Publications by authors named "Kwang Heo"

31 Publications

Large-Scale Assembly of Peptide-Based Hierarchical Nanostructures and Their Antiferroelectric Properties.

Small 2020 11 20;16(45):e2003986. Epub 2020 Oct 20.

Department of Nanotechnology and Advanced Materials Engineering, Hybrid Materials Research Center (HMC), Sejong University, Seoul, 05006, Republic of Korea.

An effective strategy is developed to create peptide-based hierarchical nanostructures through the meniscus-driven self-assembly in a large area and fabricate antiferroelectric devices based on these nanostructures for the first time. The diphenylalanine hierarchical nanostructures (FF-HNs) are self-assembled by vertically pulling a substrate from a diphenylalanine (FF) solution dissolved in a miscible solvent under precisely controlled conditions. Owing to the unique structural properties of FF nanostructures, including high crystallinity and α-helix structures, FF-HNs possess a net electrical dipole moment, which can be switched in an external electric field. The mass production of antiferroelectric devices based on FF-HNs can be successfully achieved by means of this biomimetic assembly technique. The devices show an evident antiferroelectric to ferroelectric transition under dark conditions, while the ferroelectricity is found to be tunable by light. Notably, it is discovered that the modulation of antiferroelectric behaviors of FF-HNs under glutaraldehyde exposure is due to the FF molecules that are transformed into cyclophenylalanine by glutaraldehyde. This work provides a stepping stone toward the mass production of self-assembled hierarchical nanostructures based on biomolecules as well as the mass fabrication of electronic devices based on biomolecular nanostructures for practical applications.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/smll.202003986DOI Listing
November 2020

Thermal Annealing of Molecular Layer-Deposited Indicone Toward Area-Selective Atomic Layer Deposition.

ACS Appl Mater Interfaces 2020 Sep 14;12(38):43212-43221. Epub 2020 Sep 14.

Division of Materials Science and Engineering, Hanyang University, 222 Wangsimni-ro, Seongdong-gu, Seoul 04763, Republic of Korea.

Area-selective atomic layer deposition (AS-ALD) is a promising technique for fine nanoscale patterning, which may overcome the drawbacks of conventional top-down approaches for the fabrication of future electronic devices. However, conventional materials and processes often employed for AS-ALD are inadequate for conformal and rapid processing. We introduce a new strategy for AS-ALD based on molecular layer deposition (MLD) that is compatible with large-scale manufacturing. Conformal thin films of "indicone" (indium alkoxide polymer) are fabricated by MLD using INCA-1 (bis(trimethylsily)amidodiethylindium) and HQ (hydroquinone). Then, the MLD indicone films are annealed by a thermal heat treatment under vacuum. The properties of the indicone thin films with different annealing temperatures were measured with multiple optical, physical, and chemical techniques. Interestingly, a nearly complete removal of indium from the film was observed upon annealing to ca. 450 °C and above. The chemical mechanism of the thermal transformation of the indicone film was investigated by density functional theory calculations. Then, the annealed indicone thin films were applied as an inhibiting layer for the subsequent ALD of ZnO, where the deposition of approximately 20 ALD cycles (equivalent to a thickness of approximately 4 nm) of ZnO was successfully inhibited. Finally, patterns of annealed MLD indicone/Si substrates were created on which the area-selective deposition of ZnO was demonstrated.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acsami.0c10322DOI Listing
September 2020

Recent Developments and Prospects of M13- Bacteriophage Based Piezoelectric Energy Harvesting Devices.

Nanomaterials (Basel) 2020 Jan 2;10(1). Epub 2020 Jan 2.

Department of Nanotechnology and Advanced Materials Engineering, Sejong University, Seoul 05006, Korea.

Recently, biocompatible energy harvesting devices have received a great deal of attention for biomedical applications. Among various biomaterials, viruses are expected to be very promising biomaterials for the fabrication of functional devices due to their unique characteristics. While other natural biomaterials have limitations in mass-production, low piezoelectric properties, and surface modification, M13 bacteriophages (phages), which is one type of virus, are likely to overcome these issues with their mass-amplification, self-assembled structure, and genetic modification. Based on these advantages, many researchers have started to develop virus-based energy harvesting devices exhibiting superior properties to previous biomaterial-based devices. To enhance the power of these devices, researchers have tried to modify the surface properties of M13 phages, form biomimetic hierarchical structures, control the dipole alignments, and more. These methods for fabricating virus-based energy harvesting devices can form a powerful strategy to develop high-performance biocompatible energy devices for a wide range of practical applications in the future. In this review, we discuss all these issues in detail.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3390/nano10010093DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7022932PMC
January 2020

Electroluminescent soft elastomer actuators with adjustable luminance and strain.

