Cy3-PEG-N3 (MW 10000) is a Cy3 azide fluorescent dye used for labeling amines in peptides, proteins, and oligonucleotides. As a click chemistry reagent, it contains an azide group that participates in copper-catalyzed azide-alkyne cycloaddition reactions (CuAAc) with alkyne-containing molecules. Additionally, it can undergo strain-promoted azide-alkyne cycloaddition (SPAAC) reactions with molecules containing DBCO or BCN groups.