Publications (44)133.18 Total impact
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Article: Continuous In Situ Synthesis of ZnSe/ZnS Core/Shell Quantum Dots in a Microfluidic Reaction System and its Application for Light-Emitting Diodes.
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ABSTRACT: ZnSe/ZnS core/shell quantum dots (QDs) with efficient blue emission are in situ synthesized using a novel microfluidic reaction system. This advances research on both simple one-step synthesis of core/shell QDs and their production using thermoplastic-based microfluidic reaction systems. Furthermore, QD light-emitting diodes (LEDs) are demonstrated using ZnSe/ZnS QDs as wavelength converters.Small 08/2012; · 8.35 Impact Factor -
Article: In vitro biosynthesis of metal nanoparticles in microdroplets.
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ABSTRACT: We report the use of a hydrogel polymer, recombinant Escherichia coli cell extracts, and a microdroplet-based microfluidic device to fabricate artificial cellular bioreactors which act as reactors to synthesize diverse metal nanoparticles (NPs). The combination of cell extracts, microdroplet-based microfluidic device, and hydrogel was able to produce a mass amount of artificial cellular bioreactors with uniform size and shape. For the first time, we report the alternating generation of microdroplets through one orifice for the fabrication of the artificial cellular reactors using the cell extract as inner cellular components and hydrogel as an artificial cellular membrane. Notably, the hydrogels were able to protect the encapsulated cell extracts from the surrounding environment and maintain the functionality of cellular component for the further cellular bioreactor applications. Furthermore, the successful applications of the fabricated artificial cellular bioreactors to synthesize various NPs including quantum dots, iron, and gold was demonstrated. By employing this microfluidic technique, the artificial cellular bioreactors could be applicable for the synthesis of diverse metal NPs through simple dipping of the reactors to the metal precursor solutions. Thus, the different size of NPs can be synthesized through controlling the concentration of metal precursors. This artificial cellular bioreactors offer promising abilities to biofriendly ways to synthesis diverse NPs and can be applicable in chemical, biomedical, and bioengineering applications.ACS Nano 07/2012; 6(8):6998-7008. · 10.77 Impact Factor -
Article: Highly efficient blue- and white-organic light-emitting diode based on dual recombination zones with a charge control layer.
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ABSTRACT: Highly efficient blue phosphorescent organic light-emitting diodes are investigated using iridium(Ill) bis[(4,6-di-fluorophenyl)-pyridinato-N,C2']picolinate doped in N,N'-dicarbazolyl-3,5-benzene (mCP) with a charge control layer (CCL) as the dual recombination zone (DRZ) system. DRZ with CCL was used to form a broad recombination zone and exciton confinement within each emission zone. Holes and electrons can be easily transported through the CCL, which were a mixed p-type mCP and n-type 2,2',2"-(1,3,5-benzenetryl) tris(1-phenyl)-1H-benzimidazol, for controlling the carrier movement. The CCL can play a role in triplet exciton blocking as expected from high triplet energy levels as well. Additionally, a white organic light-emitting diode was fabricated using a new phosphorescent orange emitter: bis[2-(2,4-difluorophenyl)pyridinato]iridium 2-(2-hydroxyphenyl)benzothia zolate doped in DRZ. The white device showed a maximum luminous efficiency of 23.15 cd/A, a maximum external quantum efficiency of 9.56%, and a maximum power efficiency of 13.37 lm/W. It also showed white emission with CIEx,y coordinates of (x = 0.33, y = 0.41) at 8 V.Journal of Nanoscience and Nanotechnology 07/2012; 12(7):5418-22. · 1.56 Impact Factor -
Article: Flexible top-emitting organic light-emitting diodes using semi-transparent multi-metal layers.
