Protein interactions with surfaces are key to understanding the behavior of implantable medical devices. The optical technique of reflection anisotropy spectroscopy (RAS) has considerable potential for the study of interactions between important biological molecules and surfaces. This study used RAS to investigate the adsorption of S amino acids onto Au(110) in a liquid environment under different conditions of potential and pH. Certain spectral features can be associated with the Au(110), as reported previously, while other features are assigned to bonds between the amino acids and the Au surface. The RA spectra are shown to be influenced by the structure of the amino acid, the solution pH, and the applied electrode potential. This work has assigned the negative feature at 2.5 eV to the Au-thiolate, bond while the positive feature at 2.5 eV is assigned to the disulfide bond. The broad spectral feature at 3.5 eV is attributed to the Au-amino interaction, while the sharper feature at slightly higher energy is associated with the Au-carboxylate interaction. Sulfur-containing amino acids are frequently found on the outside of protein molecules and could be used to anchor the protein to the surface.

We have investigated the adsorption of L-cysteine (L-Cys) onto Au(110) in an electrochemical cell and under ultra-high vacuum (UHV) conditions using reflection anisotropy spectroscopy (RAS). The L-Cys saturated surfaces created by both deposition methods exhibit similar RA profiles which indicates a similar adsorption process. Our results are consistent with L-Cys binding to the Au(110) surface through a goldthiolate (Au-S) linkage. Heating the L-Cys saturated surface in UHV to 580 K results in the decomposition of the adsorbate and leaves behind a sulphur/Au surface composed of different structural domains.