AIE and ICT Synergistic Lysosome-Targeted Ratiometric Fluorescence Sensor for the Detection and Imaging of Th4+ in the Liver of Zebrafish and Mice

The sensitive detection of the radioactive thorium (Th) ion with an oxidation state of +4 (Th⁴⁺) is of great significance for environmental protection and life safety. In this study, five fluorescence sensors with regulated donor-acceptor (D-A) interactions were constructed for Th⁴⁺ detection based on intramolecular charge transfer and aggregation-induced emission mechanisms. Among the developed sensors, TPE-D bearing electron-deficient π-bridge and weak D-A interactions presented ratiometric fluorescence detection behavior toward Th⁴⁺ in aqueous solution due to its aggregation-induced emission characteristics and unique D-A-D structures. Moreover, TPE-D showed excellent selectivity and sensitivity for Th⁴⁺ detection, and the detection limit was as low as 8.1 × 10^-8 M. The sensing mechanism observation revealed that Th⁴⁺ could coordinate with the hydroxyl, imine, and carbonyl groups of TPE-D accompanied by an electron transfer process. In addition, TPE-D could selectively be enriched in the lysosome. Both the detection of Th⁴⁺ in the lysosome and liver of mice and zebrafish were realized based on this strategy, and a mobile-assisted detection approach toward Th⁴⁺ in actual water samples was also established with high sensitivity. This is the first report for Th⁴⁺ detection in organelles and organs, which provides a great significance and reliable strategy for radionuclide toxicology detection and analysis applications.