TCO-PEG3-triethoxysilane is a PEG derivative containing a triethoxysilane moiety and a TCO group. Triethoxysilane is commonly used for surface modifications. This reagent can react with tetrazine-containing compounds to form a stable covalent bond without the catalysis of Cu or elevated temperatures. The inverse-electron demand Diels-Alder cycloaddition reaction of TCO with tetrazines is the fastest bioorthogonal reaction with exceptional selectivity. The hydrophilic PEG chain increases the water solubility of a compound in aqueous media.