Effective bioelectrocatalysis of bilirubin oxidase on electrochemically reduced graphene oxide

Abstract

Graphene oxide (GO) was applied for construction of an effective biocathode based on bilirubin oxidase (BOD). Separation of small-sized GO sheets together with the BOD immobilisation protocol has detrimental effects on the bioelectrocatalytic reduction of oxygen. When BOD was deposited on electrochemically reduced GO (ErGO) only a negligible current density j=2.6μAcm−2 was observed. Current density dramatically increased to a value of 46μAcm−2 once BOD was in-situ mixed with as-received GO directly on a glassy carbon electrode (GCE) with subsequent electrochemical reduction of the BOD/GO composite. When this protocol was tested with small-sized GO flakes separated simply using centrifugation, the fabricated biocathode exhibited j=120μAcm−2. A current density further increased to j=280μAcm−2 when BOD and purified GO were incubated ex-situ for 4h, followed by the BOD/GO composite collection by centrifugation, its deposition on the GCE and electrochemical reduction. Moreover, oxygen reduction current increased steeply with a steady-state current density achieved at high potential (≈500mV), close to the onset potential of oxygen reduction (≈580mV).