ULTRASENSITIVE BIOSENSORS

Bi-enzymatic amplifiers using cyclic reactions consisting of NADH inde pendent dehydrogenases and phenol oxidases were found to be highly sen sitive to several catecholamines and p-aminophenol. Amplification fact ors range from several 100 to up to 10 000 depending on substrate and enzyme loading. The detection limit for catecholamines was subnanomola r. An electrode based on tyrosinase/glucose dehydrogenase responds to peptides containing tyrosine. Applications to monitoring of cell activ ities as well as to immunodetection are described. Immunoassays were c onstructed by combining the amplification cycle with a suitable enzyme label, of which p-aminophenoi is the product of the enzymatic reactio n. Alkaline phosphatase and beta-galactosidase were tested as labels f or immunoglobulin G from goat (gtIgG), as well as adaption to hapten d etermination in a displacement format.