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ABSTRACT: In this paper, the improved device performance of top-emitting organic light-emitting diodes (TEOLEDs) with a thin multi-metal layer stack of nickel/silver/nickel (Ni/Ag/Ni) and aluminum/silver/aluminum (Al/Ag/Al) that were used as the anode and cathode on a flexible substrate is discussed. In particular, Indium-Tin-Oxide (ITO) as an anode electrode has been used recently even though it has some problems for flexible devices. Therefore we suggested that a thin multi-metal layer electrode as a new anode is fabricated instead of ITO anode. It was verified that the ITO-free TEOLEDs showed an enhanced probability of the recombination of the electrons and holes through an improved electron/hole charge balance. We also analyzed the optical and electrical characteristics using the current density, luminance, luminance efficiency, external quantum efficiency (EQE), CIE x, y coordinates, and EL spectra of flexible TEOLED devices were characterized. ITO-free, flexible, green-emitting OLEDs with a low cost and a simple process were demonstrated.Journal of Nanoscience and Nanotechnology 07/2012; 12(7):5444-8. · 1.56 Impact Factor -
Article: One-step sonochemical synthesis of a graphene oxide-manganese oxide nanocomposite for catalytic glycolysis of poly(ethylene terephthalate).
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ABSTRACT: Ultrasound-assisted synthesis of a graphene oxide (GO)-manganese oxide nanocomposite (GO-Mn(3)O(4)) was conducted without further modification of GO or employing secondary materials. With the GO nanoplate as a support, potassium permanganate oxidizes the carbon atoms in the GO support and gets reduced to Mn(3)O(4). An intensive ultrasound method could reduce the number of reaction steps and temperature, enhance the reaction rate and furthermore achieve a Mn(3)O(4) phase. The composite was characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The coverage and crystallinity of Mn(3)O(4) were controlled by changing the ratio of permanganate to GO dispersion. The synthesized nanocomposite was used as a catalyst for poly(ethylene terephthalate) (PET) depolymerization into its monomer, bis(2-hydroxylethyl) terephthalate (BHET). The highest monomer yield of 96.4% was obtained with the nanocomposite containing the lowest amount of Mn(3)O(4), while PET glycolysis with the Mn(3)O(4) without GO yielded 82.7% BHET.Nanoscale 05/2012; 4(13):3879-85. · 5.91 Impact Factor -
Article: Efficient triplet exciton confinement of blue- and white-organic light emitting diodes using a new host material.
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ABSTRACT: We have demonstrated lower driving voltage and efficient blue phosphorescent organic light emitting diodes (PHOLEDs) using iridium(III) bis[(4,6-di-fluoropheny)-pyridinato-N,C2] picolinate (Flrpic) doped in new host material 9-(4-(triphenylsilyl)phenyl)-9H-carbazole (SPC) and 2,2',2"-(1,3,5-benzenetryl)tris(1-phenyl)-1H-benzimidazol (TPBi) as double-emitting layer (D-EML) system. The D-EML was employed to have good electron transportability and exciton confinement. Additionally, we fabricated white organic light-emitting diode (WOLED) using a phosphorescent red emitter; bis(2-phenylquinolinato)-acetylacetonate iridium III (Ir(pq)2acac) doped in SPC and TPBi as D-EML. The properties of white device exhibited a maximum luminous efficiency of 19.03 cd/A, a maximum external quantum efficiency of 9.91%, and a maximum power efficiency of 12.30 lm/W. It also showed white emission with CIE(x,y) coordinates of (x = 0.38, y = 0.37) at 8 V.Journal of Nanoscience and Nanotechnology 05/2012; 12(5):4154-8. · 1.56 Impact Factor -
Article: Red phosphorescent organic light-emitting diodes based on the simple structure.
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ABSTRACT: We demonstrated that the simple layered red phosphorescent organic light-emitting diodes (OLEDs) are possible to have high efficiency, low driving voltage, stable roll-off efficiency, and pure emission color without hole injection and transport layers. We fabricated the OLEDs with a structure of ITO/CBP doped with Ir(pq)2(acac)/BPhen/Liq/Al, where the doping concentration of red dopant, Ir(pq)2(acac), was varied from 4% to 20%. As a result, the quantum efficiencies of 13.4, 11.2, 16.7, 10.8 and 9.8% were observed in devices with doping concentrations of 4, 8, 12, 16 and 20%, respectively. Despite of absence of the hole injection and transport layers, these efficiencies are superior to efficiencies of device with hole transporting layer due to direct hole injection from anode to dopant in emission layer.Journal of Nanoscience and Nanotechnology 05/2012; 12(5):4190-3. · 1.56 Impact Factor -
Article: White organic light-emitting diodes for emotion solid-state lighting.
