  In this letter, we report a chemical route for synthesizing SiO2@Au
core-shell nanoparticles. The process includes four steps: i) preparation of
the silica cores, ii) grafting gold nanoparticles over SiO2 cores, iii) priming
of the silica-coated gold nanoparticles with 2 and 10 nm gold colloids and
finally iv) formation of complete shell. The optical extinction spectra were
experimentally measured and compared to numerical calculations in order to
confirm the dimensions deduced from SEM images. Finally, the potential of such
core-shell nanoparticles for biosensing was probed by means of Surface Enhanced
Raman Scattering measurements and revealed higher sensitivities with much lower
gold quantity of such core-shell nanoparticles compared to Au nanoparticles
exhibiting similar diameters.
