Used as a fluorescent labeling reagent in bioconjugation and bioimaging applications. Its bright red fluorescence and high photostability make it ideal for detecting biomolecules such as proteins, antibodies, and nucleic acids in techniques like fluorescence microscopy, flow cytometry, and immunoassays. The carboxylic acid group allows for easy coupling to amine-containing molecules using standard carbodiimide chemistry, enabling the creation of stable fluorescent conjugates for research and diagnostic purposes.