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Abstract
Semiconductor-metal composite nanoparticles offer optical properties that are superior to those of pure materials. In this study, we exploit the epsilon near zero (ENZ) phenomenon using gold and silver nanoparticles functionalized with cyanine dyes, which form distinct J-aggregates on the surface of the particle. These J-aggregates show a distinct nonlinear optical response, and a wavelength matching approach was used to couple the plasmonic particle to the J-aggregate. When the appropriate wavelength is utilized, these particles showed an enhanced SERS signal as a result of the excitonic resonance of the J-aggregate species. The theoretical properties of the particles were simulated using FDTD techniques, and these were experimentally verified by varying the dye/particle distance and testing different molecular and plasmonic resonators. Experimental SERS spectra had excellent agreement with simulations. These composite particles were then encapsulated in a lipid bilayer, forming a multi-shell structure with properties suitable for biosensing and other detection applications.
