Synthesis and application of purine-based fluorescence probe for continuous recognition of Cu²⁺ and glyphosate

In this study, a novel fluorescent sensor, N,N-dimethyl-4-((2-(8-m-ethyl-9-(naphthalen-1-yl)-9H-purin-6-yl)hydrazineylidene)methyl)aniline(PHA), which was constructed via Schiff base reaction of purine derivatives and dimethylaminobenzaldehyde. This probe showed significant selective fluorescence quenching of Cu²⁺, and accompanying with an increase in Cu²⁺ concentration and a change in solution color from colorless to yellow. The outstanding features of PHA include low detection limit (0.429 μM), strong anti-interference ability and fast response time. We further investigated the chelation mechanism of PHA and Cu²⁺ by Job's plot experiment, density generalization theory (DFT), and the probe PHA can form a 1:2 complex with Cu²⁺ ions, leading to a fluorescence quenching process, thus realizing the rapid detection of Cu²⁺. In addition, this new fluorescent sensor [PHA-Cu²⁺] can be used to detect pesticide residues in solution. When the [PHA-Cu²⁺] system was mixed with glyphosate solution, that a fluorescence recovering was observed. This may be because glyphosate chelates more strongly with Cu²⁺ ions, making the copper ions dissociated from the [PHA-Cu²⁺] system. The detection limit of the fluorescent sensor [PHA-Cu²⁺] for glyphosate was 18.77 nM. Finally, the sensor system has been successfully applied in fluorescence imaging of glyphosate in living cells.