A convenient phase transfer protocol to functionalize gold nanoparticles with short alkylamine ligands

• Method was developed to induced gold nanoparticles to segregate to a water-organic interface.
• Citrate ligands were replaced by short alkylamine ligands at the interface.
• High efficiency phase transfer to another organic solvent was demonstrated.
• Short alkylamine stabilized gold nanoparticles are stable for at least 27 days.

HypothesisAqueous citrate-stabilized gold nanoparticles (Au NPs) cannot be directly transferred from water to an immiscible organic solution using short alkyl ligands. However, Au NPs can be transferred from water to a water-organic interface if chemical and mechanical inputs are used to modify the interfacial energy and interfacial area. Ligand exchange can then take place at this interface. After separating the particles from the liquids, they can be transferred to a different organic phase.ExperimentsHexane, alkylamine, and acetone were added to aqueous citrate-stabilized Au NPs to form a film at the system interfaces. After removing the liquid phases, Au NPs were readily redispersed into tetrahydrofuran (THF). The size and shape of the transferred Au NPs were evaluated by transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS).FindingsAu NPs with 13 nm diameter are readily segregated from water with the aid of short alkylamine ligands. They form a thin film at the water/organic solvent interface, rendering them easy to separate from the liquid phases and possible to redisperse into another organic solvent. After the phase transfer process, Au NPs were functionalized with short amine ligands. In addition, the shape and size of Au NPs were preserved. The short amine-protected Au NPs in THF can stay stable for up to 27 days or longer.

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