Site-selective self-assembly of MPA-bridged CuHCF multilayers on APTMS-supported gold colloid electrodes

(3-Aminopropyl)trimethoxysilane (APTMS)-supported gold colloid electrode was constructed by virtue of a recently developed solution-based self-assembly strategy. The preparing procedure of 3-mercaptopropionic acid (MPA)-bridged copper hexacyanoferrate (CuHCF) multilayers on a planar macroelectrode (Bharathi et al. Langmuir 2001, 17, 7468) was copied to the as-prepared colloid electrode. The optical spectra, atomic force microscopy, and electrochemistry demonstrate successful copy of the multilayer system on a macroelectrode to the as-prepared colloid electrode. Remarkably, it was found that multilayer growth is highly selective to the nanoscale sites where gold nanoparticles are immobilized, and multilayer growth does not take place on the sites without nanoparticles. Interestingly, a preliminary electrochemical investigation indicates that electrochemical properties of multilayers systems on the colloid electrode are different from their counterparts on a planar macroelectrode, which might be due to high curvature effects of the gold nanoparticles. This indicates a different motif of multilayers on the colloid electrode from that on a planar macroelectrode.

Study of electron-transfer reactions across an externally polarized water/1,2-dichloroethane interface by scanning electrochemical microscopy

A novel method to study electron-transfer (ET) reactions between ferrocene in 1,2-dichloroethane (DCE) and a redox couple of K3Fe(CN)(6) and K4Fe(CN)(6) in water using scanning electrochemical microscopy (SECM) with a three-electrode setup is reported. In this work, a water droplet that adheres to the Surface of a platinum disk electrode is immersed in a DCE solution. The aqueous redox couple serves both as a reference electrode on the platinum disk and as an electron donor/acceptor at the polarized liquid/liquid inter-face. With the present experimental approach, the liquid/liquid interface can be polarized externally, while the electron-transfer reactions between the two phases can be monitored independently by SECM. The apparent heterogeneous rate constants for the ET reactions were obtained by fitting the experimental approach curves to the theoretical values. These rate constants obey the Butler-Volmer theory i.e., them, are found to be potential dependent.

Renewable three-dimensional Prussian blue modified carbon ceramic electrode

Prussian blue (PB) supported on graphite powder was prepared by the chemical deposition technique and subsequently dispersed into methyltrimethoxysilane-derived gels to yield a conductive graphite organosilicate composite. The composite was used as the electrode material to fabricate a three-dimensional PB-modified electrode. PB acts as a catalyst, graphite powder ensures conductivity by percolation, the silicate provides a rigid porous backbone, and the methyl groups endow hydrophobicity and thus limit the wetting section of the modified electrode. The chemically modified electrode can electrocatalyze the oxidation of hydrazine, and exhibits a distinct advantage of polishing in the event of surface fouling, as well as simple preparation, good chemical and mechanical stability and good repeatability of surface-renewal. Hydrodynamic voltammetric experiments were performed to characterize the electrode as an amperometric sensor for the determination of hydrazine. (C) 2000 Elsevier Science B.V. All rights reserved.

Amperometric enzyme electrode for the determination of hydrogen peroxide based on sol-gel/hydrogel composite film

A new type of organic-inorganic composite material was prepared by sol-gel method, and a peroxidase biosensor was fabricated by simply dropping sor-gel-peroxidase mixture onto glassy carbon electrode surface. The sol-gel composite film and enzyme membrane were characterized by Fourier-transform infrared (FT-IR) spectroscopy and EQCM, the electrochemical behavior of the biosensor was studied with potassium hexacyanoferrate(II) as a mediator, and the effects of pH and operating potential were explored for optimum analytical performance by using amperometric method. The response time of the biosensor was about 10 s; the linear range was up to 3.4 mM with a detection limit of 5 x 10(-7) M. The sensor also exhibited high sensitivity (15 mu A mM(-1)) and good long-term stability. In addition, the performance of the biosensor was investigated using flow injection analysis (FIA), and the determination of hydrogen peroxide in real samples was discussed. (C)2000 Elsevier Science B.V. All rights reserved.

