Glutamate adsorption on gold electrodes at different pH values

Abstract

Advanced medical applications of gold nanoparticles can use amino acids as surface modifiers. For this reason, understanding the adsorption of amino acids on gold is crucial to improve these applications. Here, the adsorption of glutamate (Glu) on Au(1 0 0) and Au(1 1 0) electrodes has been studied using a combination of electrochemical experiments, and DFT calculations. The adsorption properties have been examined in two different regions, the double layer region, and the OH adsorption/oxide formation region. In the first one, the combined results from the electrochemical experiments and the DFT calculations indicate that Glu is adsorbed in acidic solutions by the two terminal carboxylate groups, each one in a bidentate configuration, and exchanges two electrons upon adsorption. The comparison with the results obtained for the Au(1 1 1) electrode and other molecules containing carboxylic groups confirms this adsorption mode. Glu adsorption also affects the reconstruction process of the Au(1 1 0) and Au(1 0 0) surfaces. On the other hand, in alkaline solutions, glutamate is not adsorbed because the negative charge of the surface prevents its adsorption. In the OH adsorption/oxide formation region, Glu is oxidized when OH is adsorbed, and the results indicate that OH is consumed in this oxidation process. The formation of gold surface oxides inhibits the Glu oxidation reaction.