Kazuharu Sugawara

Accumulation voltammetry of copper(II) using a carbon paste electrode modified with di-8-quinolyl disulphide

The accumulation voltammetry of copper(II) was investigated with a carbon paste electrode modified with di-8-quinolyl disulphide (DQDS). The DQDS was reduced to quinoline-8-thiol by applying a suitable potential. Copper(II) was accumulated on the electrode as the copper(II)-quinoline-8-thiol complex at a constant potential in 0.1 mol dm–3 acetate buffer. The reduction peak of the copper(II) complex was then observed at –0.30 V by scanning the potential in a negative direction using the differential-pulse mode. The calibration graph for copper(II) was linear over the range 3 × 10–9–2 × 10–6 mol dm–3 with accumulation for 5 min at –0.05 V. As copper(II) was selectively accumulated on the electrode, the influence of concomitant ions was negligible. The method was applied to the determination of copper(II) in Geological Survey of Japan rock reference materials.

Electrochemical Sensing of Avidin–Biotin Interaction Using Redox Markers

The interaction between avidin and biotin immobilized in self-assembled monolayer (SAM) on a gold electrode surface was electrochemically evaluated by monitoring the changes in the electrode response of three hydrophilic redox markers. The introduction of avidin membrane onto the biotin-SAM electrode surface caused the large changes in the electrode response of the redox marker. By using NutrAvidin instead of avidin, it was clarified that the changes of the electrode response were ascribed to the permeability of the marker through the avidin membrane on the electrode surface. At a lower pH than the isoelectric point of avidin, the electrode response of ferrocyanide ions as an anionic redox marker ions increased linearly over the range of 1.25×10–9–1.25×10–8u2005M avidin. The relative standard deviation at 2.25×10–9u2005M avidin was about 3.9% (n=5). On the other hand, the detection of biotin was performed using a competitive reaction between biotin in the solution and biotin in SAM on the electrode surface for avidin.

Electrochemical immunoassay at a 17β-estradiol self-assembled monolayer electrode using a redox marker

A simple electrochemical immunoassay was demonstrated using a 17beta-estradiol modified electrode. 17beta-estradiol was immobilized on the gold electrode surface with a self-assembly technique. The specific binding between estradiol antibody and 17beta-estradiol on the electrode surface was evaluated by monitoring the change in the electrode response with three hydrophilic redox markers. The decrease in the electrode response for the redox marker was observed, when the antibody was bound to the estradiol self-assembled monolayer (SAM) electrode surface. The change in the electrode response of the redox marker is attributed to the steric hindrance between the antibody on the electrode surface and the redox marker. The relative standard deviation at 30 microg ml(-1) estradiol antibody was 4.1% (n = 3). The competitive reaction between the antigen in the solution and 17beta-estradiol immobilized on the electrode surface for the limited binding sites on the antibody produced an increase in the electrode response with hydroquinone as the marker. The binding affinity of three antigens including 17beta-estradiol to the estradiol antibody was evaluated. Furthermore, the result obtained from this method was compared with the previously reported enzyme binding assay using the biotinylated estradiol and the biotin-immobilized microtiter plate.

Voltammetric detection of silver(I) using a carbon paste electrode modified with keratin

The voltammetric detection of silver(I) was carried out at a carbon paste electrode (CPE) modified with keratin. Silver(I) was selectively accumulated on the electrode on the basis of its interaction with the thiol and disulfide groups of keratin in 0.1 mol dm–3 acetate buffer (pH 6.7) + 0.1 mol dm–3 NaClO4. After reduction of silver(I) had been carried out, the reoxidation wave of silver(0) appeared at 0.14 V (versus Ag/AgCl) on scanning the potential in the positive direction in 0.1 mol dm–3 acetate buffer (pH 6.7). The detection limit of silver(I) was 2 × 10–8 mol dm–3 when the accumulation time was 10 min. Interference from co-existing substances was slight in the voltammetric measurement because of the interaction with sulfur atoms and the exchange of the medium. The proposed method was applied to the determination of silver(I) in a photographic developer.

Voltammetric behavior of avidin-biotin interaction at a biotin/thionine modified Au electrode

Abstract Avidin–biotin interaction at a biotin/thionine modified Au electrode was investigated with voltammetry. The electrode was modified with a self-assembled monolayer (SAM). The avidin–biotin interaction was monitored through change of the electrode response of thionine. The electrode response decreased with increasing concentration of the avidin. This is because the thionine moiety was held at the binding site due to the avidin–biotin interaction. Furthermore, the length of spacer between the thionine and biotin moieties, which influences the avidin–biotin binding, was examined.

Simultaneous multiselective spectroelectrochemical fiber-optic sensor: demonstration of the concept using methylene blue and ferrocyanide.

