TCO-PEG4-TFP Ester is an amine-reactive labelling reagent used to modify amine-containing biopolymers including proteins and antibodies. A 2,3,5,6-tetrafluorophenol (TFP) is a reactive ester that has much better stability towards hydrolysis in aqueous media, resulting in more efficiency and more reproducible labelling of biopolymers. The TFP ester of carboxylic acids reacts with primary amines, at the same rate as an NHS ester, forming a covalent amide bond that is identical to the one formed by the reaction between primary amines and NHS esters/sulfo-NHS esters.