High-Performance All-Dielectric Metasurface for Quadruple Fano Resonance-Induced Biosensing Applications in the Near-Infrared Range

In this article, an all-dielectric metasurface comprised of asymmetric dimers in the near-infrared range is presented, and a comprehensive analysis of the quadruple Fano resonances based on the theory of bound states in the continuum (BIC) is conducted. The electromagnetic field distribution and transmission spectral profile are simulated and investigated using the finite-difference time-domain (FDTD) method. Theoretical analysis of the electromagnetic distribution properties at the resonance wavelengths shows that the four Fano resonances are induced by toroidal dipole (TD), electric quadrupole (EQ), and magnetic dipole (MD), respectively. In terms of the transmission spectrum, we systematically investigate the spectral characteristics of the proposed structure under different parameters. The flexibility to control the Fano resonances is demonstrated by adjusting the geometric parameters of the structure. Furthermore, we find that the Fano resonances are sensitive to the surrounding refractive index (RI), the temperature, and the polarization direction of the incident light. Thus, the structure exhibits broad application potential in RI sensing, temperature sensing, and bidirectional optical switches. Numerical results show remarkable performance in the RI sensor, with a maximum sensitivity ( ${S}{)}$ of 508 nm/RIU, a figure of merit (FOM) of 6771 RIU $^{-{1}}$ , and an extraordinarily high ${Q}$ factor of 19474. The temperature sensor achieves a sensitivity of 34 pm/°C. In addition, the bidirectional optical switch can be realized by adjusting the polarization direction of the incident light. The suggested metasurface offers new possibilities for designing and optimizing high-performance sensors in the field of biomedical applications.