Covalent organic polymer cascade MnO2 nanosheets-based fluorescence-colorimetric dual-mode sensing system for highly sensitive detection of organophosphorus pesticides

To enable accurate visual identification of organophosphorus pesticides (OPs) in raw materials of medicinal and food homology (MFH), this study used the red-fluorescent covalent organic polymer TEPBY-DTDA to cascade MnO 2 nanosheets exhibiting oxidase-mimetic activity and suppressing fluorescence effects , enabling colorimetric and ratiometric fluorescence detection. OPs suppressed acetylcholinesterase (AChE) efficiency, consequently diminishing thiocholine (TCh) production and modulating residual MnO 2 nanosheet levels. Rising OP concentrations caused the probe's fluorescence to shift red-to-yellow, accompanied by solution yellowing. Using triazophos, methyl parathion (MP), chlorpyrifos, and phoxim as representative OPs, the probes generated a robust, linear signal over the concentration interval of 0.1–1500 μg/L. The fluorescence minimal limit of detection (LOD) was 0.058 μg/L, while the minimum LOD in colorimetric mode was 0.04 μg/L. The probe demonstrated excellent selectivity and strong anti-interference capability against OPs. Consequently, this sensing strategy not only expands the toolbox for quality monitoring of MFH materials but also holds significant potential for enhancing food safety protocols.