Influence of the linker type on the Au-S binding properties of thiol and disulfide-modified DNA self-assembly on polycrystalline gold.

We investigate the Au-S binding properties of thiol and disulfide-modified DNA on polycrystalline gold by means of X-ray photoelectron spectroscopy in conditions close to dynamic processes of biosensors. The dependence of the immobilisation period on the quality and density of the self-assembly process of thiol (SH-(CH(2))(6)-DNA), disulfide (DNA-CH(2))(6)-SS-(CH(2))(6)-DNA and DMTO-SS-(CH(2))(6)-DNA) sulfur-modified oligonucleotide solutions (1 microM) that are employed for bioreceptor immobilisation is analysed. Two electronic components are found in the analysis of the S 2p core levels. One of them is clearly associated to thiolate formation, while the other can be associated to different origins. In order to identify the origin of this last component, a quantification of the non-specifically adsorbed species has been performed by rinsing the self-assembled monolayers (SAMs) with a mercapto hexanol (MCH) solution. It has been found that non-specifically adsorbed species contribute only partially to the appearance of this sulfur peak component in SAMs formed from disulfides. Electron bombardment was performed to study the evolution of this component as a consequence of surface degradation due to radiation effects. The results are also correlated with the possible presence of disulfides. We found that MCH is not stable during the measurements. The evolution of this compound and the possible causes for this behaviour are discussed.