DBCO reagent is a class of click chemistry labeling reagents containing a very reactive DBCO ((Dibenzocyclooctyne) group, DBCO reagent can react with azide-tagged molecules or biomolecules via copper-free Click Chemistry. DBCO click chemistry can be run in aqueous buffer or in organic solvents depending on the property of the substrate molecules. Reagents with PEG arm will increases the compound's hydrophilicity. DBCO reagent has become widely used in bioconjugation, labeling and chemical biology.