This common CLIA method involves an enzyme, usually horseradish peroxidase (HRP) or alkaline phosphatase (AP), conjugated to a secondary antibody. This HRP– or secondary antibody complex AP– then catalyzes the conversion of chemiluminescent substrate, luminol, and CSPD reagent respectively. These substrates, when oxidized, provide an easy means of signal detection and quantification due to prolonged signal emission. (Shimadzu, 2021)