Smartphone-Based Fe-ZIF Nanozyme-Driven Colorimetric Sensing Platform for In Situ Visual Detection of Glyphosate Residues on Fresh Tea Leaves

Glyphosate, a widely used herbicide, poses significant food safety risks in tea production. Conventional detection methods are often instrument-dependent and require complex sample preparation. This study presents an innovative, instrument-free sensing platform that enables direct on-site detection of glyphosate residues on fresh tea leaves. The platform utilizes a Fe-ZIF nanozyme with high peroxidase-like activity. Glyphosate directly inhibits the nanozyme's active sites via chelation, reducing its ability to oxidize 3,3',5,5'-tetramethylbenzidine (TMB) and produce a blue color. This color change is captured using a portable colorimetric card and quantitatively analyzed via smartphone RGB readout. The method eliminates the need for biomolecular mediators, extraction, or centrifugation steps. This method achieves in situ glyphosate detection on tea leaves within 15 min, with high selectivity. This work provides a cost-effective, user-friendly tool for rapid field screening of glyphosate residues on fresh tea leaves.