (2.71-2.83 eV). Visible light-responsive photocatalytic activity was observed with nano-grained ceria sheets at a rate constant that was much higher than that of ceria nanoparticles.

[94] S. H. Ku, M. Lee, and C. B. Park*
Carbon-based nanomaterials for tissue engineering

Advanced Healthcare Materials, vol.2, pp.244-260, 2013 [Link]


Carbon-based nanomaterials such as graphene sheets and carbon nanotubes possess unique mechanical, electrical, and optical properties that present new opportunities for tissue engineering, a key field for the development of biological alternatives that repair or replace whole or a portion of tissue. Carbon nanomaterials can also provide a similar micro-environment as like a biological extracellular matrix in terms of chemical composition and physical structure, making them a potential candidate for the development of artificial scaffolds. In this review, we summarize recent research advances in the effects of carbon nanomaterial-based substrates on cellular behaviors, including cell adhesion, proliferation, and differentiation into osteo- or neural- lineages. The development of 3D scaffolds based on carbon nanomaterials (or their composites with polymers and inorganic components) is introduced, and the potential of these constructs in tissue engineering, including toxicity issues, is discussed. Future perspectives and emerging challenges are also highlighted.

[93] S. H. Lee, Y-C Kwon, D-M Kim, and C. B. Park*
Cytochrome P450-catalyzed O-dealkylation coupled with photochemical NADPH Regeneration

Biotechnology and Bioengineering, vol.110, pp.383-390, 2013 [Link]


Cytochrome P450 monooxygenases are multi-functional biocatalyst with potential applications in chemoenzymatic synthesis of complex chemicals as well as in studies of metabolism and xenobiotics. Widespread application of cytochrome P450s, however, is encumbered by the critical need for redox equivalents in their catalytic function. To overcome this limitation, we studied visible light-driven regeneration of NADPH for P450-catalyzed O-dealkylation reaction; we used eosin Y as a photosensitizing dye, triethanolamine as an electron donor, and Cp*Rh(bpy)H2O as an electron mediator. We analyzed catalytic activity of cell-free synthesized P450 BM3 monooxygenase variant (Y51F/F87A, BM3m2) in the presence of key components for NADPH photoregeneration. The P450-catalyzed O-dealkylation reaction sustainably maintained its turnover with the continuous supply of photoregenerated NADPH. Visible light- driven, non-enzymatic NADPH regeneration provides a new route for efficient, sustainable utilization of P450 monooxygenases.

[92] S. Kim and C. B. Park*
Bio-inspired synthesis of minerals for energy, environment, and medicinal applications

Advanced Functional Materials, vol.23, pp.10-25, 2013 [Link]


Biomineralization, the natural pathway of assembling biogenic inorganic compounds, inspires us to exploit unique, effective strategies to fabricate functional materials with intricate structures. In this article, we review the recent advances in bio-inspired synthesis of minerals, mainly those of calcium-based minerals, and its applications to the design of functional materials for energy, environment, and biomedical fields. Biomimetic mineralization is extending its application range to unconventional area such as the design of component materials for lithium-ion batteries and elaborately structured composite materials utilizing carbon dioxide gas. Materials with highly enhanced mechanical properties are synthesized through emulating the nacre structure. Studies of bioactive minerals-carbon hybrid materials show an expansion of potential applications to fields ranging from interdisciplinary science to practical engineering such as the fabrication of reinforced bone-implantable materials.

[91] H. Y. Lee, J. H. Kim, E. J. Son, and C. B. Park*
Silicon nanowires as a rechargeable template for hydride transfer in redox biocatalysis

Nanoscale, vol.4, pp.7636-7640, 2012 [Link]


Silicon nanowires have been widely used in many nanoscale devices, including solar cells, photoelectro- chemical cells, transistors, and battery electrodes. Herein, we report a new possible application of hydrogen- terminated silicon nanowires (H-SiNWs) as a rechargeable template for hydride transfer in redox biocatalysis. Redox enzymes can catalyze various types of complex organic synthesis under mild conditions but often require a stoichiometric amount of expensive nicotinamide cofactors (NADH) for their catalytic activities. We found that H-SiNWs transfer hydride efficiently to regenerate NADH from NAD+ via an Rh-based electron mediator. During the regeneration of NADH, the Si-Hx bonds on H-SiNWs were oxidized to form Si-OH and Si-O-Si bonds on the nanowire surface and evolve hydrogen. The oxidized H-SiNWs were readily recharged by treatment in a diluted HF solution for the repeated generation of NADH and continuous enzymatic reactions for the synthesis of D-lactate from pyruvate catalyzed by lactate dehydrogenase.

