Single-molecule detection by surface-enhanced resonance Raman scattering (SERRS) spectroscopy has been demonstrated for a variety of molecules. The detection of single molecules that do not have a resonance contribution, SERS, has been shown in the case of adenine. However, when colloidal particles isolated on planar substrates are used as the enhancing medium, the presence of anomalous signals significantly complicates the analysis of the spectra. Selection of a silver colloid that minimizes these spurious signals should improve the ultra-sensitive detection of non-resonant single molecules by SERS. A range of silver colloids, prepared by different methods, were investigated with respect to their activity and stability. Minimal anomalous signals were obtained from hydroxylamine-reduced silver colloids, which suggests that this colloid will be better for ultra-sensitive SE(R)RS experiments compared to the more common citrate- and borohydride-reduced silver colloids. Copyright © 2011 John Wiley & Sons, Ltd.