Improved direct electron transfer-type bioelectrocatalysis of bilirubin oxidase using thiol-modified gold nanoparticles on mesoporous carbon electrode.

Abstract Ketjen Black (KB), a mesoporous carbon material, was modified with gold nanoparticles (AuNPs) and 4-mercaptobenzoic acid (MBA). The MBA/AuNP-modified KB was utilized as an effective scaffold for the direct electron transfer (DET)-type bioelectrocatalytic reduction of dioxygen by bilirubin oxidase from Myrothecium verrucaria (BOD). Owing to the MBA/AuNP modification, the limiting current density of the steady-state catalytic wave was doubled and the half-wave potential of the catalytic wave was shifted to the positive direction by 140 mV. The kinetic analysis of the steady-state catalytic wave indicated that the modification narrowed the orientation distribution of the adsorbed BOD and shortened the mean length between the redox copper site of BOD and the electrode surface. The electrostatic attraction and π–π interactions between BOD and MBA are likely responsible for the favorable orientation of the enzyme. Graphical abstract Unlabelled Image Highlights • Ketjen Black was modified with 4-mercaptobenzoic acid and AuNPs. • Modified electrode was an effective scaffold for DET-type bioelectrocatalysis of BOD. • Half-wave potential of the catalytic wave was close to the formal potential of BOD. • Kinetic analysis of the wave provided information about the orientation of BOD. • BOD seemingly adsorbed in homogeneous and productive orientations on the electrode. [ABSTRACT FROM AUTHOR]