[90] H. Y. Lee, J. Ryu, J. H. Kim, S. H. Lee, and C. B. Park*
Biocatalyzed artificial photosynthesis by hydrogen-terminated silicon nanowires

ChemSusChem, vol.5, pp.2129-2132, 2012 [Link]


This study successfully demonstrates that hydrogen-terminated silicon nanowires (H-SiNWs) are an ideal artificial photosynthetic material, which possesses suitable photocatalytic properties to regenerate reducing power (i.e., NADH) and synthesize chemicals by photoenzymatic reaction. H-SiNWs, fabricated by a metal-assisted chemical etching process, possessed an enlarged band gap from the effect of quantum confinement and enabled a cascading electron transfer from electron donor to NAD via an Rh-based electron mediator. Approximately 80% of NADH was photo-regenerated from NAD by H-SiNWs within 2 hrs of light irradiation (wavelength > 420 nm), which was successfully coupled with the photoenzymatic synthesis of L-glutamate. Our work suggests that H-SiNWs are an ideal artificial photosynthetic material, which possesses suitable photocatalytic properties to regenerate NADH and synthesize chemicals by photoenzymatic reaction.

[89] J. W. Ko, S-W, Kim, J. Hong, J. Ryu, K. Kang, and C. B. Park*
Synthesis of graphene-wrapped CuO hybrid materials by carbon dioxide mineralization

Green Chemistry, vol.14, pp.2391-2394, 2012 [Link]


CuO possesses high theoretical capacity and safety with low cost and limited environmental toxicity, but a large volumetric change of CuO electrodes during the insertion and extraction of lithium ions can destroy its crystal structure and cause capacity decay in a short time. According to the present work, graphene-wrapped CuO hybrid material can highly enhance the stability and recyclability of CuO anode for lithium ion batteries. We successfully synthesized nanostructured graphene/CuO by converting a carbon dioxide-mineralized graphene oxide/calcium carbonate precursor to Cu-based minerals. Graphene/CuO exhibited nanoribbon-like CuO aggregates well-hybridized with graphene nanosheets. The excellent electrochemical performance of graphene/CuO is attributed to the synergic effect of CuO wrapped by highly conductive graphene sheets and graphene itself capable of Li-ion storage. Furthermore, flexible graphene sheets hybridized with CuO were beneficial for reducing the strain caused by volume changes during the charge/discharge process to show good cyclic performance. The synthesis of graphene/CuO and its application to lithium ion battery electrodes suggest a new possibility for hybridizing graphene and metal oxide nanoparticles using the inspiration of natural mineralization.

[88] S. Y. Lim, J. Ahn, J. S. Lee, M-G. Kim, and C. B. Park*
Graphene oxide-based immunosensing through fluorescence quenching by peroxidase-catalyzed polymerization

Small, vol.8, pp.1994-1999, 2012 [Link]


A graphene oxide (GO)-based immunosensor is developed for the detection of interleukin-5 (IL-5), a key cytokine associated with asthma pathology and eosinophilia. The immunosensing platform utilizes innate fluorescence of GO, not demanding biomolecules labeled with fluorescent dyes. For the construction of GO-based immunosensors, anti-IL-5 antibodies were immobilized on GO surface, then IL-5 and horseradish peroxidase (HRP)-linked antibody conjugates were consequently introduced to form a sandwich immune-complex on GO, which was investigated by using multiple analytical tools such as UV/Vis absorption, fluorescence, Raman spectroscopies, and atomic force microscopy. We found that HRP-catalyzed polymerization of 3,3-diaminobenzidine directly quenched the fluorescence of GO. The degree of GO fluorescence quenching was closely correlated to the concentration of IL-5 with a detection limit of approximately 4 pg/ml. The GO-based immunoassay system exhibited high specificity for IL-5 among other cytokines and was not affected by non-specific proteins in human serum.

[87] S. H. Ku, S. H. Lee, and C. B. Park*
Synergic effects of nanofiber alignment and electroactivity on myoblast differentiation

Biomaterials, vol.33, pp.6098-6104, 2012 [Link]


The interactions between cells and materials play critical roles in the success of new scaffolds for tissue engineering, since chemical and physical properties of biomaterials regulate cell adhesion, proliferation, migration, and differentiation. We have developed nanofibrous substrates that possess both topographical cues and electroactivity. The nanofiber scaffolds were fabricated through the electrospinning of polycaprolactone (PCL, a biodegradable polymer) and polyaniline (PANi, a conducting polymer) blends. We investigated the ways in which those properties influenced myoblast behaviors. Neither nanofiber alignment nor PANi concentration influenced cell growth and proliferation, but cell morphology changed significantly from multipolar to bipolar with the anisotropy of nanofibers. According to our analyses of myosin heavy chain expression, multinucleate myotube formation, and the expression of differentiation-specific genes (myogenin, troponin T, MHC), the differentiation of myoblasts on PCL/PANi nanofibers was strongly dependent on both nanofiber alignment and PANi concentration. Our results suggest that topographical cues and the electroactivity of nanofibers synergistically stimulate muscle cell differentiation to make PCL/PANi nanofibers a suitable scaffold material for skeletal tissue engineering.

