AN ENZYME SWITCH EMPLOYING DIRECT ELECTROCHEMICAL COMMUNICATION BETWEEN HORSERADISH-PEROXIDASE AND A POLY(ANILINE) FILM

An enzyme switch, or microelectrochemical enzyme transistor, responsiv e to hydrogen peroxide was made by connecting two carbon band electrod es (similar to 10 mu m wide, 4.5 mm long separated by a 20-mu m gap) w ith an anodically grown film of poly(aniline). Horseradish peroxidase (EC 1.11.1.7)was either adsorbed onto the poly(aniline) film or immobi lized in an insulating poly(1,2-diaminobenzene) polymer grown electroc hemically on top of the poly(aniline) film to complete the device. In the completed device, the conductivity of the poly(aniline) film chang es from conducting (between - 0.05 and + 0.3 Vvs SCE at pH 5) to insul ating (>+0.3 Vvs SCE at pH 5) on addition of hydrogen peroxide. The ch ange in conductivity is brought about by oxidation of the poly(aniline ) film by direct electrochemical communication between the enzyme and the conducting polymer. This was confirmed by measuring the potential of the poly(aniline) film during switching of the conductivity in the presence of hydrogen peroxide, The devices can be reused by rereducing the poly(aniline) electrochemically to a potential below +0.3 Vvs SCE . A blind test showed that the device can be used to determine unknown concentrations of H2O2 in solution and that, when used with hydrogen peroxide concentrations below 0.5 mmol dm(-3), the same device maybe r eused several times. The possible development of devices of this type for use in applications requiring the measurement of low levels of hyd rogen peroxide or horseradish peroxidase is discussed.