A ratiometric fluorescence probe for imaging endoplasmic reticulum (ER) hypochlorous acid in living cells undergoing excited state intramolecular proton transfer.

[Display omitted] • A novel ratiometric fluorescence probe RHE based on ESIPT process and rhodol ring opened-closed processes. • RHE has ability to fast (response time < 80 s) and sensitively (LOD = 40 nm) detect HOCl. • RHE could be applied for monitoring exogenous and endogenous HOCl. RHE can localize in the endoplasmic reticulum of living cells. Hypochlorous acid (HOCl), one of the most important ROS in living organisms, appears to serve an important role in the immune system in vivo. Endoplasmic reticulum (ER), the largest organelle in cells, manages many biological processes connected to vital activities. To better obtain insight into the relationship of ER stress and HOCl level, a ratiometric fluorescent probe RHE , based on rhodamine combined with HBT and ER-targeting group, was designed and synthesized for HOCl detection in the ER. Probe RHE shows a large stokes shift about 155 nm, which is derived to ESIPT principle. In addition, probe RHE exhibited excellent properties such as fast response (<80 s), high sensitivity with a low detection limit (40 nM), high selectivity and anti-interference. Moreover, probe RHE displayed an excellent ER-targeting ability and had been successfully applied for detection of exogenous and endogenous HOCl in HepG2 cells. [ABSTRACT FROM AUTHOR]