Dual-Band Terahertz Toroidal Metamaterial Biosensor for Detection of Bovine Serum Albumin (BSA) With Ultrahigh Sensitivity

The terahertz (THz) metamaterial sensor represents an innovative technology designed to achieve superior sensitivity for trace detection by combining the advantages of THz spectroscopy and metamaterials. Specially, the THz metamaterial sensors based on toroidal dipole resonances effectively reduce the radiative loss, making them highly promising for sensing applications. In this study, we propose a novel dual-band toroidal metamaterial consisting of an array of two sets of three strips, which induce strong field confinement between the metal strips. The electric field analysis at the resonant frequencies and the scattered power distributions of multipoles illustrate the generation of the toroidal dipole and enhanced sensing performance. Furthermore, the proposed dual-band toroidal metamaterial sensor exhibits high sensitivity to environmental perturbations, reaching up to 58 GHz/RIU at mode I and 71 GHz/RIU at mode II under a 100 nm coating analyte thickness, outperforming the sensitivity of metal-insulator-metal (MIM) metamaterial. In addition, the metamaterial sample is fabricated using a maskless laser direct write lithography system, and its resonant spectra are measured using THz time-domain spectroscopy (THz-TDS). The sensing performance of the proposed dual-band toroidal metamaterial sensor is experimentally demonstrated through detecting SiO2 layers with varying thicknesses, with results showing strong agreement with simulations. Furthermore, the proposed sensor is utilized for detecting bovine serum albumin (BSA) concentrations in the range of 0.1– $100~\mu $ g/mL with a limit of detection (LOD) of 5.4 pg/mL for mode I and 3.4 pg/mL for mode II. The proposed dual-band metamaterial sensor provides a powerful approach for THz sensing, significantly improving biosensing sensitivity.