Publications by authors named "Won Hi Hong"

36 Publications

Visible-light-driven dynamic cancer therapy and imaging using graphitic carbon nitride nanoparticles.

Mater Sci Eng C Mater Biol Appl 2018 Sep 16;90:531-538. Epub 2018 Apr 16.

Department of Biological Engineering, Biohybrid Systems Research Center (BSRC), Inha University, 100, Inha-ro, Incheon 22212, Republic of Korea. Electronic address:

Organic graphitic carbon nitride nanoparticles (NP-g-CN), less than 30 nm in size, were synthesized and evaluated for photodynamic therapy (PDT) and cell imaging applications. NP-g-CN particles were prepared through an intercalation process using a rod-like melamine-cyanuric acid adduct (MCA) as the molecular precursor and a eutectic mixture of LiCl-KCl (45:55 wt%) as the reaction medium for polycondensation. The nano-dimensional NP-g-CN penetrated the malignant tumor cells with minimal hindrance and effectively generated reactive oxygen species (ROS) under visible light irradiation, which could ablate cancer cells. When excited by visible light irradiation (λ > 420 nm), NP-g-CN introduced to HeLa and cos-7 cells generated a significant amount of ROS and killed the cancerous cells selectively. The cytotoxicity of NP-g-CN was manipulated by altering the light irradiation and the BP-g-CN caused more damage to the cancer cells than normal cells at low concentrations. As a potential non-toxic organic nanomaterial, the synthesized NP-g-CN are biocompatible with less cytotoxicity than toxic inorganic materials. The combined effects of the high efficacy of ROS generation under visible light irradiation, low toxicity, and bio-compatibility highlight the potential of NP-g-CN for PDT and imaging without further modification.
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http://dx.doi.org/10.1016/j.msec.2018.04.035DOI Listing
September 2018

Three-dimensional macroscopic assemblies of low-dimensional carbon nitrides for enhanced hydrogen evolution.

Angew Chem Int Ed Engl 2013 Oct 13;52(42):11083-7. Epub 2013 Sep 13.

Department of Chemistry and Biochemistry, University of California, Santa Barbara, CA 93106 (USA).

Simple organic cooperative assembly of triazine molecules leads to three-dimensional macroscopic assemblies of low-dimensional graphitic carbon nitrides (g-CNs), for example, nanoparticles, nanotubes, and nanosheets. The approach enables the characterization of the cooperative properties and photocatalytic activities of low-dimensional g-CN materials in hydrogen evolution reactions from water under visible light.
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http://dx.doi.org/10.1002/anie.201304034DOI Listing
October 2013

Controlled assembly of graphene oxide nanosheets within one-dimensional polymer nanostructure.

J Colloid Interface Sci 2013 Sep 10;406:24-9. Epub 2013 Jun 10.

Department of Chemical Engineering, College of Engineering, Kyung Hee University, Giheung-gu, Youngin-si, Gyeonggi-do, Republic of Korea.

We have demonstrated that the location and distribution of graphene oxide nanosheets (GONs) confined in 1D polymer composites were readily controlled depending on the processing conditions of electrospinning such as the types of polymers and the solvents used for the fabrication. The uniform bead-free poly(vinyl alcohol) (PVA)/GON composite nanofibers (NFs) even at high GON loading were obtained from the homogeneous polymer solutions attributable to the favorable interactions, as elucidated by spectroscopic data, thereby showing significant enhancement of their physical properties. The GONs were localized in the surface regions of the PVA-NFs due to the rapid convective evaporation of the water molecules, with concomitant aggregation into several sheets (<10 layers). In contrast, the co-continuous internal morphology of PVA/GON-NFs was constructed using less-volatile, polar dimethylformamide (DMF) solvents. Furthermore, the GONs were uniformly distributed in the more compatible polymer matrices such as polyacrylonitrile (PAN) and polystyrene (PS). Therefore, the distribution of GONs in 1D nanofibers was governed by the kinetics of solvent evaporation and the interaction with the polymer matrices.
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http://dx.doi.org/10.1016/j.jcis.2013.03.072DOI Listing
September 2013

Electroactive nanoparticle directed assembly of functionalized graphene nanosheets into hierarchical structures with hybrid compositions for flexible supercapacitors.

Nanoscale 2013 May 2;5(9):3976-81. Epub 2013 Apr 2.

Department of Chem. & Biomolecular Eng. (BK 21), Korea Advanced Institute of Science and Technology, Daejeon 305-701, Republic of Korea.

