Used in bioconjugation for targeted labeling and detection of biomolecules. The azide group enables click chemistry reactions, particularly copper-catalyzed azide-alkyne cycloaddition (CuAAC), allowing efficient coupling with alkyne-functionalized molecules. The PEG spacers enhance solubility, reduce aggregation, and improve accessibility of the biotin tag to streptavidin-binding sites. Commonly applied in proteomics, cell surface labeling, and development of diagnostic assays where precise tagging and strong streptavidin interaction are required. Ideal for multi-step labeling strategies due to the stability and specificity of the biotin-streptavidin system.