N-(Azido-PEG4)-biocytin is a biotin PEG derivative containing a carboxylic group and an azide group. Reaction of carboxylic with primary amino (-NH2) forms stable, irreversible amide bonds. The azide group can react with alkyne moiety in Cu(I)-catalyzed Click Chemistry reaction or DBCO moiety in copper-free Click Chemistry reaction to form a stable triazole linkage. The hydrophilic PEG spacer increases solubility in aqueous media of the molecules conjugated to the biotin compound.
