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

Dispersed loading of MnO 2 on g-C 3 N 4 resulted in enhanced oxidase-like activity. • MnO 2 @g-C 3 N 4 nanozyme exhibited excellent selectivity to carbaryl • Target nanozyme showed good anti-interference ability • Smartphone-assisted visual detection achieved good sensitivity and reliability. In present work, MnO 2 @g-C 3 N 4 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-C 3 N 4 served as a dispersing substrate for MnO 2 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 (•O 2 − ), which oxidized 3,3′,5,5′-tetramethylbenzidine (TMB) to blue products. Carbaryl can be adsorbed on g-C 3 N 4 surface through π-π stacking interactions, while its carbamate group can be bound to the active centers of MnO 2 . 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 (•O 2 − ). 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.