Used in bioconjugation to link proteins, peptides, or other biomolecules to carriers or labels. The maleimide group reacts selectively with thiol groups (-SH), commonly found in cysteine residues, while the NHS ester reacts with primary amines (-NH₂), typically present in lysine residues or N-termini of proteins. This dual reactivity allows for controlled and efficient crosslinking in the development of antibody-drug conjugates (ADCs), diagnostic probes, and targeted therapeutics. Commonly employed in preparing functionalized molecules for immunoassays, imaging agents, and drug delivery systems. Stable and effective in aqueous conditions at physiological pH, making it suitable for use in biological systems.