Cy5-PEG-N3 (MW 10000) is a Cy5 azide fluorescent dye utilized for labeling amines in peptides, proteins, and oligonucleotides. As a click chemistry reagent, it features an azide group that can undergo copper-catalyzed azide-alkyne cycloaddition (CuAAC) with molecules containing alkyne groups. Additionally, it can participate in strain-promoted azide-alkyne cycloaddition (SPAAC) with molecules that have DBCO or BCN groups.