[86] S-W. Kim, K-Y. Park, J. Ryu, J. W. Ko, W. Cho, S-M. Kim, C. B. Park, and K. Kang*
Energy storage in in-vivo synthesizable biominerals

RSC Advances, vol.2, pp.5499-5501, 2012 [Link]


For the past decades, biomaterials have been extensively studied mostly for medical applications, such as new pharmaceuticals, tissue engineering, and artificial organs, due to their excellent biocompatibilities. Nowadays, biomaterials further expand their boundaries to various functionalities in sensor, display, and energy devices. With the move towards the use of greener materials to power vehicles, environmentally-benign synthesis of energy materials is becoming an important aspect. Here, energy storage capability of Cu-based biomineral, copper oxychloride, from the jaws of Glycera dibranchiate, a marine bloodworm, is demonstrated. Copper oxychloride electrode delivered approximately 500 mAh/g with a reasonably good cycling through the conversion reaction. This study demonstrates that inorganic biominerals, which are in-vivo synthesizable, can be utilized as energy storage materials, and furthermore, suggests the applicability of sustainable production of energy devices from bio-factory. While we have examined the Cu-based biomineral in this study, there are various natural biominerals containing other transition metal ions, such as Fe and Mn, which can serve as excellent redox elements. Therefore, significant unexplored opportunities exist in natural biominerals with different electrochemical properties.

[85] D. H. Nam and C. B. Park*
Visible light-driven NADH regeneration sensitized by proflavine for biocatalysis

ChemBioChem, vol.13, pp.1278-1282, 2012 [Link]


We describe on the successful coupling of photochemical NADH regeneration with redox enzymatic synthesis by using proflavine as a light-harvesting molecule. Proflavine, a promising photosensitizer, exhibited a high capacity to drive the reduction of NAD into NADH in the presence of a Rh-based electron mediator, and the photoregenerated NADH was enzymatically active to be oxidized by NADH-dependent L-glutamate dehydrogenase for the synthesis of L-glutamate. Both the wavelength and intensity of incident light were found to significantly affect the efficiency of photochemical NADH regeneration. In contrast to proflavine, flavin derivatives, such as FAD, FMN, lumichrome, and riboflavin, accelerated solely the rate of NADH oxidation, not that of NAD reduction. Our results indicate that proflavine has the potential to become an efficient light harvesting component in biocatalytic photosynthesis driven by solar energy.

[84] J. S. Lee, H-A. Joung, M-G. Kim, and C. B. Park*
Graphene-based chemiluminescence resonance energy transfer for homogeneous immunoassay

ACS Nano, vol.6, pp.2978-2983, 2012 [Link]


We first report on chemiluminescence resonance energy transfer (CRET) between graphene nanosheets and chemiluminescent donors. In contrast to fluorescence resonance energy transfer, CRET occurs via non-radiative dipole-dipole transfer of energy from a chemiluminescent donor to a suitable acceptor molecule without an external excitation source. We designed a graphene-based CRET platform for homogenous immunoassay of C-reactive protein, a key marker for human inflammation and cardiovascular diseases, using a luminol/hydrogen peroxide chemiluminescence (CL) reaction catalysed by horseradish peroxidase. According to our results, anti-CRP antibody conjugated to graphene nanosheets enabled the capture of CRP at the concentration above 1.6 ng/mL. In the CRET platform, graphene played a key role as an energy acceptor, which was more efficiently than graphene oxide, while luminol served as a donor to graphene, triggering the CRET phenomenon between luminol and graphene. The graphene-based CRET platform was successfully applied to the detection of CRP in human serum samples in the range observed during acute inflammatory stress.

[83] S. H. Lee, H. J. Lee, K. Won, and C. B. Park*
Artificial electron carriers for photoenzymatic synthesis under visible light

Chemistry - A European Journal, vol.18, pp.5490-5495, 2012 [Link]


Enzymes have long been successfully employed as biocatalysts in organic synthesis because they possess high specificity and catalytic activity even under mild conditions. However, the applications of redox enzymes were limited, mainly because of their strict requirement of reduced nicotinamide coenzyme (i.e., NADH). For the first time, employment of NAD analogs has overcome the limitations of NAD through photochemical regeneration. We investigated four different NAD analogs (i.e., APAD, PAAD, TNAD, and NAAD) that possess substituted functional groups in their pyridine part and exhibit different spectral and redox properties from NAD. We found that APAD and PAAD were photochemically reduced more efficiently than NAD, while their reduced products showed coenzyme activity comparable to natural NAD. In contrast, TNAD formed a complex with photosensitizer, and NAAD possessed more negative reduction peak potential and a negative charge, making both TNAD and NAAD poorer than NAD in photoregeneration. The higher reduction efficiency of APAD significantly enhanced the yield of redox reaction coupled with in situ visible light-driven coenzyme regeneration. Our work shows that NAD analogs can be excellent coenzymes to be regenerated via photochemical regeneration method and to be applied to redox enzymatic reactions.

