Used in bioconjugation processes, particularly in the preparation of antibody-drug conjugates (ADCs) and protein labeling. Its structure contains a maleimide group that selectively reacts with thiol groups (cysteine residues) in proteins, enabling stable linkage. The long, hydrophilic PEG-like spacer improves solubility and reduces aggregation in biological systems, enhancing the pharmacokinetics of conjugated molecules. Commonly applied in targeted drug delivery, diagnostic probes, and immunoassays where precise coupling of payloads to biomolecules is required.