Colloidal Dispersion of Gold Nanorods and Gold-Silver Core-Shell Nanorods in Polar Organic Solvents

Gold nanorods and gold-silver core-shell nanorods were colloidally dispersed in polar organic solvents, acetonitrile, dimethylsulfoxide, and dimethylformamide, and their water mixtures. The gold nanorods showed narrow longitudinal surface plasmon bands in 100% dimethylformamide, 25% dimethylsulfoxide, and 25% acetonitrile solutions, indicating that the gold nanorods were well dispersed in these solutions. For the core-shell nanorods, acetonitrile and its water mixtures gave well-dispersed colloidal solutions. Amphiphilic molecules in the dispersions did not influence the systems; however, thiol-terminated poly(ethylene glycol) (PEG-SH) strongly stabilized the colloidal dispersions. The nanorods in the organic dispersions with the addition of PEG-SH could be redispersed in phosphate buffer saline (PBS) solutions. The zeta potentials of the gold nanorods in 1/10 PBS solutions ranged from −7.5 to +3.3 mV. Steric effects of the bulky PEG chains attached to the nanorod surfaces stabilized their colloidal dispe...