Metallic nanoparticles influence the quantum yield and lifetime of adjacent fluorophores in a manner dependent on the properties of the nanostructure. Here we directly compare the fluorescence enhancement of the near-infrared fluorophore IR800 by Au nanoshells (NSs) and Au nanorods (NRs), where human serum albumin (HSA) serves as a spacer layer between the nanoparticle and the fluorophore. Our measurements reveal that the quantum yield of IR800 is enhanced from approximately 7% as an isolated fluorophore to 86% in a NSs-HSA-IR800 complex and 74% in a NRs-HSA-IR800 complex. This dramatic increase in fluorescence shows tremendous potential for contrast enhancement in fluorescence-based bioimaging.

With clinical trials for photothermal tumor ablation using laser-excited tunable plasmonic nanoparticles already underway, increasing understanding of the efficacy of plasmonic nanoparticle-based photothermal heating takes on increased urgency. Here we report a comparative study of the photothermal transduction efficiency of SiO 2 /Au nanoshells, Au 2 S/Au nanoshells, and Au nanorods, directly relevant to applications that rely on the photothermal response of plasmonic nanoparticles. We compare the experimental photothermal transduction efficiencies with the theoretical absorption efficiencies for each nanoparticle type. Our analysis assumes a distribution of randomly oriented nanorods, as would occur naturally in the tumor vasculature. In our study, photothermal transduction efficiencies differed by a factor of 3 or less between the different types of nanoparticle studied. Both experiment and theory show that particle size plays a dominant role in determining transduction efficiency, with larger particles more efficient for both absorption and scattering, enabling simultaneous photothermal heating and bioimaging contrast enhancement.

The large optical cross sections of metallic nanoparticles at wavelengths corresponding to their plasmon resonance make them highly attractive for harvesting solar energy for a variety of applications. Here the authors determine ideal distributions of spherical metallic nanoparticles, both nanospheres and nanoshells, that match the AM 1.5 solar spectrum in a mixed component, submonolayer geometry. Both absorbing and scattering distributions are determined and their properties compared to conventional broad spectrum absorbing and scattering media.