The Process Of Cysteine Self-assembly On Gold Nanoparticle Modified Electrodes And Their Application

Sulfide or disulfide derivatives strongly interact with gold to form Self-assembled monolayers (SAMs) on the gold surface due to the strong interaction between the S atom of thiol and gold. SAMs has good stability, density, orderliness and high selectivity identification function for some molecules or ions, and can develop a fast, flexible, simple system for surface's properties of metal electrodes. Cysteine (cys) is only one amino acid containing sulphur. Cysteine molecules are often used as self-assemble reagents in the preparation of chemical modified electrodes and biological sensorsDespite many papers have been reported on the characteristic of cysteine SAMs, our understanding of the chemical processes of self assembly is still far from being complete. For example, the reports for electrochemical behavior of Cys-modified gold electrodes are paradoxical. Some papers reported that the voltammogram at Cys-modified gold electrode exhibited one pair of redox peaks in the range of -0.3–0.4 V, while others reported there were no peaks in this range. In this study, the process of Cys self-assembled onto the gold nanoparticle (AuNP) surface was investigated. The cyclic voltammogram shows a pair of well-shaped redox peaks at this modified electrode in phosphate buffer solution (pH 7.0) due to formation of hydrous gold(I) oxide. This could clearly explain why the paradoxical phenomena were reported for the electrochemical behavior of modified electrodes based on Cys self-assembly on gold surface. Moreover, the redox couple, Au*/Au(OH)x, would participate in electrocatalytic processes as mediator to improve electrochemical oxidation of hydrogen peroxide.The cysteine self-assembled on GNPs and Au-Pt alloyed nanoparticles modified elecltrodes are also investigated in this paper. The electrocatalytic properties of ascorbic acid (AA) at the Cys/AuNPs/ITO, Cys/AuOH-AuNPs/ITO and Cys/Au-PtNPs/ITO electrodes were investigated and compared. The results indicate that the Cys/Au-PtNPs/ITO modified electrode shows best electrocatalytic response to AA due to cys self-assembled film and synergic effects of Au-Pt. Its oxidation peak current get a good linear relationship to the concentration of AA from 4.0×10^-6 to 6×10^-4mol / L and the detection limit is 5.8×10^-7mol/L. It can be applied to determination of AA for the actual samples.