Facile preparation of ultra stable polymer-based sensor for highly sensitive and selective detection of paraquat in agricultural products

Electrochemical sensor has gained ever-increasing attention in screening residues in food samples for its rapid response and portability, which, however, is strongly obstructed by the poor stability and fouling effect derived from electrode materials. Herein, a novel polymer-based nanocomposite, namely Nafion co-modified with highly conductive graphene and multiwalled carbon nanotubes (Nf-Gr-MWCNTs-COOH), was developed for paraquat (PQ) detection via a facile sonication assisted preparation strategy. Electrochemical and physical characterizations together with theory calculation revealed that the conductivity and surface area of Nafion which has specific redox response to PQ were greatly enhanced by Gr-MWCNTs-COOH. Meanwhile, Nafion increased the dispersion and stability of Gr-MWCNTs-COOH. Therefore, the Nafion-based nanocomposite presented excellent sensitivity and stable output signal in PQ detection after coating on the glass carbon electrode. Under optimized conditions, the sensor displayed a wide linearity (0.01 – 15 μmol·L -1 ) and a very low limit of detection (0.005 μmol·L -1 ). Additionally, the sensor showed excellent repeatability, reproducibility and long-term stability thanks to the inherent high stability and antifouling properties of Nf-Gr-MWCNTs-COOH. The practical application of the developed sensor was evaluated by detection of PQ in real food samples including black tea, lettuce, and corn. Satisfactory recoveries, ranging from 95.00 % to 101.7 % with RSDs from 0.30 % to 3.0 %, were obtained. The high accuracy and excellent stability of the proposed sensor suggest its highly promising in commercial use.