Electrochemical Behaviors of ABTS2- on the Thiol-modified Gold Electrodes

Abstract

The electrochemical properties of the redox mediator, 2,2'-azinobis (3-ethylbenzothiazoline-6-sulfonate) (ABTS2-) were studied using cyclic voltammetry. The measured potentials (E°' vs SCE) of the two redox couples of ABTS are 0.45 V for ABTS2-/ABTS•− and 0.87 V for ABTS•−/ABTS0. The rate constant for heterogeneous electron transfer and the diffusion coefficients for ABTS2- are 5×10-3 cm s-1 and 3.1×10-6 cm2 s-1, respectively. Our interest in ABTS2- stems from the fact that this molecule functions as a substrate to the copper oxidase, laccase, by providing the reducing equivalents necessary for the biocatalyzed reduction of dioxygen to water. Consequently, when laccase is tethered to an electrode surface or dissolved in solution, ABTS2- can be used to quantify enzyme activity electrochemically.