Optical metasurfaces are planar metamaterials that can mediate highly precise light−matter interactions. Because of their unique optical properties, both plasmonic and dielectric metasurfaces have found common use in sensing applications, enabling label-free, nondestructive, and miniaturized sensors with ultralow limits of detection. However, because bare metasurfaces inherently lack target specificity, their applications have driven the development of surface modification techniques that provide selectivity. Both chemical functionalization and physical texturing methodologies can modify and enhance metasurface properties by selectively capturing analytes at the surface and altering the transduction of light− matter interactions into optical signals. This review summarizes recent advances in materialspecific surface functionalization and texturing as applied to representative optical metasurfaces. We also present an overview of the underlying chemistry driving functionalization and texturing processes, including detailed directions for their broad implementation. Overall, this review provides a concise and centralized guide for the modification of metasurfaces with a focus toward sensing applications.

The development of nanoscale optical sensors is desirable for a broad range of applications, including wearable medical‐diagnostics, biochemical detection, and environmental monitoring. Optical detection platforms based on resonant nanostructures are the golden standard for miniaturized footprint and high optical sensitivity. These sensors function by measuring a shift in resonance wavelength upon binding of analytes to their surface. However, such measurements are sensitive to intensity fluctuations of the illuminating source and its wavelength calibration, which limits their applicability. Here, a novel optical sensing concept based on diffraction measurements from resonant dielectric metagratings is proposed and experimentally demonstrated. It is shown that this approach enables the direct measurement of unknown analytes with enhanced sensitivity and without the need for intensity calibrations. The intensified sensitivity of this metagrating‐sensor is derived from combining the resonant phenomena of the nanostructures with the tailored diffraction from the metagrating, thereby providing the highest sensitivity demonstrated to date amongst grating‐based sensors. As a proof of concept, the metagrating‐sensor was validated using an antibody binding assay, achieving a femtomolar‐level limit of detection. Due to their high sensitivity and robust performance, the proposed metagrating sensors pave the way for novel miniaturized medical diagnostics and biosensing applications.

Metamaterials are engineered structures designed to interact with electromagnetic radiation, whereby the frequency range in which metamaterials respond depends on their dimensions. In this paper, it is demonstrated that a metamaterial can be functional in more than one frequency region. An advanced metamaterial is demonstrated that can interact with both terahertz (THz) and near‐infrared (NIR) frequencies, concurrently. This work exploits meander line resonators with nanoscale linewidth distributed over microscale areas, and experimentally demonstrates that such a metamaterial can simultaneously interact with NIR and THz waves. The engineered metamaterial acts as a plasmonic grating in the NIR range and simultaneously acts as an array of electric resonators in the THz range. Moreover, the performance of the engineered metamaterial is polarization‐independent in both wavelength regions. Finally, a unique feature of the proposed metamaterial is that it enables resonant frequency tuning in the THz region without affecting the NIR response. All these novel advantages of dual‐band meander metamaterial make it an ideal alternative for cutting‐edge applications such as bi‐functional sensing, imaging, filtering, modulation, and absorption.