Sandwich ELISA

A sandwich ELISA measures the amount of antigen between two layers of antibodies (capture and detection antibody). The first antibody (capture antibody) is coated to the plate. Then, the sample solution is added to the well. Finally, a second antibody (detection antibody) is added and binds to the antigen in the sample (if any).

The antigen to be measured must contain at least two antigenic epitopes capable of binding to the antibody. If the detection antibody is conjugated to an enzyme, the the assay is called a direct sandwich ELISA. If the detection antibody is unlabeled, then a second antibody is needed resulting in an indirect sandwich ELISA.