Describe the enzyme-linked immunosorbent assay (ELISA).

ELISA stands for enzyme-linked immunosorbent assay. It is a widely used method mainly for detecting the presence of specific antigens or antibodies in a sample (such as blood, saliva, or urine). ELISA is a highly sensitive and specific diagnostic tool due to its use of specific enzyme-linked antibodies in detecting the target molecule.

The principle of ELISA is based on the antigen-antibody interaction. The target molecule (antigen or antibody) in the sample is captured by specific antibodies or antigens immobilized on a solid surface (e.g., a microplate). Then, enzyme-linked detection antibodies are added, which bind specifically to the target molecules. The enzyme-linked antibodies then convert a substrate into a colored product, allowing the quantification of the target molecules based on the intensity of the color produced.

Some essential materials required for ELISA are: 1. Microplate with a suitable surface for immobilizing antibodies or antigens 2. Primary antibodies or antigens 3. Blocking buffer 4. Enzyme-linked detection antibodies 5. Substrate solution 6. Stop solution 7. Washing buffer

There are various types of ELISA, including: 1. Direct ELISA: The primary antibody with an enzyme-linked directly binds to the target molecule. 2. Indirect ELISA: A secondary antibody with an enzyme-linked detects the primary antibody bound to the target molecule. 3. Sandwich ELISA: A capture antibody is used to immobilize the target molecule, and a detection antibody with an enzyme-linked is used for detection. 4. Competitive ELISA: The target molecule and a labeled target molecule compete for binding to the primary antibody.

Here is a typical step-by-step procedure for a sandwich ELISA: 1. Coat: Coat the microplate wells with capture antibodies specific to the target molecule and incubate. 2. Block: Add blocking buffer to cover non-specific binding sites on the surface. 3. Add samples: Add the samples containing the target molecules to the wells. 4. Add detection antibodies: Add enzyme-linked detection antibodies that bind specifically to the target molecules. 5. Wash: Wash the wells to remove unbound antibodies and other components. 6. Substrate addition: Add the substrate solution to the wells, and the enzyme converts the substrate into a colored product. 7. Stop reaction: Add the stop solution to terminate the enzyme-substrate reaction. 8. Measure: Measure the absorbance of the colored product using a spectrophotometer, and calculate the concentration of the target molecules based on a standard curve.

ELISA has various applications, such as: 1. Diagnosing infectious diseases (e.g., HIV, COVID-19, hepatitis) 2. Detection of allergens in food samples 3. Measurement of hormone levels in serum or plasma samples 4. Detection of contaminants in water samples 5. Drug testing for substance abuse 6. Evaluation of the immune responses to vaccination