A Ratiometric fluorescent Nanoprobe LRH/CDs/MOF for the detection of Cu(II) and Anthrax biomarker.

2,6-Pyridinedicarboxylic acid (DPA), an anthrax biomarker, and excess copper ions (Cu2+) pose significant health risks, necessitating effective detection methods. This work presents a novel dual-emission ratiometric "on-off" fluorescent nanoprobe, LEuH@Cu-CDs@UiO-66, for sensing DPA and Cu2+. It was synthesized by intercalating LEuH and encapsulating copper-doped carbon dots (Cu-CDs) into a zirconium-based UiO-66 framework. The composite maintained the excellent optical properties of its components and exhibited good aqueous stability. Upon 275 nm excitation, it showed three distinct emission peaks at 390 nm (from Cu-CDs), 593 nm, and 617 nm (both from Eu3+). Introducing DPA significantly enhanced the Eu3+ emission peaks at 593 nm and 617 nm via an energy ligand sensitization mechanism, while the Cu-CDs peak at 390 nm remained stable. This allowed for ratiometric detection, with the intensity ratios (F617/F390 and F593/F390) increasing linearly with DPA concentration (0-50 μM), achieving a low detection limit of 31.89 nM. Conversely, adding Cu2+ to the system containing DPA progressively quenched the Eu3+ emission, causing the same intensity ratios to decrease linearly across a wide Cu2+ concentration range (0-1000 μM), facilitating a sensitive "off" response. The material was successfully applied to detect DPA in environmental water samples, demonstrating its practical potential as a versatile "on-off" ratiometric fluorescent nanoprobe for the simultaneous detection of DPA and Cu2+.