Stability of gold nanorods passivated with amphiphilic ligands.

The stability of gold nanorods (NRs) coated with amphiphilic ligands (ALs) was investigated. NRs coated with cetyltrimethylammonium bromide (CTAB) were ligand exchanged with polyoxyethylene [10] cetyl ether (Brij56), Oligofectamine (OF), and phosphatidylserine (PS). An aggregation index based on the longitudinal surface plasmon resonance peak broadening was used to measure stability of the NR-ALs under different conditions including the number of washes, pH, ionic concentration, and temperature. The aggregation index was also used to measure the stability of the NR-ALs under ultrafast laser irradiation and in the presence of proteins commonly used in cell culture. Differences in NR-AL stability were found, which were due to differences in the physical and chemical properties of the ALs. Apart from the charge on the AL headgroup, we suggest the Gibbs free energy of passivation (ΔG(p)) and enthalpy of passivation (ΔH(p)) of the AL could potentially aid in the selection of amphiphiles that can effectively passivate NRs for stability and optimize their properties and desired biological impact.