Studies on Self-Assembly Monolayers of Cysteine on Gold by XPS, QCM, and Electrochemical Techniques

Abstract

Cysteine is a commonly used self-assembly reagent in the preparation of modified electrode and biosensors. Self-assembly of cysteine on gold has been investigated by X-ray photoelectron sepectroscopy (XPS), quartz crystal micobalance (QCM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in this article. The results of QCM and EIS revealed that the formation of saturated self-assembly monolayers of cysteine on gold required at least 30 min. The interfacial properties of the gold electrode modified with self-assembled cysteine was probed with a [Fe(CN)6]3–/4– redox couple. Contrary to the previous results obtained from the same experimental procedure with self-assembly of octadecyl mercaptan, the electrochemical behavior of the redox probe was not blocked but improved with cysteine absorbed on a gold electrode. As cysteine is electroactive, the native electrochemical properties of adsorbed cysteine are discussed as well.