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Sensing Microcystin-LR (MC-LR) is an important issue for environmental monitoring, as the MC-LR is a common toxic pollutant found in freshwater bodies. The demand for sensitive detection method of MC-LR at low concentrations can be addressed by metasurface-based sensors, which are feasible and highly efficient. Here, we demonstrate an all-dielectric metasurface for sensing MC-LR. Its working principle is based on quasi-bound states in the continuum mode (QBIC), and it manifests a high-quality factor and high sensitivity. The dielectric metasurface can detect a small change in the refractive index of the surrounding environment with a quality factor of ~170 and a sensitivity of ~788 nm/RIU. MC-LR can be specifically identified in mixed water with a concentration limit of as low as 0.002 μg/L by a specific recognition technique for combined antigen and antibody. Furthermore, the demonstrated detection of MC-LR can be extended to the identification and monitoring of other analytes, such as viruses, and the designed dielectric metasurface can serve as a monitor platform with high sensitivity and high specific recognition capability.

The ability to trap light in an ultrathin photoactive layer has been of great significance for applications ranging from optoelectronics, energy to spectroscopy. However, the current broadband light trapping suffers from undesirable direct Joule heat output with plasmonics or bulkiness with photonics. Here, we report a light-trapping photonic structure using an ultrathin all-dielectric super-absorbing metasurface. This presented photonic structure features asymmetrically coupled magnetic resonances, which eliminate reflection and transmission simultaneously by introducing destructive interference between the backscattered field of the resonance and the direct reflected field of the highly reflective Fabry–Perot background. In particular, this photonic structure enables broadband light trapping by placing nanostructures of different sizes in a supercell. As a proof of concept, we experimentally demonstrate broadband (550–1280 nm) super absorption (>50%) within an ultrathin (∼200 nm) all-dielectric germanium metasurface. This work provides a design paradigm for harvesting light through flat photonic structures at the nanoscale and paves the way for cost-effective light management.