Bioconjugation is a chemical strategy to form a stable covalent link between two molecules, at least one of which is a biomolecule. This strategy allows for designing molecules with a double function.

It is one of the main strategies for delivering oligonucleotide-based drugs. 

An active molecule with a therapeutical goal – in this case, an oligonucleótide- is joined with a strong chemical bond (covalent link) to another functional molecule (it could be a protein, an oligonucleotide, or any other structure) which can recognize specific molecules in the membrane of the cells of a chosen organ. In addition, this second molecule can also enhance the specific properties of the first molecules.

Within the body, once the functional molecule reaches the cells, the covalent link is broken, and the two molecules separated. The therapeutical oligonucleotide-based molecule will start the biological function for which it was designed.

• Bioconjugation starts from an understandable and rational design of molecules. Separately, the molecules that build up a bioconjugate were previously well tested in the laboratory and their properties have been deeply studied. However, when they are joined, the bioconjugated molecule has its own properties. 
• Bioconjugated units are joined by a particular unit called a linker. These linkers are broken in specific conditions. For example, they can be broken by enzymes or the specific acidic medium within the cells..
• Because they should be considered, such as new and different molecules to their units, bioconjugates have to pass through an identical process of pharmaceutical research and development as as any other new experimental drug.