Both avidin and biotin can bind to proteins (including antigens, antibodies, enzymes, etc.) and fluorescein without affecting the biological activity of the latter. An antibody molecule can couple dozens of biotin or avidin molecules, and avidin or biotin molecules can bind to enzymes or fluorescein to form a biomagnification system, which can significantly improve the sensitivity of detection. Biotin is a small molecule that binds to avidin and streptavidin with very high affinity. When used in immunohistochemical techniques, the affinity of interaction makes biotin an excellent conjugate for detection. Biotin conjugates can be used in signal amplification technology. The commonly used methods are avidin biotin labeling method (LAB), avidin-biotin bridge method (BAB) and avidin-biotin peroxidase complex method (ABC).