A Physico-Mathematical Model for Bisubstrate Enzyme Membrane Electrodes

A physic-mathematical model has been developed that is suitable for biosensors incorporating membranes and bisubstrate enzymes. The set of equations regarding the transport of reactants across the membrane, the bisubstrate enzymatic reaction, back diffusion of reactants and reaction products, are written down and simultaneously solved and transient response of the electrode is determined as a function of time. The model is assessed experimentally employing a simple glucose enzyme pH electrode. In the range practical for the enzyme pH electrode (0.01-0.1 M) there is satisfactory agreement between the theoretical predictions and experimental results. The model described is general and as well allows the determination of enzyme activity as a function of pH thereby reflecting the range of substrate concentration that is measurable.