Used in bioconjugation to link biomolecules selectively, especially in antibody-drug conjugates and protein labeling. The TCO group reacts rapidly and specifically with tetrazine via click chemistry, enabling fast ligation under physiological conditions. The PEG3 spacer improves solubility and reduces steric hindrance, enhancing reaction efficiency. The maleimide end binds selectively to thiol groups on cysteine residues, allowing stable attachment to proteins, peptides, or thiolated surfaces. Commonly applied in drug delivery, targeted therapy, and diagnostic imaging due to its high selectivity and biocompatibility.