TOPAS-based terahertz fiber SPR biosensor enhanced by a MoS ₂ plasmonic layer

A high-sensitivity terahertz (THz) fiber-based surface plasmon resonance (SPR) biosensor is proposed and numerically investigated. The sensor employs a TOPAS microstructured optical fiber with an open-ring sensing channel and a molybdenum disulfide (MoS 2 ) excitation layer to enhance surface plasmon polariton (SPP) excitation and electromagnetic field confinement. The sensing mechanism based on phase matching between the guided core mode and the SPP mode is systematically analyzed. The finite element method (FEM) is employed to optimize the key structural parameters, including the residual cladding thickness (490 µm), open ring cavity radius (100 µm), MoS 2 excitation layer thickness (10 µm), and large and small cladding air hole diameters (210 µm and 157.5 µm). The proposed sensor operates over a biologically relevant refractive index range of 1.33-1.45, enabling detection of a wide variety of biomolecules. An ultra-high maximum wavelength sensitivity of 86,000 nm/RIU and an average sensitivity of 79,917 nm/RIU are achieved, along with a high refractive index resolution of 1.16 × 10 −6 RIU. In addition, fabrication tolerance analysis confirms the robustness and stability of the sensor design. These results demonstrate that the proposed terahertz fiber-based SPR sensor provides a highly sensitive, nondestructive, and practical platform for real-time biosensing applications.