Silica coated gold nanoaggregates prepared by reverse microemulsion method: Dual mode probes for multiplex immunoassay using SERS and fluorescence

A kind of fluorescent dye-doped, silica-coated Au aggregates was fabricated using reverse microemulsion method, which shows both strong fluorescence and intense surface enhanced Raman scattering (SERS) signals. Such a composite nanoparticle is composed of a SERS core as silica-coated Au aggregates and a fluorescent shell as dye-doped silica shell. Being prepared through reverse microemulsion method, the SERS core exhibits a sphere shape and a uniform size. Compared with a silica-coated single Au nanoparticle, our presented SERS core shows a greatly increased SERS intensity due to the Au aggregates, which is formed by simply mixing the SERS reporters and Au nanoparticles. When being excited at different wavelengths as 515 nm and 633 nm, the fluorescence and SERS signals can be separately generated, which can avoid the disturbance from each other. In addition, the potential application of such a dual mode nanoparticle in multiplex immunoassay was also demonstrated using a sandwiched structure, where the fluorescence mode can be used for indicating the occurrence of an immune reaction, and SERS mode can further be employed for distinguishing the specific kind of bio-analyte.