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It has been possible to prepare CdS nanoparticle chains with line widths equal to the size of nanoparticles. A template was created by using the electrostatic interaction between the cationic surface modifiers on the CdS nanoparticles and the phosphate groups in DNA double strands.

A biomimetic bilayer membrane immobilizing uricase (urate oxidase; EC 1.7.3.3) (UOx) and a redox agent of 1-methoxy-5-methylphenazinium (MMP) was fabricated on an Au electrode substrate with use of the Au substrate coated with a self-assembled monolayer of n-octanethiolate (OT/Au) and L-alpha-phosphatidylcholine beta-oleoyl-gamma-palmitoyl (PCOP). The preparation was carried out by successively immersing an Au electrode substrate in an ethanol solution of OT, an MMP aqueous solution, and a suspension of proteoliposome formed by PCOP containing UOx and MMP. The prepared electrode exhibited such fast steady amperometric responses to uric acid as to allow its determination within 20 s after rejecting uric acid, indicating that UOx-catalyzed electrochemical oxidation of uric acid was accomplished with assistance of electron mediation by MMP between UOx and the Au substrate. An increase in the response currents with increasing concentration of uric acid was obtained in a concentration of uric acid found in healthy human blood. Any interference in the current response that is caused by direct anodic oxidation of uric acid or ascorbic acid was not observed at the prepared sensor electrode because the densely packed bilayer effectively blocked the diffusion of these substrates toward the Au surface, making it possible to determine amperometrically uric acid at the electrode with high precision.

Electrochemical oxidation of uric acid catalyzed by uricase (uric acid oxidase, UOx; EC 1.7.3.3) was studied using several redox compounds including 5-methylphenazinium (MP) and 1-methoxy-5-methylphenazinium (MMP) as electron acceptors for UOx, which does not contain any redox cofactor. It was found that MP and MMP were useful to mediate electrons from UOx to an electrode in the enzymatic oxidation of uric acid. A novel redox polymer, poly(N-methyl-o-phenylenediamine) (poly-MPD), containing the MP units was also found to possess the mediation ability for UOx, and poly-MPD was immobilized together with UOx onto an electrode substrate covered with a self-assembled monolayer of 2-aminoethanethiolate with use of glutaraldehyde as a binding agent. The resulting electrode (poly-MPD/UOx/Au) exhibited amperometric responses to uric acid with very fast response of [approximately]30 s, allowing reagentless amperometric determination in a concentration range covering that in the blood of a healthy human being. Kinetic parameters of the apparent Michaelis constant and the maximum current response obtained at the poly-MPD/UOx/Au suggested that electrochemical oxidation of uric acid was controlled by diffusion of uric acid into the enzyme film and that the redox polymer worked well in mediating between active sites of UOx molecules and the electrode substrate.

Immobilization of cholesterol oxidase (EC 1.1.3.6) (ChOx) on a gold electrode was attempted by cross-linking using glutaraldehyde between ChOx molecules and a self-assembled monolayer of 2-aminoethanethiolate. The resulting electrode (ChOx/Au) exhibits an amperometric response to free cholesterol in the presence of thionin as an electron mediator, and a steady-state response is obtained [approximately]0 s after injection of cholesterol into the electrolyte solution. Coimmobilization of cholesterol esterase (EC 3.1.1.13) (ChE) and ChOx (ChE/ChOx/Au) allows the amperometric determination of both esterified cholesterol and free cholesterol. Cyclic voltammetry of the ChE/ChOx/Au and the dependence of the amperometric response to cholesterol on the concentration of thionin suggest that thionin is encapsulated in the enzyme film on the electrode surface. Apparent Michaelis constants of the ChOx/Au and the ChE/ChOx/Au electrodes suggest that the amperometric response was controlled by penetration of the reaction substrate into the films of the enzyme(s). The concentration of total (free and esterified) cholesterol in human serum samples, determined by using the techniques developed in the present study, is in good agreement with that determined by the well-established technique using colorimetry.

Several redox dyes of phenazine and phenothiazine derivatives including 1-methoxy-5-methylphenazinium methosulfate (MPMS), thionin, azure A, and azure C work well as electron acceptors for reduced cholesterol oxidase (EC 1.1.3.6) (ChOx). Kinetic parameters and equilibrium constants of the enzymatic oxidation of cholesterol obtained suggest that the molecular size and/or hydrophobicity of the redox dyes determines their abilities as the electron acceptors. The electrochemical sensitivity to cholesterol in the detection system using ChOx and the above-mentioned redox compounds is determined by the electron acceptability of the redox compounds, and the employment of either MPMS or thionin allows electrochemical determination of cholesterol at a low electrode potential (0 V vs SCE) in the concentration range 0.252.5 mmol [dm.sup.-3], which covers that in normal human blood.

A novel strategy for the asymmetric electroreduction of ketones and aldehydes derivatives was developed based on electrochemical reduction systems. The alcohol dehydrogenase (ADH)-catalyzed electrolysis systems A and B efficiently induced the asymmetric electoreduction of ketones and aldehyde derivatives. Optically active products with high enantiomer excess were also obtained from reaction system B which utilized ADH as the sole electrocatalyst. However, reaction system B exhibited slow rates of reaction compared to reaction system A.

