Kyuwon Kim

Room-temperature semiconductor gas sensor based on nonstoichiometric tungsten oxide nanorod film

Porous tungsten oxide films were deposited onto a sensor substrate with a Si bulk-micromachined hotplate, by drop-coating isopropyl alcohol solution of highly crystalline tungsten oxide (WO2.72) nanorods with average 75nm length and 4nm diameter. The temperature-dependent gas sensing characteristics of the films have been investigated over the mild temperature range from 20to250°C. While the sensing responses for ammonia vapor showed increase in electrical conductivity at temperatures above 150°C as expected for n-type metal oxide sensors, they exhibited the opposite behavior of unusual conductivity decrease below 100°C. Superb sensing ability of the sensors at room temperature in conjunction with their anomalous conductivity behavior might be attributed to unique nanostructural features of very thin, nonstoichiometric WO2.72.

An Electrochemically Reduced Graphene Oxide-Based Electrochemical Immunosensing Platform for Ultrasensitive Antigen Detection

We present an electrochemically reduced graphene oxide (ERGO)-based electrochemical immunosensing platform for the ultrasensitive detection of an antigen by the sandwich enzyme-linked immunosorbent assay (ELISA) protocol. Graphene oxide (GO) sheets were initially deposited on the amine-terminated benzenediazonium-modified indiun tin oxide (ITO) surfaces through both electrostatic and π-π interactions between the modified surfaces and GO. This deposition was followed by the electrochemical reduction of graphene oxide (GO) for preparing ERGO-modified ITO surfaces. These surfaces were then coated with an N-acryloxysuccinimide-activated amphiphilic polymer, poly(BMA-r-PEGMA-r-NAS), through π-π stacking interactions between the benzene ring tethered to the polymer and ERGO. After covalent immobilization of a primary antibody on the polymer-modified surfaces, sandwich ELISA was carried out for the detection of an antigen by use of a horseradish peroxidase (HRP)-labeled secondary antibody. Under the optimized experimental conditions, the developed electrochemical immunosensor exhibited a linear response over a wide range of antigen concentrations with a very low limit of detection (ca. 100 fg/mL, which corresponds to ca. 700 aM). The high sensitivity of the electrochemical immunosensor may be attributed not only to the enhanced electrocatalytic activity owing to ERGO but also to the minimized background current owing to the reduced nonspecific binding of proteins.

Bulk-micromachined submicroliter-volume PCR chip with very rapid thermal response and low power consumptionElectronic supplementary information (ESI) available: details of numerical simulation. See http://www.rsc.org/suppdata/lc/b3/b313547k/

The current paper describes the design, fabrication, and testing of a micromachined submicroliter-volume polymerase chain reaction (PCR) chip with a fast thermal response and very low power consumption. The chip consists of a bulk-micromachined Si component and hot-embossed poly(methyl methacrylate)(PMMA) component. The Si component contains an integral microheater and temperature sensor on a thermally well-isolated membrane, while the PMMA component contains a submicroliter-volume PCR chamber, valves, and channels. The micro hot membrane under the submicroliter-volume chamber is a silicon oxide/silicon nitride/silicon oxide (O/N/O) diaphragm with a thickness of 1.9 microm, resulting in a very low thermal mass. In experiments, the proposed chip only required 45 mW to heat the reaction chamber to 92 degrees C, the denaturation temperature of DNA, plus the heating and cooling rates are about 80 degrees C s(-1) and 60 degrees C s(-1), respectively. We validated, from the fluorescence results from DNA stained with SYBR Green I, that the proposed chip amplified the DNA from vector clone, containing tumor suppressor gene BRCA 1 (127 base pairs at 11th exon), after 30 thermal cycles of 3 s, 5 s, and 5 s at 92 degrees C, 55 degrees C, and 72 degrees C, respectively, in a 200 nL-volume chamber. As for specificity of DNA products, owing to difficulty in analyzing the very small volume PCR results from the micro chip, we vicariously employed the larger volume PCR products after cycling with the same sustaining temperatures as with the micro chip but with much slower ramping rates (3.3 degrees C s(-1) when rising, 2.5 degrees C s(-1) when cooling) within circa 20 minutes on a commercial PCR machine and confirmed the specificity to BRCA 1 (127 base pairs) with agarose gel electrophoresis. Accordingly, the fabricated micro chip demonstrated a very low power consumption and rapid thermal response, both of which are crucial to the development of a fully integrated and battery-powered instrument for a lab-on-a-chip DNA analysis.

