Cy5.5-PEG-N3 (MW 10000) is a Cy5.5 azide fluorescent dye used for amino groups in peptides, proteins, and oligonucleotides. It serves as a click chemistry reagent, featuring an azide group that can undergo copper-catalyzed azide-alkyne cycloaddition (CuAAc) with alkyne-containing molecules. Additionally, it can participate in strain-promoted azide-alkyne cycloaddition (SPAAC) with molecules containing DBCO or BCN groups.