Detection kits for immunohistochemistry (IHC) based on the polymers method are more recent than traditional kits using avidin and biotin conjugates such as ABC kits. Polymer-based kits offer several advantages over ABC kits, especially for multi-staining (multiplex) applications on the same tissue section or where high levels of endogenous biotin may be a problem.

The IHC detection systems based on the polymers method consist of a polymer of an active enzyme linked to a secondary antibody specific for a target primary antibody. This format makes it possible to significantly increase the amount of enzyme present at the site of localization and therefore a greater signal by converting a greater quantity of substrate into precipitate. Moreover, this system allows a one-step protocol instead of two with the ABC system (biotinylated antibody + avidin-enzyme complex).

The polymers may be based on dextran or similar molecules which have a large size (causing problems in some tissues) or micro-polymers that penetrate more easily into the tissue sections.

 

The most commonly used HRP substrates are DAB and AEC. These 2 substrates form brown (DAB) and red (AEC) insoluble precipitates when they are oxidized by HRP. It is for this reason that they are commonly called chromogens. The localization of the target proteins is then carried out by microscopic visualization of the precipitates within the tissue.