Plasmonic Resonant Cavity Provides a Flexible Substrate for Surface-Enhanced Raman Spectroscopy Detection in a Wide Band Range

Surface-enhanced Raman spectroscopy (SERS) has been broadly investigated for biological detection because of its high sensitivity and excellent selectivity. Many nanostructures with different morphologies and sizes were designed for SERS application based on the electromagnetic enhancement mechanism. For most of the nanostructures, the location of the detected molecules is strictly restricted to the surface of the nanoparticles. SERS substrates with a resonant cavity structure soften this requirement. Here, we propose a structure composed of Ag nanocubes and a gold film with spacing and analyze its electromagnetic field enhancement characteristics. This structure exhibits a large increase in the intensity of the electromagnetic field in the visible and near-infrared excitation, while the spacing varies within a range. This allows for the use of the SERS technique even when the thickness of the sample could not be precisely controlled. Additionally, the uniform enhancement field within the optical resonance cavity enables the analysis of a mixture of biological samples.