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 moieties, enhancing their stability and circulation time in the body. In nanotechnology, it is utilized to modify nanoparticles, improving their dispersibility and reducing immunogenicity. Additionally, it plays a role in surface functionalization of biomaterials, making them more suitable for biomedical applications such as tissue engineering and biosensors. Its carboxyl group allows for further chemical modifications, enabling the attachment of various bioactive molecules.