Hierarchical structures of hybrid materials with the controlled compositions have been shown to offer a breakthrough for energy storage and conversion. Here, we report the integrative assembly of chemically modified graphene (CMG) building blocks into hierarchical complex structures with the hybrid composition for high performance flexible pseudocapacitors. The formation mechanism of hierarchical CMG/Nafion/RuO2 (CMGNR) microspheres, which is triggered by the cooperative interplay during the in situ synthesis of RuO2 nanoparticles (NPs), was extensively investigated. In particular, the hierarchical CMGNR microspheres consisting of the aggregates of CMG/Nafion (CMGN) nanosheets and RuO2 NPs provided large surface area and facile ion accessibility to storage sites, while the interconnected nanosheets offered continuous electron pathways and mechanical integrity. The synergistic effect of CMGNR hybrids on the supercapacitor (SC) performance was derived from the hybrid composition of pseudocapacitive RuO2 NPs with the conductive CMGNs as well as from structural features. Consequently, the CMGNR-SCs showed a specific capacitance as high as 160 F g(-1), three-fold higher than that of conventional graphene SCs, and a capacitance retention of >95% of the maximum value even after severe bending and 1000 charge-discharge tests due to the structural and compositional features.
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http://dx.doi.org/10.1039/c3nr33674cDOI Listing
May 2013

Electrochemical assembly of MnO₂ on ionic liquid-graphene films into a hierarchical structure for high rate capability and long cycle stability of pseudocapacitors.

Nanoscale 2012 Sep 23;4(17):5394-400. Epub 2012 Jul 23.

Department of Chem. & Biomolecular Eng. BK 21, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Republic of Korea.

Hierarchical nanostructures are of prime importance due to their large surface area, easy accessibility to reaction sites, fast ion and electron transport, and mechanical integrity. Herein, we demonstrate the synthesis of hierarchically structured MnO₂/ionic liquid-reduced graphene oxide (IL-RGO) nanocomposites through the electrochemical self-assembly. The structures of MnO₂/IL-RGO nanocomposites and their formation mechanism are investigated by spectroscopic methods and as a consequence, correlated with the electrochemical behaviours. The specific capacitance (511 F g⁻¹) of conformally MnO₂-deposited IL-RGO composites is significantly higher than 159 F g⁻¹ of pure MnO₂ film. High rate capability (61% retention at 30 A g⁻¹) of the MnO₂/IL-RGO composite is attributed to the facilitated ion diffusion and electron transport, whereas its long cycle life (95% retention after 2000 cycles) is related to the mechanical robustness. These results provide a new insight into the rational design of hierarchical and complex heterostructures consisting of carbon nanomaterials and metal oxides for applications in energy conversion and storage.
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http://dx.doi.org/10.1039/c2nr31215hDOI Listing
September 2012

High performance of a solid-state flexible asymmetric supercapacitor based on graphene films.

Nanoscale 2012 Aug 29;4(16):4983-8. Epub 2012 Jun 29.

Division of Materials Science, Korea Basic Science Institute, Daejeon, 305-333, Republic of Korea.

Solid-state flexible energy storage devices hold the key to realizing portable and flexible electronic devices. Achieving fully flexible energy storage devices requires that all of the essential components (i.e., electrodes, separator, and electrolyte) with specific electrochemical and interfacial properties are integrated into a single solid-state and mechanically flexible unit. In this study, we describe the fabrication of solid-state flexible asymmetric supercapacitors based on an ionic liquid functionalized-chemically modified graphene (IL-CMG) film (as the negative electrode) and a hydrous RuO(2)-IL-CMG composite film (as the positive electrode), separated with polyvinyl alcohol-H(2)SO(4) electrolyte. The highly ordered macroscopic layer structures of these films arising through direct flow self-assembly make them simultaneously excellent electrical conductors and mechanical supports, allowing them to serve as flexible electrodes and current collectors in supercapacitor devices. Our asymmetric supercapacitors have been optimized with a maximum cell voltage up to 1.8 V and deliver a high energy density (19.7 W h kg(-1)) and power density (6.8 kW g(-1)), higher than those of symmetric supercapacitors based on IL-CMG films. They can operate even under an extremely high rate of 10 A g(-1) with 79.4% retention of specific capacitance. Their superior flexibility and cycling stability are evident in their good performance stability over 2000 cycles under harsh mechanical conditions including twisted and bent states. These solid-state flexible asymmetric supercapacitors with their simple cell configuration could offer new design and fabrication opportunities for flexible energy storage devices that can combine high energy and power densities, high rate capability, and long-term cycling stability.
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http://dx.doi.org/10.1039/c2nr30991bDOI Listing
August 2012

3D macroporous graphene frameworks for supercapacitors with high energy and power densities.

ACS Nano 2012 May 23;6(5):4020-8. Epub 2012 Apr 23.

Division of Materials Science, Korea Basic Science Institute, Daejeon, 305-333, Republic of Korea.

