Redox Systems for Electrochemical Detection of Alkaline Phosphatase, Horseradish Peroxidase, β-Galactosidase, Glucose Oxidase, Choline Oxidase, and Acetylcholine Esterase

Abstract

This chapter elaborates the redox systems for electrochemical detection of alkaline phosphatase, horseradish peroxidase, β-galactosidase, glucose oxidase, choline oxidase, and acetylcholine esterase. A high speed, sensitive electroanalytical system for the detection of redox enzymes utilizing a light-addressable potentiometric sensor (LAPS) is developed. The redox LAPS device has patterned metallized sensing regions capable of simultaneous detection of a multiplicity of redox potential signals. Alkaline phosphatase was detected with 5-bromo-4-chloro-3-indolyl-phosphate as a substrate that yields indoxol. Beta-galactosidase was detected with 5-bromo-4chloro-3-indolyl-β-d-galactopyranoside as a substrate that also yields indoxol. In both cases, enzyme-generated indoxol reduces an oxidized redox species, e.g. ferricyanide, to a reduced species such as ferrocyanide. Horseradish peroxidase (HRP) was detected with 3,5,3′,5′-tetramethylbenzidene (TMB) as a substrate yielding oxidized TMB which, in turn, oxidizes ferrocyanide to ferricyanide. Glucose oxidase was detected with glucose yielding the reduced glucose-oxidase enzyme, which reduces phanazinemethosulphate which in turn, reduces ferricyanide to ferrocyanide. Choline oxidase and acetylcholine esterase were detected by similar mechanisms.