A label-free fluorescence sensing platform based on NaY_0.47F₄:Ce_0.1,Gd_0.4,Eu_0.03@PEIF down-conversion for selective detection of Cu²⁺ in aqueous environments

The issue of Cu²⁺ contamination is severe due to its potential to induce diseases upon exposure. This study has developed a novel down-conversion fluorescent material, α-phase NaY_0.47F₄:Ce_0.1,Gd_0.4,Eu_0.03@PEIF nanoparticles (Eu@PEIF NPs). It was synthesized using thermal decomposition combined with epitaxial growth, to obtain the Eu NPs which show high crystallinity and regular morphology. After functionalization with fluorinated PEI (PEIF) Eu@PEIF NPs were obtained with good water solubility and optical properties. The Cu²⁺ can bind to Eu@PEIF NPs through surface amino groups resulting in fluorescence quenching attributed to an inner filter effect (IFE) and Förster resonance energy transfer (FRET). Thus, a new label-free fluorescence sensing platform based on Eu@PEIF NPs was constructed and Cu²⁺ was quantitatively analyzed over the concentration range of 0.03-2.5 μM, with a low detection limit and high selectivity to Cu²⁺. This fluorescence sensor exhibits excellent recovery rates (94.93-104.61%) when applied to the detection of Cu²⁺ in real water samples. This proposed method provides a new approach for Cu²⁺ detection and offers guidance for the design of Cu²⁺-sensitive fluorescent probes.