Widely used in bioconjugation and labeling applications, especially in fluorescence-based imaging and detection. Its azide group enables click chemistry reactions, particularly copper-catalyzed azide-alkyne cycloaddition (CuAAC), allowing specific and efficient attachment to alkyne-modified biomolecules such as proteins, antibodies, nucleic acids, or small molecules. The sulfo group enhances water solubility and reduces nonspecific binding, making it ideal for use in biological systems and live-cell imaging. Emits strong red fluorescence, suitable for detection with standard Cy3 filter sets in fluorescence microscopy, flow cytometry, and microarray analysis. Commonly used in proteomics, cell biology, and diagnostic assays where sensitive, specific labeling is required. The triethylamine (Et3N) salt form improves solubility and stability in aqueous buffers.