A turn-on fluorescence sensor based on Cu²⁺ modulated DNA-templated silver nanoclusters for glyphosate detection and mechanism investigation

The abuse application of glyphosate can result in a potential hazard for environment and human, however its ultrasensitive detection remains challenging. Herein, a Cu²⁺ modulated DNA-templated silver nanoclusters (DNA-AgNCs) sensor was constructed to sensitively determine glyphosate based on the turn-on fluorescence strategy. The fluorescence quenching of DNA-AgNCs occurred with the existence of Cu²⁺. Upon the presence of glyphosate, the functional groups on the surface of glyphosate could chelate with Cu²⁺, following the fluorescence recovery of DNA-AgNCs. Through the stoichiometric methods, we unveil that Cu²⁺-trigged fluorescence quenching mode is a combination of static and dynamic quenching with the static mode being predominant. In DNA-AgNCs/Cu²⁺ system, the carboxylate, amine, and phosphonate groups of glyphosate interact with Cu²⁺ through chelation, in which the carboxylate oxygen, the phosphonate oxygen atoms, and the monoprotonated secondary amine nitrogen atom and Cu²⁺ form chelate rings. This fluorescence sensor showed a desired linearity of glyphosate analysis under the optimum conditions, ranging from 15 to 100 μg/L with a low detection down to 5 μg/L. Moreover, the proposed sensor was successfully utilized to measure glyphosate in real samples, indicating a promising application in pesticide residues detection.