Probing drug-mediated fluctuations of HClO levels in the endoplasmic reticulum by a ratiometric fluorescent probe with a large emission shift

Hypochlorous acid (HClO), one of the most important reactive oxygen species (ROS), is closely associated with endoplasmic reticulum (ER) stress, and therefore it is important to develop effective methods for detecting HClO in the ER. In this work, a ratiometric fluorescent probe (PTZC-ER) based on the phenothiazine-coumarin platform was constructed for HClO detection. In response to HClO, the fluorescence emission of the probe dramatically changes from 640 nm to 510 nm in seconds. Probe PTZC-ER exhibits outstanding selectivity and sensitivity (LOD = 11.8 nM) towards HClO. The probe can sense exogenous and endogenous HClO in a ratiometric manner, showing promising ER-targeting capability in the bioimaging experiments. Importantly, PTZC-ER can monitor fluctuations in HClO levels during drug-mediated oxidative stress.