Cu-C3N4 nanoenzyme-based freezing-dried bioactive capsule integrated with 3D-printed smartphone platform for visual detection of organophosphorus pesticides paraoxon in scallion

Rapid detection of pesticide residues in vegetables has recently attracted much attention. Herein, a Cu-modified graphitic carbon nitride nanomaterial (Cu-C 3 N 4 ) with peroxidase (POD)-like property was synthesized to construct an enzyme-based colorimetric sensing platform for the detection of organophosphorus pesticides paraoxon . Cu-C 3 N 4 could catalyze H 2 O 2 produced by reaction of acetylcholine with acetylcholinesterase and choline oxidase, and then further oxidized 3,3,5,5-tetramethylbenzidine (TMB) to produce a blue colored product. Presence of organophosphorus pesticide paraoxon (PA) restrained the activity of acetylcholinesterase AChE, triggering a remarkably decreased amount of H 2 O 2 towards TMB oxidation, which led to the inhibition of oxidation reaction. After that, the reaction solutions were freeze-dried in a portable bioactive capsule with addition of trehalose as stabilizer for improved enzymes activities . On the basis of the variation in gray-scale values of blue colored TMB solutions using an application, a smartphone-based 3D printing platform was obtained with a linear range from 100 to 33,000 nM (R 2 =   0.994) and a detection limit of 13 nM (3 σ/k ). This smartphone-based 3D-printed colorimetric platform combined with a bioactive capsule offers a novel approach with the potential for rapid detection of PA in vegetables.