Improved Colloidal Stability and Phase Transfer of Gold Nanoparticles with Bidentate Dendritic Ligands

The stability and dispersibility of nanoparticles (NPs) directly affect their physicochemical properties and functional performance. In this study, we systematically investigate how ligand structure influences the colloidal stability of gold nanoparticles (Au NPs) under aggregation-inducing chemical conditions. Key structural parameters of ligands, including dendricity, binding groups, and spacer length, are varied to establish design principles for protecting the NPs. Au NPs of varying diameters (and thus surface curvatures), synthesized in both organic and aqueous media, are functionalized with these customized ligands to evaluate how ligand architecture influences colloidal stability and phase transfer efficiency. Oleylamine (OLAM)- or citrate-coated Au NPs are functionalized with these customized ligands via direct ligand exchange and subsequently exposed to a reactive solution of 1,4-butanedithiol (BDT) that triggers ligand displacement and aggregation. Our findings emphasize that the bidentate chelating effect of the lipoic acid (LA) binding group and the diverging terminal chains in the dendritic structures are pivotal in preventing ligand competition-induced clustering and aggregation. Higher-generation dendrons confer greater stability compared to small-molecule ligands, whereas ligands bearing a LA binding group are pivotal for successful phase transfer and stabilization of Au@citrate.