A MICROELECTROCHEMICAL ENZYME TRANSISTOR RESPONSIVE TO GLUCOSE

Microelectrochemical enzyme transistors, or enzyme switches, were prepared by connecting two carbon band electrodes (similar to 10 mu m wide, 4.5 mm long separated by a 20-mu m gap) with an anodically grown film of poly(aniline). Glucose oxidase (GOx, EC 1.1.3.4) was immobilized onto the poly(aniline) film in an insulating poly(1,2-diaminobenzene) polymer grown electrochemically oh top of the poly(aniline) film to complete the device. In the completed device the conductivity of the poly(aniline) film changes from insulating (>+0.3 V vs SCE at pH 5) to conducting (between -0.05 and +0.3 V vs SCE at pH 5) on-addition of glucose in the presence of TTF+ (tetrathiafulvalenium). The change in conductivity is brought about by reduction of the poly(aniline) by the enzyme mediated by TTF+ present in the homogeneous solution. This was confirmed by measuring the potential of the poly(aniline) film during switching of the conductivity in the presence of glucose. The devices can be reused by reoxidizing the poly(aniline) electrochemically at +0.5 V vs SCE. The effect of varying the poly(aniline) growth charge on the switching rate was investigated along with the conditions for the immobilization of the enzyme. The switching time has been optimized so that the device takes 10 s to switch from fully insulating to fully conducting. The sensitivity to glucose and other sugars is shown along with studies of the effects of interferent species.