Visualizing glyphosate: A low-toxicity Zn²⁺-Based fluorescent probe for rapid detection from field to organism

Glyphosate, a widely used organophosphorus herbicide, poses potential threats to the environment and human health due to its residues and slow degradation. Conventional detection methods often require expensive instrumentation and complex sample pretreatment, limiting their applicability for rapid and on-site monitoring. To address this challenge, this study developed a fluorescent probe based on a (E)-4'-(diphenylamino)-4-((2-(pyridin-2-yl)hydrazineylidene)methyl)-[1,1'-biphenyl]-3-ol- Zn²⁺ (TPA-MB-Zn²⁺) complex for the highly selective and sensitive detection of glyphosate. The probe features a donor-π-acceptor structure and coordinates with Zn²⁺ through its hydroxyl group, Schiff base nitrogen, and pyridinic nitrogen in a 1:1 stoichiometry, forming a TPA-MB-Zn²⁺ complex with significantly enhanced fluorescence. The coordination mechanism was validated by Job's plot analysis, ¹H NMR titration, DFT calculations, and fluorescence lifetime measurements. Glyphosate, possessing stronger coordination affinity for Zn²⁺, competitively displaces Zn²⁺ from the complex, leading to fluorescence quenching and enabling a "turn-off" detection mode. Under optimized conditions (MeOH/H₂O = 4:1, v/v), the system achieves a detection limit of 60 nM, a rapid response time of 15 s, excellent selectivity over 14 interfering pesticides, and stable performance across a wide pH range (4-10). The practical applicability was validated by satisfactory spike recoveries (98.00-100.80%) in real water samples (tap water, river water) and soil extracts. Furthermore, the probe enabled convenient visual imaging of glyphosate residues on the surfaces of various fruits and vegetables under UV light. Cytotoxicity assays confirmed low toxicity in HepG2 cells, and confocal imaging in cells and zebrafish demonstrated the probe's good biocompatibility and its utility for tracking glyphosate in living biological systems. This work provides a rapid, sensitive, and low-toxicity fluorescent sensing tool for monitoring glyphosate residues in environmental and biological samples.