Amino-PEG8-t-Boc-hydrazide is a crosslinker containing an amino group and a Boc-protected hydrazide. The hydrophilic PEG spacer increases solubility in aqueous media. The amine group is reactive with carboxylic acids, activated NHS esters, carbonyls (ketone, aldehyde) etc. The Boc can be deprotected under mild acidic conditions to form a reactive hydrazide, which can then be coupled with various carbonyl groups.