Compact and Sensitive Terahertz Metasurface Biosensor for Phenylalanine Detection

Terahertz (THz) technology has drawn considerable attention for its applications in nondestructive biomolecule detection, but it faces challenges in biosensing at trace levels and low concentrations. Among biomolecules, phenylalanine (Phe) is an important amino acid used in pharmaceuticals, making its detection important for the medical and pharmaceutical applications. For Phe detection, we introduce a compact design featuring two squares, each with a cross etched at its center. This new sensor features a single metal layer that exhibits Fano resonance, generated by an asymmetric gap between two square patches. The proposed sensor exhibits a simulated high-Q resonance ( Q=115 ) at 1.54 THz, with a high sensitivity of 430 GHz/RIU, a figure of merit (FoM) of 32, and a high transmittance amplitude of 82%. The structure is optimized for fabrication on a quartz substrate. The performance of this compact metasurface sensor (5 × 5 × 0.1 mm³) is verified by THz time-domain spectroscopy (THz-TDS). Measurements show a Q-factor of 96, a Phe detection limit of 5 mg/mL, and a minimal sample usage of 2µ L per test. This design benefits from high sensitivity, an ultrahigh Q-factor, and compactness, representing a promising approach for high-Q, trace-level detection in biosensing applications.