Soft Matter 2019 Oct 2;15(40):7996-8000. Epub 2019 Oct 2.

Department of Mechanical Engineering, Korea University, Seoul 02841, Republic of Korea.

We demonstrate a multifunctional soft actuator that exhibits both electroluminescence (EL) and soft actuation with a strain of 85% and a maximum luminance of 300 cd m, superior to previous devices with individual functions. This was possible by combining several strategies such as the development of highly conductive, transparent, and stretchable electrodes, incorporation of high-k nanoparticles to increase the electric field applied to the EL particles, and application of AC + DC composite signals to simplify the device structure. We expect this research to contribute to the development of new soft devices that can further enhance human-machine interactions in color displaying actuator applications.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c9sm01122fDOI Listing
October 2019

Diphenylalanine Peptide Nanotube Energy Harvesters.

ACS Nano 2018 08 7;12(8):8138-8144. Epub 2018 Aug 7.

Department of Bioengineering and Tsinghua Berkeley Shenzhen Institute , University of California , Berkeley , California 94720 , United States.

Piezoelectric materials are excellent generators of clean energy, as they can harvest the ubiquitous vibrational and mechanical forces. We developed large-scale unidirectionally polarized, aligned diphenylalanine (FF) nanotubes and fabricated peptide-based piezoelectric energy harvesters. We first used the meniscus-driven self-assembly process to fabricate horizontally aligned FF nanotubes. The FF nanotubes exhibit piezoelectric properties as well as unidirectional polarization. In addition, the asymmetric shapes of the self-assembled FF nanotubes enable them to effectively translate external axial forces into shear deformation to generate electrical energy. The fabricated peptide-based piezoelectric energy harvesters can generate voltage, current, and power of up to 2.8 V, 37.4 nA, and 8.2 nW, respectively, with 42 N of force, and can power multiple liquid-crystal display panels. These peptide-based energy-harvesting materials will provide a compatible energy source for biomedical applications in the future.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acsnano.8b03118DOI Listing
August 2018

Cellulose Nanocrystal-Based Colored Thin Films for Colorimetric Detection of Aldehyde Gases.

ACS Appl Mater Interfaces 2018 Mar 19;10(12):10353-10361. Epub 2018 Mar 19.

Department of Mechanical Engineering , Korea University , Seoul 02841 , Korea.

We demonstrate a controllable and reliable process for manifesting color patterns on solid substrates using cellulose nanocrystals (CNCs) without the use of any other chemical pigments. The color can be controlled by adjusting the assembly conditions of the CNC solution during a dip-and-pull process while aiding the close packing of CNCs on a solid surface with the help of ionic-liquid (1-butyl-3-methylimidazolium) molecules that screen the repelling electrostatic charges between CNCs. By controlling the pulling speed from 3 to 9 μm/min during the dip-and-pull process, we were able to control the film thickness from 100 to 300 nm, resulting in films with different colors in the visible range. The optical properties were in good agreement with the finite-difference time-domain simulation results. By functionalizing these films with amine groups, we developed colorimetric sensors that can change in color when exposed to aldehyde gases such as formaldehyde or propanal. A principal component analysis showed that we can differentiate between different aldehyde gases and other interfering molecules. We expect that our approach will enable inexpensive and rapid volatile organic compound detection with on-site monitoring capabilities.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acsami.7b19738DOI Listing
March 2018

Highly sensitive and flexible strain sensors based on patterned ITO nanoparticle channels.

Nanotechnology 2017 Dec;28(49):495501

Department of Mechanical Engineering, Korea University, Seoul 02841, Republic of Korea.

We demonstrate a highly sensitive and flexible bending strain sensor using tin-doped indium oxide (ITO) nanoparticles (NPs) assembled in line patterns on flexible substrates. By utilizing transparent ITO NPs without any surface modifications, we could produce strain sensors with adjustable gauge factors and optical transparency. We were able to control the dimensional and electrical properties of the sensors, such as channel height and resistance, by controlling the NP assembly speed. Furthermore, we were able to generate controlled gauge factor with values ranging from 18 to 157, which are higher than previous cases using metallic Cr NPs and Au NPs. The alignment of the ITO NPs in parallel lines resulted in low crosstalk between the transverse and longitudinal bending directions. Finally, our sensor showed high optical transmittance, up to ∼93% at 500 nm wavelength, which is desirable for flexible electronic applications.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1088/1361-6528/aa9237DOI Listing
December 2017

Engineered phage films as scaffolds for CaCO3 biomineralization.

