Used in surface modification to introduce hydrophilic PEG layers with reactive carboxyl end groups. Enables bioconjugation by coupling to amine-containing biomolecules like proteins, peptides, or antibodies through EDC/NHS chemistry. Commonly applied in biosensors, diagnostic devices, and biomedical coatings to reduce non-specific binding and improve biocompatibility. Facilitates immobilization of biomolecules on glass, silicon, or metal oxide surfaces via silane coupling. Also used in drug delivery systems and nanomaterial functionalization for targeted therapy. Stable PEG spacer enhances solubility and prolongs circulation time in biological environments.