Synthesis of thiolate-protected Au nanoparticles revisited: U-shape trend between the size of nanoparticles and thiol-to-Au ratio.

We report a new understanding of the factors controlling the size of thiolate-protected gold nanoparticles (Au NPs): the formation and the state of a protecting layer (Au(i)-thiolate motifs) outside the gold core determine the size of Au NPs, depending on the feeding thiol-to-Au ratio. As a result, a U-shape trend is identified between the size of Au NPs and the thiol-to-Au ratio as opposed to the commonly expected decreasing trend.