Enzyme immunoassay (EIA) is a microanalytical technique that combines the efficiency of enzyme catalysis with the specificity of antigen-antibody reaction. The enzyme label formed by the enzyme labeling the antigen antibody not only retains the immunological activity of the antigen or the antibody, but also retains the catalytic activity of the enzyme. When the enzyme label interacts with a corresponding antigen or antibody in the sample to be tested, an enzyme-labeled antigen-antibody complex can be formed. The color of the substrate is catalyzed by the enzyme labeled on the complex, and the color depth is related to the amount of antigen or antibody in the sample to be tested. The sensitivity of this method can reach ng~pg/ml level. Commonly used markers are horseradish peroxidase HRP and alkaline phosphatase AP. Enzyme immunoassay is divided into enzyme linked immunosorbent assay (ELISA) and enzyme immunohistochemistry technique. The former is used to determine soluble antigen or antibody, and the latter is used to determine antigen on tissue or cell surface. . Homogeneous enzyme immunoassay Taking the antigen in the labeled antibody detection sample as an example, in a simple form, in the case of an excess of the reagent antibody: Ab*+Ag-Ab*Ag+Ab* If the label "*" in Ab*Ag loses its characteristics after the antigen-antibody reaction, for example, the enzyme loses its activity, the separation of Ab*Ag and Ab* is not required, and the amount of free Ab* can be directly determined, thereby indirectly To calculate the Ag content in the specimen, this method is called homogeneous enzyme immunoassay. The object of the homogeneous enzyme immunoassay is a small molecule antigen or hapten, which is mainly used for drug determination. The measurement mode of the homogeneous enzyme immunoassay is a competition inhibition method, and the enzyme is labeled with an antigen to be tested, and the detection reagent also has a substrate for the antibody and the enzyme of the antigen to be tested. The enzyme that binds to the antibody loses its viability, so the assay can be carried out without separating the bound enzyme from the free enzyme in the reaction. The reaction process is the same as the general biochemical measurement, so it can be directly measured by an automatic biochemical analyzer. The homogeneous enzyme immunoassay mainly includes two kinds of enzyme expansion immunoassay technology and clone enzyme donor immunoassay. Heterogeneous enzyme immunoassay Enzyme immunoassay is a method for detecting enzyme-labeled antibodies or antigens as the main reagent. It is a kind of labeling immunoassay. In 1966, Nakene and Pierce used enzymes to color the substrate to obtain similar results to fluorescent antibody technology. In the early 1970s, enzyme-labeled antibody technology began to be used in immunoassays, and it has since developed rapidly. In recent years, the rapid development of labeled immunoassay, the application of different markers, the detection methods established according to different principles and different technologies emerge one after another. Enzyme immunoassay (EIA) is an immunoassay method using an enzyme as a marker to improve the sensitivity of detection by utilizing efficient catalysis of the enzyme. Enzyme immunoassays can be classified into two types, homogenous and heterogenous, depending on whether it is necessary to separate the bound and free enzyme markers after the antigen-antibody reaction. Compared with the homogeneous enzyme immunoassay technology, the heterogeneous enzyme immunoassay is more widely used in medical tests, and the separation of the binding label and the free label is required in the reaction process. The separation method mainly relies on a solid phase carrier, that is, a reactant is fixed on a solid phase carrier, and when another reactant is combined with it, it can be separated from other substances in the liquid phase by washing, centrifugation or the like. Such reactions are also known as solid phase enzyme immunoassays. Engvall and Perimann first established this method in the early 1970s, called ELISA. The so-called immunosorbent refers to the immunologically active substance ELISA adsorbed on a solid phase carrier, which is widely used in clinical and scientific research, and has become synonymous with solid phase enzyme immunoassay. Solid phase enzyme immunoassay The solid phase enzyme immunoassay mainly refers to ELISA, which is based on the principle of binding an antigen or antibody to the surface of a solid phase carrier (coating) and maintaining its immunological activity; labeling (another) antigen or antibody with an enzyme, Retaining its immunological activity and enzymatic activity; in the assay, the sample to be tested (the antibody or antigen in which it is determined) and the enzyme-labeled antigen or antibody are reacted in different steps with the antigen or antibody on the surface of the solid phase carrier; The antigen-antibody complex formed on the solid phase carrier is separated from other substances, and the amount of the enzyme bound to the solid phase carrier is proportional to the amount of the test substance in the sample; after the substrate of the enzyme reaction is added, the substrate is enzymatically Catalytic color development, so qualitative or quantitative analysis can be carried out according to the depth of the color. Due to the high catalytic efficiency of the enzyme, it has the effect of amplifying the reaction, so that the measurement method achieves high sensitivity. ELISAs have a variety of reaction types depending on the subject being measured.
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