A stain is an organic compound composed of:
- Benzene ring: organic colorless solvent.
- Chromophore: the color component.
- Chromogen = benzene component + chromophore component.
- Auxochrome: helps to modify the chromophore’s ability to absorb light; and modifies the chromogen (ionization) to help it bind to tissue/fibers.
Acidic stains: Sodium, potassium, calcium or ammonium salts ionize such that chromogen has anionic properties and has affinity for the “positive” components of a cell (e.g. picric acid).
Basic stains: Chlorides or sulfate salts of colored bases ionize such that chromogen has cationic properties and has affinity for the “negative” components of a cell (methylene blue).
Differential stains: are more complex, use 2 contrasting stains, and help to separate organisms/cells; and/or help to visualize structures such as flagella, capsule, spore, or nucleus.
Reference
Cappuccino, J. G., & Welsh, C. (2018). Microbiology: A laboratory manual.