[82] J. S. Lee, K. H. You, and C. B. Park*
Highly photoactive, low band-gap titanium dioxide nanoparticles wrapped by graphene

Advanced Materials, vol.24, pp.1084-1088, 2012 [Link]


Titanium dioxide, an oxide semiconductor, is regarded as a suitable material for various photocatalytic applications because of its strong oxidizing power, high chemical inertness, low cost, and long-term stability. However, a large band gap (3.2 eV) of anatase titanium dioxide restricts its use only to the narrow light-response range of ultraviolet (only 3~5% of total sunlight). We report on the synthesis of novel graphene-wrapped anatase titanium dioxide nanoparticles (NPs) that highly enhance the photocatalytic activity of titanium dioxide under visible light irradiation. We have prepared graphene-anatase titanium dioxide hybrid NPs by wrapping amorphous titanium dioxide NPs with graphene oxide (GO), followed by a one-step GO reduction and titanium dioxidecrystallization via hydrothermal treatment. Graphene-titanium dioxide NPs exhibited a red shift of the band edge and a significant reduction of the band gap (2.80 eV). We found that graphene-titanium dioxide NPs possess excellent photocatalytic property under visible light for the degradation of methylene blue with a rate constant of 0.0341/min, which was much higher than those of other titanium dioxide- based photocatalytic materials. The strategy presented in this study will enable a ready integration of functional semiconductor NPs and graphene nanosheets for the synthesis of highly photoactive graphene-based metal oxide hybrid materials.

[81] J. H. Kim, M. Lee, J. S. Lee, and C. B. Park*
Self-assembled light-harvesting peptide nanotubes for mimicking natural photosynthesis

Angewandte Chemie Int. Ed, vol.51, pp.517-520, 2012 [Link]


Self-assembled light-harvesting peptide nanotubes are synthesized for artificial photosynthesis. Light-harvesting by natural photosynthesis occurs by means of two large protein complexes called photosystem I and II, which are composed of light-harvesting antenna (i.e., chlorophyll a and b) and catalytic metal clusters embedded within proteins. We have succeeded in the development of light-harvesting peptide nanotubes that integrate photosynthetic units, thus mimicking natural photosynthesis. Light-harvesting peptide nanotubes were synthesized by the self-assembly of diphenylalanine (Phe-Phe, FF) and porphyrin. We found that the J-aggregation of porphyrin occurs during the self-assembly of the FF nanotubes via electrostatic attraction and hydrogen bonding. The light-harvesting peptide nanotubes were suitable for mimicking photosynthesis because of their structure and electrochemical properties similar to natural photosystem. We demonstrated that the integrated photocatalytic system is effective for visible light-driven NADH regeneration coupled with redox enzymatic synthesis of fine chemicals such as L-glutamate.

[80] S. Y. Lim, J. H. Kim, J. S. Lee, J. Ahn, M-G. Kim, and C. B. Park*
Multi-layered stacks of fluorescent dye-doped silica nanoparticles decorated by gold nanoparticles for solid-phase optical biosensing

Journal of Materials Chemistry, vol.21, pp.17623-17626, 2011 [Link]

[79] H. J. Lee, S. H. Lee, C. B. Park*, and K. Won*
Coenzyme analogs: Excellent substitutes (not poor imitations) for electrochemical regeneration

Chemical Communications, vol.47, pp.12538-12540, 2011 [Link]

[78] S. Hong+, J. S. Lee+, J. Ryu, S. H. Lee, D-P. Kim, C. B. Park*, and H. Lee*
Bio-inspired strategy for on-surface synthesis of silver nanoparticles for metal/organic hybrid nanomaterials and LDI-MS substrates

Nanotechnology, vol.22, pp.494020-494026, 2011 [Link]

[77] J. H. Kim, S. H. Lee, J. S. Lee, M. Lee, and C. B. Park*
Zn-Containing porphyrin as a biomimetic light-harvesting molecule for biocatalyzed artificial photosynthesis

Chemical Communications, vol.47, pp.10227-10229, 2011 [Link]

[76] S. Kim, J. W. Ko, and C. B. Park*
Bio-inspired mineralization of CO2 gas to hollow CaCO3 microspheres and bone hydroxyapatite/polymer composites

