Nanoscale Control of Near-Infrared Fluorescence Enhancement Using Au Nanoshells

A study was conducted to investigate the fluorescence enhancement of Indocyanine Green (ICG) molecules, as a function of distance from the surface of Au nanoshells (Au-NS). The distance between ICG molecules and the Au-NS surface was controlled, by varying the thickness of silica shell spacer layers grown on the nanoshell surface. It was observed that a fluorescence enhancement of 50×, when ICG molecules are spaced 7 nm from the Au nanoshell surface, which decreases with increasing distance of the molecule from the nanoshell surface. It was found that Au nanoshells are excellent plasmonic nanostructures for these investigations for a number of reasons. One of the reasons is that their plasmon resonances can be controllably tuned across the visible and infrared region of the spectrum by modification of their core and shell dimensions.