Enzyme-Metal Oxide Composite as Catalysts for Enzymatic Oxygen Reduction

Laccase is widely used in enzymatic fuel cell as cathode catalyst. There has been a lot of work using carbon nanostructures as immobilization support for laccase to demonstrate bio-electrocatalytic activity towards oxygen reduction reaction.^1,2,3 The metal oxide nanoparticles studied were TiO₂, ZnO and SnO₂. The immobilization of laccase on these metal oxide nanoparticles were achieved. The coupling agent was silane and the crosslinking agents were dithiobis[succinimidyl propionate] (DSP), 1,5-Difluoro-2,4-dinitrobenzene (DFDNB) and succinimidyl iodoacetate (SIA). Attenuated total resonance fourier transform infrared spectroscopy (ATR-FTIR) was performed on the nanocomposites and the results confirmed that laccase was attached on to the metal oxide nanoparticles through the molecular crosslinkers. The resulting laccase-metal oxide nanocomposites were deposited onto screen printed carbon electrode and tested for oxygen reduction electro-catalysis in an electrochemical cell using 0.2 M sodium acetate buffer as the electrolyte. The composite modified electrode showed an open circuit potential of 0.61V vs Ag/AgCl. Cyclic voltammograms showed a clear difference between unmodified and laccase modified TiO₂ in the oxygen reduction region with an onset potential of 0.57 V.  In comparison the laccase physisorbed onto TiO₂without the molecular crosslinkers showed no obvious electrocatalytic activity. The work adds significant value to the biofuel cell community as it introduces a new class of material as enzymatic support for bio-electrochemical reactions.

Fig. 1: Schematic representation of Laccase immobilized onto metal oxide nanoparticles through molecular crosslinkers.

Fig. 2: Cyclic voltammetry of crosslinked and physisorbed laccase on TiO₂ nanoparticle electrodes in O₂ saturated sodium acetate buffer electrolyte.

Acknowledgements:

The authors would like to thank University of Georgia for providing seed funds to carry out this research.

References:

1. Ramasamy, R. P.; Luckarift, H. R.; ivnitski, D. M.; Atanassov, P. B.; Johnson, G. R., High electrocatalytic activity of tethered multicopper oxidase- carbon nanotube conjugates. Chemical  Communications 2010, 46 (33), 5977-6188.

2. Naga S. Parimi; Yogeswaran Umasankar; Plamen Atanassov; Ramasamy, R. P., Kinetic and Mechanistic Parameters of Laccase Catalyzed Direct Electrochemical Oxygen Reduction Reaction. ACS Catalysis  2012, 2, 38-44.

3. Umasankar, Y.; Brooks, D. B.; B., B.; Zhou, Z.; Ramasamy, R. P., Three dimensional carbon nanosheets as novel catalyst support for enzymatic bioelectrodes. Advanced Energy Materials 2013 (accepted  paper).