Preparation and comparison between different thiol-protected Au nanoparticles

We report on the synthesis of monolayer-protected gold cluster (MPCs) in aquatic phase under different conditions. Three thiols, i.e., 2-mercaptoethanesulfonic acid (MPS), 3-mercaptopropionic acid (MPA), and cystamine (CYS) have been used as the protecting monolayer. Furthermore, we studied the effect of varying the ratio between the concentrations of the protecting layer, the gold ions, and the reducing agent in the preparation solution. Comparison was based on measuring the average diameter, stability, and size distribution of the MPCs. Best results were obtained for MPS-based MPCs and that the optimum molar concentration ratio between the protecting layer, the gold ions, and the reducing agent was 1:1:2.