Methylamino-PEG3-azide is a PEG linker containing an azide group with a methylamine 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 methylamine group is reactive with carboxylic acids, carbonyls (ketone, aldehyde) etc.