Used in bioconjugation processes to label biomolecules such as proteins, antibodies, or nucleic acids with biotin. The PFP-ester group reacts efficiently with primary amines (e.g., lysine residues) under mild conditions, forming stable amide bonds. This allows for the detection, isolation, or immobilization of biotinylated molecules using streptavidin-based systems, commonly applied in ELISA, Western blotting, flow cytometry, and affinity purification. The high reactivity of the pentafluorophenyl (PFP) ester enables labeling at lower pH and reduces hydrolysis compared to other active esters, improving conjugation efficiency.