Smartphone-assisted paper-based analytical device integrated with photo-responsive oxidase mimetic for colorimetric detection of carbosulfan

Given the significant harm caused by carbosulfan, the prominent characteristics of photo-responsive nanozymes and the bright prospects of paper-based analytical devices (PADs), developing a photo-responsive nanozymemediated colorimetric PAD for the convenient and accurate detection of carbosulfan is highly desired. Herein, carbon dots/graphitic carbon nitride (C-dots/g-C3N4) photo-responsive oxidase mimetic is constructed and employed in the field of colorimetric PAD for carbosulfan detection. C-dots/g-C3N4 with excellent photoresponsive oxidase-like activity is obtained by controlling the loading amounts of C-dots on g-C3N4, which can be ascribed to the enhanced visible light-harvesting ability and more efficient charge separation and transfer. Cdots/g-C3N4 is capable of catalyzing the oxidation of 3,3',5,5'-tetramethylbenzidine with noticeable color changes due to the formation of singlet oxygen and photogenerated holes. Whereas, the oxidase-like activity of Cdots/g-C3N4 is inhibited by the reductive sulfide compound derived from the hydrolysis of carbosulfan under acidic medium, thereby inhibiting the chromogenic reaction. Based on the above facts, a colorimetric PAD for carbosulfan detection is proposed. The designed PAD shows a good linear range of 5-60 mu M with a detection limit down to 2.52 mu M. Moreover, the PAD demonstrates high accuracy when detecting carbosulfan in real samples. This work may expand the applications of photo-responsive nanozymes in PADs.