Journal of Materials Chemistry, vol.21, pp.11070-11073, 2011 [Link]

[75] J. Ryu, S. H. Ku, M. Lee, and C. B. Park*
Bone-like peptide/hydroxyapatite nanocomposites assembled with multi-level hierarchical structures

Soft Matter, vol.7, pp.7201-7206, 2011 [Link]

[74] J. S. Lee, S. H. Lee, J. H. Kim, and C. B. Park*
Artificial photosynthesis on a chip: Microfluidic cofactor regeneration and photoenzymatic synthesis under visible light

Lab on a Chip, vol.11, pp.2309-2311, 2011 [Link]

[73] M. Lee, J. H. Kim, S. H. Lee, S. H. Lee, and C. B. Park*
Biomimetic artificial photosynthesis by light-harvesting synthetic woods

ChemSusChem, vol.4, pp.581-586, 2011 [Link]

[72] S. Kim, S. H. Ku, S. Y. Lim, J. H. Kim, and C. B. Park*
Graphene-biomineral hybrid materials

Advanced Materials, vol.23, pp.2009-2014, 2011 [Link]

[71] J. Ryu, S. H. Lee, D. H. Nam, and C. B. Park*
Rational design and engineering of quantum-dot sensitized TiO2 nanotube arrays for artificial photosynthesis

Advanced Materials, vol.23, pp.1883-1888, 2011 [Link]

[70] S. H. Lee, J. Ryu, D. H. Nam, and C. B. Park*
Photoenzymatic synthesis through sustainable NADH regeneration by SiO2-supported quantum dots

Chemical Communications, vol.47, pp.4643-4645, 2011 [Link]

[69] J. H. Kim, J. Ryu, and C. B. Park*
Selective detection of neurotoxin by photoluminescent peptide nanotubes

Small, vol.7, pp.718-722, 2011 [Link]

[68] J. S. Lee, I. Yoon, J. Kim, H. Ihee*, B. Kim*, and C. B. Park*
Self-assembly of semiconducting photoluminescent peptide nanowires in the vapor phase

Angewandte Chemie Int. Ed, vol.50, pp.1164-1167, 2011 [Link]

[67] H.-I. Ryoo+, J. S. Lee+, C. B. Park*, and D.-P. Kim*
A microfluidic system incorporated with peptide/Pd nanowires for heterogeneous catalytic reactions

Lab on a Chip, vol.11, pp.378-380, 2011 [Link]

[66] J. H. Kim, S. Y. Lim, D. H. Nam, J. Ryu, S. H. Ku, and C. B. Park
Self-assembled photoluminescent peptide hydrogel as a versatile platform for enzyme-based optical biosensors

Biosensors and Bioelectronics, vol.26, pp.1860-1865, 2011 [Link]

[65] J. Ryu+, S.-W. Kim+, K. Kang*, and C. B. Park*
Mineralization of self-assembled peptide nanofibers for rechargeable Li-ion batteries.

Advanced Materials, vol.22, pp.5537-5541, 2010 [Link]

[64] S. H. Ku and C. B. Park*
Human endothelial cell growth on mussel-inspired nanofiber scaffold for vascular tissue engineering.

Biomaterials, vol.31, pp.9431-9437, 2010 [Link]

[63] M. Lee, S. H. Ku, J. Ryu, and C. B. Park*
Mussel-inspired functionalization of carbon nanotubes for hydroxyapatite mineralization.

Journal of Materials Chemistry, vol.20, pp.8848-8853, 2010 [Link]

[62] S. H. Ku, J. S. Lee, and C. B. Park*
Spatial control of cell adhesion and patterning through mussel-inspired surface modification by polydopamine.

Langmuir, vol.26, pp.15104-15108, 2010 [Link]

[61] S.-W. Kim+, J. Ryu+, C. B. Park*, and K. Kang*
Carbon nanotube-amorphous FePO4 core-shell nanowires as cathode material for Li ion batteries.

Chemical Communications, vol.46, pp.7409-7411, 2010 [Link]

[60] S. Kim and C. B. Park*
Dopamine-induced mineralization of calcium carbonate vaterite microspheres.

Langmuir, vol.26, pp.14730-14736, 2010 [Link]

[59] J. S. Lee and C. B. Park*
Microfluidic dissociation and clearance of Alzheimers b-amyloid aggregates.

Biomaterials, vol.31, pp.6789-6795, 2010 [Link]

[58] S. Kim and C. B. Park*
Mussel-inspired transformation of CaCO3 to bone minerals.

Biomaterials, vol.31, pp.6628-6634, 2010 [Link]

[57] J. Ryu, S. H. Ku, H. Lee*, and C. B. Park*
Mussel-inspired polydopamine coating as a universal route to hydroxyapatite crystallization.

