Ald-CH2-PEG8-azide is a monodisperse PEG crosslinker containing an azide group and an aldehyde group. The azide group enables PEGylation via Click Chemistry. PEG8 spacer increases solubility in aqueous media. aldehyde can be used in PEGylation through its reaction with hydrazine or hydrazide forming a hydrolytic acyl hydrozone linkage.