Surface-enhanced Raman spectroscopy using lipid encapsulated plasmonic nanoparticles and J-aggregates to create locally enhanced electric fields

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 silver nanoparticles functionalized with a thiacyanine dye, which formed a distinct J-aggregate 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 surface-enhanced Raman spectroscopy (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 distance between the dye and particle surface. Experimental SERS spectra had excellent agreement with simulations. These composite particles were then encapsulated in a lipid bilayer, forming a multishell structure with properties suitable for biosensing and other detection applications.