Dual-Ligand Metal-Organic Framework for Ultrasensitive Fluorescence Detection of Uranium: An In Situ Trace Enrichment Strategy to Overcome Concentration Limitations.

The development of trace analysis technology for uranium pollution has become crucial for ecological protection, owing to the extensive utilization of uranium in the nuclear industry. Fluorescence method has been widely used for the detection of uranium in water, but current research still suffers from insufficient sensitivity, sluggish detection speed, and interference from coexisting ions. This is mainly due to the poor selective enrichment ability of the sensors for trace uranium. Herein, a fluorescent metal-organic framework (MOF) named dual-ligand MOF-AO (DMOF-AO) with high uranium affinity was synthesized via a mixed ligand strategy. The incorporated amidoxime groups served as specific recognition sites, achieving a high quenching selectivity against at least 17 interfering ions. The biomimetic flower-like structure coupled with the second ligand intercalation strategy greatly improves the mass transfer rate, enabling the rapid in situ enrichment of uranium even at trace concentrations. This synergistic design and trace uranium enrichment strategy resulted in high detection sensitivity (LOD of 2.72 nmol L) and ultrashort response time (10 s), surpassing most reported fluorescent sensors. Mechanistic investigations elucidated the coordination configuration and revealed the underlying fluorescence quenching mechanism caused by photoinduced electron transfer. The uranium concentrations in the actual water samples from different regions tested by DMOF-AO were consistent with the gold-standard ICP-MS results, validating the practical reliability. This study demonstrates the promoting effect of improving enrichment ability at trace concentrations on detection sensitivity and establishes an efficient, instantaneous, visualization, and reliable strategy for uranium detection using fluorescent MOF.