Wei Song, Mengyang Cong, Pengyu Wang, Zhongquan Zhang, Junchi Ma, Jianfeng Qiu
This study proposes a graphene-enhanced quasi-bound state in the continuum (QBIC) terahertz metasurface biosensor for detecting pancreatic cancer biomarkers. An asymmetric double semi-elliptical metallic structure is employed to achieve a controllable transition from symmetry-protected BIC to radiative QBIC, and the asymmetry-induced perturbation excites coupling and hybridization among the magnetic dipole (MD), electric quadrupole (EQ), and magnetic quadrupole (MQ) modes, thereby significantly enhancing the localized electromagnetic field and light-matter interactions. Meanwhile, monolayer graphene is introduced as a functional interface; the π-π stacking interaction between biomolecules and graphene modulates the Fermi level and conductivity of graphene, thus establishing a modulation-based intensity-quantitative detection strategy that is distinct from conventional refractive-index shift readout. Operating at 1 THz, the sensor achieves a high quality-factor (Q-factor) QBIC resonance (Q = 172, FoM = 121) and an ultrahigh sensitivity of 202 GHz/RIU through structural asymmetry tuning. It successfully demonstrates trace detection of the pancreatic cancer biomarkers CEA and CA19-9, with detection limits as low as 0.05 ng/mL and 0.005 U/mL, respectively. Moreover, the monolayer graphene exhibits excellent stability in solution, and the sensor can be reused following standard rinsing and drying procedures. Under ambient conditions (25 °C, 4% relative humidity), the device shows highly repeatable measurement performance. This work provides a label-free, rapid, and non-destructive terahertz sensing platform with strong potential for biosensing and biochemical monitoring.