Smartphone-assisted visual detection of carbaryl in fruit peels based on MnO₂@g-C₃N₄ nanozyme with enhanced...

In present work, MnO₂@g-C₃N₄ nanozyme was synthesized via a calcination-hydrothermal two-step method to achieve enhanced oxidase-like activity based on the conception of electron transfer regulation and effectively loading for avoiding agglomeration to expose more active sites. Herein, g-C₃N₄ served as a dispersing substrate for MnO₂ with oxidase-like activity and regulating the interfacial electron transfer, and their synergistical catalytic effect accelerated the conversion of dissolved oxygen to superoxide anion radicals (•O₂^-), which oxidized 3,3',5,5'-tetramethylbenzidine (TMB) to blue products. Carbaryl can be adsorbed on g-C₃N₄ surface through π-π stacking interactions, while its carbamate group can be bound to the active centers of MnO₂. By Lineweaver-Burk plot method, the steady-state kinetic analysis showed that carbaryl had a mixed inhibitory effect on electron transfer and the production of superoxide anion radical (•O₂^-). Based on this principle, a smartphone-based colorimetric sensor was constructed for carbaryl detection, which exhibited a linear response in the range of 6.3-210.2 μM, with a detection limit of 3.79 μM and a quantitation limit of 12.64 μM. The method achieved satisfactory recoveries (94.3-107.5%) for spiked fruit peel samples and owned great application prospect.