– Cy5-PEG-N3 (MW 5000) is a Cy5 azide fluorescent dye used for labeling amines in peptides, proteins, and oligonucleotides. As a versatile click chemistry reagent, it contains 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.