Silver coated gold nanoparticles as new surface enhanced Raman substrate at low analyte concentration

Stable silver coated gold hydrosols, with particle size varying from 12 - 200 nm, were prepared and tested as a substrate for surface enhanced Raman scattering (SERS). Nanoparticles containing a 12 nm gold core and coated with a silver shell varying from 0 - 100 nm were prepared. It is shown that SERS sensitivity depends on the Ag shell thickness and nanoparticle size. The optimum particle size for SERS was found to be between 25 - 50 nm. These particles can detect 5 x 10(-11) mol dm(-3) 4-mercaptopyridine and 5 x 10(-10) mol dm(-3) rhodamine 6G.