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 (Cu) 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 Cu. 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 Eu). Introducing DPA significantly enhanced the Eu 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 (F/F and F/F) increasing linearly with DPA concentration (0-50 μM), achieving a low detection limit of 31.89 nM. Conversely, adding Cu to the system containing DPA progressively quenched the Eu emission, causing the same intensity ratios to decrease linearly across a wide Cu 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 Cu.