生物素，链霉亲和素

The avidin-biotin system is widely used for bioanalysis and bioassays including flow cytometry, ELISA, immunohistochemical staining, western blotting and others.
Biotin labeling (biotinylation) is also commonly used for conjugating proteins, especially antibodies, and other various molecules. Biotinylation is one of the most essential methods in the field of immunoassay where antigens are detected using antibodies.
Streptavidin is a protein from the avidin family having extraordinarily high affinity for biotin, in fact, the interaction of biotin with streptavidin is among the strongest non-covalent affinities known in nature. In order to detect the biotinylated substance, modification of streptavidin with fluorescent label or enzyme is required.
The biotinylated substance and the labeled-streptavidin are used in various assays based on the avidin-biotin system.