Potential distribution at the electrode/solution interface is discussed for metal electrodes coated with a redox-active self-assembled monolayer, taking inclusion of ion pairs and triple ion formation into consideration. Theory on current-voltage curves obtained by potential sweep experiments is derived for these special cases. Explicit expressions derived in this study for the peak current and the peak potential are similar in their forms to those published previously using the Frumkin adsorption isotherm. A graphical method to evaluate the average local potential in the double layer of real systems is proposed.

Loading TiO2 particles on adsorbents significantly enhances the reaction rate of photoinduced mineralization of the typical herbicide propyzamide with the TiO2 photocatalyst. This was the result of an investigation of photodecomposition in aqueous solution of propyzamide, using naked TiO2 and TiO2-loaded adsorbent supports as photocatalysts. Aside from enhancing the rate of mineralization, the use of adsorbent supports was also found to reduce the concentration of solution-phase intermediates.

Nolte et al. recently proposed a new type of amperometric glucose sensor. This sensor is based on a microporous membrane that contains polypyrrole tubules within the pores of the membrane. The procedure for preparing these polypyrrole tubules was developed in this laboratory. Nolte et al. claim that glucose oxidase can be irreversibly adsorbed to the inside walls of these polypyrrole tubules and that the resulting device functions as a glucose sensor. Indeed, they claim that this device functions via direct electron transfer from the reduced enzyme to the polypyrrole tubule. We have recently explored the respons characteristics of this proposed new sensor. Our results suggest that this sensor does not function in the manner proposed by Nolte et al. Instead, our results indicate that the device operates by direct electrochemical oxidation o glucose at the metal (Pt) film that is coated onto one face of the membrane. This is proven by the fact that the sensitivity of the device is improved when polypyrrole and glucose oxidase are not present in the membrane.

Biocatalysts are used in the electrochemical conversion of carbon dioxide into methanol. The reduction of carbon dioxide is increased in the presence of methyl viologen which acts as mediator. An osmium complex attached poly(vinylpyridine) mediator increases the rate of reduction by hundred times.

An aqueous colloidal dispersion of Pt nanoparticles (NPs) stabilized by fullerenol C60(OH)12 (Pt:C60(OH)12) was successfully synthesized via liquid‐phase chemical reduction. The subsequent pyrolysis of Pt:C60(OH)12 at different temperatures was conducted to afford Pt‐doped carbon with different chemical compositions (Pt:C60n). X‐ray absorption spectroscopy (XAS) and Infrared (IR) absorption spectroscopy and thermogravimetric measurements revealed that the thus‐prepared nanocomposite consists of Pt NPs and high valent Pt‐C60(OH)12 complex. One distinct feature of C60(OH)12 matrix as catalyst support is the suppression of size growth of Pt NPs during the pyrolysis up to 300 °C. Electrochemical experiments using cyclic voltammetry (CV) and linear sweep voltammetry (LSV) were performed to find that Pt:C60300 (pyrolyzed at 300 °C) exhibited higher activity than others, that was attributed to the π‐extended feature of the as‐obtained carbon. [ABSTRACT FROM AUTHOR]

A series of inorganic AlCl3–alkali metal thiocyanate (AMSCN: AM = Li, Na, K) ionic liquids (ILs) are demonstrated as electrolytes for Al electrodeposition and Al-anion rechargeable batteries (AARBs) at 303–363 K. Al deposits with a unique flake nanostructure are obtained in these electrolytes. The assembled AARBs show a stable cyclability over 250 cycles with a reversible capacity of ca. 70 mA h (g-graphite)−1 at 363 K. These inorganic ILs inherit the advantages of conventional chloroaluminate ILs (applicability at near-ambient temperature) and molten salts (cost effectiveness), making them promising electrolyte candidates for industrializable electrochemical Al technologies. [ABSTRACT FROM AUTHOR]

Multinary semiconductor quantum dots (QDs) that have less toxicity and show near-infrared light responsivity have attracted much attention for in vivo bioimaging. In this study, we controlled the optical properties of Ag–In–Se QDs by modulating the nonstoichiometry and the degree of Ga3+ doping. Precise tuning of the Ag/In ratio of Ag–In–Se QDs enabled a sharp band-edge emission to emerge without broad defect-site emission. Ga3+ doping into Ag–In–Se (AIGSe) QDs enlarged their energy gap, resulting in a blue shift of the band-edge PL peak from from 890 to 630 nm. The band-edge PL intensity was remarkably enlarged by surface coating with a thin GaSx shell followed by treatment with trioctylphosphine, the highest PL yield being 38% for the PL peak at 800 nm. Thus-obtained QDs were successfully used as near-IR PL probes for three-dimensional in vivo bioimaging in which the wavelengths of excitation and detection lights could be selected in the first biological window, and then the signals were clearly detected from AIGSe@GaSx core–shell QDs injected into biological tissues by ca. 5 mm in depth. [ABSTRACT FROM AUTHOR]