Used in bioconjugation to link biotin to proteins, antibodies, or other biomolecules via primary amines. The PEG4 spacer improves solubility and reduces steric hindrance, enhancing binding efficiency to streptavidin or avidin surfaces. Commonly applied in ELISA, flow cytometry, and immunoprecipitation assays. Also used in surface functionalization of biosensors and microarrays for improved detection sensitivity. Stable under standard labeling conditions and allows for site-specific biotinylation.