Fluorescence enhancement by hollow plasmonic assembly and its biosensing application.

We have observed the enhanced surface plasmon-coupled emission (SPCE) by introducing a hollow plasmonic structure. By assembling gold nanoshells (GNSs) on a gold substrate via electrostatic adsorption and subsequently applying a fluorophore layer (approximately 30 nm) by spin-coating, SPCE fluorescence signals exhibited 30- and 110-fold enhancements compared to those of normal SPCE and free space emission, respectively. This enhancement was mainly induced by the novel "hot-spot" plasmonic structure that emerged between the GNS and gold substrate, the intense electromagnetic field of GNSs, and the strong coupling interactions between fluorescence and surface plasmons. After optimizing the conditions, we demonstrated that this GNS-enhanced SPCE system was suitable for biomolecule detection because of the scale match between the optimal fluorophore thickness and the biomolecule size, and thus was designed as an immunosensor to verify the feasibility of this system. Our strategy of combining GNSs and SPCE to enhance the fluorescence signal created a new fluorescence system based on a hollow plasmonic structure and provided a simple way to improve the detection sensitivity in fluorescence-based sensing and imaging platforms.