Substrates are detection systems that attach enzyme labels to the primary or secondary antibodies to visualize the localized antibody-antigen binding in tissue section. The enzymes are proteins that are used in IHC to convert a colorless reagent into a colored product (chromogen) that marks the site of antibody-antigen complex.
Commonly used enzyme labels for IHC procedures include:
- Horseradish peroxidase (HRP)
- Alkaline phosphatase (AP)
Others enzyme labels are ß-galactosidase and glucose oxidase.