In vivo bioimaging and sensitive detection of uranyl via a turn-on rare-earth functionalized covalent organic framework.

Uranium, a radioactive and toxic pollutant, poses significant threats to human health. The development of sensitive platforms for uranium detection and bioimaging remains challenge. Herein, a pyridine-based covalent organic framework (COF) was synthesized via a Schiff-base reaction using 2,2'-bipyridine-5,5'-dicarbaldehyde (Bpydah) and 1,3,5-tris(4-aminophenyl)benzene (TAPB). Subsequently, europium ions (Eu3+) were anchored to the pyridinic nitrogen sites of the COF framework via post-synthetic coordination, enhancing the intrinsic fluorescence and yielding a europium-functionalized sensor (COF@Eu). Attributed to the combined contributions of photoinduced electron transfer (PET) and Förster resonance energy transfer (FRET), COF@Eu exhibits a fluorescence "turn-on" response toward uranyl ion (UO22+), with a detection limit of 3.3 nM and good reliability in complex sample matrices (RSD < 2.9%). Moreover, the "turn-on" fluorescence response, coupled with favorable biocompatibility and low cytotoxicity of COF@Eu, facilitates UO22+ imaging in cells and mice. This in vivo imaging capability highlights the potential of COF@Eu for visualizing internal uranium exposure. This work establishes a multifunctional platform, offering a potential strategy for environmental monitoring and nuclear toxicology.