What effect does using alcohol-based counterstain or mounting media have on aqueous-based chromogens?

• A. It will remove aqueous-based chromogens
• B. It will preserve chromogen color
• C. It will enhance chromogen intensity
• D. It will convert chromogens to fluorescence

Answer: (A)

The effect comes from solubility and solvent compatibility. Aqueous-based chromogens are water-soluble, so when you expose them to alcohol-based counterstains or mounting media, the alcohol can dissolve the chromogen and wash it away from the tissue. That leaches out the colored deposits and bleaches the signal, rather than preserving or enhancing it. To keep aqueous-based chromogens visible, use aqueous-compatible mounting media or select chromogens that are stable in alcohol, depending on the protocol. This is why the color is removed, not preserved or intensified, and certainly not turned into fluorescence.