Advanced Functional Materials, vol.20, pp.2132-2139, 2010 [Link]

[56] D. H. Nam, S. H. Lee, and C. B. Park*
CdTe, CdSe, CdS nanocrystals for highly efficient regeneration of nicotinamide cofactor under visible light.

Small, vol.6, pp.922-926, 2010 [Link]

[55] S. H. Ku, J. Ryu, S. K. Hong, H. Lee*, and C. B. Park*
General functionalization route for cell adhesion on non-wetting surfaces.

Biomaterials, vol.31, pp.2535-2541, 2010 [Link]

[54] J. Ryu, S.-W. Kim, K. Kang*, and C. B. Park*
Synthesis of diphenylalanine/cobalt oxide hybrid nanowires and their application to energy storage.

ACS Nano, vol.4, pp.159-164, 2010 [Link]

[53] J. Ryu and C. B. Park*
High stability of self-assembled peptide nanowires against thermal, chemical, and proteolytic attacks.

Biotechnology and Bioengineering, vol.105, pp.221-230, 2010 [Link]

[52] S. Y. Lim, J. S. Lee, and C. B. Park*
In situ growth of gold nanoparticles by enzymatic glucose oxidation within alginate gel matrix.

Biotechnology and Bioengineering, vol.105, pp.210-214, 2010 [Link]

[51] S. Y. Lim, J. H. Kim, J. S. Lee, and C. B. Park*
Gold nanoparticle enlargement coupled with fluorescence quenching for highly sensitive detection of analytes.

Langmuir, vol.25, pp.13302-13305, 2009 [Link]

[50] S. H. Lee, D. H. Nam, and C. B. Park*
Screening xanthene dyes for visible-light driven NADH regeneration and photoenzymatic synthesis.

Advanced Synthesis and Catalysis, vol.351, pp.2589-2594, 2009 [Link]

[49] S. H. Lee, K. Won, H-K. Song*, and C. B. Park*
Colloidal nanoparticles as a wireless booster for electroenzymatic reactions.

Small, vol.5, pp.2162-2166, 2009 [Link]

[48] S. Y. Lim, K-O. Kim, D-M. Kim*, and C. B. Park*
Silica-coated alginate beads for in vitro protein synthesis via transcription/translation machinery encapsulation.

Journal of Biotechnology, vol.143, pp.183-189, 2009 [Link]

[47] S. H. Lee, D. H. Nam, J. H. Kim, J-O. Baeg, and C. B. Park*
Eosin Y-sensitized artificial photosynthesis via highly efficient visible-light driven regeneration of nicotinamide cofactor.

ChemBioChem, vol.10, pp.1621-1624, 2009 [Link]

[46] J. S. Lee, J. Ryu, and C. B. Park*
Bio-inspired fabrication of superhydrophobic surfaces through peptide self-assembly.

Soft Matter, vol.5, pp.2717-2720, 2009 [Link]

[45] J. Ryu and C. B. Park*
Synthesis of diphenylalanine/polyaniline core/shell conducting nanowires by peptide self-assembly.

Angewandte Chemie Intl. Ed., vol.48, pp.4820-4823, 2009 [Link]

[44] J. S. Lee, J. Ryu, and C. B. Park*
High-throughput analysis of Alzheimers b-amyloid aggregation using a microfluidic self-assembly of monomers.

Analytical Chemistry, vol.81, pp.2751-2759, 2009 [Link]

[43] J. Ryu, S. Y. Lim, and C. B. Park*
Photoluminescent peptide nanotubes.

Advanced Materials, vol.21, pp.1577-1581, 2009 [Link]

[42] K-O. Kim, S. Y. Lim, G-H. Hahn, S. H. Lee, D-M. Kim *, and C. B. Park*
Cell-free synthesis of functional proteins using transcription/translation machinery entrapped in silica sol-gel matrix.

Biotechnology and Bioengineering, vol.102, pp.303-307, 2009 [Link]

[41] S. H. Ku and C. B. Park*
Highly accelerated self-assembly and fibrillation of prion peptide on solid surfaces.

Langmuir, vol.24, pp.13822-13827, 2008 [Link]

[40] C. B. Park, S. H. Lee, E. Subramanian, B. B. Kale, S. M. Lee, and J-O. Baeg*
Solar energy in production of L-glutamate through visible light active photocatalyst - redox enzyme coupled bioreactor.

Chemical Communications, vol.0., pp.5423-5425, 2008 [Link]

[39] J. S. Lee, E. Um, J-K. Park, and C. B. Park*
Microfluidic self-assembly of insulin monomers into amyloid fibrils on a solid surface.

Langmuir, vol.24, pp.7068-7071, 2008 [Link]

[38] J. Ryu and C. B. Park*
High-temperature self-assembly of peptides into vertically well-aligned nanowires by aniline vapor.

