Used in bioconjugation processes to link proteins, peptides, or antibodies with other molecules such as drugs, labels, or surfaces. The PEG spacer provides increased solubility and reduced aggregation, while the SPDP group enables cleavable disulfide bond formation. Commonly applied in the development of antibody-drug conjugates (ADCs) and targeted therapeutics where controlled release is required. Also utilized in immobilizing biomolecules on biosensor surfaces or nanoparticles for diagnostic and research applications.