Solvent-Mediated End-to-End Assembly of Gold Nanorods

We demonstrate a new method for the bottom-up assembly of anisotropic nanoparticles, showing that alkanethiol molecules can induce controlled end-to-end assembly of gold nanorods in mixed water/acetonitrile solutions. The assembly is driven by solvent-mediated interactions among hydrophobic alkanethiol ligands selectively bound to the ends of the nanorods and among hydrophilic cetyltrimethylammonium bromide (CTAB) surfactants on the sides of the rods. It occurs only when the gold-nanorod samples have been aged for approximately two weeks. We compare the kinetics of solvent-mediated assembly using undecanethiol ligands to assembly processes driven by covalent bonding using alpha,omega-undecanedithiol ligands and processes driven by hydrogen bonding using 11-mercaptoundecanoic acid ligands. Our experiments demonstrate the different assembly mechanisms involved as well as the conditions needed to obtain selective end-to-end assembly.