PDMPO SE is a PH fluorescent probe, existing pH probes are not suitable for studying acidic organelles such as lysosomes, endosomes, phagosomes, sperm and acrosomes because their fluorescence is greatly reduced at lower pH values. Although proportional imaging has received a lot of attention in the past few decades, the growth potential of proportional imaging has been greatly limited by the lack of suitable acid organelle fluorescent probes. PDMPO is characterized by double excitation and double emission of pH probes to acidity. A strong yellow fluorescence is emitted at lower pH values, while a strong blue fluorescence is emitted at higher pH values. This unique ph-dependent fluorescence makes PDMPO an ideal pH probe for acidic organelles with pKa = 4.47. In addition, the large Stokes shift and excellent photostability of PDMPO make it an excellent fluorescent acidic agent for fluorescence imaging and flow cytometry applications. The unique fluorescent properties of PDMPO may provide researchers with a new tool to study endocytosis, phagocytosis, and acid organelles in living cells. In flow cytometry applications, PDMPO can be excited well by a 405 nm purple laser. PDMPO SE can be easily used to manufacture a variety of bioconjugates for imaging or blood flow applications, enabling specific detection of phagocytosis and endocytosis with reduced signal variability and greater accuracy. These conjugations can also be used for cell function multiplexing analysis with green dyes such as GFP, Fluo-8, calcein, or FITC-labeled antibodies.