Diazonium Electrografting vs. Physical Adsorption of Azure A at Carbon Nanotubes for Mediated Glucose Oxidation with FAD-GDH

The electrochemical reduction of aryldiazonium salts is a versatile and direct route to obtain robust covalently modified electrodes. We report here a comparative study of Azure A modified carbon nanotube electrodes prepared by diazonium electrografting and by physical adsorption for bioelectrocatalytic glucose oxidation with fungal FAD-glucose dehydrogenase from Aspergillus sp. The electrografted and adsorbed electrodes exhibited different reversible electroactivity consistent with polymer-type and monomer-type phenothiazine surface assemblies, respectively. The electrografted Azure A electrodes exhibited superior mediated bioelectrocatalysis compared to the adsorbed Azure A electrodes. A more than 10-fold higher catalytic current up to 2 mA cm⁻² at 0.2 V vs. Ag/AgCl together with a similarly low onset potential of −0.05 V vs. Ag/AgCl was observed at the electrografted electrodes. Faster estimated electron transfer kinetics and a +200 mV potential shift for the polymer-type redox couple vs. the adsorbed monomer-type couple underlines the favourable driving force for mediated electron transfer with the buried FAD active site for the diazonium-derived bioelectrode.