In order to develop energy storage devices with high power and energy densities, electrodes should hold well-defined pathways for efficient ionic and electronic transport. Herein, we demonstrate high-performance supercapacitors by building a three-dimensional (3D) macroporous structure that consists of chemically modified graphene (CMG). These 3D macroporous electrodes, namely, embossed-CMG (e-CMG) films, were fabricated by using polystyrene colloidal particles as a sacrificial template. Furthermore, for further capacitance boost, a thin layer of MnO(2) was additionally deposited onto e-CMG. The porous graphene structure with a large surface area facilitates fast ionic transport within the electrode while preserving decent electronic conductivity and thus endows MnO(2)/e-CMG composite electrodes with excellent electrochemical properties such as a specific capacitance of 389 F/g at 1 A/g and 97.7% capacitance retention upon a current increase to 35 A/g. Moreover, when the MnO(2)/e-CMG composite electrode was asymmetrically assembled with an e-CMG electrode, the assembled full cell shows remarkable cell performance: energy density of 44 Wh/kg, power density of 25 kW/kg, and excellent cycle life.
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http://dx.doi.org/10.1021/nn3003345DOI Listing
May 2012

A fluorescent sensor for selective detection of cyanide using mesoporous graphitic carbon(IV) nitride.

Chem Commun (Camb) 2012 Apr 15;48(33):3942-4. Epub 2012 Mar 15.

Department of Chemical and Biomolecular Engineering, KAIST, 291 Daehak-ro, Yuseong-gu, Daejeon, Republic of Korea.

A turn-on fluorescence sensor, Cu(2+)-c-mpg-C(3)N(4), was developed for detection of CN(-) in aqueous solution by simply mixing cubic mesoporous graphitic carbon nitride (c-mpg-C(3)N(4)) and aqueous solution of Cu(NO(3))(2). The highly sensitive detection of CN(-) with a detection limit of 80 nM is not only possible in aqueous solution but also in human blood serum.
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http://dx.doi.org/10.1039/c2cc17909aDOI Listing
April 2012

Study on the water flooding in the cathode of direct methanol fuel cells.

J Nanosci Nanotechnol 2011 Jul;11(7):5788-94

Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 305-701, Republic of Korea.

Water flooding phenomena in the cathode of direct methanol fuel cells were analyzed by using electrochemical impedance spectroscopy. Two kinds of commercial gas diffusion layers with different PTFE contents of 5 wt% (GDL A5) and 20 wt% (GDL B20) were used to investigate the water flooding under various operating conditions. Water flooding was divided into two types: catalyst flooding and backing flooding. The cathode impedance spectra of each gas diffusion layer was obtained and compared under the same conditions. The diameter of the capacitive semicircle became larger with increasing current density for both, and this increase was greater for GDL B20 than GDL A5. Catalyst flooding is dominant and backing flooding is negligible when the air flow rate is high and current density is low. An equivalent model was suggested and fitted to the experimental data. Parameters for catalyst flooding and backing flooding were individually obtained. The capacitance of the catalyst layer decreases as the air flow rate decreases when the catalyst flooding is dominant.
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http://dx.doi.org/10.1166/jnn.2011.4504DOI Listing
July 2011

Charge transfer interactions between conjugated block copolymers and reduced graphene oxides.

Chem Commun (Camb) 2011 Oct 22;47(37):10293-5. Epub 2011 Aug 22.

Department of Chem. & Biomolecular Eng. (BK 21), KAIST, 335 Gwahagno, Yuseong-gu, Daejeon 305-701, Republic of Korea.

The charge transfer interactions between reduced graphene oxides and conjugated block copolymers were confirmed by various spectroscopic methods, giving rise to manipulation of the electrical properties of the former.
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http://dx.doi.org/10.1039/c1cc13465eDOI Listing
October 2011

Facilitated ion transport in all-solid-state flexible supercapacitors.

ACS Nano 2011 Sep 10;5(9):7205-13. Epub 2011 Aug 10.

Department of Chemical & Biomolecular Engineering (BK21 program), KAIST, Daejeon 305-701, Republic of Korea.

The realization of highly flexible and all-solid-state energy-storage devices strongly depends on both the electrical properties and mechanical integrity of the constitutive materials and the controlled assembly of electrode and solid electrolyte. Herein we report the preparation of all-solid-state flexible supercapacitors (SCs) through the easy assembly of functionalized reduced graphene oxide (f-RGO) thin films (as electrode) and solvent-cast Nafion electrolyte membranes (as electrolyte and separator). In particular, the f-RGO-based SCs (f-RGO-SCs) showed a 2-fold higher specific capacitance (118.5 F/g at 1 A/g) and rate capability (90% retention at 30 A/g) compared to those of all-solid-state graphene SCs (62.3 F/g at 1A/g and 48% retention at 30 A/g). As proven by the 4-fold faster relaxation of the f-RGO-SCs than that of the RGO-SCs and more capacitive behavior of the former at the low-frequency region, these results were attributed to the facilitated ionic transport at the electrical double layer by means of the interfacial engineering of RGO by Nafion. Moreover, the superiority of all-solid-state flexible f-RGO-SCs was demonstrated by the good performance durability under the 1000 cycles of charging and discharging due to the mechanical integrity as a consequence of the interconnected networking structures. Therefore, this research provides new insight into the rational design and fabrication of all-solid-state flexible energy-storage devices as well as the fundamental understanding of ion and charge transport at the interface.
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http://dx.doi.org/10.1021/nn202020wDOI Listing
September 2011

Programmable peptide-directed two dimensional arrays of various nanoparticles on graphene sheets.

