This study reports facile synthesis of monometallic and bimetallic core–shell nanoparticles using ascorbic acid as reducing agent. Monometallic silver nanoparticles (AgNP–CTAB–NA) with a bilayer of cationic surfactant, cetyltrimethylammonium bromide (CTAB) supported by n-nonylamine (NA) were first synthesized. Bimetallic core–shell nanoparticles, AgNP@Au–CTAB–NA, were synthesized using AgNP–CTAB–NA as precursor. We characterize AgNP–CTAB–NA and AgNP@Au–CTAB–NA colloids by proton nuclear magnetic resonance (¹H NMR) spectroscopy, UV-visible spectroscopy, Fourier transform infrared (FTIR) spectroscopy, dynamic light scattering (DLS), high-resolution transmission electron microscopy (HR-TEM) and energy dispersive X-ray (EDX) line analysis. We demonstrate that both AgNP–CTAB–NA and AgNP@Au–CTAB–NA colloids are excellent surface enhanced Raman scattering (SERS) substrates for Raman active analyte molecules at sub-micromolar concentrations.