A benzooxazine-based ratiometric fluorescent probe for pH imaging in living cells and bacteria

Abstract Acid-base balance is associated with various cellular functions, and its disorders could cause several diseases. The real-time detection of intracellular pH fluctuation is of vital importance for the prevention of multiple diseases. Therefore, the development of pH-sensitive probes has always been a considerable requirement. Here, we report a ratiometric fluorescent probe Ox-L based on the 3H-indolium dye, which enables highly sensitive detection of pH fluctuations via the intramolecular charge transfer (ICT) process. The probe exhibits a large Stokes shift at 145 nm, excellent photostability, reversibility and low cytotoxicity— all which are conducive for intracellular pH imaging. Based on these properties, Ox-L has been suitably applied to visualize pH fluctuation in the living cell, and to monitor the periplasmic pH of E. coli. These results showed that the probe possesses great potential in biological systems.