Europium-decorated carbon quantum dots for dual Cu(2+)/Fe(3+) detection and live-cell bioimaging.

The present study demonstrated europium-decorated carbon quantum dots (Eu-CQDs), which were synthesized through a one-pot hydrothermal process using sucrose and melamine as the carbon and nitrogen sources and EuCl as the rare earth metal ion of Eu. The resulting blue-emissive Eu-CQDs were confirmed using spectroscopic and microscopic techniques, including UV-Vis absorption, fluorescence (FL), FT-IR, XRD, TEM, and XPS. The Eu-CQDs showed significant UV-Vis and FL emission at wavelengths of 320 and 424 nm, respectively, with a quantum yield (QY) of 33.6%. TEM analysis revealed well-dispersed spherical Eu-CQDs with an average size of 3.19 ± 0.21 nm. Remarkably, the Eu-CQDs served as an outstanding FL probe for the selective sensing of ferric ions (Fe) and copper ions (Cu) through FL dynamic quenching, especially photo-induced electron transfer (PET), while other metal ions produced minimal intensity changes. The detection limits were 65.6 nM for Cu and 72.1 nM for Fe, with a linear relationship observed in the range of 0-20 µM. However, the dynamic quenched FL of Eu-CQDs/Cu and Eu-CQDs/Fe was swiftly enhanced by EDTA via a turn-on response. The practical use of the Eu-CQDs probe for quantifying the Cu and Fe ion concentrations was conducted with real water samples, and the findings indicated satisfactory recoveries (101.1% for Cu and 104.8% for Fe) and good reproducibility, which aligned with the results obtained from UV-Vis spectroscopy. Additionally, the WST assay was assess the cytotoxic effects of Eu-CQDs, and their capability to image live HCT-116 (human colon cancer cell line) cells was assessed. These results indicate that the Eu-CQDs used for the nanoscale sensing of Fe and Cu metal ions are both selective and sensitive, and they can be successfully used for live cell imaging of cancer cell lines when used with this probe.