Sulfo-Cy7.5 azide is a derivative of the Cyanine 7.5 (Cy7.5) dye, featuring azide and sulfonate functional groups. The sulfonate group enhances the compound's solubility in water, making it suitable for aqueous solutions. As a near-infrared fluorescent dye, Cy7.5 is widely used in biological labeling and cell imaging. The azide group of Sulfo-Cy7.5 azide enables click chemistry reactions with molecules containing alkyne functional groups, such as alkynes or cyclooctynes, allowing it to form covalent bonds. This property facilitates its conjugation with biomolecules like proteins and antibodies for tracking their location and dynamics in biological samples. The compound can participate in copper-catalyzed azide-alkyne cycloaddition (CuAAC) with alkyne groups or undergo strain-promoted alkyne-azide cycloaddition (SPAAC) with molecules containing DBCO or BCN groups.