Metal nanoparticle plasmon-enhanced light-harvesting in a photosystem I thin film.

Silver metal nanoparticle (NP) enhanced fluorescence is investigated in thin films of cyanobacterial Photosystem I trimer complexes (PSI) by correlating confocal laser scanning microscopy, dark-field imaging, and fluorescence lifetime measurements. PSI represents an interesting light-harvesting complex with a 20 nm diameter that is not uniformly contained within the surface-localized plasmon field of the NPs. With weak far-field illumination, 5- to 20-fold fluorescence enhancement is observed for PSI complexes adjacent to NPs, arising from efficient nanoparticle light collection and subsequent localized, surface plasmon excitation of PSI. Enhanced PSI fluorescence is detected most prominently near "rafts" of aggregated NPs that more completely fill the confocal field of view. These results demonstrate opportunities to probe energy transfer within photosynthetic complexes using plasmonic excitation and to design nanostructures for optimizing artificial light-harvesting systems.