Nanoscale 2016 Aug;8(34):15696-701

Department of Materials Science and Engineering, University of California, Berkeley, CA 94720, USA. and Biological Systems and Engineering, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.

M13 bacteriophages (phage) were exploited as CaCO3 mineralization scaffolds for hard tissue engineering applications. M13 phage was first self-assembled into biomimetic fibrous scaffolds, followed by CaCO3 biomineralization via the polymer-induced liquid precursor process. The phage scaffolds successfully incorporated calcium carbonate, facilitating nucleation and growth of spherulitically textured calcite. The Young's modulus of the scaffolds increased by an order of magnitude after mineralization while also supporting the growth of mouse fibroblasts. These findings demonstrate that phage-based biomaterials are a feasible platform for creating biomineralized hard tissue constructs, in support of future studies in hard tissue engineering and biomedical applications.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c6nr04322dDOI Listing
August 2016

Carbon and metal nanotube hybrid structures on graphene as efficient electron field emitters.

Nanotechnology 2016 Jul 27;27(27):275301. Epub 2016 May 27.

Department of Physics and Astronomy and Institute of Applied Physics, Seoul National University, Seoul 08826, Korea. Department of Nanotechnology and Advanced Materials Engineering, Sejong University, Seoul 05006, Korea.

We report a facile and efficient method for the fabrication of highly-flexible field emission devices by forming tubular hybrid structures based on carbon nanotubes (CNTs) and nickel nanotubes (Ni NTs) on graphene-based flexible substrates. By employing an infiltration process in anodic alumina oxide (AAO) templates followed by Ni electrodeposition, we could fabricate CNT-wrapped Ni NT/graphene hybrid structures. During the electrodeposition process, the CNTs served as Ni nucleation sites, resulting in a large-area array of high aspect-ratio field emitters composed of CNT-wrapped Ni NT hybrid structures. As a proof of concepts, we demonstrate that high-quality flexible field emission devices can be simply fabricated using our method. Remarkably, our proto-type field emission devices exhibited a current density higher by two orders of magnitude compared to other devices fabricated by previous methods, while maintaining its structural integrity in various bending deformations. This novel fabrication strategy can be utilized in various applications such as optoelectronic devices, sensors and energy storage devices.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1088/0957-4484/27/27/275301DOI Listing
July 2016

Bi-Assisted CdTe/CdS Hierarchical Nanostructure Growth for Photoconductive Applications.

Nanoscale Res Lett 2015 Dec 19;10(1):1037. Epub 2015 Aug 19.

Department of Physics and Astronomy, Seoul National University, Seoul, 151-747, Republic of Korea,

We developed a method to control the structure of CdTe nanowires by adopting Bi-mixed CdTe powder source to a catalyst-assisted chemical vapor deposition, which allowed us to fabricate CdTe/CdS hierarchical nanostructures. We demonstrated that diverse nanostructures can be grown depending on the combination of the Bi powder and film catalysts. As a proof of concepts, we grew CdTe/CdS branched nanowires for the fabrication of photodetectors. The hierarchical nanostructure-based photodetectors showed an improved photoresponsivity compared to the single CdTe nanowire (NW)-based photodetector. Our strategy can be a simple but powerful method for the development of advanced optoelectronic devices and other practical applications.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1186/s11671-015-1037-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4539310PMC
December 2015

Real-time detection of chlorine gas using Ni/Si shell/core nanowires.

Nanoscale Res Lett 2015 28;10:18. Epub 2015 Jan 28.

School of Mechanical Engineering, Korea University, 145 Anam-Ro, Seongbuk-Gu, Seoul 136-713 Korea.

