Cy3-PEG-N3 (MW 3400) is a Cy3 azide fluorescent dye used for labeling amino groups in peptides, proteins, and oligonucleotides. As a click chemistry reagent, it features an azide group that can participate in a copper-catalyzed azide-alkyne cycloaddition reaction (CuAAC) with alkyne-containing molecules. Additionally, it can undergo a strain-promoted alkyne-azide cycloaddition reaction (SPAAC) with molecules possessing DBCO or BCN groups.