Mediator-Less Direct Electron Transfer and Oxygen Reduction By Bilirubin Oxidase Adsorbed on to a Bucky Paper Electrode
Authors: Walgama Charuksha , Pathirana Anuruddha , Means Nick , Goff Alan Le , Cosnier Serge , Krishnan Sadagopan 
Published: February 2020

Direct immobilization of enzyme films on nanostructured electrodes has the advantage of enhancing electrocatalytic currents. Bilirubin oxidase (BOD), a blue multi-copper enzyme, extracted from Myrothecium verrucaria has been recognized as a highly efficient oxygen reduction catalyst at near neutral pH with a minimal overpotential requirement. BOD contains four redox active Cu centers, which are classified based on their spectroscopic characteristics as T1 (one), T2 (one), and T3 (two). T1 Cu-center of BOD has been proposed to be the electron-receiving center from electrode and the catalytic oxygen reduction was suggested to occur at the tri-nuclear Cu clusters of T2/T3.1 Direct electron transfer between BOD and the electrode has been shown in slightly acidic and anaerobic conditions without mediators (E°´
T1 = ~0.5 V, E°′
T2/T3 = ~0.16 V vs Ag/AgCl).2
,3a Reported studies showed that the oxygen reduction by BOD is highly effective with electrodes modified with a redox polymer hydrogel,3b a poly-lysine composite film,4 gold nanoparticles,5 carbon nanotube-pyrene units,6 and functionalized multiwalled nanotubes (MWNT).7
,
8
Here we will present our findings on the direct electron transfer and electrocatalytic oxygen reduction currents by a BOD film directly adsorbed on to bucky paper electrodes prepared from MWNT. Our preliminary work also suggests the role of bucky paper thickness in controlling the extent of catalytic currents and direct electrochemistry. BOD integrated bucky papers have immense usability in highly efficient biological fuel cells and we envision employing these BOD electrodes as cathodes for enzymatic fuel cell applications.6,9

Acknowledgements. Financial support by the Oklahoma State University is greatly acknowledged.

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