Resonant Metasurfaces for Spectroscopic Detection: Physics and Biomedical Applications

Metasurfaces are ultrathin metamaterials consisting of subwavelength scatterers (e.g., meta-atoms) arranged in a specific sequence that generates low radiation losses and fantastic optical resonances. According to the electromagnetic response properties, metasurfaces can be divided into two categories: metallic nanostructures based on the response of plasmonic excitations (e.g., noble metals and graphene) and all-dielectric nanostructures based on near-field scattering (e.g., Mie scattering). Metasurfaces supporting various optical modes possess optical localization and electromagnetic field enhancement capabilities on the subwavelength scale, making them a promising platform for label-free detection in biomedical sensing. Metasurface-based optical sensors offer several outstanding advantages over conventional spectroscopic detection solutions, such as planar structures, low loss, miniaturization, and integration. Recently, novel sensing and even imaging tools based on metasurfaces have widely loomed and been proposed. Given recent advances in the field of metasurface spectroscopic detection, this review briefly summarizes the main resonance mechanisms of metasurfaces and the notable achievements, including refractive index sensing, surface-enhanced Raman scattering, surface-enhanced infrared absorption, and chiral sensing in the ultraviolet to terahertz wavelengths. Ultimately, we draw a summary of the current challenges of metasurface spectroscopic detection and look forward to future directions for improving these techniques. As the subject is broad and growing, our review will not be comprehensive. Nevertheless, we will endeavor to describe the main research in this area and assess some of the relevant literature.