Trace protein detection by graphene-integrated terahertz meta-sensor and enhanced sensitivity using gold nanoparticles-assisted.

With the rapid development of terahertz (THz) biosensing technology, the research on trace protein detection via THz metasurfaces has attracted significant attention. Here, we propose a graphene-integrated toroidal split-ring resonator (TSRR) THz meta-sensor for detecting protein at trace levels based on the Dirac property of chemical vapor deposition (CVD) graphene. The experimental results show that the designed meta-sensor can realize the detection of midkine with a 125 pg/mL limit of detection (LOD). Furthermore, benefiting from the charge accumulation generated by the local surface plasmon resonance of gold nanoparticles (AuNPs) to induce the enhancement of the local electric field of graphene, trace carcinoembryonic antigen (CEA) detection with an LOD of 10 pg/mL is achieved assisted by CEA antibody-AuNPs. The proposed meta-sensor realizes picogram-level protein detection, providing new ideas for applying metasurface-based THz sensors in biosensing.