Mizuki Kondo

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.

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.