Widely used in bioconjugation and drug delivery systems due to its cleavable disulfide linker and hydrophilic PEG spacers. The dual acid termini allow for easy activation and coupling to amine-containing molecules such as peptides, proteins, or small molecule drugs. The PEG3 segments enhance solubility and reduce aggregation, while the SS (disulfide) bond is sensitive to reducing environments, enabling intracellular release of payloads—especially in the cytoplasm where glutathione levels are high. Commonly employed in the synthesis of antibody-drug conjugates (ADCs), targeted therapies, and stimuli-responsive nanocarriers. Its bifunctional structure supports the construction of symmetric conjugates or cross-linked complexes in controlled drug release and bioconjugate engineering.