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ABSTRACT: The authors have demonstrated white organic light-emitting diodes for emotion solid-state lighting (ESSL) by using hole modulating layer (HML), N,N'-diphenyl-N,N'-bis-[4-(phenyl-m-tolyl-amino)-phenyl]-biphenyl-4,4'-diamine and N,N'-bis-(1-naphyl)-N,N'-diphenyl-1,1'-biphenyl-4, 4'-diamine, and mixed spacer (MS), 4,4',4"-tris(N-carbazolyl)-triphenylamine and {9,9-dimethyl-7-[10-(naphthalen-2-yl)anthracen-9-yl]-9H-fluoren-2-yl}triphenylsilane, respectively. The HML and MS were used for unbalance of holes and electrons. The ESSL showed various white light chromaticities of Commission Internationale de l'Eclairage coordinates from (0.46,0.42) as warm white emission to (0.29, 0.36) as cold white emission.Journal of Nanoscience and Nanotechnology 05/2012; 12(5):4215-8. · 1.56 Impact Factor -
Article: Quantitative studies of carbohydrate-protein interaction using functionalized bacterial spores in solution and on chips
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ABSTRACT: Carbohydrate-protein interaction is one of the most important molecular events deemed critical for numerous biological processes. Therefore, understanding this interaction is essential. In this study, we used bacterial spore display techniques to present multiple copies of streptavidin on the surface of spores to explore carbohydrate-protein interaction in solution and on chips. By applying bacterial spores displaying streptavidin, we developed a new method which allows sensitive, versatile, and passive detection of carbohydrate-protein interactions with a 10-fold increase in sensitivity. The linear relationship of interactions between carbohydrates and labeled concanavalin A (con A) in solution and on functionalized bacterial spore chips has also been confirmed. To the best of our knowledge, this is the first example of development and characterization of binding behavior in carbohydrateprotein interactions using bacterial spore-displayed streptavidin. We believe this strategy may enable new high-throughput screening of carbohydrate interactions as well as establish a basis for monitoring inhibitors of carbohydrate-binding proteins when developing new drugs. Keywordsbacterial spore display–carbohydrate-protein interaction–concanavalin A–immobilization–lectinBiotechnology and Bioprocess Engineering 04/2012; 16(1):190-195. · 1.28 Impact Factor -
Article: Polyhydroxyalkanoate chip for the specific immobilization of recombinant proteins and its applications in immunodiagnostics
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ABSTRACT: In this study, a novel strategy was developed for the highly selective immobilization of proteins, using the polyhydroxyalkanoate (PHA) depolymerase substrate binding domain (SBD) as an active binding domain. In order to determine the appropriacy of this method for immunodiagnostic assays, the single-chain antibody (ScFv) against the hepatitis B virus (HBV) preS2 surface protein and the severe acute respiratory syndrome coronavirus (SARS-CoV) envelope protein (SCVe) were fused to the SBD, then directly immobilized on PHA-coated slides via microspotting. The fluorescence-labeled HBV antigen and the antibody against SCVe were then utilized to examine specific interactions on the PHA-coated surfaces. Fluorescence signals were detected only at the spotted positions, thereby indicating a high degree of affinity and selectivity for their corresponding antigens/antibodies. Furthermore, we detected small amounts of ScFv-SBD (2.7 ng/mL) and SCVe-SBD fusion proteins (0.6 ng/mL). Therefore, this microarray platform technology, using PHA and SBD, appears generally appropriate for immunodiagnosis, with no special requirements with regard to synthetic or chemical modification of the biomolecules or the solid surface.Biotechnology and Bioprocess Engineering 04/2012; 11(2):173-177. · 1.28 Impact Factor -
