Cobalt(II)hexacyanoferrate film modified glassy carbon electrode for construction of a glucose biosensor

An amperometric glucose biosensor was constructed based on a glassy carbon electrode modified with a Cobalt(II)hexacyanoferrate film which catalyzes electroreduction of hydrogen peroxide. Gelatin was used as immobilization matrix. Interference could be effectively eliminated by the combination of low detection potential with a Nafion coating. A low applied potential can avoid oxidation of interferences such as ascorbic acid, uric acid, p-acetyl-aminophenol, etc.. Nafion coating prevents interferences from access to the electrode surface by electrostatic repulsion. A wide linear range of detection was obtained. Analytical performance parameters are given and kinetic analysis discussed.

Oxidation of NADH by dopamine incorporated in lipid film cast onto a glassy carbon electrode

Stable lipid film was made by casting lipid in chloroform onto a glassy carbon electrode. This model of a biological membrane was used to investigate the oxidation of dihydronicotinamide adenine dinucleotide (NADH) by dopamine. After this electrode had been immersed in dopamine solution for 10 h, it was found that some dopamine had been incorporated in the film. The cyclic voltammogram was obtained for the oxidation of 2.0 X 10(-3) mol 1(-1) NADH with dopamine incorporated in the films. All electrochemical experiments were performed in 0.005 mol 1(-1) phosphate buffer (pH 7.0) containing 0.1 mol 1(-1) NaCl without oxygen. The oxidation current increased gradually with successive sweeps and reached steady state. It was a different phenomenon from previous results. The anodic overpotential was reduced by about 130 mV compared with that obtained at a bare glassy carbon electrode. The diffusion coefficient for 2.0 X 10(-3) mol 1(-1) NADH was 6.7 X 10(-6) cm(2) s(-1). (C) 1999 Elsevier Science S.A. All rights reserved.

Chemiluminescent determination of luminol and hydrogen peroxide using hematin immobilized in the bulk of a carbon paste electrode

A new method for immobilization of a chemiluminescent reagent is presented. It is based on immobilizing hematin, a catalyst for luminol reaction, in the bulk of a carbon paste electrode. Bulk-immobilization allows renewal of the surface by simple polishing or cutting to expose anew and fully active surface in the case of fouling or deactivation by other means. By using a hematin-modified carbon paste electrode, the applied potential shifted negatively compared with that of unmodified carbon paste electrode or a glassy carbon electrode. The shift in potential changed the reaction processes and effectively stabilized the chemiluminescent signal during successive measurements. Under this condition, the signal was stable during 3 hours of continuous operation. The log-log plots of the emitted light intensity vs. luminol concentration and hydrogen peroxide concentration were linear over the region 10(-8)-10(-3) mol L-1 with a correlation coefficient of 0.999 and 3.9 x 10(-6)-10(-3) mol L-1 with a correlation coefficient of 0.994, respectively. Application of this method for other chemiluminescent and bioluminescent systems is suggested.

Determination of surface pK(a) of SAM using an electrochemical titration method

A self-assembled monolayer (SAM) of 3-mercaptopropionic acid (HSCH2CH2COOH) was formed on a gold electrode. The effect of the charge of the end group on the electrochemical response of Fe(CN)(6)(3-) at the SAM modified electrode was studied by using cyclic voltammetry. At high pH, when the -COOH groups are dissociated, Fe(CN)(6)(3-) current is suppressed; as the solution pH is lowered, Fe(CN)(6)(3-) current increases. The electrochemical titration curve was obtained by correlating the currents to the different electrolyte pH values, from which the surface pK(a) was obtained to be 5.2+/-0.1. Furthermore, a calculation equation was presented to simulate the electrochemical titration. As comparison, the surface pK(a) was also measured by contact angle titration as 5.6+/-0.1. The surface pK(a) values determined by the two methods in our work are consistent and accurate.

