Fig. 5: Schematic showing how different factors contribute to plasmonic fluorescence enhancement and quenching.

Fluorescence quenching is experienced by fluorophores near the nanoparticle surface due to strong energy losses involving the scattering of electrons in the metal. The enhancement of the electric field (E-field) through localized surface plasmons (LSPs) on plasmonic nanoparticles leads to increased absorption and/or radiative rate for adsorbed fluorophores, extending up to several tens of nanometers (approximately 30 nm, as shown here). Nanosurface energy transfer (NSET) occurs between the transition dipole moment of the fluorophore emission and the LSPs on the nanoparticle, resulting in a distance-dependent enhancement or quenching of the signal. Typically, both NSET and E-field enhancement happen concurrently, resulting in a combination of quenching and enhancement, referred to as "quenchancement." Reprinted from ref. 130 with permission from The Royal Society of Chemistry.