Herein, we present a novel spectroelectrochemical fiber-optic sensor that combines electrochemistry, spectroscopy, and electrostatic adsorption in three modes of selectivity. The proposed sensor is simple and consists of a gold mesh cover on a multimode fiber optic that uses attenuated total reflection as the optical detection mode. The sensing is based on changes in the attenuation of the light that passes through the fiber-optic core accompanying the electrochemical oxidation-reduction of an analyte at the electrode. Methylene blue and ferrocyanide were used as model analytes to evaluate the performance of the proposed sensor. The optical transmission changes generated by electrochemical manipulation showed a good linear relationship with the concentration and the limits of detection (3σ) for methylene blue and ferrocyanide at 2.0 × 10(-7) and 1.6 × 10(-3) M, respectively. The sensor responses were successfully enhanced with an additional level of selectivity via an electrostatically adsorbed, self-assembled monolayer (SAM), which consisted of a silane coupling layer, a polyanion, and a polycation. The improvement observed in the sensitivity of a SAM-modified fiber-optic sensor was rather encouraging. The optimized sensor had detection limits (3σ) of 8.3 × 10(-9) M for methylene blue and 7.1 × 10(-4) M for ferrocyanide. The developed sensor was successfully applied to the detection of ferrocyanide in simulated nuclear waste.

Evaluation of concanavalin A-mannose interaction on the electrode covered with collagen film

An electrode covered with a lectin/collagen film was constructed to investigate whether the film was usable as a reaction field of binding between the lectin and sugar. The protein-sugar binding on cell surface plays an important role to various physiologic processes. The film is considered to be a cell surface, due to its biocompatibility. The immobilization of concanavalin A (Con A) which is one of proteins was attempted by an electrostatic interaction of the protonated functional groups of film to the negative charged Con A. The merit of this immobilization is that the interaction hardly causes any changes in the protein structure. Because Con A recognizes mannose moiety, the mannose was labeled with an electroactive compound. The binding was estimated from the changes of the electrode response based on the holding of electroactive moiety in the binding site of Con A to the mannose moiety. However, the electrode responses of glucose and galactose labeled with the same substance did not change. The result shows that Con A is immobilized on the film and combines with labeled mannose. Therefore, it is clear that the collagen film is suitable as the reaction field to evaluate the protein-sugar binding.

Voltammetric evaluation for the binding of wheat germ agglutinin to glucosamine-modified magnetic microbead

Binding of wheat germ agglutinin (WGA) on glucosamine-modified magnetic microbeads was investigated with voltammetry. A magnetic bead was considered as a cell, and the beads with amino groups were modified with the sugar by using a cross-linking reagent. To evaluate the binding, glucose labeled with an electroactive daunomycin was prepared as a probe. After WGA and the beads were mixed in 0.1M phosphate buffer (pH 7.0), the labeled glucose was added to the solution. The binding was monitored from the changes in the electrode response of labeled glucose because the labeled glucose was held to the binding site of WGA for the sugar. In contrast, other lectin not having the binding site to glucosamine or glucose was incubated with the glucosamine-modified beads. As a result, the change of peak current was not observed. Therefore, it is clear that the binding of WGA to glucosamine moiety on the bead surface selectively takes place. This method would be powerful for evaluation of interaction between protein and sugar chain existing at cell surface.

Voltammetric sensing of sugar by an electrode covered with wheat germ agglutinin/chitin film

The binding between wheat germ agglutinin (WGA) and N-acetylglucosamine at the electrode covered with chitin film was investigated with voltammetry. Chitin, beta-1,4-poly-N-acetylglucosamine, is one of the biolpolymers which have a high biocompatibility. WGA is immobilized to the surface of chitin film by the affinity of WGA to N-acetylglucosamine residue of chitin. To investigate the binding event of WGA on the chitin modified electrode, N-acetylglucosamine labeled with an electroactive compound was prepared. The binding causes the changes in the electrode response of labeled sugar. The peak current of labeled sugar decreased due to the specific binding with WGA on the chitin film modified at the electrode. N-Acetylglucosamine was successfully determined by using the competitive reaction with labeled sugar to WGA on the chitin film electrode.

Development of an Attenuated Total Reflection Based Fiber-Optic Sensor for Real-time Sensing of Biofilm Formation

A fiber-optic sensor capable of real-time monitoring of biofilm formation in water was developed. The sensor can be easily fabricated by removing the cladding of a multimode fiber optic to expose the core. The sensing action is based on the penetration of an evanescent wave through a biofilm formed on the surface of the exposed fiber core during total internal reflection. The proposed setup can be used to analyze the transmittance response over a wide wavelength range using a white-light source and a spectroscopy detector. The change in transmittance with respect to the biofilm formation on the fiber core surface was observed. The findings from this study showed that the sensor detection had better sensitivity at near-infrared wavelengths than at visible-light wavelengths. Moreover, the sensitivity of this sensor could be controlled by surface modifications of the core surface through electrostatic interactions, involving a silane coupling layer, polyanions, and polycations. The developed sensor was successfully applied to evaluating of the effectiveness of a commercial biofilm inhibitor.