EQCM characterization of self-assembled kinetics of 4-pyridyl hydroquinone at Pt surface and its ion transfer in electrochemical redox

The adsorbed kinetics, proton transportation in electrochemical redox process of 4-pyridyl hydroquinone (4PHQ) self-assembled monolayer (SAM) modified Pt electrode were studied by electrochemical quartz crystal microbalance (EQCM) in situ. It proved that the electrode was modified by a monolayer and underwent a rapid electron transfer. It was a slow adsorbed kinetic process. The ion transfer in the electrochemical redox at the SAM-modified electrode surface mainly involved into the hydrate hydrogen ion.

Voltammetric behavior of tetracine on glassy garbon electrode and its application

The anodic voltammetric behavior of anaesthetic tetracine and its application were studied. In 0.1 mol/L HClO4 solution, the potential of anodic peak for tetracine is 1.04 V(vs. Ag/AgCl) at a glassy carbon electrode. A linear relationship between the peak height and the concentration of tetracine in the range of 5 x 10(-4) similar to 1 x 10(-1) g/L was obtained. The peak current decreases with the decreasing acidity of the solution. the mehtod has been used for the direct determination of tetracine in injections. The average recoveries of tetracine in urine samples were 98.5%. The mechanism of the electrode reaction was also discussed.

Electrochemical preparation and characterization of silicotungstic heteropolyanion monolayer electrostatically linked aminophenyl on carbon electrode surface

In this paper, an organic-inorganic composite film of heteropolyanion was Formed by attaching a Keggin-type heteropolyanion, SiW12O404-, on carbon electrode surface derivatized by 4-aminophenyl monolayer. The composite film thus grafted on carbon electrode surface has good stability because of the ionic bonding character between SiW12O404- and surface aminophenyl groups. X-ray photoelectron spectroscopy, scanning tunneling microscopy, and cyclic voltammetry were used to characterize the composite film. Compared with SiW12O404- electrodeposited on a bare glassy carbon electrode (GCE), the composite film gives three more sharp and well-defined redox couples attributed to two one- and two-electron processes, and the analyses of the voltammograms of SiW12O404- anion in the composite film modified on GCE shows that its surface coverage is close to a closest packing monolayer. STM characterization shows that a two-dimensional order heteropolyanion monolayer was formed on HOPG substrate. The composite film provides a favorable environment for electron and proton transfer between SiW12O404- ion and electrode surface, which may make it suitable for various applications in sensors and microelectronics devices.

Atomic force microscopy imaging of molybdenum oxide film electrodeposited on a carbon electrode

Non-stoichiometric mixed-valent molybdenum(VI, V) oxide film was grown on carbon substrates by the electrodeposition method. Responses of the prepared molybdenum oxide thin films to potential and to different solution acidities were studied by cyclic voltammetry, and the corresponding morphological changes of the film were monitored by atomic force microscopy (AFM). AFM images of the molybdenum oxide film show that the characteristic domed structure on the film surface increased during the transition from the oxidized state to the reduced state without signification change in the KMS surface roughness value. Furthermore, AFM studies show that the solution acidity has great effect on the morphology of the films, and the films undergo a homogenizing process with increasing pH of the solutions. (C) 1999 Elsevier Science S.A. All rights reserved.

The channel behavior of gramicidin D in the self-assembled monolayer

It was found for the first time that gramicidin D (GD) molecules can be incorporated into the ODM monolayer which is self-assembled on the surface of the gold electrode and form monovalent cation channels.

