Steady-state and time-resolved fluorescence studies on the conjugation of Rose Bengal to gold nanorods

• Examination of fluorescence performance of Rose Bengal conjugated to gold nanorods.
• Emission enhancement controlled by chemical and electromagnetic environment.
• Radiative and non-radiative deactivation revealed by fluorescence lifetime studies.
• Promising applications of Rose Bengal-gold nanorods in imaging and cancer therapy.

This work examines the fluorescence properties of Rose Bengal (RB) molecules conjugated to cetyltrimethylammonium bromide (CTAB) – coated gold nanorods (GNRs) by performing steady-state and time-resolved fluorescence measurements. We show that the quantum yield and fluorescence lifetime can be significantly modified by the electromagnetic coupling of RB to GNRs but the overall fluorescence signal depends also on the environmental conditions in which RB molecules reside – in solution or on solid substrate. For example, we have observed the increase of fluorescence intensity after binding RB to GNRs (RB@GNR) as result of both non-radiative rate decrease and contribution from the electromagnetic coupling of RB to GNRs. For RB@GNRs conjugates deposited on solid substrate we can provide evidence for a clear metal-enhanced fluorescence (MEF) mechanism by observing the decrease of fluorescence lifetime of RB from an average of 2.1 ± 0.36 ns, when complexed to CTAB solely, to 1.6 ± 0.26 ns, when conjugated to GNRs, together with the increase of fluorescence intensity. Our findings contribute to the development and evaluation of novel fluorescent tags based on plasmonic nanoparticles for biomedical applications.