A new rhodamine B-based lysosomal pH fluorescent indicator

A rhodamine B-based pH fluorescent probe can selectively stain lysosomes and monitor lysosomal pH changes in living cells. •A new rhodamine B-based fluorescent pH probe was synthesized.•This probe has a pKa of 4.71 which is valuable for studying acidic organelles in living cells.•This probe exhibits excellent membrane-permeable and low cytotoxicity.•This probe was successfully used to monitor lysosomal pH changes in HeLa cells. We designed and synthesized a new pH fluorescent probe, RCE, based on structural changes of rhodamine dye at different pH values. The probe exhibits high selectivity, high sensitivity and quick response to acidic pH, as well as low cytotoxicity, excellent photostability, reversibility and cell membrane permeability. Fluorescence intensity at 584nm was increased more than 150-fold within pH range 7.51–3.53. This probe has pKa value 4.71, which is valuable for studying acidic organelles. Because of its long absorption and emission wavelengths, RCE can avoid associated cell damage. The probe can selectively stain lysosomes and monitor lysosomal pH changes in living cells.