A colorimetric/down-conversion fluorescence dual-readout probe for the recognition of Cu2+ and its application in environmental water by single PEI@NaYF4: Eu3+ nanoparticles

The pollution caused by heavy metals like Cu2+ remains a pressing issue, as the release of Cu2+-laden sewage can lead to detrimental effects on both soil ecosystems and human well-being. Herein, a novel colorimetric and down-conversion fluorescence probe, i.e. PEI@NaYF4: Eu3+ NPs, for selective and sensitive detection of Cu2+ with colorimetric and down-conversion fluorescence dual signal changes was reported. Such dual-signal detection mode offers enhanced sensitivity, accuracy, and cost-effectiveness in detecting Cu2+. The probe with spherical shape and excellent monodispersity was synthesized by a high temperature reflux method. The PEI moiety of the NPs is chosen due to the ability to chelate Cu2+ forming copper amine complexes. Such a unique feature is invoked to develop a versatile detection platform for the colorimetric detection of Cu2+ ions. In the presence of Cu2+, the visual color of probe in solution changes from colorless to blue with a low detection limit of 100 nM without any assistance of equipment. The probe emits down-conversion fluorescence with two main typical emission peaks centered at 592 and 614 nm under an excitation of 394 nm. The copper amine complexes formed by the combination of Cu2+ and the PEI moiety of the NPs quench down-conversion fluorescence by an internal filtration effect. Probe shows a specific on–off response to Cu2+ in aqueous solution with nanomolar LOD, fast response, and good selectivity, and without interference by a range of metal ions. A practical application shows that PEI@NaYF4: Eu3+ NPs have good recovery ranges of 96–105 % for Cu2+ detection in real environment water samples from different locations. This strategy proves that a colorimetric and down-conversion fluorescence probe is a potential tool for addressing heavy metal ions-induced water pollution.