Advanced Materials, vol.20, pp.3754-3758, 2008 [Link]

[37] J. Ryu and C. B. Park*
Solid-phase growth of nanostructures from amorphous peptide thin film: Effect of water activity and temperature.

Chemistry of Materials, vol.20, pp.4284-4290, 2008 [Link]

[36] K. Girigoswami, S. H. Ku, J. Ryu, and C. B. Park*
A synthetic amyloid lawn system for high-throughput analysis of amyloid toxicity and drug screening.

Biomaterials, vol.29, pp.2813-2819, 2008 [Link]

[35] J. Ryu, K. Girigoswami, C. Ha, S. H. Ku, and C. B. Park*
Influence of multiple metal ions on b-amyloid aggregation and dissociation on a solid surface.

Biochemistry, vol.47, pp.5328-5335, 2008 [Link]

[34] J. Ryu, H-A. Joung, M-G. Kim*, and C. B. Park*
Surface plasmon resonance analysis of Alzheimers b-amyloid aggregation on a solid surface: From monomers to fully-grown fibrils.

Analytical Chemistry, vol.80, pp.2400-2407, 2008 [Link]

[33] J. Ryu, M. Kanapathipillai, G. Lentzen, and C. B. Park*
Inhibition of b-amyloid peptide aggregation and neurotoxicity by a-D-mannosylglycerate, a natural extremolyte.

Peptides, vol.29, pp.578-584, 2008 [Link]

[32] H-K. Song, S. H. Lee, K. Won, J. H. Park, J. K. Kim, H. Lee, S-J. Moon, D. K. Kim, and C. B. Park*
Electrochemical regeneration of NADH enhanced by platinum nanoparticles.

Angewandte Chemie Intl. Ed., vol.47, pp.1749-1752, 2008 [Link]

[31] M. Kanapathipillai, S. H. Ku, K. Girigoswami, and C. B. Park*
Small stress molecules inhibit aggregation and neurotoxicity of prion peptide 106-126.

Biochemical and Biophysical Research Communications, vol.365, pp.808-813, 2008 [Link]

[30] T. H. Han, J. Kim, J. S. Park, C. B. Park, H. Ihee*, and S. O. Kim*
Liquid crystalline peptide nanowires.

Advanced Materials, vol.19, pp.3924-3927, 2007 [Link]

[29] W-S. Kim, M-G. Kim, J-H. Ahn, B-S. Bae, and C. B. Park*
Protein micropatterning on bifunctional organic-inorganic sol-gel hybrid materials.

Langmuir, vol.23, pp.4732-4736, 2007 [Link]

[28] C. Ha, J. Ryu, and C. B. Park*
Metal ions differentially influence the aggregation and deposition of Alzheimers b-amyloid on a solid template.

Biochemistry, vol.46, pp.6118-6125, 2007 [Link]

[27] E. Siu, K. Won, and C. B. Park*
Electrochemical regeneration of NADH using conductive vanadia-silica xerogels.

Biotechnology Progress, vol.23, pp.293-296, 2007 [Link]

[26] K. Won, E. Siu, and C. B. Park*
Conductive sol-gel hybrid materials for novel cofactor regeneration in biocatalysis.

Solid State Phenomena, vol.124, pp.1087-1090, 2007 [Link]

[25] C. Ha and C. B. Park*
Ex situ atomic force microscopy analysis of b-amyloid self-assembly and deposition on a synthetic template.

Langmuir, vol.22, pp.6977-6985, 2006 [Link]

[24] Boonyaratanakornkit, J. C. Lopez, C. B. Park, and D. S. Clark*
Pressure affects transcription profiles of Methanocaldococcus jannaschii despite the absence of baraphilic growth under gas-transfer limitation.

Environmental Microbiology, vol.8, pp.2031-2035, 2006 [Link]

[23] C. B. Park, B. Boonyaratanakornkit, and D. S. Clark*
Toward large scale cultivation of hyperthermophiles in high temperature and high pressure.

Methods in Microbiology, vol.35, pp.109-126, 2006 [Link]

[22] C. Ha and C. B. Park*
Template-directed self-assembly and growth of insulin amyloid fibrils.

Biotechnology and Bioengineering, vol.90, pp.848-855, 2005 [Link]

[21] M. Y. Lee, C. B. Park, J. S. Dordick*, and D. S. Clark*
Metabolizing enzyme toxicology assay chip (MetaChip) for high-throughput microscale toxicity analyses.

Proc. Natl. Acad. Sci. USA, vol.102, pp.983-987, 2005 [Link]

[20] M. Kanapathipillai, G. Lentzen, M. Sierks, and C. B. Park*
Ectoine and hydroxyectoine inhibit aggregation and neurotoxicity of Alzheimers beta-amyloid.