Faradaic impedance titration of pure 3-mercaptopropionic acid and ethanethiol mixed monolayers on gold

Abstract Interfacial proton transfer reactions of pure 3-mercaptopropionic acid (MPA) and ethanethiol (EtSH) mixed self-assembled monolayers (SAMs) have been studied using the faradaic impedance titration method. The Fe(CN) 6 3− is used to probe the charge development of the terminal COOH group of the monolayers. The charge-transfer resistance ( R ct ) is measured with the monolayer composition, adsorption coverage, and the ionic strength of pH solution. The surface p K determined for the pure MPA is 6.0 at a monolayer coverage and 0.1 M ionic strength. The in-plane electrostatic force effect, which causes a broadening of the titration curves, on the surface p K for the MPA SAM is not significant at an ionic strength over 0.1 M. The p K value for the pure MPA SAM shifts negatively as the surface coverage decreases, indicating that the in-plane interactions between acids and the hydrophobicity surrounding acids decrease at the same time. When the pure MPA SAM is compared with the EtSH mixed SAM, the surface p K of the mixed SAM is larger than that of the pure SAM. Such positive p K shifts are more pronounced at the pure MPA SAM with a lower coverage. This implies that the p K shifts of sparsely adsorbed acidthiol SAM are more sensitive to the introduction of hydrophobicity than to the decrease of the in-plane interactions.

Comparison of the Nonspecific Binding of DNA-Conjugated Gold Nanoparticles between Polymeric and Monomeric Self-Assembled Monolayers

The nonspecific binding of DNA-conjugated gold nanoparticles (AuNPs) to solid surfaces is more difficult to control than that of DNA molecules due to the more attractive interactions from the large number of DNA molecules per AuNP. This paper reports that the polymeric self-assembled monolayers (SAMs) formed on indium-tin oxide (ITO) electrodes significantly inhibit the nonspecific binding of DNA-conjugated AuNPs. The random copolymers used to prepare the polymeric SAMs consist of three functional parts: an ITO-reactive silane group, a DNA-blocking poly(ethylene glycol) (PEG) group, and an amine-reactive N-acryloxysuccinimide group. In order to compare the polymeric SAMs with various monomeric SAMs, the relative nonspecific binding of the DNA-conjugated AuNPs to the ITO electrodes modified with (3-aminopropyl)triethoxysilane (APTES), 3-aminopropylphosphonic acid, 3-phosphonopropionic acid, or 11-phosphonoundecanoic acid is examined by measuring the electrocatalytic anodic current of hydrazine caused by the nonspecifically absorbed AuNPs and by counting the AuNPs adsorbed onto modified ITO electrodes. Carboxylic-acid-terminated and amine-terminated monomeric SAMs cause high levels of nonspecific binding of DNA-conjugated AuNPs. The monomeric SAM modified with the carboxylic-acid-terminated poly(amidoamine) dendrimer shows low levels of nonspecific binding (2.0% nonspecific binding relative to APTES) due to the high surface density of the negative charge. The simply prepared polymeric SAM produces the lowest level of nonspecific binding (0.8% nonspecific binding relative to APTES), resulting from the combined effect of (i) DNA-blocking PEG and carboxylic acid groups and (ii) dense polymeric SAMs. Therefore, thin and dense polymeric SAMs may be effective in electrochemical detection and easy DNA immobilization along with low levels of nonspecific binding.

In Situ Growth of Prussian Blue Nanostructures at Reduced Graphene Oxide as a Modified Platinum Electrode for Synergistic Methanol Oxidation

Herein, we report a facile synthetic strategy for the in situ growth of Prussian blue nanostructures (PB NSs) at the amine-functionalized silicate sol-gel matrix (TPDT)-RGO composite via the electrostatic interaction. Subsequently, Pt nanostructures are electrodeposited onto the preformed ITO/TPDT-RGO-PB electrode to prepare the RGO/PB/Pt catalyst. The significance of the present method is that the PB NSs are in situ grown by interconnecting the RGO layers, leading to 3D cage-like porous nanostructure. The modified electrodes are characterized by FESEM, EDAX, XRD, XPS, and electrochemical techniques. The RGO/PB/Pt catalyst exhibits synergistic electrocatalytic activity and high stability toward methanol oxidation. The porous nature of the TPDT and PB and unique electron-transfer mediating behavior of PB integrated with RGO in the presence of Pt nanostructures facilitated synergistic electrocatalytic activity for methanol oxidation.

