Optimisation of enzyme electrodes

Enzyme electrodes have been fabricated in a variety of ways and used successfully for aqueous solution measurement. Knowledge about the fundamental basis of their operation has increased substantially in recent years, but the final, partly technological, hurdle of adaptation for practical use remains to be fully surmounted. Key aspects requiring attention are dependence on solution parameters capable of changing the kinetics of the immobilised enzyme reaction, direct fouling at the enzyme electrode, and the distorting effect of the biological matrix, notably blood and tissue, on the electrode environment due to the deposition of surface-active macromolecules and cellular elements. This review of enzyme electrode optimisation deals primarily with the various membranes which have been used to try to overcome such highly practical limitations to the biomedical use of enzyme electrodes. The classical amperometric glucose electrode based on detection of H2O2/O2 by the underlying sensor will be emphasised, but pH-based sensors for pyruvate and urea will also be discussed. The amperometric systems described indicate that with appropriate covering membranes, many, though by no means all, interfacing problems can be overcome, and also that the type of optimisation engineered is dictated by the specific application envisaged.