Supramolecular-assembly-mediated functionalization of gold nanorods (GNRs) has been developed by reversible phase transfer between water and oils, which offers a facile method for fabricating robust GNRs with surface-charge tunability. In this regard, trimethylammonium (TMA) GNRs were initially prepared from conventional cetyltrimethylammonium bromide (CTAB) GNRs by means of a ligand-exchange reaction in the presence of an excess amount of TMA ligands. To further expand their functionality and potential applications, electrostatic assemblies of positively charged TMA-GNRs with negatively charged oleate ions were prepared. These assemblies (OA-GNRs) can undergo facile phase transfer from water to hexane. Interestingly, the reversible electrostatic assembly between the TMA and OA ions fabricated onto GNRs can be easily disrupted by treatment with HCl, which removes the OA ions from the GNRs to re-form the TMA-GNRs, which can be made soluble in aqueous media again. In addition, OA-GNRs can be further used for the synthesis of negatively charged GNRs such as 11-mercaptoundecanoic acid (MUA) GNRs, which are hard to prepare directly from CTAB-GNRs. This versatile method for phase transfer and functionalization on GNRs is expected to broaden the scope of their applications in sensing, biomedical imaging, photothermal therapies, and drug delivery systems.

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