Preclinical Services - ELISA Assays

Enzyme-Linked Immunosorbent Assay (ELISA), is a biochemical technique used mainly in immunology to detect the presence of an antibody or an antigen in a sample. The ELISA has been used as a diagnostic tool in medicine and pathology, as well as a quality control check in various industries.  Because the ELISA can be performed to evaluate either the presence of antigen or the presence of antibody in a sample, it is a useful tool for determining serum antibody concentrations and can also be used in toxicology as a rapid presumptive screen for certain classes of drugs.

Types of ELISA Assays:

Direct ELISA
The direct detection method uses an enzyme linked primary antibody that reacts directly with an antigen that is directly immobilized on the assay plate.
Indirect ELISA
The indirect method uses an enzyme linked secondary antibody, which has specificity for the primary antibody.
Sandwich ELISA
In the sandwich ELISA assay, a capture antibody is immobilized on the assay plate.  Detection is completed by using
  • a primary (detecting) antibody which binds to the antigen and
  • a secondary (enzyme-linked) antibody which is specific to the primary (detecting) antibody and not to the capture antibody.

    • Elissa Assay

    Competitive ELISA
    In a competitive ELISA assay, an unlabeled antibody and an antigen (the sample) are added to an antigen coated assay plate.  The assay plate is then washed to remove unbound antibody – the more antigen in the sample, the less antibody will be able to bind to the antigen coating (hence the “competition”).  An enzyme linked secondary antibody specific to the primary antibody is then used.  In a competitive ELISA assay, the higher the sample antigen concentration, the weaker the eventual signal.