Article: Microcontact printing of biotin for selective immobilization of streptavidin-fused proteins and SPR analysis
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ABSTRACT: In this study, a simple procedure is described for patterning biotin on a glass substrate and then selectively immobilizing proteins of interest onto the biotin-patterned surface. Microcontact printing (μCP) was used to generate the micropattern of biotin and to demonstrate the selective immobilization of proteins by using enhanced green fluorescent protein (EGFP) as a model protein, of which the C-terminus was fused to a core streptavidin (cSA) gene ofStreptomyces avidinii. Confocal fluorescence microscopy was used to visualize the pattern of the immobilized protein (EGFP-cSA), and surface plasmon resonance was used to characterize biological activity of the immobilized EGFP-cSA. The results suggest that this strategy, which consists of a combination of μμCP and cSA-fused proteins, is an effective way for fabricating biologically active substrates that are suitable for a wide variety of applications, one such being the use in protein-protein assays.Biotechnology and Bioprocess Engineering 04/2012; 9(2):137-142. · 1.28 Impact Factor -
Article: Efficient deep-blue organic light-emitting diodes using double-emitting layer.
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ABSTRACT: Efficient deep-blue organic light-emitting diodes were demonstrated using 1,4-tetranaphthalene doped in double-emitting layers (D-EMLs) consisting of 2-methyl-9,10-di(2-naphthyl)anthracene and 4'-(dinaphthalen-2-yl)-1,1'-binaphthyl as blue hosts. The device with D-EML exhibits good confinement of holes and electrons, as well as a broad recombination zone. The optimized device showed a peak current efficiency of 3.67 cd/A, a peak external quantum efficiency of 3.97%, and Commission Internationale de L'Eclairage coordinates of (0.16, 0.10).Journal of Nanoscience and Nanotechnology 04/2012; 12(4):3451-4. · 1.56 Impact Factor -
Article: Development of label-free optical diagnosis for sensitive detection of influenza virus with genetically engineered fusion protein.
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ABSTRACT: An active immobilization method utilizing the metal-binding property was developed and examined for its ability to facilitate the biosensing of avian influenza virus. The special biosensing performance with optical plasmonic analysis, including surface plasmon resonance (SPR) was evaluated on gold substrate and also by SPR imaging (SPRi) and localized SPR (LSPR) system where antigen-antibody interaction occurs. A complete optical analytical system was developed by integrating microarray and fabricating nanoparticles onto a single glass chip, thus allowing specific and sensitive diagnosis with subsequent binding. Reaction condition for the maximum reactivity was optimized by SPR analysis and more sensitive interaction was performed by SPRi analysis. Furthermore, ultra-sensitive detection was successfully developed up to the target molecules of 1 pg mL(-1) by LSPR analysis. The advanced phase-in of enhanced plasmonic sensing system allows more efficient and sensitive detection by switching fabrication processes, which were prepared on the gold surface using the nanoparticles. This inflow contains the gold binding polypeptide (GBP)-fusion protein, which was expressed in recombinant Escherichia coli cells, was bound onto the gold substrates by means of specific interaction. The GBP-fusion method allows immobilization of proteins in bioactive forms onto the gold surface without surface modification suitable for studying antigen-antibody interaction. It was used for the detection of influenza virus, an infectious viral disease, as an example case.Talanta 01/2012; 89:246-52. · 3.79 Impact Factor -
Article: Development of a Plastic-Based Microfluidic Immunosensor Chip for Detection of H1N1 Influenza.
