Microelectrochemical enzyme transistors

Birkin, Peter Robert (1994) Microelectrochemical enzyme transistors. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

An investigation into the effects of glucose on the diffusion coefficients of ferrocene monocarboxylic acid in solution and through an electropolymerised film has been undertaken using the analysis of a potential step technique. These Cottrell studies showed that both diffusion coefficients fell by ca. 10% over the concentration range 0-100 mmol dm^-3. Furthermore the thickness of the polymer film could be determined using this in situ technique and was found to be independent of glucose concentration.

Microelectrochemical enzyme transistors, or enzyme switches, were prepared by connecting two carbon band electrodes (�10 μm wide, 4.5 mm long separated by a 20 μm gap) with an anodically grown film of poly(aniline). Glucose oxidase (GOx, E.C.1.1.3.4) or Horse Radish Peroxidase (HRP, E.C.1.11.1.7) was immobilised onto the poly(aniline) film in an insulating poly(1,2diaminobenzene) polymer grown electrochemically on 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 V and + 0.3 V vs SCE at pH 5) on addition of glucose in the presence of TTF⁺ (tetrathiafulvalenium) or vice versa for the HRP switch in the presence of hydrogen peroxide alone. The change in conductivity is brought about by reduction of the poly(aniline) by the GOx mediated by TTF⁺ present in the homogeneous solution or oxidation of the poly(aniline) film by the direct electrochemistry discovered between HRP and poly(aniline) in the presence of hydrogen peroxide. This was confirmed by measuring the potential of the poly(aniline) film during switching of the conductivity in the presence of the substrate of the enzyme. The devices can be reused by reoxidising or re-reducing the poly(aniline) electrochemically. The high stability of poly(aniline) in a hydrogen peroxide environment is shown. The responses of both devices were tested in a flowing pH 5 buffer stream (FIA). (DX183786)

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