Electrochemically Active L-Cysteine Gold Modified Electrodes

• MPA was used to covering gold electrode surface and anchoring L-cysteine molecules.
• The mechanism of formation and breaking of disulfide bridge is pH-dependent.
• The modified electrode was applied to the electrocatalytic detection of quercetin.

Gold electrodes were easily modified using MPA (3- mercaptopropionic acid) to produce a self assemble monolayer, SAM, in which electrochemically active cysteine molecules were anchored to produce Au/MPA and Au/MPA/CSH electrodes. The functional groups, present on the modified electrode surfaces, were identified using cyclic voltammetry and ferricyanide ions, an electrochemical probe, at variable pH values. The steps which describe the global electrode process were identified and characterized using cyclic voltammetry. It involves the deprotonation of the R-SH superficial groups; production of R-S free radicals from R-S- electrochemical oxidation and attack and of R-S free radicals to the RSH adjacent molecules on the electrode surface, followed by the second electrochemical oxidation step to produce RSSR. The Au/MPA/CSH electrode showed electrocatalytic activity toward oxidation of quercetin in the range of 0.50 to 12.2 μmolL−1 with a detection limit of 0.15 μmolL−1.