Azide-PEG4-Tos is widely used in bioconjugation and click chemistry applications. Its azide group enables efficient reactions with alkynes via copper-catalyzed azide-alkyne cycloaddition (CuAAC), making it valuable for labeling biomolecules such as proteins, peptides, and nucleic acids. The PEG4 spacer enhances solubility and reduces steric hindrance, improving reaction efficiency. The tosyl group allows for further functionalization or attachment to specific targets, making it a versatile tool in drug delivery systems, surface modification, and the development of bioconjugates for research and therapeutic purposes.