Enzyme-Metal Oxide Composite as Catalysts for Enzymatic Oxygen Reduction

Abstract

The immobilization of laccase on metal oxide nanoparticles was achieved using a silane coupling agent and a homobifuntional cross-linking agent. The metal oxide nanoparticles studied were TiO2, ZnO and SnO2. The coupling agent was silane and the crosslinking agents was 1,5-Difluoro-2,4-dinitrobenzene (DFDNB). The resulting laccase-metal oxide bio-nanocomposites were deposited onto screen printed carbon electrode and tested as electrocatalysts for oxygen reduction in an electrochemical cell using 0.2 M pH 4.5 sodium acetate buffer as the electrolyte. The bio-nanocomposite modified electrode showed an open circuit potential as high as 0.61 V vs Ag/AgCl. Cyclic voltammograms showed a clear difference between unmodified and laccase modified metal oxide nanoparticles in the oxygen reduction region with an onset potential of ~ 0.57 V. In comparison, the laccase physisorbed onto the metal oxide nanoparticles without the molecular crosslinkers showed no obvious electrocatalytic activity. The work adds significant value to the bio-electrochemistry literature, as a new class of support material with photocatalytic properties have been found to serve as excellent enzyme immobilization support that has potential applications in biosensors and biological fuel cells.