Thiol-PEG3-phosphonic acid ethyl ester is widely used in bioconjugation and surface modification applications. Its thiol group enables it to form stable bonds with gold, silver, and other metal surfaces, making it valuable for creating self-assembled monolayers (SAMs) in nanotechnology and biosensor development. The PEG3 spacer enhances solubility and reduces non-specific interactions, which is crucial in biomedical applications. Additionally, the phosphonic acid ethyl ester group allows for strong anchoring to metal oxide surfaces, such as titanium or iron oxide, facilitating its use in drug delivery systems and functionalized nanoparticles. This compound is also employed in the synthesis of targeted drug conjugates, where it acts as a linker to attach therapeutic agents to biomolecules like antibodies or peptides. Its versatility makes it a key component in designing advanced materials for diagnostics, therapeutics, and nanotechnology.