High-sensitivity polarization-independent terahertz Taichi-like micro-ring sensors based on toroidal dipole resonance for concentration detection of A beta protein

Terahertz (THz) metamaterial sensor is a newly-developing interdisciplinary technology, which combines the essential characteristics of THz spectroscopy and meta-materials, to obtain better sensitivity for trace detection of the different target analytes. Toroidal dipole resonances show great sensing potential due to their suppression of the radiative loss channel. Here, we found a high-quality planar toroidal dipole resonance in the breaking Chinese Taichi-like ring and then designed a novel polarization-independent terahertz toroidal sensor by combining four Taichi-like rings into a cycle unit. The sensor shows high-sensitivity sensing characteristics for the ultrathin analyte and refractive index. The optimized sensitivity of pure analytes under 4 mu m coating thickness can numerically reach 258 GHz/RIU in the corresponding similar to 1.345 THz freque-ncy domain, which is much higher than that of previously reported sensors. We further fabricated experimentally the sensor and demonstrated its fascinating polarization-independent characteristics. Finally, it was successfully applied to the low-concentration detection (ranging from 0.0001 mg/mL to 10 mg/mL) of A(3 protein associated with Alzheimer's disease. Our high-sensitivity polarization-independent THz toroidal dipole sensor would give access to rich applications in label-free biosensing.