Used as a fluorescent labeling agent in biochemical and cellular studies, particularly for tagging proteins and peptides. Its maleimide group reacts selectively with thiol groups (cysteine residues), making it ideal for conjugation in bioconjugation techniques. Widely applied in fluorescence microscopy, flow cytometry, and immunoassays due to its strong and stable fluorescence. Also employed in studying protein-protein interactions and cellular localization in live and fixed cells.