Amidoxime-Based Near-Infrared Fluorescent Sensor for Highly Sensitive Uranium Detection in Living Systems

The biological detection of uranium is crucial for nuclear emergency medical treatment, since uranium is the major nuclear fuel and its uptake would pose severe health risk to the workers and the public. But there is yet no clinical agent that can provide rapid and accurate evaluation of uranyl internal contamination level, which hampers the timely diagnosis and treatment. Herein, the fluorescent detection method was employed for in vivo uranyl monitoring owing to its advantages of noninvasiveness as well as high specificity and sensitivity. The fluorescent probe NRhB-AO was designed by conjugating the amidoxime group for uranyl selectivity and a hemicyanine backbone to facilitate near-infrared (NIR) emission at 750 nm, yielding a remarkable uranyl-triggered 71.5-fold fluorescence enhancement. Density functional theory (DFT) calculations indicate that uranyl chelation by the carbonyl/amidoxime groups induces spirolactam ring-opening, leading to a pronounced fluorescence increase through the formation of a 1:1 complex. The rapid and quantitative detection of intracellular uranyl was achieved in NRK-52E cells. The in vivo imaging experiment of uranyl exposed mice further demonstrated a rapid signal enhancement (∼1.7-fold) in kidneys, which is a major deposition organ of uranyl. This work validates the utility of NRhB-AO for sensitive uranyl detection in biological environments, which will facilitate the immediate medical care of uranium-toxic people.