mPEG-COOH is widely used in bioconjugation and drug delivery systems due to its ability to improve the solubility, stability, and biocompatibility of therapeutic agents. It is commonly employed to modify proteins, peptides, and nanoparticles, enhancing their circulation time in the body and reducing immunogenicity. In drug delivery, it serves as a linker to attach targeting molecules or drugs, enabling controlled release and targeted therapy. Additionally, it is utilized in the development of hydrogels and biomaterials for tissue engineering, where it promotes cell adhesion and growth. Its carboxyl group allows for easy functionalization, making it a versatile tool in biomedical research and pharmaceutical applications.