m-PEG9-phosphonic acid is widely used in the field of bioconjugation and surface modification due to its unique properties. It is often employed to improve the solubility and stability of biomolecules, such as proteins and peptides, by attaching the PEG chain to their surfaces. This modification helps reduce immunogenicity and prolongs circulation time in biological systems, making it valuable in drug delivery applications. Additionally, the phosphonic acid group allows for strong binding to metal oxide surfaces, enabling the functionalization of nanoparticles, implants, or medical devices to enhance biocompatibility and reduce fouling. Its use is also explored in creating stealth liposomes and targeted therapeutic systems for improved efficacy in cancer treatment and other medical therapies.