Used in surface modification to introduce hydrophilic and reactive functional groups. The COOH group allows conjugation with amines via EDC/NHS chemistry, making it useful for immobilizing biomolecules like proteins, peptides, or antibodies onto surfaces such as glass, silicon, or metals. The PEG spacer reduces non-specific binding and enhances stability in biological environments. Commonly applied in biosensors, diagnostic devices, and bioconjugation. Also used in nanoparticle coating to improve solubility and biocompatibility. Enables the creation of functional coatings in medical devices and drug delivery systems.