Ultrasensitive terahertz metasurface for biomolecule detection based on toroidal dipole resonance

Abstract

The presented study proposed a metasurface design with an I-shaped structure for detecting biomolecules in the terahertz (THz) region. The proposed metasurface exhibits three sharp resonance modes f1, f2, and f3 appearing in the transmittance spectra at frequencies of 3.78, 4.32, and 5.00 THz, respectively. The modes f1 and f2 correspond to Fano resonance and mode f3 represents a toroidal dipole resonance. The toroidal dipole resonance arises in the structure as the displacement currents form interconnected loops. An exceptionally high Q-factor of 14 443 is achieved for the toroidal dipole resonance. A maximum figure of merit of 838/RIU was attained when the sensing performance was examined for biomolecules with refractive indices in the range of 1.0–1.4, where RIU is refractive index unit. Additionally, the metasurface demonstrates outstanding sensitivity, with a maximum value of 2163 GHz/RIU, in terms of detecting malaria-infected red blood cells (RBCs) from healthy RBCs. The proposed biosensor holds significant potential for applications in biosensing, enabling the detection and analysis of trace amounts of biomolecules.