Used in bioconjugation reactions for labeling and modifying biomolecules due to its bifunctional nature. The aldehyde group reacts selectively with primary amines or hydrazides, while the azide enables copper-catalyzed or strain-promoted click chemistry with alkynes. Commonly applied in PEGylation of peptides, proteins, and nanoparticles to improve solubility, stability, and biocompatibility. Also utilized in constructing complex molecular architectures for drug delivery systems, diagnostic probes, and surface functionalization in biosensors. The long PEG spacer reduces steric hindrance, enhancing reaction efficiency and accessibility in biological environments.