Sulfo DBCO-PEG4-TFP ester is a short PEG linker featuring a DBCO group, a sulfate, and a TFP ester. DBCO is a click chemistry handle which efficiently reacts with azide groups on target molecules, while the TFP is a good leaving group which is readily displaced by nucleophiles such as amines. Finally, the sulfate group is able to increase the solubility of this linker.