Bifunctional chitosan-based fluorescent nanosensor for simultaneous detection and adsorptive removal of uranyl ions

The widespread use and increasing consumption of uranium source in nuclear energy applications has led to inevitable environmental release of uranyl ions (UO₂²⁺), which accumulate through the food chain and pose severe risks to human health and ecosystem. Therefore, it is highly significant and desirable to develop a simple yet efficient method, capable of not only rapid and accuracy detection but also facile and robust adsorption of UO₂²⁺. Herein, we would like to report a novel dual-functional fluorescent nanoprobe, designated CS-Nap-HBT, capable of simultaneously detecting and adsorbing UO₂²⁺. This nanoprobe was fabricated by self-assembling a pre-synthesized small-molecule UO₂²⁺-sensitive fluorescent chemosensor onto a chitosan-based adsorbent framework. The resulting nanosensor CS-Nap-HBT exhibits the advantageous sensing behaviors, such as ultra-fast response (< 2 s), excellent selectivity, and reliable ratiometric fluorescence signal (I₅₀₀/I₅₆₀). Based on the excellent optical performance, a portable detection platform was developed by integrating a smartphone equipped with color analysis App and CS-Nap-HBT-impregnated test strip device, enabling on-site quantitative monitoring of UO₂²⁺ levels. Further, the nanosensor was incorporated into a hydrogel matrix to fabricate a CS-Nap-HBT-loaded hydrogel with enhanced UO₂²⁺ adsorption capacity. Based on ICP-MS analysis and the derived equilibrium concentration (Cₑ) and adsorption capacity (Qₑ), the adsorption of UO₂²⁺ onto this hydrogel followed a monolayer mechanism well described by the Langmuir isotherm model. The hydrogel achieved a maximum adsorption capacity of 24.98 mg/g, 36.9% higher than that of pristine chitosan hydrogel, and maintained >99.99% removal efficiency over five consecutive adsorption-desorption cycles, demonstrating excellent reusability.