Amplification of antigen-antibody interactions based on biotin labeled protein-streptavidin network complex using impedance spectroscopy

Antibody was covalently immobilized by amine coupling method to gold surfaces modified with a self-assembled monolayer of thioctic acid. The electrochemical measurements of cyclic voltammetry and impedance spectroscopy showed that the hexacyanoferrate redox reactions on the gold surface were blocked due to the procedures of self-assembly of thioctic acid and antibody immobilization. The binding of a specific antigen to antibody recognition layer could be detected by measurements of the impedance change. A new amplification strategy was introduced for improving the sensitivity of impedance measurements using biotin labeled protein- streptavidin network complex. This amplification strategy is based on the construction of a molecular complex between streptavidin and biotin labeled protein. This complex can be formed in a cross-linking network of molecules so that the amplification of response signal will be realized due to the big molecular size of complex. The results show that this amplification strategy causes dramatic improvement of the detection sensitivity of hIgG and has good correlation for detection of hIgG in the range of 2-10 mug/ml. (C) 2001 Elsevier Science B.V. All rights reserved.

Cyclic voltammetric and in situ Fourier transform infrared spectroelectrochemical studies on the reaction of Cd2+ on the plussian blue/platinum modified electrode

Plussian blue(PB)/Pt modified electrode Tvas studied in the CdCl2 electrolyte solution by cyclic voltammetry and in situ FTIR spectroelectrochemistry. It was found that Cadmium ion was capable of substituting the high-spin iron of PB in an electrochemically induced substitution reaction and hexacyanoferrate cadmium (CdHCF) can be formed in the PB film. But PB and CdHCF in mixture film showed their own electrochemistry properties without serious effect on each other. The mechanism of substitution reaction has been given in detail.

Electrochemical quartz crystal microbalance study for vanadium hexacyanoferrates: monitoring of film growth and ion effects during redox reactions

An electrochemical quartz crystal microbalance was employed to monitor directly the growth of vanadium hexacyanoferrate (VHF) films on platinum substrates during electrodeposition and interfacial coagulation in the solution containing sulfuric acid electrolyte, vanadium(IV) and hexacyanoferrate(III). Mass changes of the gold/crystal working electrode were correlated with cyclic voltammetry data. Effects of cations (NH4+, Li+, Na+ and K+), anions (SO42- and NO3-) and solvent during redox reactions of the films were studied. The results show that cations were incorporated into the film during reduction and expelled from the film during oxidation. Solvent also participates in VHF electrochemistry, and its role cannot be neglected. Anions play no role in VHF electrochemistry. (C) 1997 Elsevier Science S.A.

ELECTROCHEMISTRY AND IN-SITU IR MICROSPECTROELECTROCHEMISTRY IN A VERSATILE THIN-LAYER REFLECTION FOURIER-TRANSFORM IR MICROSPECTROELECTROCHEMICAL CELL

A simple, convenient and versatile thin layer reflection Fourier transform IR microspectroelectrochemical (FTIRMSEC) cell has been described and characterized. Electrochemistry and in situ FTIR microspectroscopy were studied by using the hexacyanoferrate redox couple in aqueous sulphate solution, indicating that this type of cell is characteristic of both micro- or ultramicroelectrode and thin layer spectroelectrochemistry. Furthermore, the application of this FTIRMSEC cell to IR for characterization of the products of electrochemical reactions was carried out for the oxidation of (mesotetraphenylporphinato)manganese(III) perchlorate in dichloromethane + tetrabutylammonium perchlorate solution. Finally, the advantages and problems of this type of cell compared with a conventional optically transparent thin layer FTIR spectroelectrochemical cell were discussed.