Terahertz metasurface sensor with graphene microstrips for biosensing: Modeling and application

The present numerical study is devoted to development and optimization of a metasurface-based sensor with graphene constituents for potential biosensing applications. A unit cell of the proposed metasurface consists of a thin flexible dielectric substrate layer with a centrally positioned graphene microstrip. As a result of numerical modeling of spectral properties of the metasurface by COMSOL Multiphysics software in terahertz range from 5 to 35 THz the absorption spectrum maxima (resonance modes) at f1 = 8.7 THz and f2 = 26.5 THz are revealed. Structural parameters of the developed metasurface with graphene microstrips have been tuned to achieve the optimal resonance properties. The following stages of the study demonstrate that placement of a layer of tested liquid sample [water or bovine serum albumin (BSA) solution] on the metasurface causes a low-frequency shift of the plasmonic resonance mode f1 chosen for biosensing measurements. This frequency shift, along with the change in the amplitude of the absorption peak, are highly sensitive to the refractive index of the tested liquid sample. The resonance behavior of the developed metasurface structure is governed by the excitation of localized plasmon resonance in the graphene elements and near-field electromagnetic coupling effect between the short edges of the graphene microstrips. Evaluation of the influence of dielectric substrate’s material on the sensitivity of the metasurface-based sensor to variations in BSA concentration indicates that Kapton substrate provides higher effectiveness compared with SiC substrate. The obtained results demonstrate the potential of the developed metasurface-based sensor with graphene microstrips for application as a sensing structure to determine proteins and other biomolecules in liquid samples.