Metallic nanostructures exhibit unique plasmonic properties when optically excited, which includes modification of the spontaneous emission and lifetime of fluorophores in their vicinity. Here we utilize silica (SiO2) core encapsulated in gold (Au) shell nanoshells for emission enhancement of weak near-infrared (NIR) emitting fluorophores, including Indocyanine green (ICG) and IR800. The fluorescence enhancement of ICG molecules as a function of distance from the surface of nanoshells was studied. A maximum enhancement of 50X at a distance of 7 nm from the nanoshells surface, and minimum enhancement of 7X at 42 nm from nanoshells surface was achieved. Additionally, fluorescence enhancement of IR800 molecules induced by nanoshells was compared with that of Au nanorods. The quantum yield of IR800 was enhanced from 7% to 86% in the case of nanoshells and 74 % for nanorods. The native lifetime of IR800 decreased from 564 ps to 121 ps when conjugated to nanorods and 68 ps for nanoshells.
We then demonstrated a biomedical application of plasmon enhanced fluorescence sensing by utilizing nanoshell based complexes (nanocomplexes) for simultaneous fluorescence optical imaging as well as magnetic resonance imaging of cancer cells in vitro and in vivo. Nanocomplexes were fabricated by encapsulating nanoshells with a SiO2 epilayer doped with iron oxide nanoparticles and ICG molecules, which resulted in a high T2 relaxivity (390 mM-1sec-1) and 45X fluorescence enhancement of ICG. The nanocomplexes were covalently conjugated with antibodies to enable active targeting in vitro and in vivo. In addition they were utilized for photothermal therapy of cancer cells in vitro.
Furthermore, other plasmonic nanostructures relevant for biomedical applications were also synthesized in the sub-100 nm regime including Au/SiO2/Au nanoshells and cuprous oxide core coated with Au shell nanoshells. Excellent agreement between their experimental and theoretical optical properties was achieved. Additionally, physical and chemical properties of mesostructures relevant for photonic devices including sub-micrometer zinc oxide structures and Mesostars composed of a mixture of iron oxides and Au were also studied
