Influence of the molecular-scale structures of 1-dodecanethiol and 4-methylbenzenethiol self-assembled monolayers on gold nanoparticles adsorption pattern

In an effort to understand the effects of the molecular structures of self-assembled monolayers on the patterns formed by immobilized Au nanoparticles (AuNPs), we characterized and compared the morphologies and properties of AuNPs adsorbed onto self-assembled monolayers formed by 1-dodecanethiol (DDT-SAM) or 4-methylbenzenethiol (MBT-SAM) assembled on Au(1. 1. 1) surfaces. The AuNP adsorption pattern on the MBT-SAM surface was well-dispersed and characterized by a low degree of corrugation. By contrast, an aggregated and highly corrugated AuNP pattern was observed on the surface of the DDT-SAM. This difference was attributed to the retention or removal of citrate anions present on the AuNPs during adsorption onto the SAM surface. Direct interactions between the AuNPs and the highly corrugated hydrophobic surfaces of the DDT-SAMs could strip the citrate layers from the AuNP surfaces, leading to aggregated adsorption. The water molecules appeared to mediate the adsorption of the AuNPs by reducing the hydrophobicity of the MBT-SAM surface and promoting a more dispersed adsorption configuration.