Mediatorless bioelectrocatalysis of dioxygen reduction at indium-doped tin oxide (ITO) and ITO nanoparticulate film electrodes

Highlights: → We introduced ITO nanoparticulate films for enzyme immobilization. → The material promotes mediatorless bioelectrocatalysis towards dioxygen reduction. → The electrocatalytical current increase with the thickness of nanoparticulate film. → There is no difference in electrocatalytic current in the presence or absence of mediator. → The stability of the electrode can be improved by crosslinking of the enzyme with bovine serum albumin and glutaraldehyde. - Abstract: Bilirubin oxidase was immobilised on ITO electrodes: bare or covered by ITO nanoparticulate film. The latter material was obtained by immersion and withdrawal of the substrate into ITO nanoparticles suspension. Formation of a protein deposit was confirmed by scanning electron microscopy, atomic force microscopy and X-ray photoelectron spectroscopy. The electrode surface is covered by a protein film in the form of globular aggregates and it exhibits mediatorless electrocatalytic activity towards dioxygen reduction to water at pH 4.8. Modification of the electrode with ITO particles increases its catalytic activity about ten times up to 110 μA cm-2 seen for electrodes prepared by twelve immersion and withdrawal steps into ITO nanoparticle suspension. The catalytic activity is almost unaffected by addition of mediator to solution. The stability of the electrodes is increased by cross-linking of the enzyme with bovine serum albumin and glutaraldehyde. This electrode was applied as biocathode in a zinc-dioxygen battery operating in 0.1 mol dm-3 McIlvaine buffer (pH 4.8).