HO-PEG-COOH is widely used in bioconjugation and drug delivery systems due to its biocompatibility and water solubility. It serves as a linker molecule, connecting drugs or therapeutic agents to targeting molecules like antibodies or peptides, enhancing their stability and circulation time in the body. In nanotechnology, it is utilized to modify the surface of nanoparticles, improving their dispersibility and reducing immune system recognition. Additionally, it is employed in the development of hydrogels for tissue engineering, providing a scaffold for cell growth and regeneration. Its carboxyl group allows for further functionalization, making it versatile in creating tailored biomaterials for medical and research applications.