Electrochemical growth and characterization of polyoxometalate-containing monolayers and multilayers on alkanethiol monolayers self-assembled on gold electrodes

A general strategy has been developed for fabrication of ultrathin monolayer and multilayer composite films composed of nearly all kinds of polyoxometalates (POMs), including isopolyanions (IPAs), and heteropolyanions (HPAs). It involves stepwise adsorption between the anionic POMs and a cationic polymer on alkanethiol (cysteamine and 3-mercaptopropionic acid) self-assembled monolayers (SAMs) based on electrostatic interaction. Here a Keggin-type HPA SiMo11VO405- was chosen as a main representative to elucidate, in detail, the fabrication and characterization of the as-prepared composite films. A novel electrochemical growth method we developed for film formation involves cyclic potential sweeps over a suitable potential range in modifier solutions. It was comparatively studied with a commonly used method of immersion growth, i.e., alternately dipping a substrate into modifier solutions. Growth processes and structural characteristics of the composite films are characterized in detail by cyclic voltammetry, UV-vis spectroscopy (UV-vis), X-ray photoelectron spectroscopy (XPS), micro-Fourier transform infrared reflection-absorption spectroscopy (FTIR-RA), and electrochemical quartz crystal microbalance (EQCM). The electrochemical growth is proven to be more advantageous than the immersion growth. The composite films exhibit well-defined surface waves characteristic of the HPAs' redox reactions. In addition, the composite films by the electrochemical growth show a uniform structure and an excellent stability. Ion motions accompanying the redox processes of SiMo11VO405- in multilayer films are examined by in situ time-resolved EQCM and some results are first reported. The strategy used here has been successfully popularized to IPAs as well as other HPAs no matter what structure and composition they have.

Chemiluminescent determination of glucose with a modified carbon paste electrode

A flow injection analysis detection method for glucose is presented which is based on the oxidation of glucose by glucose oxidase followed by chemiluminescent detection of hydrogen peroxide. Both glucose oxidase and hematin, a chemiluminescent reaction catalyst, were bulk-immobilized conveniently by direct mixing with carbon paste, which allows renewal of the electrode surface by simply polishing or cutting to expose a new and fully active surface in the case of fouling. Luminol in reagent solution passed through the flow cell and reacted with hydrogen peroxide produced by the enzyme reactor in the presence of the catalyst to yield light. An applied potential of -0.4 V avoided the electrode fouling effectively. The log-log plot of the emitted light intensity vs glucose concentration was linear over the range of 1-100 mmol L-1 with a correlation coefficient of 0.992. Application of this method to other chemiluminescent and bioluminescent systems is suggested. (C) 1999 Academic Press.

Ion channel sensor

The ion channel sensor is reviewed. The concept and sensing principle of this kind of sensor are briefly discussed. The fabrication of the sensing membrane and the application of the ion channel sensor in electroanalytical chemistry are evaluated. The future developing direction is also anticipated.

In-situ Fourier transform infrared spectroelectrochemistry as a probe of the glassy carbon electrode chemically modified by nickel (II)-cyanometallates

A new nickel (II)-cyanometallates modified on glassy carbon electrode was prepared by a new method and studied by cyclic voltammetry and in situ Fourier transform infrared (FTIR) spectroelectrochemistry. It was found that the NiHCF film existed in two forms: Ni2Fe(II)-(CN)(6) and M2NiFe(II)(CN)(6), Fe(CN)(3)(6-) codeposited in the NiHCF film existing in free cation or bridged-bond state depended on the property of the cations in electrolyte: in NaCl and LiCl solution, it is in bridges-bonded, but in HCl and KCl, it is free.

Simultaneous voltammetric determination of acetophenetidin, aminopyrine, acetaminophenol and aminophenol on a glassy carbon electrode

The voltammetric behaviour of acetophenetidin(A(1)) aminopyrine(A(2)) acetaminophenol(A(3)) and aminophenol(A(4)) was investigated by linear-sweep, differential-pulse, cyclic voltammetry at a glassy carbon electrode. In a medium of 0.1 mol/L NaOH solution, 4 high sensitivity and resolution anodic peaks were obtained. Their peak potentials are about at 0.68 V, 0.51, 0.22 and - 0.06 V( vs. Ag/AgCl). They can be used for direct determination of A(1), A(2),A(3),A(4) in samples respectively. The method is simple and rapid. The mechanism of the electrode reaction was discussed.

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.