AMPLIFICIATION AND SWITCHING BY ENZYMES IN BIOSENSORS

Abstract

Biospecific electrodes based on the membrane technology (first generation of biosensors) for nine metabolites (glucose, lactose, maltose, lactate, pyruvate, urea, uric acid, glutamate, and phosphate) and for the determination of six enzyme activities (o-amylase, lactate dehydrogenase, pyruvate kinase, creatine kinase, alanine aminopeptidase, and choline esterase) have been brought into the clinical laboratory by our group. These sensors contain a dialysis membrane and up to three sequentially acting enzymes. For mono-enzyme electrodes 200 - 300 samples per hour, a functional stability of 5,000 - 10,000 samples per membrane and a lower limit of detection of 1 zum have been achieved. An increase of sensitivity up to the lower nanomolar range has been achieved by analyte recycling enzyme systems. In addition to the couples lactate/pyruvate, glucose/gluconolactone, NAD*/NADH, ADP/ATP, in the enzyme system laccase/cytochrome bs benzoquinone/hydroquinone have been amplified. This sensor exhibits a cosubstrate-dependent thresholdlike sensitivity. Cofactor-dependent anti-interference layers, e.g., hexokinase or glucose dehydrogenase, represent another type of enzymatic switches. Their selectivity may be changed by turning on the eliminating enzyme.