AUGMENTATION OF ENZYME ELECTRODE SENSITIVITY USING BIOCATALYTIC PRECONCENTRATION

A method for increasing the sensitivity of enzyme sensors based on biocatalytic accumulation of an intermediate product was investigated using a biospecific electrode consisting of an immobilized glucose dehydrogenase-lactate dehydrogenase-lactate monooxygenase membrane and an electrochemical oxygen probe. Addition of the analyte (glucose) and an excess of NAD+ to the background solution permits NADH to be biocatalytically preconcentrated in the enzyme membrane. When this reaction has approached equilibrium, the sensor signal is generated by injection of an excess of pyruvate, thus starting oxygen consumption catalysed by the sequential lactate dehydrogenase-lactate monooxygenase reaction. Glucose can be determined at concentrations between 10 and 100-mu-M. Compared with operation of the sensor without NADH preconcentration, the increase in the sensitivity to glucose is 18-fold in the current-time mode and 40-fold in the derivative current-time mode. The measuring regime permits interferences from the sample solution to be avoided.