Used extensively in biochemical and cellular research as a fluorescent labeling reagent. It is particularly effective for tagging proteins, peptides, and other biomolecules due to its reactive NHS ester group, which forms stable amide bonds with primary amines. This labeling enables visualization and tracking of biomolecules in various assays, such as fluorescence microscopy, flow cytometry, and ELISA. Its high quantum yield and pH-sensitive fluorescence make it suitable for studying cellular processes, including endocytosis, receptor binding, and intracellular pH changes. Additionally, it is employed in drug delivery studies to monitor the uptake and distribution of therapeutic agents in cells and tissues.