Azido-PEG3-phosphonic acid ethyl ester is widely used in bioconjugation and chemical biology research. Its azide group enables click chemistry reactions, particularly copper-catalyzed azide-alkyne cycloaddition (CuAAC), making it valuable for labeling, modifying, or linking biomolecules like proteins, peptides, and nucleic acids. The PEG spacer enhances solubility and reduces steric hindrance, improving reaction efficiency in aqueous environments. Additionally, the phosphonic acid ethyl ester group allows for further functionalization or attachment to surfaces, making it useful in developing biosensors, drug delivery systems, and surface coatings. Its versatility supports applications in drug discovery, diagnostics, and materials science.