Used in bioconjugation to link biomolecules such as peptides, proteins, or antibodies with other molecules like fluorophores, drugs, or nanoparticles. The maleimide group reacts selectively with thiol groups (-SH) from cysteine residues, forming stable thioether bonds. The PFP ester end reacts efficiently with primary amines (-NH₂) on target molecules, enabling dual functionalization. The PEG4 spacer improves solubility, reduces aggregation, and increases flexibility between conjugated components, making it ideal for developing antibody-drug conjugates (ADCs), diagnostic probes, and targeted therapeutics. Commonly used in pharmaceutical research and development of bioactive conjugates.