Used in bioconjugation to modify proteins, peptides, and nanoparticles by attaching polyethylene glycol (PEG) chains, improving solubility, stability, and circulation time in biological systems. Commonly applied in drug delivery systems to reduce immunogenicity and prevent rapid clearance. Enables controlled attachment of PEG to primary amines on biomolecules under mild reaction conditions. Widely used in developing PEGylated therapeutics and functionalizing surfaces in diagnostic assays and biosensors.