Imaging and Measuring Vesicular Acidification with a PlasmaMembrane-Targeted Ratiometric pH Probe

:tracking the pH variation of intracellular vesicles throughout theendocytosis pathway is of prior importance to better assess the cell trafficking andmetabolism of cells. Small molecularfluorescent pH probes are valuable tools inbioimaging but are generally not targeted to intracellular vesicles or are directly targetedto acidic lysosomes, thus not allowing the dynamic observation of the vesicularacidification. Herein, we designed Mem-pH, afluorogenic ratiometric pH probe basedon chromenoquinoline with appealing photophysical properties, which targets theplasma membrane (PM) of cells and further accumulates in the intracellular vesicles byendocytosis. The exposition of Mem-pH toward the vesicle's lumen allowed to monitorthe acidification of the vesicles throughout the endocytic pathway and enabled themeasurement of their pH via ratiometric imaging