Ag nanoparticles synthesized on porous silicon samples were studied and applied as substrates for surface-enhanced Raman scattering (SERS). The metallic nanostructures prepared by immersion plating were characterized by UV–Vis reflectance spectroscopy and scanning electron microscopy. SERS activity of the substrates was tested using Cyanine dye 1,3,3,1′,3′,3′-esamethyl-5,5′-dimethoxyindodicarbocyanine iodide (Cy5-OCH3) as a probe molecule. The Raman spectra obtained for different excitation wavelengths indicate amplifications ascribed to plasmonic resonances with an enhancement factor up to 107. CGIYRLRS peptides were chemisorbed on the Ag nanoparticles with the plasmonic resonance tuned at the excitation energy. Such oligopeptides were used as baits for a specific polyclonal antibody. The overall Raman enhancement allowed to evidence a good selectivity to the target analyte as required by most of the SERS applications on biological assays. Copyright © 2011 John Wiley & Sons, Ltd.