2-(Azido-PEG3-amido)-1,3-bis(NHS Ester) is a branched PEGylation reagent. The azide groups enable PEGylation via Click Chemistry. The NHS ester can be used to label the primary amines (-NH2) of proteins, amine-modified oligonucleotides, and other amine-containing molecules. The PEG spacer allows for enhanced hydrophilic properties.