NH2-PEG-COOH is widely used in bioconjugation and drug delivery systems due to its dual functional groups. The amine (NH2) group allows for easy attachment to carboxylic acids or activated esters, while the carboxyl (COOH) group can be coupled with amines or other nucleophiles. This makes it a versatile linker for modifying proteins, peptides, and nanoparticles. In drug delivery, it enhances solubility and stability of therapeutic agents, prolonging their circulation time in the body. It is also employed in surface modification of materials to improve biocompatibility and reduce immunogenicity. Additionally, NH2-PEG-COOH is utilized in the development of hydrogels and other biomaterials for tissue engineering applications.