Nanoscale 2011 Aug 22;3(8):3208-13. Epub 2011 Jun 22.

Department of Chem. & Biomolecular Eng. (BK 21), KAIST, 291 Daehak-ro, Yuseong-gu, Daejeon, 305-701, Republic of Korea.

In this research, we report an innovative, chemical strategy for the in situ synthesis and direct two-dimensional (2D) arraying of various nanoparticles (NPs) on graphenes using both programmed-peptides as directing agents and graphenes as pre-formed 2D templates. The peptides were designed for manipulating the enthalpic (coupled interactions) constraint of the global system. Along with the functionalization of graphene for the stable dispersion, peptides directed the growth and array of NPs in a controllable manner. In particular, the sequences of peptides were encoded by the combination of glutamic acid (E), glycine (G), and phenylalanine (F) amino acids as follows: (E-G-F)(3)-G, with E for the interaction with NPs and F and G for the interaction with graphenes. For the entropic (restricted geometry) constraint, graphene was used as a 2D scaffold to tune the size, density, and position of NPs, while maintaining the intrinsic properties for electrochemical applications. The excellent quality of the resultant hybrids was demonstrated by their high electrocatalytic activity in the electrooxidation of methanol. This synergistic combination of peptides and graphenes allowed for a uniform 2D array and spontaneous organization of various NPs (i.e., Pt, Au, Pd, and Ru), which would greatly expand the utility and versatility of this approach for the synthesis and array of the advanced nanomaterials.
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http://dx.doi.org/10.1039/c1nr10276aDOI Listing
August 2011

Site-specific immobilization of gold binding polypeptide on gold nanoparticle-coated graphene sheet for biosensor application.

Nanoscale 2011 Jul 3;3(7):2950-6. Epub 2011 Jun 3.

Department of Chemical & Biomolecular Engineering, BK21 program, KAIST, 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, Republic of Korea.

The effective and strong immobilization of enzymes on solid surfaces is required for current biological applications, such as microchips, biofuel cells, and biosensors. Gold-binding polypeptide (GBP), a genetically designed peptide, possesses unique and specific interactions with a gold surface, resulting in improved enzyme stability and activity. Herein we demonstrated an immobilization method for biosensor applications through site-specific interactions between GBP-fused organophosphorus hydrolase (GBP-OPH) and gold nanoparticle-coated chemically modified graphene (Au-CMG), showing enhanced sensing capability. A flow injection biosensor was fabricated by using GBP-OPH/Au-CMG to detect paraoxons, a model pesticide, showing higher sensitivity, lower detection limit and better operating stability compared that of OPH/Au-CMG. This strategy, which integrates biotic and abiotic moieties through site-specific interactions, has a great potential for use in biosensing and bioconversion process.
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http://dx.doi.org/10.1039/c1nr10197hDOI Listing
July 2011

Innovative polymer nanocomposite electrolytes: nanoscale manipulation of ion channels by functionalized graphenes.

ACS Nano 2011 Jun 6;5(6):5167-74. Epub 2011 May 6.

Department of Chemical & Biomolecular Engineering (BK21 program), KAIST, Daejeon 305-701, Republic of Korea.

The chemistry and structure of ion channels within the polymer electrolytes are of prime importance for studying the transport properties of electrolytes as well as for developing high-performance electrochemical devices. Despite intensive efforts on the synthesis of polymer electrolytes, few studies have demonstrated enhanced target ion conduction while suppressing unfavorable ion or mass transport because the undesirable transport occurs through an identical pathway. Herein, we report an innovative, chemical strategy for the synthesis of polymer electrolytes whose ion-conducting channels are physically and chemically modulated by the ionic (not electronic) conductive, functionalized graphenes and for a fundamental understanding of ion and mass transport occurring in nanoscale ionic clusters. The functionalized graphenes controlled the state of water by means of nanoscale manipulation of the physical geometry and chemical functionality of ionic channels. Furthermore, the confinement of bound water within the reorganized nanochannels of composite membranes was confirmed by the enhanced proton conductivity at high temperature and the low activation energy for ionic conduction through a Grotthus-type mechanism. The selectively facilitated transport behavior of composite membranes such as high proton conductivity and low methanol crossover was attributed to the confined bound water, resulting in high-performance fuel cells.
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http://dx.doi.org/10.1021/nn2013113DOI Listing
June 2011

Cubic mesoporous graphitic carbon(IV) nitride: an all-in-one chemosensor for selective optical sensing of metal ions.

