Briefly describe the technical types of enzyme-linked immunosorbent assay.

Enzyme-linked immunosorbent assay Enzyme-linked immunosorbent assay (ELISA) is the most widely used technology in enzyme immunoassay. The basic method is to adsorb known antigens or antibodies on the surface of solid phase carrier (polystyrene micro-reaction plate), so that the enzyme-labeled antigen-antibody reaction is carried out on the surface of solid phase, and the free components in liquid phase are washed away by washing. The commonly used ELISA methods are double antibody sandwich method and indirect method. Since Engvall and Perlman( 197 1) first reported the establishment of enzyme-linked immunosorbent assay (ELISA), ELISA has the advantages of rapidity, sensitivity, simplicity and easy standardization. It has been rapidly developed and widely used. Although the specificity of early ELISA was not enough to hinder its practical application, the specificity of ELISA was greatly improved with the continuous improvement of methods and materials, especially the preparation of genetically engineered coated antigens and the blocking ELISA test of monoclonal antibodies against an epitope. In addition, the use of highly computerized ELISA detector makes ELISA more simple, practical and standardized, thus making it one of the most widely used detection methods. At present, ELISA has been widely used in the diagnosis of many diseases such as bacteria and viruses. In animal quarantine, ELISA has been widely used as a standard method to diagnose porcine infectious gastroenteritis, bovine paratuberculosis, bovine infectious rhinotracheitis, porcine pseudorabies and bluetongue disease.