Cyclization-induced NIRF and functional specificity: NIR probe based on phenothiazine core for ultra-fast detecting mitochondrial HClO during cell ferroptosis

Ferroptosis, a recently identified form of iron-dependent cell death, is closely associated to reactive oxygen species (ROS). Hypochlorous acid (HClO), a typical ROS primarily produced in mitochondria, plays a crucial role in various physiological processes. Ferroptosis leads to abnormal alterations in intracellular HClO levels, and monitoring the dynamic changes of HClO during this process can provide valuable insights into its biological functions. In this study, three different fluorescent probes capable of detecting mitochondrial HClO were designed. Among them, PTZQ-OH exhibits the longest emission wavelength (653 nm) and the high fluorescence enhancement (1364.7-fold) in the presence of HClO, making it an excellent tool for HClO detection. It also features a fast response time (< 6 s) and a low detection limit (53.2 nM). Cell imaging experiments show that PTZQ-OH can effectively detect both endogenous and exogenous HClO in live cells. Furthermore, PTZQ-OH has been successfully applied to monitor HClO in erastin-induced ferroptosis models. By modulating the concentration and duration of erastin treatment, as well as applying the ferroptosis model, PTZQ-OH can accurately track fluctuations in mitochondrial HClO during ferroptosis.