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.