Magnetic toroidal dipole resonance terahertz wave biosensor based on all-silicon metasurface

Optical sensing is crucial in many applications and has received widespread attention in recent years. Transmission spectroscopy with narrow linewidth resonances is indispensable for improving metasurface sensing performance. However, the narrower linewidth results in a smaller resonant modulation range, which seriously hinders the application of metasurfaces in sensing detection. We designed an all-silicon metasurface sensor. The structural layer of the metasurface works together with the substrate layer. Multiple magnetic ring dipoles are generated in the structural layer and multiple magnetic dipoles are generated in the substrate layer. The two work together to stimulate sharp Fano resonance, with a quality factor of up to 272.84. Based on the characteristics of metasurface, when applied to sensing and detection, the theoretical sensitivity can reach 59.64 GHz/RIU. Metasurface samples were successfully prepared using photolithography and dry etching. After characterizing the transmission spectrum of the prepared metasurface, the actual quality factor reached 76.8. At the same time, the metasurface sensor was used to detect bovine serum albumin (BSA) solutions of different concentrations. Based on the test results, it is calculated that the detection limit of the metasurface sensor for detecting BSA can reach 0.027 mg/mL, and the detection sensitivity can reach 9.7 GHz/(ng/mm2). The results of theoretical simulation and biological experiments show that the sensor has good sensing performance. This work is of great significance to the research of all-silicon metasurfaces and the application of metasurface sensors.