Angew Chem Int Ed Engl 2010 Dec;49(50):9706-10

Department of Chemical and Biomolecular Engineering, KAIST, 335 Gwahak-ro, Yuseong-gu, Daejeon, 305-701, Korea.

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http://dx.doi.org/10.1002/anie.201004975DOI Listing
December 2010

Microwave-assisted synthesis of highly water-soluble graphene towards electrical DNA sensor.

Nanoscale 2010 Dec 25;2(12):2692-7. Epub 2010 Oct 25.

Department of Chemical & Biomolecular Engineering (BK21), KAIST, 335 Gwahangno, Yuseong-gu, Daejeon 305-701, Republic of Korea.

Graphene sheets have the potential for practical applications in electrochemical devices, but their development has been impeded by critical problems with aggregation of graphene sheets. Here, we demonstrated a facile and bottom-up approach for fabrication of DNA sensor device using water-soluble sulfonated reduced graphene oxide (SRGO) sheets via microwave-assisted sulfonation (MAS), showing enhanced sensitivity, reliability, and low detection limit. Key to achieving these performances is the fabrication of the SRGOs, where the MAS method enabled SRGOs to be highly dispersed in water (10 mg mL(-1)) due to the acidic sulfonated groups generated within 3 min of the functionalization reaction. The water-soluble SRGO-DNA (SRGOD) hybrids prepared by electrostatic interactions between a flat single layer of graphene sheets and DNAs are suitable for fabrication of electrical DNA sensor devices because of the unique electrical characteristics of SRGODs. The high sensing performance of SRGOD sensors was demonstrated with detection of DNA hybridization using complementary DNAs, single base mismatched DNAs, and noncomplementary DNAs, with results showing higher sensitivity and lower detection limit than those of reduced graphene oxide-based DNA sensors. Simple and easy fabrication of DNA sensor devices using SRGODs is expected to provide an effective way for electrical detection of DNA hybridization using miniature sensors without the labor-intensive labeling of the sensor and complex measurement equipment.
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http://dx.doi.org/10.1039/c0nr00562bDOI Listing
December 2010

Immobilization of genetically engineered fusion proteins on gold-decorated carbon nanotube hybrid films for the fabrication of biosensor platforms.

J Colloid Interface Sci 2010 Oct 30;350(2):453-8. Epub 2010 Jun 30.

Department of Chemical Engineering, Kyung Hee University, 1 Seocheon-dong, Giheung-gu, Yongin-si, Gyeonggi-do 446-701, Republic of Korea.

We have demonstrated the fabrication of the biosensor platforms by means of the integration of the genetically engineered fusion proteins and the uniform gold nanoparticle-deposited multi-walled nanotube hybrid (Au-MWNT-HB) films for the detection of C-reactive protein (CRP). Au-MWNT-HB films were used as a good electrochemical transducer due to their excellent electrical properties and large surface areas for the signal transduction, while the genetically engineered fusion proteins, or 6His-GBP-SpA fusion proteins, specifically bind onto the surface of the Au-MWNT-HB films and efficiently immobilize bioreceptors for the detection of CRP. As-obtained biosensor platforms were characterized by electrochemical and optical analysis and revealed better performance compared to conventional Au-based biosensors. The concept delineated herein opens a new insight into nanobiotechnology through the integration of genetically engineered biomaterials with carbon nanotube (CNT)-based nanohybrids for emerging applications.
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http://dx.doi.org/10.1016/j.jcis.2010.06.058DOI Listing
October 2010

Rapid separation of bacteriorhodopsin using a laminar-flow extraction system in a microfluidic device.

Biomicrofluidics 2010 Jan 27;4(1):14103. Epub 2010 Jan 27.

A protein separation technology using the microfluidic device was developed for the more rapid and effective analysis of target protein. This microfluidic separation system was carried out using the aqueous two-phase system (ATPS) and the ionic liquid two-phase system (ILTPS) for purification method of the protein sample, and the three-flow desalting system was used for the removal of salts from the sucrose-rich sample. Partitioning of the protein sample was observed in ATPS or ILTPS with the various pHs. The microdialysis system was applied to remove small molecules, such as sucrose and salts in the microfluidic channel with the different flow rates of buffer phase. A complex purification method, which combines microdialysis and ATPS or ILTPS, was carried out for the effective purification of bacteriorhodopsin (BR) from the purple membrane of Halobacterium salinarium, which was then analyzed by sodium dodecyl sulfatepolyacrylamide gel electrophoresis and matrix-assisted laser desorptionionization time-of-flight. Furthermore, we were able to make a stable three-phase flow controlling the flow rate in the microfluidic channel. Our complex purification methods were successful in purifying and recovering the BR to its required value.
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http://dx.doi.org/10.1063/1.3298608DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2905269PMC
January 2010

Solution chemistry of self-assembled graphene nanohybrids for high-performance flexible biosensors.

ACS Nano 2010 May;4(5):2910-8

Department of Chemical & Biomolecular Engineering, KAIST, Daejeon 305-701, Korea.

