The Biotin-Avidin-System (BAS) is a new type of bioreactor amplification system developed in the late 1970s. The strong combination of high affinity between biotin and avidin and multi-stage amplification effect make BAS immunolabeling and related tracer analysis more sensitive. BAS has been widely used in the qualitative, quantitative detection and localization observation of antigens and antibodies.

Biotin (B) is widely distributed in animal and plant tissues, and is often extracted from high content yolk and liver tissue with a molecular weight of 244.31 Da. The biotin molecule has two cyclic structures (Fig. 1), wherein the ring I is an imidazolidone ring and is the main site of binding to avidin; the ring II is a thiophene ring, and the C2 has a valeric acid side chain, and the terminal carboxyl group It is the only structure that binds antibodies and other biological macromolecules. After chemical modification, biotin can become a derivative with multiple active groups - activated biotin (Figure 2).

Avidin (AV), also known as avidin, avidin, is a basic glycoprotein consisting of four identical subunits extracted from ovalbumin with a molecular weight of 68 kD. Four identical subunits allow each avidin to bind up to four molecules of biotin. Biotin and avidin have a strong affinity, and the affinity between antigen and antibody is much higher. Moreover, the combination of the two is stable and specific.


Sensitive biotin easily combines with proteins, nucleic acids and other biomacromolecules to form biotin derivatives that not only maintain the original biological activity of macromolecular substances, but also have multivalent properties. In addition, each avidin molecule has four biotin binding sites that simultaneously bind to biotinylated macromolecular derivatives and labels in a multivalent form. Therefore, the BAS has a multi-stage amplification effect, which greatly improves the sensitivity of the detection method when applied.


The binding between specific avidin and biotin is highly specific. Therefore, the multi-level amplification of BAS does not increase non-specific interference while increasing sensitivity. Moreover, the BAS binding properties are not affected by the high dilution of the reagents. Therefore, the non-specific effects of the reagents can be minimized in practical applications.


The affinity constant of the stable avidin binding biotin can be a million times of the antigen-antibody reaction, and the dissociation constant of the combination of the two forms is small and irreversible; and the acid, the base, the denaturing agent, and the protein Hydrolysis enzymes and organic solvents do not affect their binding. Therefore, in practical applications, the stability of the product is high, which can reduce the operation error and improve the accuracy of the measurement.


Applicability Biotin and avidin can form a wide variety of derivatives. These derivatives can be used for a series of detection and isolation purification by labels (such as enzymes, fluorescein or radioactive elements), including antigen-antibodies, hormone-receptors, nucleic acid systems, and the like in cells, tissues, and body fluids. At the same time, some BAS-based reagents that have been marketed have also facilitated clinical diagnosis and research.


Other BAS can be made into a variety of general-purpose reagents (such as biotinylated secondary antibodies) according to the specific experimental methods, and can be highly diluted, with a small amount and low experimental cost; especially BAS and The costly antigen-specific primary antibody is coupled to use, which can greatly reduce the amount of the latter and save the experimental cost. In addition, because the combination of biotin and avidin has fast and efficient characteristics, although the reaction level of BAS is more, the incubation time required is not long, and the experiment often takes only a few hours to complete.


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