Full-range intracellular pH sensing by an aggregation-induced emission-active two-channel ratiometric fluorogen

Intracellular pH (pH_i) is an important parameter associated with cellular behaviors and pathological conditions. Sensing pH_i and monitoring its changes in live cells are essential but challenging due to the lack of effective probes. We herein report a pH-sensitive fluorogen for pH _i sensing and tracking. The dye is a tetraphenylethene-cyanine adduct (TPE-Cy). It is biocompatible and cell-permeable. Upon diffusing into cells, it responds sensitively to pH_i in the entire physiological range, visualizing the acidic and basic compartments with intense red and blue emissions, respectively. The ratiometric signal of the red and blue channels can thus serve as an indicator for local proton concentration. The utility of TPE-Cy in pH_i imaging and monitoring is demonstrated with the use of confocal microscopy, ratiometric analysis, and flow cytometry.