Cy3-PEG-N3 (MW 2000) is a Cy3 azide fluorescent dye designed for labeling amino groups in peptides, proteins, and oligonucleotides. This compound acts as a click chemistry reagent, featuring an azide group that can partake in a copper-catalyzed azide-alkyne cycloaddition reaction (CuAAc) with molecules containing alkyne groups. Additionally, it is capable of undergoing strain-promoted alkyne-azide cycloaddition (SPAAC) with molecules that have DBCO or BCN groups.