We demonstrate the selective adsorption of Ni/Si shell/core nanowires (Ni-Si NWs) with a Ni outer shell and a Si inner core on molecularly patterned substrates and their application to sensors for the detection of chlorine gas, a toxic halogen gas. The molecularly patterned substrates consisted of polar SiO2 regions and nonpolar regions of self-assembled monolayers of octadecyltrichlorosilane (OTS). The NWs showed selective adsorption on the polar SiO2 regions, avoiding assembly on the nonpolar OTS regions. Utilizing these assembled Ni-Si NWs, we demonstrate a sensor for the detection of chlorine gas. The utilization of Ni-Si NWs resulted in a much larger sensor response of approximately 23% to 5 ppm of chlorine gas compared to bare Ni NWs, due to the increased surface-to-volume ratio of the Ni-Si shell/core structure. We expect that our sensor will be utilized in the future for the real-time detection of halogen gases including chlorine with high sensitivity and fast response.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1186/s11671-015-0729-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4314467PMC
April 2015

Direct-write complementary graphene field effect transistors and junctions via near-field electrospinning.

Small 2014 May 5;10(10):1920-5. Epub 2014 Mar 5.

Department of Physics, University of California at Berkeley, USA; Berkeley Sensor and Actuator Center, University of California at Berkeley, USA.

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/smll.201302965DOI Listing
May 2014

Graphene-based materials functionalized with elastin-like polypeptides.

Langmuir 2014 Mar 19;30(8):2223-9. Epub 2014 Feb 19.

Department of Bioengineering, University of California, Berkeley , Berkeley, California 94720, United States.

Graphene-based materials commonly require functionalization for biological applications in order to control their physical/colloidal properties and to introduce additional capabilities, such as stimuli-responsiveness and affinity to specific biomolecules. Here, we functionalized CVD-grown graphene and graphene oxide with a genetically engineered elastin-like polypeptide fused to a graphene binding peptide and then showed that the resulting hybrid materials exhibit thermo- and photoresponsive behaviors. Furthermore, we demonstrate that our genetic engineering strategy allows for the facile introduction of bioactivity to reduced graphene oxide. The stimuli-responsiveness and genetic tunability of our graphene-protein nanocomposites are attractive for addressing future biomedical applications.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/la404333bDOI Listing
March 2014

Biomimetic virus-based colourimetric sensors.

Nat Commun 2014 ;5:3043

1] Department of Bioengineering, University of California, Berkeley, California 94720, USA [2] Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.

Many materials in nature change colours in response to stimuli, making them attractive for use as sensor platform. However, both natural materials and their synthetic analogues lack selectivity towards specific chemicals, and introducing such selectivity remains a challenge. Here we report the self-assembly of genetically engineered viruses (M13 phage) into target-specific, colourimetric biosensors. The sensors are composed of phage-bundle nanostructures and exhibit viewing-angle independent colour, similar to collagen structures in turkey skin. On exposure to various volatile organic chemicals, the structures rapidly swell and undergo distinct colour changes. Furthermore, sensors composed of phage displaying trinitrotoluene (TNT)-binding peptide motifs identified from a phage display selectively distinguish TNT down to 300 p.p.b. over similarly structured chemicals. Our tunable, colourimetric sensors can be useful for the detection of a variety of harmful toxicants and pathogens to protect human health and national security.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/ncomms4043DOI Listing
November 2015

Observation of localized strains on vertically grown single-walled carbon nanotube forests via polarized Raman spectroscopy.

Nanotechnology 2014 Jan 12;25(2):025705. Epub 2013 Dec 12.

Department of Physics, Chung-Ang University, Seoul, 156-756, Korea.

Vertically grown single-walled carbon nanotube (V-SWCNT) forests, synthesized by water-assisted plasma-enhanced chemical vapor deposition, were studied using polarized micro-Raman spectroscopy. Among three different sections (root, center and end) along the vertical growth direction, the degree of V-SWCNT alignment was highest in the center section. Raman frequency red-shifts up to 7 and 13 cm(-1), for RBM and G-band, respectively, were observed in the center section, with respect to the Raman frequencies measured in the root and the end sections. Raman frequency downshift and concurrent linewidth broadening of the G-band, revealing a localized strain, were also observed in the center section. The existence of a localized strain in the center section of the V-SWCNT was further confirmed by observing a strong polarization anisotropy of up to 8 cm(-1) in the G-band Raman frequency for different polarized Raman scattering configurations at the same probed spot.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1088/0957-4484/25/2/025705DOI Listing
January 2014

Sub-diffraction limit imaging of inorganic nanowire networks interfacing cells.

Small 2014 Feb 3;10(3):462-8. Epub 2013 Sep 3.

