Bioconjugation is the process of coupling two biomolecules together in a covalent linkage.[1] Common types of bioconjugation chemistry are amine coupling of lysine amino acid residues (typically through amine-reactive succinimidyl esters), sulfhydryl coupling of cysteine residues (via a sulfhydryl-reactive maleimide), and photochemically initiated free radical reactions, which have broader reactivity. The product of a bioconjugation reaction is a bioconjugate.
The most common bioconjugations are coupling of a small molecule (such as biotin or a fluorescent dye) to a protein, or protein-protein conjugations, such as the coupling of an antibody to an enzyme. Other less common molecules used in bioconjugation are oligosaccharides, nucleic acids, synthetic polymers such as polyethylene glycol (a.k.a. PEG a.k.a. polyethylene oxide),[2] and carbon nanotubes. [3]