Resonant metasurfaces for spectroscopic detection: Physics and biomedical applications

The review firstly describes two keys to enhance the sensing detection of target analytes with geometries much smaller than the operating wavelength from the perspective of physical mechanisms, i.e., exploring the relevant physical mechanisms and employing an optimized photonic structure design for effective electromagnetic modulation of light-target analyte interactions. Several typical electromagnetic modes of equipartitioned excitonic/medium micro- and nanostructures are briefly described, including the physical connotations of the mechanisms of surface plasmon resonance, Fano resonance, surface lattice resonance, and bound states in the continuous domain. In terms of applications, different superstructured surfaces (plasmonic/dielectric/hybrid superstructured surfaces) are reviewed for various high-performance biomedical sensing and even imaging applications, including refractive index sensing, surface Raman-enhanced scattering, surface-enhanced infrared absorption and chiral sensing. It is summarized that from the ultraviolet to mid-infrared wavelengths, the spectroscopic detection system based on the superstructured surfaces has demonstrated superior detection performance for liquid biopsies (including nucleic acids, biomarkers, proteins, cytokines, extracellular vesicles, and pathogens, etc.), biopsies of tissue slices (cells, etc.), small molecules of pharmaceuticals, and gases in the experiments. Finally, the current challenges and future development trends of superstructured surfaces in spectroscopic detection are summarized and outlooked, including spectroscopic detection devices based on novel optical mechanisms/surface functionalization, dynamically tunable or reconfigurable, and smart wearable or implantable. Based on the emerging work on spectroscopic detection of these superstructured surfaces mentioned above, this review provides a prospective outlook on their future directions in terms of principles and applications.