We report the preparation of free-standing flexible conductive reduced graphene oxide/Nafion (RGON) hybrid films by a solution chemistry that utilizes self-assembly and directional convective-assembly. The hydrophobic backbone of Nafion provided well-defined integrated structures, on micro- and macroscales, for the construction of hybrid materials through self-assembly, while the hydrophilic sulfonate groups enabled highly stable dispersibility ( approximately 0.5 mg/mL) and long-term stability (2 months) for graphene. The geometrically interlocked morphology of RGON produced a high degree of mechanical integrity in the hybrid films, while the interpenetrating network constructed favorable conduction pathways for charge transport. Importantly, the synergistic electrochemical characteristics of RGON were attributed to high conductivity (1176 S/m), facilitated electron transfer (ET), and low interfacial resistance. Consequently, RGON films obtained the excellent figure of merit as electrochemical biosensing platforms for organophosphate (OP) detection, that is, a sensitivity of 10.7 nA/microM, detection limit of 1.37 x 10(-7) M, and response time of <3 s. In addition, the reliability of RGON biosensors was confirmed by a fatigue test of 100 bending cycles. The strategy described here provides insight into the fabrication of graphene and hybrid nanomaterials from a material perspective, as well as the design of biosensor platforms for practical device applications.
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http://dx.doi.org/10.1021/nn100145xDOI Listing
May 2010

Spectroscopic and computational insight into the intermolecular interactions between Zwitter-type ionic liquids and water molecules.

Chemphyschem 2010 Jun;11(8):1711-7

Department of Chemical Engineering, College of Engineering, Kyung Hee University, 1 Seochong, Giheung, Yongin, Gyeonggi, 446-701, Republic of Korea.

Geometric and conformational changes of zwitter-type ionic liquids (ZILs) due to hydrogen-bonding interactions with water molecules are investigated by density functional theory (DFT), two-dimensional IR correlation spectroscopy (2D IR COS), and pulsed-gradient spin-echo NMR (PGSE NMR). Simulation results indicate that molecular structures in the optimized states are strongly influenced by hydrogen bonding of water molecules with the sulfonate group or imidazolium and pyrrolidinium rings of 3-(1-methyl-3-imidazolio)propanesulfonate (1) and 3-(1-methyl-1-pyrrolidinio)propanesulfonate (2), respectively. Concentration-dependent 2D IR COS reveals kinetic conformational changes of the two ZIL-H(2)O systems attributable to intermolecular interactions, as well as the interactions of sulfonate groups and imidazolium or pyrrolidinium rings with water molecules. The dramatic changes in the (1)H self-diffusion coefficients elucidate the formation of proton-conduction pathways consisting of ZIL networks. In ZIL domains, protons are transferred by a Grotthuss-type mechanism through formation, breaking, and restructuring of bonds between ZILs and H(2)O, leading to an energetically favorable state. The simulation and experimental investigations delineated herein provide a perspective to understanding the interactions with water from an academic point of view as well as to designing ILs with desired properties from the viewpoint of applications.
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http://dx.doi.org/10.1002/cphc.200900925DOI Listing
June 2010

Energy transfer in ionic-liquid-functionalized inorganic nanorods for highly efficient photocatalytic applications.

Small 2010 Jan;6(2):290-5

Department of Chem. & Biomolecular Eng. (BK 21), KAIST, Daejeon, Republic of Korea.

Energy transfer in self-assembled ionic liquids (ILs) and iron oxyhydroxide nanocrystals and the controlled surface chemistry of functionalized nanomaterials for photocatalytic applications are reported. Self-assembled ILs play the role of multifunctional materials in terms of constructing a well-designed nanostructure, controlling the surface chemistry, and triggering the energy transfer of functionalized materials. IL-functionalized beta-FeOOH nanorods show approximately 10-fold higher performances than those of commercial materials due to the synergistic effect of well-defined nanomaterials in diffusion-controlled reactions, specific interactions with target pollutants, and energy transfers in hybrid materials. In particular, the energy transfer in C(4)MimCl-functionalized beta-FeOOH nanorods enhances photocatalytic activity due to the generation of Fe(2+). The strategy described herein provides new insight into the rational design of functionalized inorganic nanomaterials for applications in emerging technologies.
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http://dx.doi.org/10.1002/smll.200901592DOI Listing
January 2010

Tracking the transition behavior and dynamics of ionic transport in crystalline ionic gel electrolytes.

Chem Commun (Camb) 2009 Nov 24(42):6388-90. Epub 2009 Sep 24.

Department of Biological Engineering, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA 02139, USA.

The transition behavior and dynamics of ionic transport were strongly influenced by changes in the crystal structure and interaction field of the crystalline ionic gel electrolytes with respect to chemical compositions, as proven by impedance, (7)Li NMR, PCA and 2D IR COS.
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http://dx.doi.org/10.1039/b910600fDOI Listing
November 2009

Green one-pot assembly of iron-based nanomaterials for the rational design of structure.

