Masato Shimomura

Immobilization of glucose oxidase on carbon paper electrodes modified with conducting polymer and its application to a glucose fuel cell.

A carbon paper electrode was modified with the conducting copolymer of 3-methylthiopene and thiophene-3-acetic acid prepared electrochemically on the electrode, and an enzyme electrode was fabricated by covalent immobilization of glucose oxidase on the modified electrode. The modification with the conducting copolymer increased the surface area of the electrode and the amount of the immobilized enzyme. As a result, the enzyme electrode showed a high catalytic activity. Moreover, it was found that the increased surface area led to a high rate of electron transfer reaction between the electrode and p-benzoquinone employed as an electron mediator. The enzyme electrode fabricated with the modified carbon paper gave a larger glucose oxidation current than that fabricated with the bare one. In addition, the glucose oxidation current was found to increase with increasing content of the conducting copolymer in the modified carbon paper. Corresponding to the large glucose oxidation current, high performance was confirmed for the glucose fuel cell constructed with the enzyme electrode based on the modified carbon paper.

Covalent immobilization of glucose oxidase on poly[1-(2-carboxyethyl)pyrrole] film for glucose sensing

Poly[1-(2-carboxyethyl)pyrrole] film (PPy-COOH film) was electrochemically prepared and glucose oxidase (GOD) was covalently immobilized on the PPy-COOH film by the condensation reaction with carboxyl groups of the PPy-COOH. The apparent activity of the GOD immobilized on the PPy-COOH film was 152 mU cm −2 . The GOD-immobilized PPy-COOH film (PPy-GOD film) was applied to amperometric glucose sensing. Plots of response current versus glucose concentration gave a straight line with a slope of 1.7 μ A cm −2 per 1 mM glucose up to 80 mM. The glucose oxidation with the GOD on the PPy-GOD film was considered to proceed through a Michaelis—Menten mechanism.

Covalent Immobilization of Glucose Oxidase on Magnetite Particles via Graft Polymerization of Acrylic Acid

Abstract A new technique for immobilizing enzyme molecules on magnetite particles via the graft polymerization of acrylic acid is presented. The polymerization of acrylic acid was carried out in a redox system consisting of ceric ion and mercapto groups introduced onto magnetite particles. In the course of the polymerization, poly(acrylic acid) was attached to the magnetite particles. Glucose oxidase was covalently immobilized on the magnetite particles by the condensation reaction with the carboxyl groups of the poly(acrylic acid). It was shown that 2.8 mg of glucose oxidase was immobilized on 1 g of the magnetite attached with poly(acrylic acid), and the immobilized glucose oxidase had a specific activity of 81 units/mg, which was 50% of that of the native enzyme. Due to the immobilization, the optimum pH for glucose oxidase was shifted to a higher value and the temperature dependency of activity was diminished. A kinetic study of the glucose oxidation reaction with immobilized enzyme showed that the im...

Sugar-binding property of magnetite particles modified with dihydroxyborylphenyl groups via graft polymerization of acrylic acid

Abstract In order to combine sugar-binding property and magnetism, dihydroxyborylphenyl (DHBP) groups were attached to magnetite particles via graft polymerization of acrylic acid. The graft polymerization was carried out in a redox system consisting of mercapto groups introduced onto the surfaces of magnetite particles and ceric ions. DHBP groups were attached through amide linkages by the condensation reaction of 3-aminophenylboronic acid with carboxyl groups of the grafted poly(acrylic acid). Complexation of the attached DHBP groups was examined with various sugars and compared with that of the free phenylboronic acid. The attached DHBP groups gave a large value of binding constant K for the complexation with adenosine having a pair of cis -OH groups, whereas the K values for the DHBP groups with adenosine phosphates were extremely small. With respect to the complexation with 2′-deoxyadenosine, cooperative interaction of neighboring DHBP groups was suggested. Although the value of acidity index p K a of the attached DHBP was larger than that of free phenylboronic acid, the p K a value was decreased by coexistent basic groups.

Bioelectrocatalytic O2 reduction with a laccase-bearing poly(3-methylthiophene) film based on direct electron transfer from the polymer to laccase

This communication reports on O2 reduction with a biocathode composed of poly(3-methylthiophene) (P3MT) and laccase based on direct electron transfer (DET). The biocathode was fabricated simply by adsorption of laccase on a P3MT film which was formed on a gold electrode by electrochemical polymerization. Properties of the biocathode were examined by measuring steady-state currents at an arbitrary potential in buffer solutions saturated with O2 or N2 at room temperature. Efficient O2 reduction was achieved with the biocathode, which was attributed to DET from the P3MT film to laccase. The biocathode gave the O2 reduction current density of -150μA/cm(2) at +0.40V (vs. Ag/AgCl). The onset potential of O2 reduction was +0.64±0.01V (vs. Ag/AgCl) at pH4.5. The O2 reduction current became maximum in the pH range 4.0-5.0. This pH dependency of the O2 reduction current is corresponding to that of the activity of native laccase. In addition, the O2 reduction current increased markedly with increasing amount of the charge passed through in the formation of the P3MT film.

