The bimetallic core-shell nanoparticles show unique plasmonic properties and their preparations and characterizations are currently under investigation. A new type of Au core-Ag shell (Au@Ag) nanoparticles is prepared by sandwiching the chemically attached Raman reporter molecules (RRMs) and a 12-base-long oligonucleotide between the 13 nm average size core-gold nanoparticles (AuNPs) and 9 nm and 21 nm average size of Ag shell. The synthesized Au@Ag nanoparticles are tested for their surface-enhanced Raman scattering (SERS) performance. It is found that the chemical attachment of the oligonucleotides along with the RRM improved the enhancement in Raman scattering more than one order of the magnitude with the Au@Ag nanoparticles with an average 9-nm shell thickness while the Au@Ag nanoparticles with 21 nm average shell thickness have poor SERS activity. A minimum enhancement factor of 1.0 x 10(7) is estimated for the SERS active oligonucleotide-mediated Au@Ag nanoparticles. The approach may provide new routes for preparation of highly sensitive new generation of bimetallic core-shell nanoparticles.