Widely used as a fluorescent probe for measuring intracellular pH due to its high sensitivity and pH-dependent emission properties. It is cell-permeable, allowing it to enter live cells where esterases cleave the acetoxymethyl groups, trapping the charged form inside. This makes it ideal for monitoring pH changes in organelles and cytoplasm using fluorescence microscopy or flow cytometry. Commonly applied in cell biology and physiology studies to assess acidification processes, endosomal trafficking, and lysosomal activity. Its multiple carboxyl groups enhance water solubility and reduce nonspecific binding, improving signal accuracy.