A nano-enhanced Raman scattering (NERS)-active structure includes a substrate, a monolayer of nanoparticles disposed on a surface of the substrate, and a spacer material surrounding each nanoparticle in the monolayer of nanoparticles. The monolayer of nanoparticles includes a first plurality of nanoparticles and a second plurality of nanoparticles. The nanoparticles of the second plurality are interspersed among the first plurality and exhibit a plasmon frequency that differs from any plasmon frequency exhibited by the first plurality. Also described are a method for forming such a NERS-active structure and a NERS system that includes a NERS-active structure, an excitation radiation source, and a detector for detecting Raman scattered radiation.