Plasmonic silica-gold core-shell nanoparticles: Interaction with organic dyes for light-induced applications

The interaction of plasmonic nanoparticles with ground- and excited states of dyes can strongly affect the fluorescence of the organic molecules, as well as the generation of reactive oxygen species (ROS). This interaction can be exploited in bioimaging and photodynamic therapy (PDT) of tumors. In this line, we prepare here gold-decorated silica nanoparticles (SiO2@Au NPs) via a novel method, which combines the synthesis of gold nuclei through reduction of a Au3+ salt, with a photochemical route driving the growth of the metallic nuclei. In this hybrid nanomaterial, the surface groups of the silica particle can potentially act as adsorption sites for the dyes in a range close to the gold nanoparticles, favoring the interaction. The ability of SiO2@Au NPs to enhance fluorescence and generation of ROS upon irradiation of riboflavin and Rose Bengal is evaluated. SiO2@Au enhance the fluorescence emission of both dyes, although through different mechanisms. The excitation of the flavin is enhanced, whereas for Rose Bengal the radiative decay rate is increased by the nanoparticles. For neither of the two dyes, SiO2@Au affect ROS generation as measured by Electron Paramagnetic Resonance (EPR) spectroscopy. However, the increase in fluorescence emission observed for both dyes demonstrates the potential application of SiO2@Au in fluorescence-sensing methods and bioimaging.