Amidoxime-functionalized layered photonic hydrogels for rapid and visual detecting UO22+ in tap water

To address the urgent need for on-site and rapid detection of uranyl ions (UO 2 2+ ), we developed a visual sensing platform based on the structural color of a lamellar photonic crystal. A periodic lamellar structure was fabricated via surfactant-directed self-assembly of dodecyl glyceryl itaconate (DGI) and subsequently immobilized in a polyacrylamide (PAAm) network, yielding an anisotropic, amidoxime-functionalized h-PAO-PDGI/PAAm hydrogel. The hydrogel exhibited an equilibrium swelling ratio of 2296% and excellent mechanical properties, with a tensile strength of 0.014 MPa and elongation at break of 281.21%. It contains abundant amidoxime, carboxyl, and amide groups that serve as specific binding sites for UO 2 2+ coordination. Binding of UO 2 2+ induces hydrogel shrinkage, decreasing the interlayer spacing and causing a blueshift of the diffraction peak. This blueshift shifts the structural color from red to blue within 25 min. The sensor exhibits a linear response to UO 2 2+ in the 0.01–100 μM range, with a detection limit of 9.7 nM. Featuring instrument-free operation, visual readout, and good reusability, this sensor provides a promising approach for on-site monitoring and pollution control of UO 2 2+ in environmental waters.