Cell/membrane permeable, non-toxic, pH-sensitive fluorescent dye (blue-green range) for live imaging of pH alteration in acidic organelles, lysosomes, autophagolysosomes, vesicles, cells, tissue and even small, transparent whole animals without side effects. Useful as intracellular pH indicator with a wide range of fluorescence (pH 3 to pH 13). pH-dependent dual-emission peaks, can be used for ratiometric evaluation of pH (F400/440). No esterases are involved, therefore no toxic by-products occur. Long-term stable; is barely metabolized. Fluorescence co-localizes with LysoTracker® Red DND-99. (LysoTracker® is a registered trademark of Molecular Probes, Inc.)