Aldehyde-Functionalized Benzenediazonium Cation for Multiprobe Immobilization on Microelectrode Array Surfaces

We report in situ generation of aldehyde-functionalized benzenediazonium cation (ABD) and its use as a suitable linker molecule for fast and selective immobilization of biomolecules on indium-tin-oxide (ITO) electrode surfaces. We prepared ABD through a new reaction procedure, a simultaneous diazotation of the amine group and deprotection of the aldehyde group from an aniline derivative, 2-(4-aminophenyl)-1,3-dithiane, which was revealed on the ITO electrode surfaces through the electrodeposition of the reaction product and the characterization of the resulting surfaces with cyclic voltammetry, X-ray photoelectron spectroscopy, and protein immobilization. We also showed that successive electrodeposition of ABD and probe molecules on individually addressable microarray electrode surfaces can provide a useful platform for efficient detection of multianalyte. The usage of ABD has been demonstrated by the patterning of three different probe molecules on a single substrate and the simultaneous detection of two target molecules.

Photoregulation of Ion Permeation through a Polyelectrolyte Multilayer Membrane by Manipulating the Chromophore Orientation

Toward the realization of nanoscale device control, we report a novel method for photoregulation of ion flux through a polyelectrolyte multilayer membrane by chromophore orientation that is adjusted either by illumination at normal incidence or by slantwise irradiation at an angle of 10 degrees with respect to the surface. Our results indicate that the chromophore reorientation caused by the slantwise irradiation controls the effective pore size and, consequently, the transport behavior on the nanoscale. The slantwise illumination, which includes six EZE photoisomerization cycles generated by alternately irradiating with ultraviolet (lambda = 360 nm) and visible (lambda = 450 nm) light, reversibly switches the orientation of E-azobenzene in the membrane between 53 +/- 2 degrees (high tilt) and 17 +/- 5 degrees (low tilt) with respect to the surface. The novel feature of this light-gated valve system is its extremely long-lived open-switch state; this behavior stands in contrast to that of other systems based on labile photoisomers, which tend to instantly return to the thermodynamically stable state.

The first observation of four-electron reduction in [60]fullerene-metal cluster self-assembled monolayers (SAMs)Electronic supplementary information (ESI) available: CV spectra, half-wave potentials and XPS data. See http://www.rsc.org/suppdata/cc/b2/b209024d/

Self-assembled monolayers (SAMs) of a mu 3-eta 2:eta 2:eta 2-C60 triosmium cluster complex Os3(CO)8(CN(CH2)3Si(OEt)3)(mu 3-eta 2:eta 2:eta 2-C60) (2) on ITO or Au surface exhibit ideal, well-defined electrochemical responses and remarkable electrochemical stability being reducible up to tetranionic species in their cyclic voltammograms.

Gold dendrites Co-deposited with M13 virus as a biosensor platform for nitrite ions

We developed a biosensor for nitrite ion on an electrode surface modified with M13 viruses and gold nanostructures. Gold dendritic nanostructures (Au-DNs) are electrochemically co-deposited from 4E peptides engineered M13 virus (M134E) mixed electrolyte on to the ITO electrode. The M134E could specifically nucleate Au precursor (Gold (III) chloride), which enable the efficient growth of dendritic nanostructures, whereas such dendritic structures were not obtained in the presence of wild-type and Y3E peptides engineered M13 viruses. The structural features of the Au-DNs and their interfacing mechanism with ITO electrode are characterized by SEM, EDX and XRD analyses. The growth of Au-DNs at ITO electrode has been monitored by time dependent SEM study. The M134E induces the formation and plays a crucial role in shaping the dendritic morphology for Au. Biosensor electrode was constructed using Au-DNs modified electrode for nitrite ions and found improved sensitivity relative to the sensor electrode prepared from wild-type M13, Y3E peptides engineered M13 and without M13. Sensor electrode exhibited good selectivity toward target analyte from the possible interferences. Furthermore, 4E native peptides were used as additive to deposit Au nanostructures and it is compared with the structure and reactivity of the Au nanostructures prepared in the presence of M134E. Our novel biosensor fabrication can be extended to other metal and metal oxide nanostructures and its application might be useful to develop novel biosensor electrode for variety of biomolecules.