Multiarchitecture-Based Plasmonic-Coupled Emission Employing Gold Nanoparticles: An Efficient Fluorescence Modulation and Biosensing Platform.

Surface plasmon-coupled emission (SPCE) is an efficient surface-enhanced fluorescence method based on the near-field coupling process of surface plasmons and fluorophores. Based on this, we developed multiple coupling structures for an SPCE system by introducing gold nanoparticles (AuNPs) with different architectures by adjusting different modification methods and configurations. By assembling AuNPs on a gold substrate through electrostatic adsorption and spin-coating, 40- and 55-fold enhancements were obtained compared to free space (FS) emission, respectively. After theoretical simulations and the optimization of experimental conditions, a novel "hot-spot" plasmonic structure, an intense electromagnetic field within the system, plasmonic properties, and the coupled process were found to be mainly responsible for the diverse enhancement effects observed. For the spin-coating deposition method, new enhancing systems with high efficiency can be easily built without complex modification. Additionally, the subsequent detection system based on the uniform modification of AuNPs through electrostatic adsorption is convenient to establish with high sensitivity and stability, which can broaden the application of SPCE in both fluorescence-based sensing and imaging. This AuNP-enhanced SPCE using an electrostatic adsorption method was designed as an immunosensor to prove feasibility.

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.