Department of Physics and Astronomy, Seoul National University, Seoul, 151-747, Korea.

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/smll.201301214DOI Listing
February 2014

Multilayered nano-prism vertex tips for tip-enhanced Raman spectroscopy and imaging.

Analyst 2013 Oct;138(19):5588-93

Department of Physics and Astronomy, Seoul National University, Seoul 151-747, Korea.

We presented a scalable fabrication method for the preparation of multilayered nano-prism vertex (NV)-tips whose dimensions can be controlled for tip-enhanced Raman spectroscopy (TERS). The NV-tip had sharp vertices (diameter ~20 nm) originated from the chemical lift-off process after the angle-grinding process, enabling high resolution imaging. TERS measurements were performed on brilliant cresyl blue (BCB) molecules using a Ag/Au NV-tip, revealing the enhanced field localization at the vertices of the NV-tip. Furthermore, we could observe the polarization effect of the NV-tip. Our NV-tips should be a powerful tool for basic research on TERS experiments and SPM applications.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c3an00808hDOI Listing
October 2013

Quantum dot-engineered M13 virus layer-by-layer composite films for highly selective and sensitive turn-on TNT sensors.

Chem Commun (Camb) 2013 Jul;49(54):6045-7

Department of Chemistry, Pohang University of Science and Technology(POSTECH), Pohang, 790-784, South Korea.

We developed quantum dot-engineered M13 virus layer-by-layer hybrid composite films with incorporated fluorescence quenchers. TNT is designed to displace the quenchers and turn on the quantum dot fluorescence. TNT was detected at the sub ppb level with a high selectivity.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c3cc42032aDOI Listing
July 2013

Reply to comment on 'Metallic nanowire-graphene hybrid nanostructures for highly flexible field emission devices'.

Nanotechnology 2012 Jul 25;23(28):288002. Epub 2012 Jun 25.

Department of Physics and Astronomy, Seoul National University, Seoul, Korea.

In our previous paper (Arif et al 2011 Nanotechnology 22 355709), we developed a method to prepare metallic nanowire-graphene hybrid nanostructures and applied it to the fabrication of flexible field emission devices. For the quantitative analysis of the devices, the basic Fowler-Nordheim model was used. However, as pointed out by Forbes (2012 Nanotechnology 23 288001) the basic Fowler-Nordheim model should be corrected when the quantum confinement effect and the screening effect are considered. Forbes also developed a method that checks quantitatively the consistency between the experimental data and the theoretical assumptions. These discussions should provide an important theoretical framework in the quantitative analysis of our devices as well as large area field emitters in general.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1088/0957-4484/23/28/288002DOI Listing
July 2012

Nanotube-bridged wires with sub-10 nm gaps.

Nano Lett 2012 Apr 28;12(4):1879-84. Epub 2012 Mar 28.

Department of Physics and Astronomy, Seoul National University, Seoul 151-747, Korea.

We report a simple but efficient method to synthesize carbon nanotube-bridged wires (NBWs) with gaps as small as 5 nm. In this method, we have combined a strategy for assembling carbon nanotubes (CNTs) inside anodized aluminum oxide pores and the on-wire lithography technique to fabricate CNT-bridged wires with gap sizes deliberately tailored over the 5-600 nm range. As a proof-of-concept demonstration of the utility of this architecture, we have prepared NBW-based chemical and biosensors which exhibit higher analyte sensitivity (lower limits of detection) than those based on planar CNT networks. This observation is attributed to a greater surface-to-volume ratio of CNTs in the NBWs than those in the planar CNT devices. Because of the ease of synthesis and high yield of NBWs, this technique may enable the further incorporation of CNT-based architectures into various nanoelectronic and sensor platforms.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/nl204259tDOI Listing
April 2012

High-performance photoconductive channels based on (carbon nanotube)-(CdS nanowire) hybrid nanostructures.

Small 2012 Jun 21;8(11):1650-6. Epub 2012 Mar 21.

Department of Physics and Astronomy, Seoul National University, Seoul, Korea.

A photoconductive channel based on hybrid nanostructures comprising carbon nanotubes (CNTs) and CdS nanowires is fabricated by a directed assembly strategy and catalyst-assisted chemical vapor deposition (CVD). The photoconductive channels simultaneously exhibit large photocurrent and fast response speed. Furthermore, it can be easily applied to surfaces that are not flat, such as a glass tube. This is a simple but efficient strategy for various optoelectronic applications.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/smll.201102628DOI Listing
June 2012

Scanning noise microscopy on graphene devices.