A novel system combining biocatalytic dephosphorylation of L-ascorbic acid 2-phosphate and electrochemical oxidation of resulting ascorbic acid.

An enzyme electrode was prepared with acid phosphatase (ACP) for development of a new electric power generation system using ascorbic acid 2-phosphate (AA2P) as a fuel. The properties of the electrode were investigated with respect to biocatalytic dephosphorylation of AA2P and electrochemical oxidation of resulting ascorbic acid (AA). The enzyme electrode was fabricated by immobilization of ACP through amide linkage onto a self-assembled monolayer of 3-mercaptopropionic acid on a gold electrode. AA2P was not oxidized on a bare gold electrode in the potential sweep range from -0.1 to +0.5 V vs. Ag/AgCl. However, the enzyme electrode gave an oxidation current in citric buffer solution of pH 5 containing 10 mM of AA2P. The oxidation current began to increase at +0.2V, and reached to 5.0 μA cm(-2) at +0.5 V. The potential +0.2 V corresponded to the onset of oxidation of ascorbic acid (AA). These results suggest that the oxidation current observed with the enzyme electrode is due to AA resulting from dephosphorylation of AA2P. The oxidation current increased with increasing concentration of AA2P and almost leveled off at around the concentration of 5mM. Thus the enzyme electrode brought about biocatalytic conversion of AA2P to AA, followed by electrochemical oxidation of the AA. The oxidation current is likely to be controlled by the biocatalytic reaction.

Temperature-conductivity characteristics of the composites consisting of fractionated poly(3-hexylthiophene) and conducting particles

Poly (3-hexylthiophene) (P3HT) synthesized by oxidative polymerization was fractionated by molecular weight by using organic solvents. The fraction of higher average molecular weight gave higher regioregularity and conductivity. Composites of the P3HT fraction having the highest molecular weight were prepared by use of the following conducting particles as fillers: titanium carbide (TiC), indium tin oxide (ITO), and carbon black (CB). Temperature-conductivity profiles of the composites showed that the resistance change with PTC (positive temperature coefficient) effect was strongly influenced by the content and size of conducting particles and the molecular weight of P3HT. Although no significant PTC effect for P3HT-CB composite and little effect for P3HT-ITO composite system were observed, the P3HT-TiC composite containing TiC of 70-80 wt % showed an obvious PTC effect that brought the conductivity change by about four orders of magnitude near the glass transition temperature of P3HT. However, such a remarkable PTC effect was not observed for the P3HT-TiC composite prepared with the P3HT fraction of low-molecular weight. It was shown that a good PTC effect could be achieved by the composite consisting of the P3HT of high-molecular weight and the conducting particles of relatively large size.

Preparation of polypyrrole covalently attached with glucose oxidase and its application to glucose sensing

Abstract Glucose oxidase (GOD) was covalently attached to polypyrrole having carboxyl groups (PPy-CGOH), and polypyrrole attached with GOD(PPy-GOD) was applied to glucose sensing. The PPy-COOH was prepared by oxidative polymerization of 1-(2-cyanoethyl) pyrrole followed by hydrolysis of the cyano groups to convert them into carboxyl groups. GOD was bound to the PPy-COOH by condensation reaction between carboxyl groups of the PPy-COOH and amino groups of GOD by use of a carbodiimide reagent. The electrode made of the PPy-GOD thus obtained being used, amperometric response to glucose was monitored. The result shows that the PPy-GOD is a promising material for glucose sensor.

Positive temperature coefficient characteristics of poly(3-alkylthiophene)s

Abstract Poly(3-alkylthiophene)(P3AT) films were prepared by both electrochemical and chemically oxidative polymerization methods, and their positive temperature coefficient(PTC) characteristics were investigated in the range from 0 to 200°C. The change in the amount of tetrafluoroborate ion(BF 4 −) or iron(III) perchlorate(FeCl 3 ) which were doped into P3AT film was also estimated by infrared(IR) and ultraviolet(UV) spectrophotometry. It was found that the P3AT films chemically polymerized at a low temperature had PTC characteristics, which was not affected by the dedoping involved in thermal treatment

Glucose-sensing characteristics of conducting polymer bound with glucose oxidase

Abstract Glucose-sensing characteristics of poly [1-(2-carboxyethyl)pyrrole] film bound with glucose oxidase (PPy-GOD) were studied in relation to the enzyme activity. The pH and temperature profiles of amperometric response of the PPy-GOD film to glucose were found to correspond to those of the activity of the glucose oxidase immobilized on pol y [1-(2-carboxyethyl)pyrrole] film.