Amino acid mediated oxidative activation of multi-walled carbon nanotubes to introduce reversible proton-coupled electron transfer species.

Protein and enzyme film electrochemistry is a powerful technique which enables the energetics and kinetics of biological electron transfer processes to be quantified. One of the major challenges is finding a suitable electrode surface upon which a redox active protein or enzyme can be adsorbed in an electroactive configuration. Multi-walled carbon nanotubes (MWCNTs) have been a useful class of electrode modifiers which facilitate electroactive protein adsorption and provide a substantial increase in electrode surface area. MWCNTs are therefore commonly used in bioelectrochemical studies, with applications in analytical electrochemistry and electrochemical sensing. Herein, we report the effect of electrochemical oxidation on a MWCNT-functionalised glassy carbon electrode in the presence of adsorbed protein. Previously uncharacterised redox functionalities are introduced by sweeping to oxidising potentials (> 0.8 V vs. SHE), with two reversible electron transfer signals subsequently appearing with midpoints of 80 and 390 mV at pH 7.0. This redox activity is hypothesised to be a result of the irreversible oxidation of the MWCNT-protein system resulting in the introduction of species capable of performing fast, reversible electron transfer.