Synergistic graphene-aptamer coating on a flexible metasurface enables on-apple terahertz sensing of pesticides.

Abstract

The critical need for rapid, on-site pesticide detection has driven interest in terahertz (THz) sensing. This study presents a flexible THz metasurface functionalized with an aptamer-graphene hybrid layer for specific detection of chlorpyrifos. Graphene enriches target molecules via π-π stacking, while the aptamer ensures precise recognition. Using dual-parameter readout (transmittance and frequency shift), the sensor achieves a detection limit of 0.1 ppm for chlorpyrifos. Compared with an unmodified metasurface, ss the dual-modification strategy reduces the detection limit by two orders of magnitude and increases transmission response by more than 6-fold. The sensor shows high specificity, the response to chlorpyrifos is >3 times that of non-specific pesticides at 1000 ppm. On apple surfaces, the sensor retains ∼80% sensitivity with strong linearity (R2 > 0.92) over the concentration range of 0.1-1000 ppm. This work demonstrates the potential of THz biosensing for rapid, label-free pesticide residue detection.