Ultrasensitive Biosensors

Cyclic reactions have provided an effective increase of sensitivity both in amperometric enzyme electrodes and enzyme immunoassays (1, 2). We have used the copper enzyme laccase (EC. 1.10.3.2.) from Coriolus hirsutus, which catalyzes the oxidation of a wide range of substances (among them epinephrine) by dissolved oxygen. To complete the cycle the reduction of the formed quinones or ferric compounds is accomplished by pyrroloquinoline quinone (PQQ) containing (NADH independent) glucose dehydrogenase (EC.1.1.99.17.), which converts /spl beta/-D-glucose to gluuconolactone. Owing to the broad spectrum of substrates for both enzymes, the sensor responds to various catecholamines, aminophenols and ferrocene derivatives in the lower nanomolar range. The recycling sensor was used to trace the secretion of catecholamines in cultures of adrenal chromaffin cells. Furthermore both a sandwich assay for IgG and displacement of enzyme labelled cocaine have been indicated by the amplification enzyme sensor.