A ratiometric fluorescence sensor based on a bifunctional Cu-MOF nanozyme for dual-signal detection of glyphosate in actual samples

Abstract

This study proposes a glyphosate (GLY) detection strategy based on metal–organic framework (MOF) nanozymes, achieved by synthesizing a copper-based MOF nanozyme (Cu-MOF) via a one-pot hydrothermal method and integrating it into a ratiometric fluorescence sensing platform. This Cu-MOF nanozyme exhibits not only oxidase activity but also strong fluorescence properties, with a maximum emission wavelength of 435 nm under 328 nm excitation light. In the presence of o-phenylenediamine (OPD), due to the oxidase activity of the Cu-MOF, it catalyzes the oxidation of OPD to 2,3-diaminophenazone (oxOPD). This compound fluoresces at 570 nm while quenching the Cu-MOF fluorescence at 435 nm. Upon GLY addition, it forms chelates with Cu²⁺ sites in the MOF, thereby inhibiting the oxidase activity and reducing oxOPD production. This results in reduced fluorescence quenching at 435 nm and decreased the emission intensity at 570 nm. This ratiometric sensor exhibits high selectivity toward GLY, with a linear range of 0–14 µM and a detection limit of 43 nM. Additionally, we developed a smartphone-based detection platform. By capturing fluorescence images and processing RGB values, this platform enables rapid on-site detection, providing a practical solution for GLY monitoring.