Microscopic Perspective of Synergy between Localized Surface Plasmon Resonance and Disruption of Dye Aggregates in Metal Nanoparticle-Enhanced Fluorescence

The interaction of rose bengal (RB) aggregates with silver nanoparticles (AgNPs) is investigated to understand the factors that contribute toward metal nanopaticle enhanced fluorescence (MEF), such as reproducibility, spectral shift, and distortion. Various shapes and sizes of RB aggregates (spherical, rods, and fibrils) are formed upon preparing films from their solution in solvent with different polarities. These molecular aggregates are disrupted in the presence of AgNPs, resulting in different enhancement factors, not only because of MEF but also due to hindrance to aggregation-caused quenching. Microspectroscopic studies provide valuable insights into the microheterogeneity of these mixed aggregates. Interestingly, the excited state decay pathways remain the same at the nanosecond time scale for different emission wavelengths. Additionally, the lifetime distribution is very narrow due to the interaction of RB deaggregates with the plasmonic AgNPs.