N-DBCO-N-bis(PEG2-NHS ester) is a PEG derivative which contains two PEG2-NHS ester groups and a DBCO group. The DBCO group allows for the compound to undergo copper-free Click Chemistry reactions. The NHS esters can be used to label the primary amines (-NH2) of proteins, amine-modified oligonucleotides, and other amine-containing molecules. The hydrophilic PEG linker increases the water solubility properties of the compound.