Used in bioconjugation to link proteins, peptides, or other biomolecules selectively through thiol groups. The maleimide group reacts efficiently with cysteine residues, forming stable thioether bonds, while the NHS ester reacts with primary amines, enabling dual functionality for crosslinking. Commonly applied in preparing antibody-drug conjugates, immobilizing biomolecules on surfaces, and labeling proteins with fluorescent dyes or biotin. Its spacer arm provides flexibility and reduces steric hindrance, improving reaction efficiency in aqueous solutions at physiological pH.