Computation-Assisted Development of a Rhodamine-Based off-to-on Fluorescent Nanoprobe for Precise Uranyl Ion Detection in Diverse Real-Life Scenarios

Abstract Uranyl ion (UO22+), a highly toxic and radioactive heavy metal species, poses severe threats to human health and environmental safety. Therefore, developing easy-to-operate, rapid, and efficient strategies for UO22+ detection is of critical importance. Herein, leveraging the fluorescence “off-to-on” transition triggered by the transformation of a five-membered spirocyclic ring within the rhodamine framework, this work proposes the rational design of a star fluorophore, termed RBN with the aid of computational chemistry. To enable practical usages, RBN was assembled onto a chitosan-based polymer carrier to fabricate the dual-functional fluorescent nanoprobe (Nano-RBN). The resulting system exhibits ultrafast fluorescence response (1 s), a low detection limit (1.32 μM), and a remarkable 40-fold fluorescence turn-on upon interacting with UO22+. These exceptional optical properties empower this nanoprobe to be successfully applied for the quantitative determination of UO22+ levels in real-world samples, including water, soil, seafood, and living cells. Next, a portable and field-deployable detection platform was established by incorporating Nano-RBN-impregnated test strips or gels with a smartphone-based photographing system, allowing for on-site, visual, and quantitative monitoring of UO22+. Finally, a Nano-RBN-based hydrogel was developed and demonstrated high efficiency in absorbing UO22+ from aqueous solutions, highlighting its promise for environmental remediation.