Fabrication & characterisation of enzyme electrodes for biosensor and biofuel cell applications

Abstract

Enzyme electrodes are biochemical transducers. They function by converting biochemical reactions into electrochemical processes. This functionality could potentially give rise to a new generation of implantable medical devices such as biofuel cells and biosensors. The main aim of this study was to fabricate and characterise enzyme electrodes for potential use in these applications. Specifically, the electrodes were fabricated with a view to addressing current problems with enzyme electrodes, problems such as stability, lifetime, activity, interference and ease of fabrication. The approach involved testing various materials such as different types of enzyme, polymeric electron transfer mediators, enzyme entrapment materials, conductive supports and matrices and biocompatible polymers. The main enzyme used was Glucose Oxidase. Additional work was also carried out on Bilirubin Oxidase, Pyranose 2-Oxidase Acyl-CoA Oxidase and Acetyl-CoA Synthetase. Various immobilisation methods were used including direct adsorption, covalent binding and physical entrapment. Polymeric electron transfer mediators were fabricated and tested. The main mediator used was Ferrocene and its derivatives. Coenzyme Q was also tested as a mediator for 10 enzyme electrodes. The biomimicking polymer poly(2-methacryloyloxyethyl phosphorylcholine-co-n-butyl methacrylate) was also adapted and incorporated into a Glucose Oxidase enzyme electrode. A rapid and straightforward enzyme electrode fabrication method using Ferrocene and Nafion was developed and used to test Pyranose- 2-Oxidase for potential use as a glucose oxidising enzyme for enzyme electrodes. Thismethod was also used to develop an enzymatic biofuel cell using Glucose Oxidase for glucose oxidation at the anode and Bilirubin Oxidase for oxygen reduction at the cathode. Finally, this fabrication method was used with Glucose Oxidase, Acyl-CoA Oxidase and Acetyl-CoA Synthetase for preliminary investigations into the viability of a multi analyte biosensor. The investigation was based primarily on electrochemical techniques such as voltammetry, amperometry, electrochemical impedance spectroscopy and fuel cell diagnostics. The materials and immobilisation techniques presented could potentially be used to improve future enzyme electrodes. This may be achieved through the novel use of biocompatible and biomimicking polymers, through simple biofuel cell fabrication and with the use of multi analyte biosensors developed during this investigation.