SERS using nanostar-in-cavity structures

Particle in cavity nanostructures were produced by sedimentation of silver nanostars (AgNSs) onto sphere segment void (SSV) cavity structures produced by electrodeposition of gold around templates formed by assembling close packed monolayer arrays of 220 or 600 nm diameter polystyrene spheres. The resulting AgNS@SSV nanostructures were characterized by scanning electron microscopy and their performance as substrates for surface enhanced Raman spectroscopy (SERS) was examined. The enhancement factors obtained for the different structures were evaluated using benzenethiol as Raman probe, which adsorbs on Ag and Au to form a monolayer with uniform coverage, so allowing the enhancement to be quantified. Higher enhancements were obtained for the AgNSs@SSV substrates as compared with the gold SSV structures. The greatest enhancements were obtained when matching cavity and nanostar dimension so that only one nanostar could be accommodated in the cavity. The AgNS@SSV substrates were then shown to be promising substrates for the highly sensitive detection of dyes and, particularly, for the lake-pigment cochineal lake, providing useful information and novel analytical tool for application in the field of cultural heritage diagnostics and conservation.