Multimetallic graphene-coated THz metasurface biosensor for high-sensitivity hCG detection in pregnancy testing: A simulation study
K. Vijayakumar, S. Subha, N. K. Anushkannan, Kumaravel Kaliaperumal, U. Arun Kumar
Abstract
Conventional pregnancy testing methods face significant limitations including low sensitivity, cross-reactivity issues, and requirement for sophisticated laboratory equipment, particularly in resource-limited settings. This research introduces an innovative terahertz (THz) biosensor using a graphene-metallic hybrid metasurface architecture to improve pregnancy detection by optical sensing of human chorionic gonadotropin (hCG) indicators. The sensor demonstrates remarkable performance with a maximum sensitivity of 1000 GHz/RIU achieved at the optimal resonant frequency of 0.309 THz within the 0.1–0.55 THz frequency band, corresponding to a refractive index of 1.343 RIU. The frequency-dependent sensitivity analysis reveals that the maximum sensitivity of 1000 GHz/RIU is achieved at 0.309 THz, where the electromagnetic field enhancement reaches its peak value. This optimal operating point corresponds to the fundamental resonance mode of the hybrid metasurface structure, where the coupling between the central graphene resonator and the surrounding metallic rings creates the strongest field localization. The sensitivity decreases progressively at frequencies away from this resonant peak, with values of 500 GHz/RIU at 0.310 THz and 200 GHz/RIU at 0.311 THz, demonstrating the critical importance of precise frequency tuning for optimal sensor performance. Comparative analysis shows competitive or superior performance against existing biosensor designs, offering significant potential for point-of-care pregnancy testing applications with enhanced sensitivity, real-time detection capability, and reduced sample preparation requirements. • Graphene-coated circular THz resonator with four multimetallic rings enhances plasmonic sensing response. • Achieves 1000 GHz/RIU sensitivity and high figure of merit of 40 RIU −1 for superior detection performance. • Strong linear R² = 0.88947 correlation ensures accurate refractive index sensing with reliable frequency shifts. • Low detection limit of 0.0373 RIU with stable resonance linewidth (FWHM = 0.0250 THz) enables precision sensing. • Practical for portable, point-of-care pregnancy tests; validated via EM modeling and graphene Kubo conductivity.