DBCO (Dibenzocyclooctyne) is a cycloalkyne that can reacts with azides via strain-promoted 1,3-dipolar cycloaddition in aqueous solution, a bioorthogonal reaction also termed Cu-free click reaction.  This reaction has excellent selectivity and biocompatibility, such that the complimentary reagents can form covalent bonds with richly functionalized biological systems. The Cu-free click reaction has been a powerful tool in catalyst-free bioconjugation. DBCO reagents posses fast kinetcs and stability in aqueous buffer and they can be used to label azide-modified biomolecules with high specificity and reactivity.