Tantra, Ratna; (1998) Novel Strategies for Electrochemical Biosensors. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

In this work, two approaches to the design of electrochemical biosensors have been assessed. Measurement of glucose through its oxidation catalyzed by glucose oxidase has been the model for the assessment. The first approach was to use photoelectrochemistry at a semiconductor electrode as the detection methodology. The n-Si/electrolyte interface in buffered neutral electrolyte was studied. In this electrolyte, oxide growth on the Si dominated the electrochemistry. Hydrogen peroxide in solution changed the transient current response to pulse illumination. The effect was attributed to an increase in electron-hole pair recombination at the semiconductor-oxide electrolyte contact and was shown to be localized at particular sites. The feasibility of glucose measurement was demonstrated through a transient photoelectrochemical method, of hydrogen peroxide generated by the enzyme-catalyzed oxidation of glucose in the presence of oxygen. The second approach used amperometry in a cell where anode and cathode were closely-spaced parallel gold bands, with a suitable redox couple in solution. When the potential difference between the two electrodes was large enough that both electrodes operated with current limited by diffusion of the redox couple, the current became very sensitive to the ratio of concentration of the oxidized and reduced form of the couple. The theory for dependence of current on concentration, assuming an electrochemically reversible couple, is given. A combination of polymeric membranes was employed to immobilize glucose oxidase and a redox mediator on the dual gold band electrode, to control diffusion and to protect the electrode from fouling. Measurement of glucose in fluid extracted through the skin was demonstrated. The work shows how a sensor for glucose, that may simply be placed on the skin, can be designed.

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