THE ELECTROCHEMICAL DETECTION OF GLUCOSE : A STUDY ON ENZYMATIC REACTORS AND MEDIATED ENZYME ELECTRODE SYSTEMS IN FIA

Abstract

This thesis describes some studies into the electrochemical detection of glucose, a molecule of extreme importance and whose detection and quantification is not only a challenge to analytical chemists but is also an industry in its own right. Chapter 1 is an introduction to the work carried out in this thesis. It is a survey of the relevant literature and a critical assessment of FIA-ED as an electrochemical technique of routine application. Enzyme electrodes as the basis for biosensor development is described. The key to enzyme electrodes is the immobilisation of enzymes. This is a well-documented field of which the literature is exhaustive. The immobilisation of enzymes is however, described in somewhat detail to underscore its importance as the central theme in this thesis. Chapter 2 is about the GOD carbon fibre enzymatic reactor. Here GOD was immobilised onto carbon fibres. GOD has been immobilised onto glass beads and other materials before but not on fibres. Carbon fibres offer several advantages: high tensile strength, non-porous surface, surface that can be easily functionalised and the fibres can be packed tightly quite easily. The wall-jet detector was used. The use of an immobilised GOD carbon fibre enzymatic reactor coupled to a wall-jet detector represented a novel approach to the FIA detection of glucose. Ferrocene mediated GOD enzyme electrodes as a glucose biosensor was the next major area of study. Chapter 3 discusses the experiments conducted in the steady state mode, primarily cyclic voltammetry of ferrocene mediated GOD enzyme electrodes of various base electrodes: platinum, glassy carbon, graphite, gold-glassy carbon and gold-graphite. Chapter 4 describes the performance of these electrodes in a FIA system for the detection of glucose. Various parameters such as pH, applied potential, flow rate etc. were examined. Calibration studies were also carried out. FIA determination of glucose using these electrodes was successfully carried out. However, these electrodes exhibited limited stability (about one week). The next piece of work was directed at using the ferrocene GOD enzyme electrodes in real analysis. The detection of glucose in blood which is an important clinical measurement was chosen as the testing ground. Blood samples were injected into the FIA system and the results obtained were compared against corresponding values from an established routine clinical method. The values from the electrodes were generally higher than values obtained from the clinical methods. Two explanations were offered: interference by electroactive species present in blood and viscosity of blood. Chapter six lists a few suggestions for future work in this area.