N-(Azido-PEG4)-N-bis(PEG4-acid) is widely used in bioconjugation and chemical biology due to its dual functional groups. The azide group enables click chemistry reactions, particularly copper-catalyzed azide-alkyne cycloaddition (CuAAC), for labeling and modifying biomolecules. The PEG4 spacers enhance solubility and reduce steric hindrance, making it suitable for attaching molecules to surfaces, proteins, or nanoparticles. Its bis(PEG4-acid) groups allow further functionalization, such as coupling with amines or creating crosslinked structures. This compound is valuable in drug delivery systems, where it aids in creating targeted and biocompatible conjugates. Additionally, it is employed in material science for modifying surfaces to improve biocompatibility or enable specific interactions. Its versatility makes it a key reagent in developing probes, therapeutic agents, and advanced biomaterials.