How does indirect ELISA work?

In an indirect ELISA, the antigen is immobilized on the microplate well and bound by a target-specific primary antibody. An enzyme-conjugated secondary antibody then binds to the primary antibody and generates the measurable signal.

The secondary antibody can provide signal amplification and allows one labeled reagent to be used with multiple compatible primary antibodies. Indirect ELISA is commonly used to detect or quantify antibodies in a sample.