ACS Nano 2011 Nov 6;5(11):8620-8. Epub 2011 Oct 6.

Department of Physics and Astronomy,Seoul National University, Seoul 151-747, Korea.

We developed a scanning noise microscopy (SNM) method and demonstrated the nanoscale noise analysis of a graphene strip-based device. Here, a Pt tip made a direct contact on the surface of a nanodevice to measure the current noise spectrum through it. Then, the measured noise spectrum was analyzed by an empirical model to extract the noise characteristics only from the device channel. As a proof of concept, we demonstrated the scaling behavior analysis of the noise in graphene strips. Furthermore, we performed the nanoscale noise mapping on a graphene channel, allowing us to study the effect of structural defects on the noise of the graphene channel. The SNM method is a powerful tool for nanoscale noise analysis and should play a significant role in basic research on nanoscale devices.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/nn202135gDOI Listing
November 2011

Metallic nanowire-graphene hybrid nanostructures for highly flexible field emission devices.

Nanotechnology 2011 Sep 9;22(35):355709. Epub 2011 Aug 9.

Department of Physics and Astronomy, Seoul National University, Seoul, Korea.

We report a simple but efficient method to prepare metallic nanowire-graphene (MN-G) hybrid nanostructures at a low temperature and show its application to the fabrication of flexible field emission devices. In this method, a graphene layer was transferred onto an anodic alumina oxide template, and vertically aligned Au nanowires were grown on the graphene surface via electrodeposition method. As a proof of concept, we demonstrated the fabrication of flexible field emission devices, where the MN-G hybrid nanostructures and another graphene layer on PDMS substrates were utilized as a cathode and an anode for highly flexible devices, respectively. Our field emission device exhibited stable and high field emission currents even when bent down to the radius of curvature of 25 mm. This MN-G hybrid nanostructure should prove tremendous flexibility for various applications such as bio-chemical sensors, field emission devices, pressure sensors and battery electrodes.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1088/0957-4484/22/35/355709DOI Listing
September 2011

Electrical immunosensor based on a submicron-gap interdigitated electrode and gold enhancement.

Biosens Bioelectron 2011 Aug 19;26(12):4690-6. Epub 2011 May 19.

BioMonitoring Research Center, KRIBB, Daejeon 305-806, Republic of Korea.

We demonstrated that the detection of human interleukin 5 (IL5) with a higher sensitivity than the enzyme-linked immunosorbent assay (ELISA) was possible using mass-producible submicron-gap interdigitated electrodes (IDEs) combined with signal amplification by a gold nanoparticle (AuNP) and gold enhancement. IDEs, facing comb-shape electrodes, can act as simple and miniaturized devices for immunoassay. An IDE with a gap size of 400nm was fabricated by a stepper photolithography process and was applied for the immunoassay of human IL5. A biotinylated anti-human IL5 was immobilized on the streptavidin-modified IDE, and biotin-bovine serum albumin (BSA) and BSA were added sequentially to reduce non-specific binding between the streptavidin-immobilized IDE surface and other proteins. The immunoassay procedure included three main steps: the reaction of human IL5 to form antigen-antibody complexes, the binding of AuNP conjugation with an antibody against human IL5 for the sandwich immunoassay, and gold enhancement for electrical signal amplification. The measurement of electrical current at each step showed that the gold enhancement step was very critical in detection of the concentration of human IL5. Analysis by scanning electron microscope (SEM) showed that close to 1μm particles were formed from 10nm AuNP by the gold enhancement reaction using gold ions and hydroxylamine. Under optimized conditions, human IL5 could be analyzed at 1pgmL(-1) with a wide dynamic range (from 10(-3) to 100ngmL(-1) concentrations).
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.bios.2011.05.027DOI Listing
August 2011

Carbon nanotube monolayer cues for osteogenesis of mesenchymal stem cells.

Small 2011 Mar 7;7(6):741-5. Epub 2011 Feb 7.

Department of Physics and Astronomy, Seoul National University, Seoul, 151-747, Korea.

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/smll.201001930DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3181004PMC
March 2011

Large-scale assembly of highly flexible low-noise devices based on silicon nanowires.

Nanotechnology 2010 Apr 10;21(14):145302. Epub 2010 Mar 10.

Interdisciplinary Program in Nano-Science and Technology, Seoul National University, Seoul, Korea.

