Electro-conductive enzyme membrane

Abstract

An electro-conductive enzyme membrane has been synthesized at a platinum electrode surface by electrochemical polymerization of pyrrole in the presence of glucose oxidase, while retaining enzyme activity and reversible electron transfer between the enzyme molecules and the electrode.Electrochemical synthesis of conductive polymer membranes has gained an increasing interest as it is a simple process with many applications. Electropolymerized electrodes of polymer batteries have been extensively studied along with electrochromic displays. 1 4 Murray and his co-workers reported an ion-gate membrane which is made of electrochemically synthesized polypyrrole and is electrochemically controllable by ion permeability.5 Electrochemical control of amino acid permeability has also been performed with an electrochemically synthesized polypyrrole membrane .6 Shinohara et al. have assembled an artificial synapse using an electrochemically synthesized polypyrrole membrane, which electrically released neurotransmitter molecules in the cell.7.8A technique, for the entrapment of an enzyme in a conductive polymer, was p r o p ~s e d . ~ However, the technique had difficulty with the electroconductivity of the enzymeentrapped polymer and electron transfer between the enzyme and polymer matrix. A novel membrane, electro-conductive enzyme membrane, has been prepared by electrochemical polymerization of pyrrole in the presence of glucose oxidase. Electron transfer has been shown between glucose oxidase and polypyrrole matrix in the membrane.Electrochemical polymerization was carried out in a glass vessel equipped with a platinum wire electrode (0.5 mm in diameter, 7.5 mm in length), a platinum plate electrode (10 x 5 mm2), and a Ag/AgCl reference electrode. These electrodes were connected to a potentiostat (Hokuto Denko, Model HA-301) and a coulometer (Hokuto Denko, Model HF-201). Pyrrole was dissolved in 0.1 mol dm-3 KCl solution to make a 0.1 mol dm-3 solution which was deoxygenated before use. Glucose oxidase (GOD)(TOYOBO Co., grade 11, 113 U mg-1) was added to 1 cm3 of the solution, which was transferred to the glass vessel. The electrode potential of the platinum wire electrode was set at 0.7 V vs. Ag/AgCl to initiate electrochemical polymerization, this was held at a fixed charge. A black membrane deposited on the electrode surface. The membranes were synthesized at various concentrations of GOD and at different charges, and were thoroughly washed with 0.1 mol dm-3 KCl solution.The polypyrrole/GOD membrane was assayed for enzyme activity and characterized by electrochemical measurements. The membrane was immersed in a 0.1 mol dm-3 citrate buffer solution (pH 5.5) containing 0.17 mmol dm-3 3,3'-dimethoxy benzidine, 93 mmol dm-3 glucose, and 7 mU cm-3 peroxidase (TOYOBO Co., grade 111, 127 U mg--1).10 The solution was incubated at 25°C and stirred. An aliquot was assayed for absorbance at 436 nm with a spectrophotometer (Japan Spectroscopic Co., Model UVIDEC-610C).Each membrane, synthesized under different conditions, showed enz...

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