Adsorption of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate) on multiwalled carbon nanotubes-silicate film: application to bioelectrocatalytic dioxygen reduction.

Multiwalled carbon nanotubes were entrapped in sol-gel processed hydrophilic silicate thin film on tin-doped indium oxide support. Microscopic images show that the nanotubes form large agglomerates of largely separated nanotubes covered by silicate film. The measurements of capacitive current prove that approximately 10% of them remain electrochemically active. The surface confined cyclic voltammetry indicate adsorption of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate) on this material. The oxidation charge estimated after the adsorption saturated shows that this compound is adsorbed on almost all the surface of the immobilised carbon nanotubes. After further modification of the electrode with extracellular laccase from Cerrena unicolor electrocatalytic dioxygen reduction is observed. The immobilised enzyme exhibits catalytic action whereas 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate) adsorbed on carbon nanotubes serves as electron mediator between protein and electrode. Bioelectrocatalysis is also observed in the absence of adsorbed mediator but the efficiency of the process is approximately one order of magnitude smaller.