Different Types and Advantages of ELISA Tests
Elisa is a special reagent analysis method, which is an immunoassay technology developed on the basis of immunoenzymatic techniques. It connects the analyte to the enzyme according to the specific reaction between the antigen and the antibody, and then produces a color reaction through the enzyme and the substrate. It is used in the quantitative determination of antibodies or antigens. The application of ELISA test is to detect macromolecular antigens and specific antibodies, which is very fast, sensitive, and simple. And there are different types of ELISA tests, which will be introduced next.
Different Types of ELISA Tests
ELISA can be classified into five main types, which are direct, indirect, sandwich, competitive, and capture methods. These different ELISA tests are explained below:
- Direct ELISA: Direct ELISA is mainly used for the detection of antigens, which requires high specificity of antibodies. The direct method is to fix the antigen or sample directly on the solid phase carrier ELISA plate, add the enzyme-labeled specific antibody after washing the unattached antigen, and add the substrate to develop color after washing the unattached excess substance. Direct ELISA has fewer experimental steps and faster detection speed, but does not use secondary antibodies, the signal is not amplified, and the sensitivity of the assay is slightly lower.
- Indirect ELISA: The indirect method is mainly used for the detection of antibodies, and requires high specificity for antigens. The specific antigen is coated on the surface of the solid phase carrier ELISA plate, and the detection antibody is added to specifically bind the antigen. After washing, the enzyme-labeled antibody is added, and the substrate is used for color development after washing. Indirect ELISA offers greater flexibility and sensitivity than direct ELISA.
- Sandwich ELISA: The sandwich method is the most common type of ELISA, which sandwiches the antigen with two specific antibodies. Immobilize the capture antibody in the well of the ELISA plate first, then add the sample, and then add the detection antibody. The detection antibody is an enzyme-labeled antibody, which is called direct sandwich ELISA; if the detection antibody is unlabeled, it is necessary to use an enzyme-labeled secondary antibody to bind to the detection antibody, which is called indirect sandwich ELISA. The enzyme-labeled secondary antibody is specific to the detection antibody and can react with the substrate to complete the detection. Sandwich ELISA is used for direct or indirect detection, which has high flexibility. However, the detection time is generally longer, and the requirements for paired antibodies are high.
- Competitive ELISA: The competitive method is usually used to detect small molecules with fewer epitopes, and can also detect impure samples. It has high data reproducibility but poor specificity. The competitive method is to pre-coat the antibody in the ELISA well plate, and then add the test substance and enzyme-labeled antigen. If the object to be detected has no antigen, the enzyme-labeled antigen will bind to the solid-phase antibody. If the substance to be tested has an antigen, it will have the same opportunity to compete with the enzyme-labeled antigen to bind to the antibody pre-coated on the solid phase. Finally, a substrate is added for color development, and the color development result is inversely proportional to the antigen content in the sample.
- Capture ELISA: Capture methods can be used to detect certain antibody subtypes in serum. First, fix the IgM antibody on the solid-phase carrier ELISA well plate, then add the diluted serum sample, the IgM antibody in it will be captured by the solid-phase antibody, and wash to remove irrelevant substances. Then add the specific antigen reagent, which only binds to the specific IgM to be tested. The next step is to add an enzyme-labeled antibody specific for the antigen, which will react with the antigen bound to the solid phase. Finally, the enzyme substrate is added to develop the color, and if the color is displayed, it means that the specific IgM antibody in the serum sample exists.
Advantages of ELISA Tests
- ELISA has high sensitivity due to the use of enzymes as reporter groups.
- Selectivity from antibody or antigen allows for a high degree of robust specificity.
- Compared to older laboratory techniques, ELISA test methods are more accurate, more straightforward, and easier to perform.
- ELISA provides fast results. It is highly efficient and allows easy simultaneous analysis without complex sample pretreatment.
- The application of ELISA test is very wide, which providing many conveniences for doctors and laboratories.
All about different ELISA tests and the ELISA test advantages are above. Hope it helps. If you need relevant consumables like transparent, white, and black 96 well ELISA strip plates, Hawach manufactures reliable products for you.