Recently, integrated flexible devices based on silicon nanowires (Si-NWs) have received significant attention as high performance flexible devices. However, most previous assembly methods can generate only specifically-shaped devices and require unconventional facilities, which has been a major hurdle for industrial applications. Herein, we report a simple but very efficient method for assembling Si-NWs into virtually generally-shape patterns on flexible substrates using only conventional microfabrication facilities, allowing us to mass-produce highly flexible low-noise devices. As proof of this method, we demonstrated the fabrication of highly bendable top-gate transistors based on Si-NWs. These devices showed typical n-type semiconductor behaviors, and exhibited a much lower noise level compared to previous flexible devices based on organic conductors or other nanowires. In addition, the gating behaviors and low-noise characteristics of our devices were maintained, even under highly bent conditions.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1088/0957-4484/21/14/145302DOI Listing
April 2010

Association of thyroid autoantibodies with moyamoya-type cerebrovascular disease: a prospective study.

Stroke 2010 Jan 19;41(1):173-6. Epub 2009 Nov 19.

Department of Neurology, Samsung Medical Center, Sungkyunkwan University, 50 Irwon-dong, Gangnam-gu, Seoul 135-710, South Korea.

Background And Purpose: To investigate the association between thyroid autoantibodies and moyamoya disease (MMD) in patients with an apparent euthyroid state.

Methods: We prospectively studied angiographically diagnosed patients with MMD. We compared demographic profiles, thyroid function test, and thyroid autoantibody status between MMD and control groups.

Results: A total of 63 patients with MMD, 71 patients with non-MMD stroke, and 200 healthy control subjects were included. The prevalence of elevated thyroid autoantibodies was higher in the MMD group than in other groups (P<0.01 for MMD versus non-MMD; P<0.001 for MMD versus control subjects). After adjusting for covariates, the elevated thyroid autoantibodies (OR, 4.871; 95% CI, 1.588 to 15.277) and smoking habits (OR, 0.206 for current smoker; 95% CI, 0.054 to 0.786) were independently associated with MMD versus non-MMD stroke.

Conclusions: Elevated thyroid autoantibodies were frequently observed in patients with MMD. The results of the present study suggest that immune aberrancies associated with or underlying thyroid autoimmunity are also playing a role in developing MMD.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1161/STROKEAHA.109.562264DOI Listing
January 2010

Functionalization of silicon nanowires with actomyosin motor protein for bioinspired nanomechanical applications.

Small 2009 Dec;5(23):2659-64

Department of Physics and Astronomy, Seoul National University, Seoul, Korea.

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/smll.200900964DOI Listing
December 2009

Large-scale assembly of silicon nanowire network-based devices using conventional microfabrication facilities.

Nano Lett 2008 Dec;8(12):4523-7

Interdisciplinary Program in Nano-Science and Technology, Department of Physics and Astronomy, School of Chemical and Biological Engineering, Seoul National University, Seoul 151-747, Korea.

We present a method for assembling silicon nanowires (Si-NWs) in virtually general shape patterns using only conventional microfabrication facilities. In this method, silicon nanowires were functionalized with amine groups and dispersed in deionized water. The functionalized Si-NWs exhibited positive surface charges in the suspensions, and they were selectively adsorbed and aligned onto negatively charged surface regions on solid substrates. As a proof of concepts, we demonstrated transistors based on individual Si-NWs and long networks of Si-NWs.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/nl802570mDOI Listing
December 2008

Scalable assembly method of vertically-suspended and stretched carbon nanotube network devices for nanoscale electro-mechanical sensing components.

Nano Lett 2008 Dec;8(12):4483-7

Department of Physics and Astronomy, Interdisciplinary Program in Nano-Science and Technology, Seoul National University, Seoul 151-747, Korea.

For the first time, vertically suspended and stretched carbon nanotube network junctions were fabricated in large quantity via the directed assembly strategy using only conventional microfabrication facilities. In this process, surface molecular patterns on the side-wall of the Al structures were utilized to guide the assembly and alignment of carbon nanotubes in the solution. We also performed extensive experimental (electrical and mechanical) analysis and theoretical simulation about the vertically suspended single-walled carbon nanotube network junctions. The junctions exhibited semiconductor-like conductance behavior. Furthermore, we demonstrated gas sensing and electromechanical sensing using these devices.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/nl802434sDOI Listing
December 2008