Insights on the kinetics of concanavalin A adsorption on platinum and glassy carbon electrodes from electrochemical impedance spectroscopy data
By Diniz, Flamarion Borges; Silva, Diego José Raposo da; Ueta, Roseli Rudnick; Ribeiro, Rogério Tavares
Published in Colloids and Surfaces A: Physicochemical and Engineering Aspects
2019
Abstract
Electrochemical impedance spectroscopy was applied to investigate the adsorption of concanavalin A on glassy carbon and platinum electrodes. A redox probe, K4Fe(CN)6/K3Fe(CN)6, was used to yield a well defined charge transfer resistance across the electrode/solution interface. Adsorption on glassy carbon electrode was a diffusion controlled process during its initial stages. From the time dependence of the electrode coverage, by means of a simple rate law and the Stoke-Einstein equation, it was possible to estimate a protein effective radius of 3.7 nm and to estimate the protein monolayer coverage of 2 mg m–2. On platinum electrode the kinetics could be explained in terms of a fast initial adsorption, followed by a slow protein conformational change. The locked protein (Concanavalin A with bound Ca2+ and Mn2+) adsorbs faster than the unlocked protein. The presence of an oxide layer on the electrode seems to affect more the unlocked protein than the locked one. It is suggested that the Ca2+ and Mn2+ ions present in the locked protein may play a role on the adsorption process.