Used primarily as a fluorescent labeling reagent for thiol groups in biomolecules such as proteins and peptides. Its high reactivity toward sulfhydryl groups allows selective tagging, enabling detection and visualization in biochemical assays. Commonly applied in fluorescence microscopy, flow cytometry, and gel-based imaging to track protein localization and interactions. Also employed in the development of fluorescent probes and sensors due to its strong emission and photostability. Suitable for both in vitro and cellular applications where sensitive detection is required.