On-Site Ratiometric Analysis of UO₂²⁺ with High Selectivity

Uranyl ions (UO₂²⁺) are recognized as important indicators for monitoring sudden nuclear accidents. However, the interferences coexisting in the complicated environmental matrices impart serious constraints on the reliability of current on-site monitoring methods. Herein, a novel ratiometric method for the highly sensitive and selective detection of UO₂²⁺ is reported based on a [Eu(diaminoterephthalic acid)] (Eu-DATP) metal-organic framework. Benefiting from the unique chemical structure of Eu-DATP, energy transfer from DATP to UO₂²⁺ was enabled, resulting in the up-regulated fluorescence of UO₂²⁺ and the simultaneous down-regulated fluorescence of Eu³⁺. The limit of detection reached as low as 2.7 nM, which was almost 2 orders of magnitude below the restricted limit in drinking water set by the United States Environmental Protection Agency (130 nM). The Eu-DATP probe showed excellent specificity to UO₂²⁺ over numerous interfering species, as the intrinsic emissions of UO₂²⁺ were triggered. This unprecedentedly high selectivity is especially beneficial for monitoring UO₂²⁺ in complicated environmental matrices with no need for tedious sample pretreatment, such as filtration and digestion. Then, by facilely equipping a Eu-DATP-based sampler on a drone, remotely controlled sampling and on-site analysis in real water samples were realized. The concentrations of UO₂²⁺ were determined to be from 16.5 to 23.5 nM in the river water of the Guangzhou downtown area, which was consistent with the results determined by the gold-standard inductively coupled plasma mass spectrometry. This study presents a reliable and convenient method for the on-site analysis of UO₂²⁺.