  Plasmonic coupling of metallic nanoparticles and adjacent pigments can
dramatically increase the brightness of the pigments due to the enhanced local
electric field. Here, we demonstrate that the fluorescence brightness of a
single plant light-harvesting complex (LHCII) can be significantly enhanced
when coupled to single gold nanorods (AuNRs). The AuNRs utilized in this study
were prepared via chemical reactions, and the hybrid system was constructed
using a simple and economical spin-assisted layer-by-layer technique.
Enhancement of fluorescence brightness of up to 240-fold was observed,
accompanied by a 109-fold decrease in the average (amplitude-weighted)
fluorescence lifetime from approximately 3.5 ns down to 32 ps, corresponding to
an excitation enhancement of 63-fold and emission enhancement of up to
3.8-fold. This large enhancement is due to the strong spectral overlap of the
longitudinal localized surface plasmon resonance of the utilized AuNRs and the
absorption or emission bands of LHCII. This study provides an inexpensive
strategy to explore the fluorescence dynamics of weakly emitting photosynthetic
light-harvesting complexes at the single molecule level.
