Integrating smartphone-assisted ratiometric fluorescent sensors with in situ hydrogel extraction for visual detection of organophosphorus pesticides

Rapid, reliable and on-site detection of organophosphorus pesticides (OPs) on fruit or vegetable surfaces is necessary in real life. Here, a smartphone-assisted ratiometric fluorescent sensor integrated with in situ hydrogel extraction was developed for the visual detection of OPs. Carbon dots (CDs) with dual emission at 450 and 675 nm under 365 nm excitation were synthesized. OPs can inhibit acetylcholinesterase to suppress the production of thiocholine (binding with Ag+). Then, free Ag+ oxidizes o-phenylenediamine to 2,3-diaminophenazine (Abs. maximum at 420 nm, Em. maximum at 560 nm), which quenches CD emission at 450 nm to construct a ratiometric sensor for OPs. In particular, for real sample detection, OPs rapidly diffused into surface deposited sodium alginate (SA) solution and were then extracted by an in situ formed SA hydrogel network. After that, the released OPs were visually detected using a smartphone-assisted platform. The fluorescent images presented a distinct color variation from blue to orange with a wide linear range from 1.2 to 57.0 mu g L-1 and a low limit of detection at 0.50 mu g L-1 for parathion-methyl, a model sample of OPs. The facileness, high sensitivity and nondestructive technology for OP measurement provided new insight into food safety evaluation.