Chem Commun (Camb) 2009 Jul 29(27):4058-60. Epub 2009 May 29.

Department of Chemistry & Biomolecular Engineering (BK 21), KAIST, 335 Gwahagno, Yuseong-gu, Daejeon 305-701, Republic of Korea.

Green one-pot solution chemistry described herein could delicately manipulate the size and shape of iron oxyhydroxide nanocrystals, even in the aqueous phase, and easily derive a family of iron-based nanomaterials.
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http://dx.doi.org/10.1039/b906464hDOI Listing
July 2009

Ionic-liquid-assisted sonochemical synthesis of carbon-nanotube-based nanohybrids: control in the structures and interfacial characteristics.

Small 2009 Aug;5(15):1754-60

Department of Chemsitry and Biomolecular Engineering (BK 21), Korea Advanced Institute of Science and Technology, Yuseong-gu, Daejeon, 305-701, Republic of Korea.

A versatile, facile, and rapid synthetic method of advanced carbon nanotube (CNT)-based nanohybrid fabrication, or the so-called ionic-liquid-assisted sonochemical method (ILASM), which combines the supramolecular chemistry between ionic liquids (ILs) and CNTs with sonochemistry for the control in the size and amount of uniformly decorated nanoparticles (NPs) and interfacial engineering, is reported. The excellence in electrocatalysis of hybrid materials with well-designed nanostructures and favorable interfaces is demonstrated by applying them to electrochemical catalysis. The synthetic method discussed in this report has an important and immediate impact not only on the design and synthesis of functional hybrid nanomaterials by supramolecular chemistry and sonochemistry but also on applications of the same into electrochemical devices such as sensors, fuel cells, solar cells, actuators, batteries, and capacitors.
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http://dx.doi.org/10.1002/smll.200900128DOI Listing
August 2009

Clean and facile solution synthesis of iron(III)-entrapped gamma-alumina nanosorbents for arsenic removal.

ChemSusChem 2008 ;1(4):356-62

Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology (KAIST), Yusong-gu, Daejeon, Korea.

Iro (III)-entrapped gamma-alumina nanosorbents were prepared by an environmentally benign method using an ionothermal process based on an ionic liquid to synthesize the gamma-alumina host and a sonochemical method to entrap the iron(III) guest. The morphology of the alumina depends on the aluminum precursor used, giving aligned bundled and randomly debundled gamma-alumina nanorods as well as wormlike mesoporous alumina. In particular, the rodlike structure shows significantly greater mesoporosity than the wormlike porous gamma-alumina structure. Moreover, entrapment of iron(III) in the gamma-alumina nanosorbents with randomly debundled rodlike structures leads to the greatest AsV removal capacity and the fastest adsorption rate as compared to the other FeIII-entrapped adsorbents, as a result of its larger surface area and pore sizes. Thus, this method provides a clean and effective route to an advanced host-guest adsorbent system for application in the removal of arsenic from drinking water.
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http://dx.doi.org/10.1002/cssc.200700119DOI Listing
July 2008

Analysis of the CO2 and NH3 reaction in an aqueous solution by 2D IR COS: formation of bicarbonate and carbamate.

J Phys Chem A 2008 Jul 27;112(29):6558-62. Epub 2008 Jun 27.

Department of Chemical and Biomolecular Engineering, BK21 Program, KAIST, Yusong-gu, Daejeon, Republic of Korea.

The two-dimensional (2D) infrared correlation spectra obtained from the reaction time- and concentration-dependent IR spectra elucidates the reaction of CO2 and NH3 in an aqueous solution for CO2 absorption. In the synchronous 2D correlation spectra, the interrelation of the proton with carbamate and bicarbonate indicates that the pH level affected the formation reactions of the two products. Furthermore, the interrelation of carbamate with bicarbonate confirmed the conversion of carbamate into bicarbonate with the release of protons (or the decrease of the pH). From the experimental results including the asynchronous 2D correlation spectra, the reaction of the CO2 and aqueous ammonia proceeded through the following steps: formation of carbamate, formation of bicarbonate, release of protons, and conversion of carbamate into bicarbonate. The analysis of the formation of carbamate and bicarbonate by 2D infrared correlation spectroscopy provides useful information on the reaction mechanism of CO2 and NH3 in aqueous solutions.
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http://dx.doi.org/10.1021/jp800991dDOI Listing
July 2008

Advanced cleanup process of the free-flow microfluidic device for protein analysis.

Ultramicroscopy 2008 Sep 15;108(10):1365-70. Epub 2008 May 15.

Department of Chemical and Biomolecular Engineering (BK21 program), Korea Advanced Institute of Science and Technology, Daejeon 305-701, Republic of Korea.

