Direct electron transfer between tyrosinase and multi-walled carbon nanotubes for bioelectrocatalytic oxygen reduction

We report the fabrication of a tyrosinase bioelectrode by mechanical compression of a MWCNT enzyme mixture. Cyclic voltammetry of the nanostructured bioelectrode demonstrated a Direct Electron Transfer (DET) process between tyrosinase, a copper enzyme, and MWCNT. The latter led to an enzyme redox potential of +0.30V vs SCE, close to the redox potential described for the T3 binuclear copper center. Furthermore, we demonstrate, for the first time, a bioelectrocatalytic reduction of oxygen performed by tyrosinase directly wired within the MWCNT disk. A maximum current density of 0.55mAcm−2 was recorded by chronoamperometric measurements at 0V vs SCE. The bioelectrode exhibits excellent stability over time, conserving more than 50% of its activity after one week. DET between MWCNTs and the T3 binuclear copper centers have been further investigated by studying the influence of two tyrosinase inhibitors: benzoic acid and cyanide. As previously reported for “blue” multicopper oxidases, such as bilirubin oxidase and laccase, tyrosinase can achieve oxygen reduction via DET between MWCNT and its T3 binuclear copper center, representing an alternative in the design of oxygen biocathodes for biofuel cells. ► Biocathode design by compression of multi-walled carbon nanotube matrix and enzyme ► Direct electrical wiring of tyrosinase exhibiting a redox potential of +0.30V vs SCE ► The bioelectrocatalytic reduction of oxygen by tyrosinase without redox mediator