Highly Stable Luminescent Metal–Organic Frameworks for Ultrasensitive Detection of Nitroaniline Isomers: Application in In Situ Imaging of Toxic Pesticides

A powerful and promising route for developing chemically stable luminescent sensors for visible sensing of toxic pesticides in water and actual food samples is presented. Herein, a novel twofold interpenetrated luminescent metal–organic framework (MOF), Cd-TM, is prepared by incorporating 2-methyl-1H-imidazole-5-carbaldehyde as the imidazole-containing tridentate coordination linker and the luminescent organic bridging linker 4,4′,4″-tricarboxyltriphenylamine (H3tca) into a framework. Thanks to the imidazole coordination and structurally interpenetrated nature, the MOF exhibits high fluorescence stability and water stability up to 6 months. Fluorescence titration experiments reveal that Cd-TM shows rapid and ultrasensitive fluorescence response to p-nitroaniline compared with other nitroanilines with the limit of detection of about 8 nM. In particular, the Cd-TM material also shows high sensitivity to detect dicloran (DCN, 2,6-dichloro-4-nitroaniline) pesticides with the structure similar to that of p-NA. The detection limit is 7.6 nM, which is found to be superior to those of the recently reported MOF-based sensors. In addition, the detection mechanism of DCN is studied by FT-IR analysis, SEM/EDX elemental mapping, XPS, and theoretical calculations. Practically, the recoveries of spiked environmental samples were found to be satisfactory (95.8–106.4%). Further, Cd-TM is also used for the rapid in situ nondestructive imaging detection of pesticide residues in simulated fresh agricultural products. These results indicate that Cd-TM has the potential to detect organophosphorus pesticide contamination with rapid in situ imaging via easy-to-read visual signals.