Bromo-PEG3-azide is a PEG linker containing a bromide group and an azide group. The hydrophilic PEG spacer increases solubility in aqueous media. The azide group can react with alkyne, BCN, DBCO via Click Chemistry to yield a stable triazole linkage. The bromide (Br) is a very good leaving group for nucleophilic substitution reactions.