Interaction between bilirubin oxidase and Au nanoparticles distributed over dimpled titanium foil towards oxygen reduction reaction

Abstract

Spatial distribution of enzymes on electrodes is a key point to understand and optimize bioelectrocatalysis, although not largely investigated. In this work, Ti nanodimples serve as a platform for getting a controlled spatial distribution of gold nanoparticles (AuNPs). By varying the thickness of the initial gold layer, AuNPs with average sizes ranging from 13±6, 46±12 to 81±13 nm are obtained. AFM and TEM allow to localize the AuNPs in the dimples. It is in particular highlighted that the smallest NPs are present not only at the bottom but also on the edges of the Ti dimple, with TiO2 layer in their close surrounding. Enzymatic O2 reduction by immobilized Myrothecium verrucaria bilirubin oxidase (Mv BOD) is then investigated on the different materials. After having demonstrated the occurrence of the bioelectrocatalytic reaction on AuNPs excluding the Ti surface, the efficiency of the catalysis is discussed as a function of the AuNP size. The shape and fitting of the cyclic voltammetry curves obtained with the smallest AuNPs suggest a decrease in the electron transfer rate as a consequence of the colocalization of AuNPs and semiconducting TiO2. Interestingly, high stability of the enzymatic current is obtained with the highest AuNPs even in the presence of high concentration of salts.