ELISA and Immunoassays

Enzyme-linked immunosorbent assay (ELISA) is a biochemical technique to detect the presence of an antibody or an antigen in a sample. Whereas an indirect ELISA is used to determine the amount of antibodies to a specific antigen in a sample, a Sandwich-ELISA is used to determine the concentration of the analyte by use of antibodies that bind to the analyte (and a standard). A different way of determining the analyte concentration is a competitive ELISA, often called EIA. This technique is preferred for small analytes.