Used in bioconjugation processes to label biomolecules such as proteins, antibodies, and nucleic acids. The ester reacts with primary amines to form stable amide bonds, allowing biotin to be attached to target molecules. Once biotinylated, these molecules can be detected or captured using streptavidin or avidin systems, which are commonly used in ELISA, Western blotting, immunohistochemistry, and flow cytometry. The 4-nitrophenyl group enhances reactivity and provides a leaving group that improves labeling efficiency. Also employed in the development of biosensors and diagnostic assays where high-affinity biotin-streptavidin interaction is leveraged for signal amplification and detection.