A novel sensing layer based on metal–organic framework UiO-66 modified with TiO 2–graphene oxide: application to rapid, sensitive and simultaneous determination of paraoxon and chlorpyrifos.

In this paper, a novel enzymeless electrochemical sensor with high sensitivity was constructed based on TiO2 functionalized graphene oxide@UiO-66 (TGO@UiO-66) for simultaneous detection of paraoxon and chlorpyrifos. TGO@UiO-66 for electrode modification possesses good conductivity and a distinctive structure, which promotes the electron transfer rate and improves the efficiency of electrochemical sensors. In this work, a TGO@UiO-66 modified glassy carbon electrode (TGO@UiO-66/GCE) was used for simultaneous determination of paraoxon and chlorpyrifos. The square wave voltammogram of TGO@UiO-66/GCE in the presence of paraoxon and chlorpyrifos showed two characteristic cathodic peaks at 0.45 and 1.3 V (vs. Ag/AgCl). Also, excellent electrochemical characteristics of the proposed sensor were evidenced by impedance and cyclic voltammetry studies in a Fe(CN)6 4/3 solution. Different experimental parameters such as the type of electrolyte, pH of the electrolyte, and scan rate were optimized, and calibration curves were plotted under the optimal conditions. The designed sensor exhibited low detection limits of 0.2 and 1.0 nM within the linear ranges of 1.0–100.0 nM and 5.0–300.0 nM for paraoxon and chlorpyrifos, respectively. The developed sensor was successfully applied to pesticide residue monitoring in vegetable and water samples.