Acid-PEG3-SS-PEG3-acid is a is a homobifunctional, cleavable PEG linker. Carboxylic acids can react with primary amines in the presences of activators such as EDC and HATU. The disulfide bonds can be cleaved by Dithiothreitol (DTT) reagent. PEG spacer increase the compound's solubility.