Release Mechanism of Octadecyl Rhodamine B Chloride from Au Nanorods by Ultrafast Laser Pulses

We investigated the release of octadecyl rhodamine B chloride (R18) loaded onto cetyltrimethylammonium bromide (CTAB) coated gold nanorods (NR) by pulsed ultrafast laser excitation. R18 intercalates into the hydrophobic CTAB bilayer on the NR surface and can exchange on and off the NR with free CTAB micelles in solution. We find that laser excitation accelerates the rate of both R18 release from the NR and R18 binding to the NR with increasing fluence. However, at laser fluences >220 μJ/cm2 thermal degradation of the R18 dominates. We also find that the concentration of CTAB, particularly around the critical micelle concentration, strongly influences the release and binding rates.