How are stains classified?
Stains are classified based on the pH of their chromophore (color bearing ion) into acidic, basic and neutral. Acidic dyes have anionic chromophore eg., sodium+ eosinate-. Basic dyes have cationic chromophore eg., methylene blue+ chloride-. Acidic dyes combine more strongly with cytoplasmic components of bacteria, especially the nucleus that is basic in nature. Neutral dyes have both acidic and basic component that nullify each other. They are Romanowskys stain and are used in staining parasitic forms. Stains can be either natural (eg: carmine and hematoxylin) or coal-tar derivatives /aniline stains (eg: methylene blue, crystal violet). Supravital (cells removed from the body) and intravital (cells still a part of the body).
