All-dielectric core/shell resonators: From plasmon-free SERS to multimodal analysis

All-dielectric materials are emerging as a new class of substrates for enhanced Raman scattering. As ohmic losses are reduced in the absence of plasmonic metals, Raman data obtained with dielectrics are very reproducible and reliable. This mini-review summarizes our recent work in the field of core/shell dielectric resonators designed for Raman purposes, with a special focus on SiO2/TiO2 (T-rex) core/shell beads. These systems are able to exploit the evanescent field generated by total internal reflection and multiple scattering of light at the sphere-to-sphere interface to multiply the number of Raman photons, improving the sensitivity of Raman detection and extending the application of surface enhanced Raman scattering for investigating surface chemical reactions. Examples of the application of T-Rex beads in detecting and monitoring environmental pollutants, greenhouse gases, biochemical species, and biochemical reactions are presented. The use of core/shell resonators for multimodal analysis based on the combination of surface enhanced Raman scattering with either mass spectrometry or refractive index optical sensing is also discussed, suggesting different possible future developments