In a competitive format assay, as antigen concentration in a sample increases, signal intensity decreases.The central concept behind a competitive ELISA is that a larger quantity of analyte in a sample results in fewer free antibodies in solution and by extension a smaller number of labeled antibodies bound to the standard on the plate.
A primary antibody (unlabeled) is incubated with sample antigen. They are then added to 96-well plates which are pre-coated with the same antigen, followed by a washing step. Antigen quantity in the sample determines the amount antibody binding on the well. The secondary antibody that is specific to the primary antibody and conjugated with an enzyme is added. A substrate is added, and remaining enzymes elicit a chromogenic or fluorescent signal. The competitive assay is an appealing option if no suitable antibody pair can be identified for sandwich ELISA, or if the analyte in question is too small to permit binding of both a capture and detection antibody. Our support team will gladly help you with finding the right ELISA kit for your needs. Please contact us via phone, email or use our live chat system.