The treatment of samples preparation is generally recognized as a bottleneck for the rapid analysis of protein because of the off-chip performance in many cases. In this study, we used the charge characteristics of protein to develop a simple and rapid electro-microfluidic desalting system as an effective means of cleaning up protein sample. When we loaded a urea-rich protein sample and a buffer solution into a free-flow zone electrophoresis (FFZE) chamber, the microfluidic device was able to separate the charged protein sample and the non-charged urea. With a 90 V electric field in the FFZE chamber, the removal efficiency of the urea was about 88% and the recovery of the protein was 78%. In addition, the desalted protein sample used in this device showed significant improvement with respect to the MALDI-TOF-MS spectrum signal of a fusion protein, which was fused to the gold-binding polypeptide with enhanced green fluorescent protein, as a model protein. The inflow of the purified fusion protein sample can be successfully immobilized on the gold surface and analyzed by confocal fluorescence microscopy and surface plasmon resonance for biotechnological sensors.
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http://dx.doi.org/10.1016/j.ultramic.2008.04.085DOI Listing
September 2008

Development of a fully integrated microfluidic system for sensing infectious viral disease.

Electrophoresis 2008 Jul;29(14):2960-9

Department of Chemical and Biomolecular Engineering (BK21 program), KAIST, Yuseong-gu, Daejeon, Korea.

An active micromixer system utilizing the magnetic force was developed and examined for its ability to facilitate the mixing of more than two fluid flows. The mixing performance of the active micromixer was evaluated in aqueous-aqueous systems including dyes for visual observation. A complete analytical microfluidic system was developed by integrating various functional modules into a single chip, thus allowing cell lysis, sample preparation, purification of intracellular molecules, and subsequent analysis. Upon loading the cell samples and lysis solution into the mixing chamber, the integrated microfluidic device allows efficient cell disruption by rotation of a micromagnetic disk and control of mixing time using the Teflon-coated hydrophobic film as a microvalve. This inflow is followed by separating the cell debris and contaminated proteins from the cell lysate sample using the acrylamide (AAm)-functionalized SPE. The inflow of partially purified cell lysate sample containing the gold binding polypeptide (GBP)-fusion protein was bound onto the gold micropatterns by means of its metal binding affinity. 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 severe acute respiratory syndrome (SARS), an infectious viral disease, as an example case.
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http://dx.doi.org/10.1002/elps.200700823DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7163465PMC
July 2008

Influence of additives including amine and hydroxyl groups on aqueous ammonia absorbent for CO2 capture.

J Phys Chem B 2008 Apr 19;112(14):4323-8. Epub 2008 Mar 19.

Department of Chemical and Biomolecular Engineering (BK21 Program), KAIST, 373-1 Guseong-dong, Yuseong-gu, Daejeon, Republic of Korea.

Aqueous ammonia absorbent (10 wt %) was modified with four kinds of additives (1 wt %) including amine and hydroxyl groups, i.e., 2-amino-2-methyl-1-propanol (AMP), 2-amino-2-methyl-1,3-propandiol (AMPD), 2-amino-2-ethyl-1,3-propandiol (AEPD), and tri(hydroxymethyl) aminomethane (THAM), for CO(2) capture. The loss of ammonia by vaporization was reduced by additives, whereas the removal efficiency of CO(2) was slightly improved. These results were attributed to the interactions between ammonia and additives or absorbents and CO(2) via hydrogen bonding, as verified by FT-IR spectra and computational calculation. Molecular structures as well as binding energies were obtained from the geometries of (ammonia + additives) and (ammonia + additives + CO(2)) at the optimized state. These experimental and theoretical findings demonstrate that additives including amine and hydroxyl group are suitable for modifying aqueous ammonia absorbent for CO(2) removal.
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http://dx.doi.org/10.1021/jp711113qDOI Listing
April 2008

Removal of bovine serum albumin using solid-phase extraction with in-situ polymerized stationary phase in a microfluidic device.

J Chromatogr A 2008 Apr 13;1187(1-2):11-7. Epub 2008 Feb 13.

Department of Chemical and Biomolecular Engineering (BK21 program), KAIST, 335 Gwahangno, Yuseong-gu, Daejeon 305-701, South Korea.

Serum albumin, one of the most abundant serum proteins, blocks the expression of other important biomarkers. The objective of this study is to remove serum albumin effectively by using solid-phase extraction (SPE) in microfluidic devices. Photo-polymerized adsorbent as a stationary phase of SPE was used to remove bovine serum albumin (BSA). The adsorption capacity was examined with the effect of pH and concentration in BSA solution, and adjustment of monomer concentration such as hydrophilic 2-acrylamido-2-methyl-1-propanesulfonic acid and acrylamide in the adsorbent. The effect of hydrophobic butyl methacylate on BSA adsorption was also studied. Selective removal in a bicomponent with BSA and bovine gamma-globulin was performed by adjusting the pH as required.
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http://dx.doi.org/10.1016/j.chroma.2008.01.084DOI Listing
April 2008
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