Surface Modification of Citrate-Capped Gold Nanoparticles Using CTAB Micelles

Experimental Section

We adopted the Turkevich and the seeded growth method to synthesize 12 and 32 nm AuNPs, respectively.24 The exact sizes measured by TEM (JEM-2100F, JEOL) were 12.2 ± 1.1 nm (N = 102) and 31.7 ± 3.3 nm (N = 104). After the synthesis, the AuNPs were centrifuged and re-dispersed into water to remove residual reagents in solution. The aqueous 32 nm AuNP solutions (0.7 nM, 2 mL) were added to CTAB solutions (Aldrich, > 99％) prepared in different concentrations ranging from 0 to 1.5 mM in 2 mL. Then, the changes in color and UV-vis spectra were measured after the two solutions were mixed and fully equilibrated (15 h).

UV-vis spectra were acquired using Lambda 25 (Perkin-Elmer). Zeta potential was measured using ELS-Z (Otsuka Electronics). The cryo-TEM images were acquired from a thin film of aqueous solution (4 µL) transferred to a lacey supported grid by the plunge-dipping method. The thin aqueous films were prepared at ambient temperature and with humidity of 97-99％ within a custom-built environmental chamber in order to prevent evaporation of water from sample solution. The excess liquid was blotted with filter paper for 2-3 s, and the thin aqueous films were rapidly vitrified by plunging them into liquid ethane (cooled by liquid nitrogen) at its freezing point. The sample was observed with a JEOL-JEM-3011 HR instrument operating at 300 kV. The data were analyzed with Gatan Digial Micrograph.

Supporting Information. Response of 12 nm AuNPs to addition of CTAB, response of AuNPs to addition of other cationic ligands, stability of CTAB micelle-stabilized AuNPs.