• Bulletin of the Korean Chemical Society
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• v.27 no.3
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• pp.381-385
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• 2006

The temperature dependence on the electron transfer rate constant $(k_{app})$ for hydroquinone redox center in $H_2Q(CH_2)_n$SH-SAMs (n = 1, 4, 6, 8, 10, and 12) on gold electrode was investigated to obtain reorganization energy $(\lambda)$ using Laviron’s formalism and Arrhenius plot of ln $[k_{app}/T^{1/2}]$ vs. T^{-1} based on the Marcus densityof-states model. All the symmetry factors measured for the SAMs were relatively close to unity and rarely varied to temperature change as expected. The electron tunneling constant $(\beta)$ determined from the dependence of the $k_{app}$ on the distance between the redox center and the electrode surface gives almost the same $\beta$ values which are quite insensitive to temperature change. Good linear relationship of Arrhenius plot for all $H_2Q(CH_2)_n$SH-SAMs on gold electrode was obtained in the temperature range from 273 to 328 K. The slopes n Arrhenius plot deduced that $\lambda$ of hydroquinone moiety is ca. 1.3-1.4 eV irrespectively of alkyl chain length of the electroactive SAM.

• Biotechnology and Bioprocess Engineering:BBE
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• v.10 no.6
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• pp.505-509
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• 2005

For the purpose of developing a direct label-free electrochemical detection system, we have systematically investigated the electrochemical signatures of each step in the preparation procedure, from a bare gold electrode to the hybridization of label-free complementary DNA, for the streptavidin-modified electrode. For the purpose of this investigation, we obtained the following pertinent data; cyclic voltammogram measurements, electrochemical impedance spectra and square wave voltammogram measurements, in $Fe(CN)_6^{3-}/Fe(CN)_6^{4-}$ solution (which was utilized as the electron transfer redox mediator). The oligonucleotide molecules on the streptavidin-modified electrodes exhibited intrinsic redox activity in the ferrocyanide-mediated electrochemical measurements. Furthermore, the investigation of electrochemical electron transfer, according to the sequence of oligonucleotide molecules, was also undertaken. This work demonstrates that direct label-free oligonucleotide electrical recognition, based on biofunctional streptavidin-modified gold electrodes, could lead to the development of a new biosensor protocol for the expansion of rapid, cost-effective detection systems.

• Journal of the Korean Electrochemical Society
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• v.10 no.3
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• pp.159-168
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• 2007

An electrochemical study related to the redox characteristics of Ethyl-3-acetyl-6-methyl-1, 4-diphenyl-4, 3a-dihydro-1, 3, 4-triazolino[3, 4-a] pyrimidine-5-carboxylate ester and its derivatives (1a-f) and (2a-e) in nonaqueous solvents such as 1, 2-dichloroethane (DCE), dichloromethane (DCM), acetonitrile (AN), dimethylsulphoxide (DMSO) and tetrahydrofurane (THF) using $0.1\;mol\;dm^{-3}$ tetrabutylammonium perchlorate (TBAP) as a supporting electrolyte at platinum, glassy carbon and gold electrodes, has been performed using cyclic voltammetry (CV). Controlled potential electrolysis (CPE) is also carried out to elucidate the course of different electrochemical reactions through the separation and identification of the intermediates and final electrolysis products. The redox mechanism is suggested and proved. It was found that all the investigated compounds in all solvents are oxidized in a single irreversible one electron donating process following the well known pattern of the EC-mechanism to give a dimer. On the other hand, these compounds are reduced in a single irreversible one electron step to form the anion radical, which is basic enough to proton from the media forming the radical which undergoes tautomerization and then dimerization processes to give also another bis-compound through N-N linkage formation.

• Analytical Science and Technology
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• v.24 no.3
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• pp.219-224
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• 2011

Voltammetric analysis of Cl(I) ion was performed using a metal gold (Au) electrode (AE) and a carbon nanotube electrode (CNTE). After the examination, the AE was found to have more sensitively detected Cl(I) than CNTE. The optimum analytical conditions for the cyclic voltammetry (CV) and the square wave (SW) stripping voltammetry were performed using AE. The detection limit of $6.5\;{\mu}g/L$ Cl(I) was attained. The developed techniques were compared with the common Cl meter and applied to water systems.

