ICG PEG N3 (MW 2000) is an indocyanine green (ICG) azide fluorescent dye utilized for labeling amino groups in peptides, proteins, and oligonucleotides. This compound serves as a click chemistry reagent, featuring an azide group that enables copper-catalyzed azide-alkyne cycloaddition (CuAAC) with alkynyl-containing molecules. It can also participate in strain-promoted azide-alkyne cycloaddition (SPAAC) with molecules containing DBCO or BCN groups, exhibiting excitation and emission at 785/813 nm respectively.