Recent Progress in Surface-Enhanced Fluorescence Using Gold Nanorods

Plasmonic nanoparticles have been intensely used in research because they possess powerful optical properties. Gold nanorods (Au NRs), in particular, feature the interesting ability to absorb and scatter light in the near-infrared region through their longitudinal localized surface plasmon resonance. This property is particularly interesting in biology because these wavelengths are associated with maximum tissue penetration. The interplay between plasmonic nanoparticles and fluorophores has also triggered exciting research. Specifically, illuminating the Au NRs produces an enhanced electromagnetic field in the vicinity of the particles. This allows nearby fluorophores to feature enhanced optical properties through a phenomenon known as surface-enhanced fluorescence. This effect, however, must be counterbalanced by potential quenching that can happen from the Au NRs to the fluorophore. Systems have been developed whereby a spacer layer insulates the Au NR from the fluorophore. Multiple studies have explored different materials to use as the spacer layer such as silica or polyelectrolyte multilayers. Many of these studies have also investigated the optimal spacer thickness for achieving maximum enhancement. This review summarizes and provides an outlook on important developments in this field that have been reported in the last 10 years.