A highly selective and sensitive colorimetric assay for specific recognition element-free detection of uranyl ion

•A formic acid-assisted photolysis of UO22+ initiated chromogenic reaction is fabricated for colorimetric detection of UO22+.•This colorimetric assay realizes visualization of UO22+ at a concentration of 0.5 μM.•It possesses excellent selectivity over common inorganic ions with even 50-fold higher concentration than UO22+. Current strategies for visual detection of uranyl ion (UO22+) often require DNAzymes and organophosphorus receptors as well as various nanomaterials that may affect the selectivity, sensitivity, and accuracy in a complicated environment. Here, we circumvent these drawbacks by introducing a formic acid (FA)-assisted photolysis of UO22+ initiated chromogenic reaction for specific recognition element-free colorimetric detection of UO22+. The colorless 2, 2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) is oxidized by the superoxide anion from the photolysis of UO22+ to generate green ABTS radical, which enables the determination of UO22+ at a concentration of 0.5 μM with the naked eye. The present colorimetric assay is able to determine concentrations of UO22+ from 0.1 to 100 μM, with a limit of detection as low as 0.01 μM. Impressively, the specific recognition element-free colorimetric assay possesses excellent selectivity over common inoganic ions with even 50-fold higher concentration than UO22+. In addition to good sensitivity and selectivity, this colorimetric assay is also capable of determining UO22+ in natural water samples with satisfactory recoveries.