Stain Theory Flashcards
What is a dye
a coloured substance that has an affinity for a particular substrate
What are synthetic dyes
aromatic hydrocarbons which are substituted with various functional groups to absorb different wavelengths of light
What are the four natural dyes
hematoxylin, carmine, orcein, saffron
What is a chromophore
a molecular structure that absorbs visible wavelengths of light. Most include double or triple bons
What is a chromogen
the part of the dye that contains the chromophore
What is an auxochrome
a molecular structure that allows the dye to attach to the tissue
What is an acid dye
a dye that contains an anionic auxochrome
What is a basic dye
a dye that contains a cationic auxochrome
What do anionic auxochromes include
carboxyl, hydroxyl and sulphonic groups
What are common anionic dyes
eosin, orange G, Biebrich scarlet and acid fuchsin
What is the cationic auxochrome
amino group
What are common cationic dyes
hematoxylin, crystal violet, methylene blue, basic fuchsin
What is a mordant
a metal salt reagent that links the dye to the tissue
What is a dye lake
a dye combined with a mordant
What is an accentuator
they increase the intensity of the dye
What is a neutral dye
a staining solution containing a mix of acid and basic dyes
What is metachromasia
tissues stain a different colour than that of the staining solution. Occurs when cationic dyes form dye aggregates when staining substrates that contain many negatively-charged sites in close proximity
What is polychromasia
using a staining solution that contains several different dyes
What is covalent bonding
a strong bond formed by the sharing of electrons between atoms
What is ionic bonding
relies on attraction between unlike charges. The most common mechanism of histo staining
What is hydrogen bonding
attraction between hydrogen atoms of one molecule and nitrogen or oxygen atoms of another molecule. Used in elastin stains and congo red stain
What is selective solubility
the dye is only slightly soluble in a chosen solvent and readily soluble in fat causing the dye molecules to migrate from the solvent into the lipids
What is porosity
a combination of physical and chemical methods, the smallest dye molecules are applied first and larger dye molecules later bump the smaller dyes molecules out of larger pores
What are Van der Waals forces
transient intermolecular attractions and dispersions that occur due to molecular polarity
What are histochemical methods
they utilize a chemical reaction that forms a coloured end product
What do silver staining methods rely on
the fact that silver nitrate solutions are easily reduced forming metallic silver deposits
What is an argentaffin substance
any substance that can bind silver from solution and reduce it to its metallic form
What is an argyrophil substance
components that can bind silver from solution but cannot reduce it to the metallic form meaning a chemical reducing agent must be applied
What is metallic substitution
silver will react with the carbonate and phosphate anions of calcium salts replacing the calcium. Bright lights are then used to reduce the silver salt to metallic silver. Any sites that contain silver are assumed to have held calcium