• Journal of Electrochemical Science and Technology
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• v.8 no.1
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• pp.25-34
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• 2017

Concurrent electrocatalysis and sensing of hydrazine, sulfite ions, and nitrite ions in a mixture were studied using electrodes modified by electrodeposited Au nanostructures (NSs). The ${\beta}$-cyclodextrin-mixed silicate sol-gel composite was drop-casted on the electrode surface and nucleation guided by ${\beta}$-cyclodextrin occurred, followed by the electrodeposition of Au NSs. The additive, ${\beta}$-cyclodextrin, played an evident role as a structure-directing agent; thus, small raspberry-like Au NSs were obtained. The modified electrodes were characterized by surface characterization techniques and electrochemical methods. The Au NSs-modified electrodes effciently electrocatalyzed the oxidation of toxic molecules such as hydrazine and sulfite and nitrite ions even in the absence of any other electron transfer mediator or enzyme immobilization. Well-resolved oxidation peaks along with decreased overpotentials were noticed during the electrooxidation process. The fabricated Au nanostructured electrode clearly distinguished the electrooxidation peaks of each of the three analytes from their mixture.

• Journal of Sensor Science and Technology
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• v.14 no.3
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• pp.137-143
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• 2005

Research in the field of biosensor has enormously increased over the recent years. The metal-oxide semiconductor field effect transistor (MOSFET) type protein sensor offers a lot of potential advantages such as small size and weight, the possibility of automatic packaging at wafer level, on-chip integration of biosensor arrays, and the label-free molecular detection. We fabricated MOSFET protein sensor and proposed the gold-black electrode as the gate metal to improve the response. The experimental results showed that the output voltage of MOSFET protein sensor was varied by concentration of albumin proteins and the gold-black gate increased the response up to maximum 13 % because it has the larger surface area than that of planar-gold gate. It means that the expanded gate allows a larger number of ligands on same area, and makes the more albumin proteins adsorbed on gate receptor.

• Journal of the Korean Vacuum Society
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• v.9 no.4
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• pp.379-381
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• 2000

Organic materials have potential advantages to be utilized as semiconductors in field effect transistors and light emmiting diodes. Gold, Aluminium, Silver, Chromium and Indium are used by electrodes. Gold is ohmic contact and the others are schottky contact. In this study, Pentacene and various electrode materials were deposited by Organic Molecular Beam Deposition (OMBD) and vacuum evaporation respectively. Those films were photolithographically patterned for measurements. These devices showed no degration after a 15 days of storage in laboratory environment.

• Bulletin of the Korean Chemical Society
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• v.28 no.12
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• pp.2266-2270
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• 2007

Electron transfer of a redox protein at a bare gold electrode is too slow to observe the redox peaks. A novel Nafion-riboflavin functional membrane was constructed during this study and electron transfer of cytochrome c, superoxide dismutase, and hemoglobin were carried out on the functional membrane-modified gold electrode with good stability and repeatability. The immobilized protein-modified electrodes showed quasireversible electrochemical redox behaviors with formal potentials of 0.150, 0.175, and 0.202 V versus Ag/AgCl for the cytochrome c, superoxide dismutase and hemoglobin, respectively. Whole experiment was carried out in the 50 mM MOPS buffer solution with pH 6.0 at 25 oC. For the immobilized protein, the cathodic transfer coefficients were 0.67, 0.68 and 0.67 and electron transfer-rate constants were evaluated to be 2.25, 2.23 and 2.5 s?1, respectively. Hydrogen peroxide concentration was measured by the peroxidase activity of hemoglobin and our experiment revealed that the enzyme was fully functional while immobilized on the Nafion-riboflavin membrane.

• Journal of the Korean Electrochemical Society
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• v.10 no.1
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• pp.1-6
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• 2007

Mercaptopropionic acid(mpa) has been used to make self-assembled monolayer(SAMs) on the surface of graphite electrode incorporating gold nano particles, which are subsequently modified with dopamine(dopa). Such modified electrodes haying types of Gr(Au)/mpa-dopa were employed in the electrocatalytic oxidation of NADH. The responses of such modified electrodes were studied in terms of electron transfer kinetics and reaction procedure in the reaction. The reaction of the surface immobilized dopa with NADH was studied using the rotating disk electrode technique and a value of $5.06{\times}10^5M^{-1}s^{-1}$ was obtained for the second-order rate constant in 0.1 M phosphate buffer(pH=7.0), which was a $EC_{cat}$ and kinetic controlled procedure. But, the modified electrodes were diffusion controlled reaction having $4.64{\times}10^{-4}cm^2s^{-1}$ of the coefficient within $10^{-3}s$ after starting the reaction.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.210-210
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• 2011

Ultrasmall electodes are of great importance for basic electrochemical study and applications. We fabricated single crystal (111) Au nanowire (NW) by growth mechanism on substrate without any catalyst. Consequently, these high aspect NW combined with tungsten microwire and the electrodes having NW tip on their end were obtained. These single crystal Au (111) NWs were characterized by electron microscope and electrochemical analysis. We show that precise electrochemical measurement could be possible on these NW electrode by obtaining underpotential deposition (UPD) and ferricyanide CV profiles on the electrode. The immersed depth of electrode into solution was controlled in micrometer scale by piezo-driven manipulator.