Abstract
A SERS-active structure is disclosed. A SERS-active structure comprises a substrate, at least one metal nanoparticle, a dielectric layer and a metal nanolayer. The metal nanoparticles are disposed on the substrate. The substrate and the metal nanoparticles are covered by the dielectric layer, so that the dielectric layer forms a recessed portion. The dielectric layer is covered by the metal nanolayer and the metal nanolayer has a nanogap located at the recessed portion.