Used in bioconjugation and surface modification, it serves as a linker molecule to attach biomolecules like proteins or peptides to surfaces or nanoparticles. Its phosphonic acid group enables strong binding to metal oxides, making it valuable in creating stable coatings for medical devices or biosensors. The PEG4 spacer enhances solubility and reduces steric hindrance, improving efficiency in drug delivery systems. It is also employed in nanotechnology for functionalizing materials to enhance biocompatibility and targeting capabilities.