Used in bioconjugation to link molecules via primary amines, particularly in the development of antibody-drug conjugates (ADCs) and targeted therapeutics. The NHS ester reacts efficiently with lysine residues or N-terminal amines on proteins, while the maleimide group enables selective coupling to thiol-containing molecules like cysteine residues or thiolated peptides. The PEG3 spacer improves solubility, reduces aggregation, and enhances the stability of conjugates. Commonly applied in pharmaceutical research, diagnostics, and surface functionalization of nanoparticles and biosensors.