Week 9 Flashcards
What is a dye
-color in powder form
What is a stain
-dye product in a solution with alcohol and water as a solvent
What is staining
-process of colouring tissue or cellular components
for the purpose of visualization
staining is alcoholic or aqueous
What are the characteristics of a dye
- Coloured aromatic salt (organic compound)
◦ Coal tar or benzene derivatives - Exhibits resonance - delocalization of the electron
- Imparts color to another substance when in a solution
resonance - double bonds shift constantly
Why are dyes coloured?
◦ Benzene absorbs electromagnetic radiation @ 200 nm
(infrared range) → not @ visible range (400 – 700 nm range)
◦ Dyes are made up of 3 components to enhance color:
1. Chromophore- color bearing
2. Chromogen - benzene ring and chromophore
3. Auxochrome - ionizing chemical component
What is a chromophore
-color bearing substance responsible for light absorption in visible range
-has chromophoric groupings (unstable electrons and double bonds): more bonds = more intensity
-double bonds are unstable
-Chromophoric groupings :Quinoid rings, Azo linkage, Nitro grouping
-easily reduced - high affinity for hydrogen
-if reduced the chromophore will be destroyed and color will be lost
how are they formed
Benzene MINUS 2 hydrogen atoms = quinoid ring -strongest chromophore
-which has two double rings outside the benzene ring
in para or ortho form
Azo coupling and Nitro grouping
A benzene ring or naphthalene ring attached by N = N bond
nitro grouping - nitrogen oxide
-PHENOL + 3 NO2 = PICRIC ACID
-not allowed to dry out
-explosive when dry
What is a Chromogen
-benzene derivative containing chromophoric groupings.
◦ Can impart color but it is NOT a true dye…yet.
◦ Eventually washes off the tissue upon rinsing.
◦ A true dye would have an ionizing group (auxochrome) that will link firmly to the tissue
What is a auxochrome
◦ Ionizing group that converts a chromogen into a true dye that attach to tissue binding sites
◦ AUXO - “auxein” – increase CHROME - color
◦ Basic auxochrome: AMINO (–NH2)
◦ Positively charged.
◦ Attach to basophilic tissue components (e.g., nuclei-negatively charged).
◦ Acid auxochrome: SULFONIC (–SO3H ); CARBOXYL (–COOH), HYDROXYL (–OH)
◦ Negatively charged.
◦ Attach to acidophilic tissues components (e.g., RBCs, muscles, collagen fibers). positively charged
What is “THREE in ONE”
Chromophore + Other groups = CHROMOGEN
Chromogen + Auxochrome = TRUE DYE
What are Modifiers
◦ Chemical groups that alter the color of the dye by altering the energy of the unstable electrons
◦ They do not directly participate in the light absorption
◦ CH3, C2H5, C6H5, Cl-, Br-, I
Acid/Basic Dyes
Anionic/Cationic Dyes
◦ Acid dye = anionic dye → negative charge
◦ Binds to acidophilic tissues with positive charge
◦ Stains intensely in an acidic environment
◦ Basic dye = cationic dye → positive charge
◦ Binds to basophilic tissues with negative charge
◦ Stains intensely in a basic environment
Amphoteric dyes are cationic below IEP and anionic above IEP (pH required to change charges on a chemical compound) .
Actual staining of tissue has nothing to do with pH of the dye. It’s all about charges.
Dyes that stain lipids
◦ AKA Lysochromes
◦ Non-ionic (cannot bind electrolytically with the target since the target is also charge-free)
◦ No charges
◦ Neutral dyes
◦ Insoluble in water but soluble in organic reagents (e.g., alcohol)
◦ Dye is more soluble in the fat of the tissue section than it is in the solvent of the staining solution.
Note: Lipids can only be stained if tissues are fresh and cut on the cryostat (i.e., frozen section).
cant do it on processed tissue because the reagents liek xylene and alcohol are organic reagents and would dissolve out the lipids = tissue with only adipocytes and no lipids
origin of natural dye vs synthetic
◦ Carmine – extract of female cochineal insect
◦ Orcein – lichens
◦ Saffron – saffron flower
◦ Hematoxylin – logwood tree heartwood
Synthetic dyes
◦ Based on organic compounds – benzene, aniline
Factors affecting dye binding
The pH of the solution
◦ Acidified eosin vs alkaline eosin
◦ Acidified methylene blue vs alkaline methylene blue
Factors affecting dye binding
Temperature
◦ Increase in temp = increased diffusion rate of staining
◦ Tissue swells
Factors affecting dye binding
Concentration of the staining solution
◦ Increased concentration increases dye binding
Factors affecting dye binding
Presence of salt in the staining solution
◦ Salts dissolved in the staining solution could increase or decrease staining intensity.
-because salt ions and dye ions compete for the same binding site
Factors affecting dye binding
Fixatives used and length of time in them
Increased eosinophilia, decreased basophilia:
◦ Acidic fixatives (Zenker solution, Bouin solution, unbuffered formalin)
◦ Potassium dichromate-based fixative will decrease basophilia (nuclear staining).
Decreased eosinophilia, increased basophilia:
◦ Formaldehyde, mercuric chloride, osmium tetroxide.
How is differentiation achieved
◦ Regressive staining – overstaining then removal of excess stain by differentiation
◦ Mordants – are substances or metals that act as link between the dye and the tissue- high affinity for both
◦ Mordant + dye = LAKE → act as a basic (cationic) dye.
◦ Negatively charged in action.
aluminum hematoxylin
What are two differentiation methods
- Weak acid solutions and weak alkaline solutions (solvent: water or alcohol) – used for cationic dyes and anionic dyes, - remove excess stain
◦ ACID DIFFERENTIATION: HCl – aluminum hematoxylin for nucleui
◦ ALKALINE DIFFERENTIATION: NaOH – eosin- collagen muscle rbc - Excess mordant as differentiator→ breaks the dye-mordant complex
◦ more mordant molecules in differentiator than mordant bound to the tissue.
-tissue are stained dark, excess dye molecules must be removed by using salt of heavy metal . so using the excess mordant as a differentiator in order to diff the tissue components . The excess mordant in the differentiator will break the bond between the dye and the mordant on the tissue. Excess mordant in the diff will attract the molecules not attached to target allowing target tissue to be seen better after differentiating because there is more dye for target
◦ Structures that have bound the most dye molecules would be the last to lose color.
Acid Differentiation VS Mordant Differentiation
ACID DIFFERENTIATION
* Use of acid alcohol for H&E stain
* Breaks the LAKE-TISSUE salt linkage
-acid alcohol
MORDANT DIFFERENTIATION
* Use of excess mordant
* Mordant in solution competes with mordant in tissue for the dye molecule
* Breaks the DYE-MORDANT bond
* Only mordant is attached to tissue
how are oxidizers used as differentiation methods
-oxidize the dyes to colorless substance. When
stopped at the appropriate time, substances that retained the most dye molecules will remain stained.
chromic acid
potassimin permanganate
how are solvents and buffers used as differentiation methods
solvents
-remove access dye from tissue
Eosin is differentiated in H&E stain using low grade alcohol
Buffer-acts as acidic or basic diff
-in hematology slides - wright stain