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ABSTRACT: Lab-on-a-chip can provide convenient and accurate diagnosis tools. In this paper, a plastic-based microfluidic immunosensor chip for the diagnosis of swine flu (H1N1) was developed by immobilizing hemagglutinin antigen on a gold surface using a genetically engineered polypeptide. A fluorescent dye-labeled antibody (Ab) was used for quantifying the concentration of Ab in the immunosensor chip using a fluorescent technique. For increasing the detection efficiency and reducing the errors, three chambers and three microchannels were designed in one microfluidic chip. This protocol could be applied to the diagnosis of other infectious diseases in a microfluidic device.Sensors 01/2012; 12(8):10810-9. · 1.74 Impact Factor -
Article: Label-free electrochemical diagnosis of viral antigens with genetically engineered fusion protein.
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ABSTRACT: We have developed a simple electrochemical biosensing strategy for the label-free diagnosis of hepatitis B virus (HBV) on a gold electrode surface. Gold-binding polypeptide (GBP) fused with single-chain antibody (ScFv) against HBV surface antigen (HBsAg), in forms of genetically engineered protein, was utilized. This GBP-ScFv fusion protein can directly bind onto the gold substrate with the strong binding affinity between the GBP and the gold surface, while the recognition site orients toward the sample for target binding at the same time. Furthermore, this one-step immobilization strategy greatly simplifies a fabrication process without any chemical modification as well as maintaining activity of biological recognition elements. This system allows specific immobilization of proteins and sensitive detection of targets, which were verified by surface plasmon resonance analysis and successfully applied to electrochemical cyclic voltammetry and impedance spectroscopy upto 0.14 ng/mL HBsAg.Sensors 01/2012; 12(8):10097-108. · 1.74 Impact Factor -
Article: Synthesis of bioactive microcapsules using a microfluidic device.
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ABSTRACT: Bioactive microcapsules containing Bacillus thuringiensis (BT) spores were generated by a combination of a hydro gel, microfluidic device and chemical polymerization method. As a proof-of-principle, we used BT spores displaying enhanced green fluorescent protein (EGFP) on the spore surface to spatially direct the EGFP-presenting spores within microcapsules. BT spore-encapsulated microdroplets of uniform size and shape are prepared through a flow-focusing method in a microfluidic device and converted into microcapsules through hydrogel polymerization. The size of microdroplets can be controlled by changing both the dispersion and continuous flow rate. Poly(N-isoproplyacrylamide) (PNIPAM), known as a hydrogel material, was employed as a biocompatible material for the encapsulation of BT spores and long-term storage and outstanding stability. Due to these unique properties of PNIPAM, the nutrients from Luria-Bertani complex medium diffused into the microcapsules and the microencapsulated spores germinated into vegetative cells under adequate environmental conditions. These results suggest that there is no limitation of transferring low-molecular-weight-substrates through the PNIPAM structures, and the viability of microencapsulated spores was confirmed by the culture of vegetative cells after the germinations. This microfluidic-based microencapsulation methodology provides a unique way of synthesizing bioactive microcapsules in a one-step process. This microfluidic-based strategy would be potentially suitable to produce microcapsules of various microbial spores for on-site biosensor analysis.Sensors 01/2012; 12(8):10136-47. · 1.74 Impact Factor -
Article: Sustainable fabrication of micro-structured lab-on-a-chip.
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ABSTRACT: We have demonstrated a robust platform that can not only sustainably fabricate a lab-on-a-chip (LOC) device using microinjection molding but also elucidate the filling process of microstructures based on the multiscale analysis. In addition, a novel dimensionless number, i.e., the filling number μ(f) which can provide an insight into the underlying filling mechanism for micropillars, has been proposed based on the understanding of the characteristics of polymeric flow and cavity dimension. This study suggests a solid experimental and numerical tool for the production of microfluidic devices with the use of a micromolding technique, which is expected to help materialize the commercialization of the LOC devices in a more sustainable manner.Lab on a Chip 09/2011; 11(23):3999-4005. · 5.67 Impact Factor -
Article: Highly efficient and stable white organic light emitting diode base on double recombination zones of phosphorescent blue/orange emitters.
