Portable label-free electrochemical aptasensor for sensitive detection of paraquat herbicide mediated by oxygen reduction reaction

Paraquat (PQ) is a highly toxic herbicide that has been prohibited in almost 70 countries, but remains in use worldwide. Thus, routine on-site PQ monitoring is a key mechanism to ensure safety and efficiently enforce regulations. Herein, a label-free portable electrochemical aptasensor for the detection of PQ was developed by utilizing aptamer designed to specifically recognize PQ. The aptasensor employs square-wave voltammetry (SWV) to quantify PQ binding on the aptamer-functionalized electrode surface by tracking the downstream oxygen reduction reaction. It provided a detection range spanning from 0.01 to 100.0 μg mL⁻¹ PQ with a limit of detection (LOD) of 8.9 ng mL⁻¹. Validation against spiked tap water, pomegranate juice, and orange juice revealed recovery rate performances of 75 %–130 %. The aptasensor demonstrates promising feasibility for PQ detection in real-world applications, offering remarkable portability and operational simplicity. Notably, it can operate without supplementary redox agents, requiring only sample incubation and subsequent washing steps.