Stain Theory

Question 1

What is a dye

Answer 1

a coloured substance that has an affinity for a particular substrate

Question 2

What are synthetic dyes

Answer 2

aromatic hydrocarbons which are substituted with various functional groups to absorb different wavelengths of light

Question 3

What are the four natural dyes

Answer 3

hematoxylin, carmine, orcein, saffron

Question 4

What is a chromophore

Answer 4

a molecular structure that absorbs visible wavelengths of light. Most include double or triple bons

Question 5

What is a chromogen

Answer 5

the part of the dye that contains the chromophore

Question 6

What is an auxochrome

Answer 6

a molecular structure that allows the dye to attach to the tissue

Question 7

What is an acid dye

Answer 7

a dye that contains an anionic auxochrome

Question 8

What is a basic dye

Answer 8

a dye that contains a cationic auxochrome

Question 9

What do anionic auxochromes include

Answer 9

carboxyl, hydroxyl and sulphonic groups

Question 10

What are common anionic dyes

Answer 10

eosin, orange G, Biebrich scarlet and acid fuchsin

Question 11

What is the cationic auxochrome

Answer 11

amino group

Question 12

What are common cationic dyes

Answer 12

hematoxylin, crystal violet, methylene blue, basic fuchsin

Question 13

What is a mordant

Answer 13

a metal salt reagent that links the dye to the tissue

Question 14

What is a dye lake

Answer 14

a dye combined with a mordant

Question 15

What is an accentuator

Answer 15

they increase the intensity of the dye

Question 16

What is a neutral dye

Answer 16

a staining solution containing a mix of acid and basic dyes

Question 17

What is metachromasia

Answer 17

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

Question 18

What is polychromasia

Answer 18

using a staining solution that contains several different dyes

Question 19

What is covalent bonding

Answer 19

a strong bond formed by the sharing of electrons between atoms

Question 20

What is ionic bonding

Answer 20

relies on attraction between unlike charges. The most common mechanism of histo staining

Question 21

What is hydrogen bonding

Answer 21

attraction between hydrogen atoms of one molecule and nitrogen or oxygen atoms of another molecule. Used in elastin stains and congo red stain

Question 22

What is selective solubility

Answer 22

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

Question 23

What is porosity

Answer 23

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

Question 24

What are Van der Waals forces

Answer 24

transient intermolecular attractions and dispersions that occur due to molecular polarity

Question 25

What are histochemical methods

Answer 25

they utilize a chemical reaction that forms a coloured end product

Question 26

What do silver staining methods rely on

Answer 26

the fact that silver nitrate solutions are easily reduced forming metallic silver deposits

Question 27

What is an argentaffin substance

Answer 27

any substance that can bind silver from solution and reduce it to its metallic form

Question 28

What is an argyrophil substance

Answer 28

components that can bind silver from solution but cannot reduce it to the metallic form meaning a chemical reducing agent must be applied

Question 29

What is metallic substitution

Answer 29

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