An antigen is a molecule (such as protein) that causes the immune system to produce antibodies and trigger an immune response. In the case of COVID-19, structural proteins were found on the surface of SARS-CoV-2 virus. Therefore, it is possible to determine whether a person is infected with virus by detecting the presence of these proteins of the SARS-CoV-2 virus. At present, the authorized antigen detection is mainly to detect the spike or nucleocapsid protein antigen of SARS-CoV-2 virus from nasal swabs or similar clinical specimens to quickly diagnose active infection. Antigen detection is usually less sensitive than molecular detection, so false negative antigen detection results may be obtained. To avoid this, rapid antigen detection should be performed within the first few days of symptom onset and in asymptomatic individuals who have had recent direct contact with a COVID-19 positive person.
Commonly used antigen detection methods
As with antibody detection, the most commonly used antigen detection methods are enzyme-linked immunosorbent assay (ELISA) and lateral flow immunoassay (LFIA).
ELISA is the most widely used type of immunoassay. It is usually used to detect antigens, but can also be used to detect other substances. To detect viral antigens in patient samples, ELISA plates are coated with antibodies specific for SARS-CoV-2 viral proteins. If viral antigens, usually spike or nucleocapsid proteins, are present in the sample, these antigens will bind to the coated antibodies to form antigen-antibody complexes. Enzyme-labeled secondary antibodies and a substrate are then added to bind to the antigen-antibody complexes to produce color .
LFIA is one of the most successful analytical platforms for conducting on-site detection of target substances. Briefly, a sample is placed on a coupling pad where the antigen is bound by conjugated antibodies. The analyte-antibody mixture then migrates along a membrane by capillary flow across both 'test' and 'control' strips. These test strips are coated with antibodies to detect the target analyte (antigen) and positive tests are confirmed by the appearance of colored control and detection lines . Typically, these tests require only a self-administered nasal swab or saliva sample, which is then mixed with the buffer. This type of test is relatively quick (<20 minutes) and inexpensive, and most can be used at the point of care.
Rapid diagnosis of patients with COVID-19 is critical to slowing the spread of the disease. Fortunately, many diagnostic companies have developed short turnaround time SARS-CoV-2 antigen detection methods to speed up the detection process. Alfa Chemistry provides you with raw materials for antigen detection to assist your research. If you do not find what you need, please contact us. We also offer product customization according to customer's detailed requirements.
- Alhamid, G.; et al. SARS-CoV-2 detection methods: A comprehensive review. Saudi Journal of Biological Sciences. 2022: 103465.
- Peto, T.; et al. COVID-19: Rapid antigen detection for SARS-CoV-2 by lateral flow assay: A national systematic evaluation of sensitivity and specificity for mass-testing. EClinicalMedicine. 2021, 36: 100924.
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