Methyltetrazine-PEG4-DBCO is a multifunctional linker comprising two distinct chemical moieties: a methyltetrazine group that enables rapid bioorthogonal ligation via inverse electron-demand Diels-Alder reactions, and a dibenzocyclooctyne (DBCO) group for copper-free click chemistry. The PEG4 spacer imparts water solubility and reduces steric hindrance, thereby enhancing the molecule’s overall performance.