Amperometric determination of butanone peroxide and hydroxylamine via direct electron transfer at a horseradish peroxidase-modified platinum electrode

Abstract

An amperometric organic-phase peroxide biosensor was constructed by immobilizing horseradish peroxidase (HRP) entrapped within poly(ester-sulfonic acid) Eastman AQ-55D polymer matrix on a platinum electrode surface. The enzyme electrode functioned by direct electron transfer between the HRP redox centre and the platinum surface. This mediator-free biosensor was applied to the determination of butanone peroxide and hydroxylamine, which are HRP substrate and inhibitor, respectively. Fast sensor responses were obtained in 30 s for both the substrate and the inhibitor. The biosensor showed higher catalytic efficiency in acetonitrile (1.1 µA l mmol^–1) than in methanol (0.9 µA l mmol^–1). However, the sensor exhibited greater percentage inhibition of HRP activity in the less catalytically efficient methanol medium (516% inhibition 1 mmol^–1) than in acetonitrile (345% inhibition l mmol^–1). This reversal in the performance of the sensor towards hydroxylamine in the organic solvents is attributed to the reaction media polarity combined with the butanone peroxide-induced conformational change of the enzyme active site.