Polyethylenimine (PEI)-Functionalized Polymer of Intrinsic Microporosity (PIM-1) Polymer Dots for Detection of Metribuzin Herbicides via Fluorescence Spectroscopy

Herbicides play a crucial role in modern agriculture, but the accumulation of their residues presents substantial ecological and health hazards. This study introduces a fluorescent probe, polyethylenimine (PEI)-functionalized polymer of intrinsic microporosity (PIM-1) polymer dots (PIM@PEI Pdots), synthesized via coprecipitation for detecting Metribuzin. The PIM@PEI Pdots exhibit strong excitation-independent fluorescence at 490 nm. Metribuzin detection occurs through an “on–off” quenching mechanism by interactions (hydrogen bonding and electrostatic forces) between the probe’s amine groups and Metribuzin that cause probe aggregation and fluorescence quenching. Density functional theory (DFT) calculations support these findings, showing the PEI’s amine-rich structure facilitates interactions via intramolecular H-bonding, while Metribuzin provides binding sites through its N-groups and carbonyl. This “on–off” approach provides a sensitive probe for detecting Metribuzin in real water and soil samples.