Pyrene/Methoxy-Functionalized Covalent-Organic Framework as an OFF-ON Fluorescence Sensing Probe for Fluorescence/Smart Visual Detection of Cartap

Cartap, as an efficient and broad-spectrum insecticide, is susceptible to residues in aquatic ecosystems, causing adverse effects on the safety of agricultural products and human health. Herein, a covalent-organic framework (COF) (Py-DMTA-COF) was constructed through a Schiff base reaction of 4,4',4″,4‴-(pyrene-1,3,6,8-tetrayl)tetraaniline (TAPPy) and 2,5-dimethoxybenzene-1,4-dicarboxaldehyde (DMTA) for the fluorescence (FL)/smart visual detection of cartap. The p-π conjugation effect of Py-DMTA-COF was induced by methoxy functionalization, resulting in the reinforcement of interlayer interactions and promoting a highly ordered crystal structure and large specific surface area. In terms of FL performance, a photoinduced electron transfer (PET) occurs between TAPPy and DMTA, as well as strong interlayer interactions of the COF, giving rise to the quenching of the original FL emission of the TAPPy in Py-DMTA-COF (FL-OFF). Interestingly, cartap drives the FL recovery (FL-ON) of the Py-DMTA-COF by causing an energy level mismatch between TAPPY and DMTA to block PET and weakening the interlayer interactions of the COF to reduce nonradiative transitions. The FL intensity of Py-DMTA-COF exhibited an excellent linear relationship with the concentration of cartap (0.004-25 μg mL^-1), with a limit of detection of 0.11 ng mL^-1. In addition, the FL image digital quantization technology based on a smartphone-assisted visual platform was adopted to conduct visual quantitative detection of cartap (linear range: 0.05-16 μg mL^-1, LOD: 0.0138 μg mL^-1). The highly sensitive FL quantitative method, combined with the excellent color data digitization function of smartphones, has excellent application potential for the high-precision detection of food hazardous substances.