Carbon dots have drawn extensive attention in the detection of metal ions with good stability, excellent biocompatibility and low toxicity. Meanwhile, the quantum yield, response rate and the detection mechanism for Cu2+ions are vital to their development and application. To obtain more selective and sensitive materials to detect Cu2+ions, N-doped carbon dots (DN-CDs) were synthesized by a one-step hydrothermal method using citric acid as the carbon source and diethylenetriamine (DETA) as the nitrogen source. The obtained DN-CDs exhibited stable and intense blue light emission and special near-infrared up-conversion fluorescence at 820 nm, attributed to the effect of introducing N atoms into the structure of carbon dots. Due to the dynamic quenching of the DN-CDs by Cu2+ions, the fluorescence intensity (λex = 820 nm) of DN-CDs was quantitatively decreased in the presence of Cu2+ions. The DN-CDs had a rapid response within 3 min. The DN-CD system exhibited a linear relationship with a concentration range from 2.5 to 50 µM and low detection limit (LOD) of 42 nM. After careful investigation, an interesting conclusion was proposed: N-doped CDs with N/O = 1:1 or higher with relatively abundant N atoms prefer to detect Cu2+ions while those with N/O = 1:2 or lower prefer to detect Fe3+ions.Keywords:carbon dots;up-conversion fluorescence;Cu2+ions detection
Wang Jing,Li Shuangbao,Ren Lu,Wang Zian,Liu Yanqi,Zhang Dawei
The compounds with an imidazole structure, DHH and DHM, were synthesized using benzoyl, ammonium acetate, 2-hydroxy-5-methylisophthalaldehyde, and 2-(3-aldehyde-4-hydroxyphenyl)- 4-methylthiazole-5-carboxylate as raw materials. The structures of probes DHH and DHM were characterized by FT-IR, 1 H NMR, 13 C NMR, and HR-MS. This study found that DHH and DHM can rapidly and highly selectively recognize Cu 2+ in EtOH-H 2 O (1:1 v/v). The spectral characteristics of DHH and DHM were studied using fluorescence spectroscopy and UV–vis spectroscopy. The results show that the combination of DHH and DHM with Cu 2+ produces a significant fluorescence quenching effect, and the influence of other metal ions can be neglected. Subsequently, through Job’s plot analysis, 1 H NMR titration, and DFT calculations, the binding mechanisms of probes DHH and DHM with Cu 2+ were explored, and it was found that they coordinate in a 2:1 ratio. The experimental study on standard addition recovery showed that probes DHH and DHM could be used for the quantitative detection of Cu 2+ in actual water samples. The probes were also successfully applied to the monitoring of Cu 2+ in living cells. Graphical abstract
The compounds containing imidazole structures in probes DHH and DHM were successfully synthesized and characterized. Test strips made of DHH and DHM were used for rapid “naked-eye” detection of Cu2 + in an aqueous medium. The probes were successfully used to monitor Cu2 + in living cells and real water samples.
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