Electropolymerisation in biosensor design

Scott, Manuela (1997) Electropolymerisation in biosensor design. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

The immobilisation of glucose oxidase as a model enzyme was carried out by entrapping it in electropolymerised poly(phenol) and poly(1,2-diaminobenzene) films deposited onto Pt electrodes. Biosensors were produced applying a wide range of different experimental conditions. The characteristics of the sensors were investigated by studying their response to the substrate glucose. Two different mediators, O₂ and TTF⁺ were used to achieve electron transfer between the enzyme and the electrode. A theoretical model describing the kinetics of such 'thin film' electrodes is also presented. The substrate responses were analysed according to the model resulting in specific kinetic constants for each individual electrode which was produced. Interpretations are supported by various other electroanalytical methods including ellipsometry.

The studies on poly(phenol)/GOx electrodes showed that many factors influence the characteristics of the sensors. These are most importantly the electrode surface condition, particularly the surface roughness and surface functionalities, the concentration of monomer and its electropolymerisation time, the concentration of the glucose oxidase present during film growth , and the time allowed for pre-adsorption of the enzyme. Furthermore the pH of the growth solution and of the solution in which the response to β-D-glucose was tested, have an impact on the kinetics of the poly(phenol)/GOx electrode, as does the concentration of the electrolyte. Variations arise due to varying enzyme loadings and enzyme activities, varying film thicknesses and densities and subsequently varying permeabilities, and also adsorption competition between various components present in the electropolyermisation solution. Glucose oxidase is also observed to adsorb on top of the poly(phenol) film.

Investigations into poly(1,2-diaminobenzene)/GOx electrode characteristics by ellipsometry show a final film thickness of 45-47 nm. The condition of the film is very sensitive to experimental conditions resulting in different characteristics (i.e. thickness and density) for each set of experimental conditions. Glucose oxidase was again observed to adsorb on top of the polymer layer. This increased the final thickness, determined by ellipsometry to a maximum of 69 nm. A parallel rise in the extinction coefficient of the film was detected.

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