What is ELISA (Enzyme-Linked Immunosorbent Assay)?
ELISA is a type of immunological test (immunoassay) that uses combinations of antigen-antibody reactions.
It detects the enzyme activity of an enzyme-labeled antigen or antibody as a color change, fluorescence, or chemiluminescence. ELISA is a highly specific method and allows the user to select an assay that best suits their needs.
ELISA can be broadly classified into two types: competitive ELISA and non-competitive ELISA (sandwich ELISA).
Competitive ELISA
In competitive ELISA, an antibody that binds to the target protein is coated on the surface of the microplate. The target protein (antigen) reacts with a known amount of enzyme-labeled antigen to produce an enzyme reaction and detect enzyme activity. The target protein and the labeled antigen bind competitively to a given amount of antibody.
When the sample contains less target protein, more of the enzyme-labeled antigen binds to the antibody, resulting in stronger coloration; when the sample contains more target protein, less of the enzyme-labeled antigen binds to the antibody, resulting in weaker coloration.
This assay is effective for detecting low molecular weight proteins that are difficult to detect by sandwich ELISA.
Sandwich ELISA
In sandwich ELISA, an antibody that binds to the target protein is coated on the surface of the microplate. This antibody reacts with the target protein first. Next, an enzyme-labeled antibody reacts with the target protein, followed by an enzymatic reaction to detect enzyme activity. When the target protein binds to the antibody, a sandwich-like complex is formed between the two antibodies.
When the sample contains a smaller amount of target protein, the binding amount of the enzyme-labeled antibody gets low, resulting in weaker coloration; when the sample contains a larger amount of target protein, the binding amount of the enzyme-labeled antibody gets high, resulting in stronger coloration.
The sandwich ELISA uses two kinds of antibodies, making it a more specific assay.
