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3,3’-diaminobenzidine (DAB) and 3-amino-9-ethylcarbazole (AEC)

DAB produces a brown to black end product that is insoluble in alcohol and solvents such as xylene. This is a permanent chromogen that will not be removed when dehydrating and clearing slides at the end of the staining. One can use solvent-based or synthetic resins for coverslipping to produce a permanent cover.
AEC forms a rose-red end product, which is soluble in organic solvents. Specimens that were IHC stained with AEC must NOT be immersed in alcohol or solvents. Aqueous counterstains and coverslip media should be used to maintain the color. AEC is also sensitive to light and can fade if exposed to excessive light.
Other red chromogens that are insoluble in alcohol and solvents are preferred, such as Texas red, for slides that are archived and may be pulled out years later for viewing.