FEBS Letters, vol.579, pp.4775-4780, 2005 [Link]

[19] R. Liu, H. Barkhordarian, S. Emadi, C. B. Park, and M. R. Sierks*
Trehalose differentially inhibits aggregation and neurotoxicity of beta-amyloid 40 and 42.

Neurobiology of Disease, vol.20, pp.74-81, 2005 [Link]

[18] A. Arora, C. Ha, and C. B. Park*
Insulin amyloid fibrillization at above 100 degree C: New insights into protein folding under extreme temperatures.

Protein Science, vol.13, pp.2429-2436, 2004 [Link]

[17] A. Arora, C. Ha, and C. B. Park*
Inhibition of insulin amyloid formation by small stress molecules.

FEBS Letters, vol.564, pp.121-125, 2004 [Link]

[16] Q. Li, J-S. Lee, C. Ha, C. B. Park, G. Yang, W. B. Gan, and Y-T. Chang*
Solid phase synthesis of styryl dyes and their application as amyloid sensors.

Angewandte Chemie Intl. Ed., vol.43, pp.6331-6335, 2004 [Link]

[15] D. Wang, C. Ha, C. B. Park, and Y. Joo*
CMOS Focal-plane-array for analysis of enzymatic reaction in system-on-chip spectrophotometer.

SPIE-IS&T, vol.5301, pp.67-75, 2004

[14] C. B. Park, D.D.Y. Ryu, and S. B. Lee*
Inhibitory effect of L-pyroglutamate on extremophiles: correlation with growth temperature and pH.

FEMS Microbiology Letters, vol.221, pp.187-190, 2003

[13] C. B. Park and D. S. Clark*
Rupture of the cell envelope by decompression of the deep-sea methanogen Methanococcus jannaschii.

Applied and Environmental Microbiology, vol.68, pp.1458-1463, 2002

[12] C. B. Park and D. S. Clark*
Sol-gel encapsulated enzyme arrays for high throughput screening of biocatalytic activity.

Biotechnology and Bioengineering, vol.78, pp.229-235, 2002

[11] B. Boonyaratanakornkit, C. B. Park, and D. S. Clark*
Pressure effects on intra- and intermolecular interactions within proteins.

Biochimica et Biophysica Acta, vol.1595, pp.235-249, 2002

[10] C. B. Park, S. B. Lee, and D.D.Y. Ryu*
L-Pyroglutamate spontaneously formed from L-glutamate inhibits growth of the hyperthermophilic archaeon Sulfolobus solfataricus.

Applied and Environmental Microbiology, vol.67, pp.3650-3654, 2001

[9] C. B. Park†, Y-D. Kim†, and D. S. Clark* († equally-contributing authors)
Stable sol-gel microstructured and microfluidic networks for protein patterning.

Biotechnology and Bioengineering, vol.73, pp.331-337, 2001

[8] C. B. Park, S. B. Lee*, and D.D.Y. Ryu
Enhanced enzymatic synthesis of cefazolin with addition of ethyl acetate and carbon tetrachloride.

Journal of Molecular Catalysis B: Enzymatic, vol.9, pp.275-281, 2000

[7] C. B. Park and S. B. Lee*
Effects of exogenous compatible solutes on growth of the hyperthermophilic archaeon Sulfolobus solfataricus.

Journal of Bioscience and Bioengineering, vol.89, pp.318-322, 2000

[6] Y. M. Chung, C. B. Park, and S. B. Lee*
Partial purification of esterase from Sulfolobus solfataricus.

Biotechnology and Bioprocess Engineering, vol.5, pp.53-56, 2000

[5] C. B. Park and S. B. Lee*
Inhibitory effect of mineral ion accumulation on high density growth of the hyperthermophilic archaeon Sulfolobus solfataricus.

Journal of Bioscience and Bioengineering, vol.87, pp.315-319, 1999

[4] C. B. Park and S. B. Lee*
Cultivation of hyperthermophilic archaeon Sulfolobus solfataricus in low-salt media.

Biotechnology and Bioprocess Engineering, vol.4, pp.21-25, 1999

[3] I. S. Suh, C. B. Park, J.-K. Han , and S. B. Lee*
Cultivation of cyanobacteria in various types of photobioreactors for biological CO2 fixation.

Studies in Surface Science and Catalysis, vol.114, pp.471-474, 1999

[2] C. B. Park and S. B. Lee*
Ammonia production from yeast extract and its effect on growth of Sulfolobus solfataricus.

Biotechnology and Bioprocess Engineering, vol.3, pp.115-118, 1998

[1] C. B. Park and S. B. Lee*
Constant-volume fed-batch operation for high density cultivation of hyperthermophilic aerobes.

Biotechnology Techniques, vol.11, pp.277-281, 1997

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