Used in bioconjugation to label biomolecules such as proteins, peptides, and antibodies with a fluorescent tag. The NHS ester group reacts efficiently with primary amines, forming a stable amide bond, making it ideal for labeling amine-containing molecules under mild conditions. Commonly applied in fluorescence microscopy, flow cytometry, and immunostaining to visualize cellular components. Also used in nucleic acid labeling when coupled to modified oligonucleotides, enabling detection in hybridization assays. Its bright fluorescence and photostability support sensitive detection in imaging and analytical applications.