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ABSTRACT: We demonstrated efficient and stable white phosphorescent organic light-emitting diodes (OLEDs) with double-emitting layers (D-EMLs), which were comprised of two emissive layers with a hole transport-type host of N,N'-dicarbazolyl-3,5-benzene (mCP) and a electron transport-type host of 2,2',2"-(1,3,5-benzenetryl)tris(1-phenyl)-1H-benzimidazol (TPBi) with blue/orange emitters, respectively. We fabricated two type white devices with single emitting layer (S-EML) and D-EML of orange emitter, maintaining double recombination zone of blue emitter. In addition, the device architecture was developed to confine excitons inside the D-EMLs and to manage triplet excitons by controlling the charge injection. As a result, light-emitting performances of white OLED with D-EMLs were improved and showed the steady CIE coordinates compared to that with S-EML of orange emitter, which demonstrated the maximum luminous efficiency and external quantum efficiency were 21.38 cd/A and 11.09%. It also showed the stable white emission with CIE(x,y) coordinates from (x = 0.36, y = 0.37) at 6 V to (x = 0.33, y = 0.38) at 12 V.Journal of Nanoscience and Nanotechnology 08/2011; 11(8):7151-4. · 1.56 Impact Factor -
Article: Efficient organic photovoltaic devices by using PEDOT:PSSs with excellent hole extraction ability.
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ABSTRACT: We have demonstrated the poly(3-hexyl-thiophene-1,5-diyl) (P3HT):[6,6]-phenyl C61-butyric acid methyl ester (PCBM) bulk heterojunction (BHJ) organic photovoltaic (OPV) devices on various poly(3,4-ethylene-dioxythiophene):poly(styrenesulfonate) (PEDOT:PSSs). The device with PEDOT:PSS of PH 500 adding 1% dimethyl sulfoxide (DMSO) showed the best performances in term of the fill factor and power conversion efficiency (PCE) than others. The hole extraction ability of PEDOT:PSS is very important to balance between holes and electrons mobility because the carrier mobility of PCBM (approximately 10(-4) cm2/Vs) is higher than that of P3HT (approximately 10(-6) cm2/Vs) in P3HT:PCBM BHJ structure. The optimized BHJ OPV with PEDOT:PSS of PH 500 adding 1% DMSO showed a short-circuit current density of 8.92 mA/cm2 and a PCE of 2.97%, which was nearly increased to 2.5 times than that of control device with PEDOT:PSS of P VP Al 4083.Journal of Nanoscience and Nanotechnology 08/2011; 11(8):7307-10. · 1.56 Impact Factor -
Article: Organoclay-assisted interfacial polymerization for microfluidic production of monodisperse PEG-microdroplets and in situ encapsulation of E. coli.
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ABSTRACT: We developed a novel one-pot synthetic strategy for preparing monodisperse polyethylene glycol diacrylate (PEGDA) microdroplets via organoclay-assisted interfacial polymerization approach for Escherichia coli encapsulation. Based on the mechanism of spontaneous and rapid polymerization of PEGDA precursor solution with Mg-organoclay, the prepared PEGDA microdroplets have uniform size and fine round shape, with size range of 74-118 µm. The size of microdroplets can be controlled through the changing continuous phase flow rate. Organoclay-assisted polymerization method provides a unique environment to produce non-toxic ways of fabricating microorganism encapsulated microdroplets and to prohibit microdroplets merge during the processes. Furthermore, we successfully carried out to entrap E. coli inside of the PEGDA microdroplets. E. coli expressing a green fluorescent protein shows a good viability inside the PEGDA microdroplets. The in situ microfluidic synthetic method provides a novel approach for the preparation of monodisperse PEGDA microdroplets via a one-pot route.Biotechnology and Bioengineering 08/2011; 109(1):289-94. · 3.95 Impact Factor
Top co-authors
Top Journals
Institutions
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2012
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Chungnam National University
Seongnam, Gyeonggi, South Korea
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2008–2012
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Hongik University
Seoul, Seoul, South Korea
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2004–2011
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Korea Advanced Institute of Science and Technology
- • Department of Chemical and Biomolecular Engineering
- • Metabolic and Biomolecular Engineering National Research Laboratory
Seoul, Seoul, South Korea
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