How does Congo red staining work?
The Congo red staining principle is based on the formation of hydrogen bridge bonds with the carbohydrate component of the substrate. Congo red is an anionic dye and is capable of depositing itself in amyloid fibrils, which then exhibit a conspicuous dichroism under polarized light.
Can Congo red stain bacteria?
The stain gathers around the cell which often appears larger than stained cells. Congo red (1% aqueous) Solution is used as negative stain for bacteria and spirochaetes.
What stain uses Congo red?
Amyloid
Histochemical properties Amyloid stains pink with H&E and metachromatically with crystal violet and methyl violet. It stains selectively with Congo red; in addition, amyloid stained by Congo red gives an apple-green birefringence when viewed in polarized light (Fig.
What is Congo red test?
Congo red is an azo dye, which exhibits an affinity towards filamentous protein aggregates and is used as a gold standard test to identify amyloid fibrils [15].
What is Congo red assay?
Congo red (CR) binding, monitored by characteristic yellow-green birefringence under crossed polarization has been used as a diagnostic test for the presence of amyloid in tissue sections for several decades. This assay is also widely used for the characterization of in vitro amyloid fibrils.
What is the purpose of Congo red dye?
Congo red was formerly used to dye cotton but has been superseded by dyes more resistant to light and to washing. It is still used in histology to stain tissues for microscopic examination, and to serve as an acid-base indicator, since it turns red in the presence of alkalies and blue when exposed to acids.
How do you make a Congo red indicator?
Indicator Preparation Make a 1% solution of Congo red indicator by adding 1 g of Congo red to 100 mL of distilled or deionized water. Rinse the sponge (including new sponges) with water to remove residual soap, surfactants, or acids.
Why is it called Congo red stain?
Conclusions: The Congo red stain was named “Congo” for marketing purposes by a German textile dyestuff company in 1885, reflecting geopolitical current events of that time.
What is Congo Red test?
What is the pH of Congo Red?
pH 5.0
Congo Red is an indicator dye that is blue-violet at pH 3.0 and red at pH 5.0. It contains a 3,3′-(biphenyl-4,4′-diyldidiazene-2,1-diyl)bis(4-aminonaphthalene-1-sulfonate).
Why is Congo Red anionic?
Congo red (CR) is a benzidine-based anionic diazo dye that can cause allergic reactions and can be metabolized to benzidine, a carcinogenic product19. Depending on pH, various molecular structures of CR can be present in aqueous solution20, which hinders its elimination.
Is Congo red a cationic or anionic dye?
Congo red (CR) is a benzidine-based anionic diazo dye that can cause allergic reactions and can be metabolized to benzidine, a carcinogenic product19.
What are anionic dyes?
Acid dyes are anionic, soluble in water and are essentially applied from acidic bath. These dyes possess acidic groups, such as SO3H and COOH and are applied on wool, silk and nylon when ionic bond is established between protonated –NH2 group of fibre and acid group of dye.
How do you make Congo red stain?
Prepare the staining solution: prepare a solution of 80% EtOH: 20% DDI water and add a saturating amount of NaCl. Stir this solution for a few minutes and filter away the excess NaCl. Add a saturating amount of Congo Red, stir, and filter to obtain thefinal working solution.
How to prepare Congo red birefringence assay?
Procedures for Congo Red birefringence assay: 1. Prepare the staining solution: prepare a solution of 80% EtOH: 20% DDI water and add a saturating amount of NaCl. Stir this solution for a few minutes and filter away the excess NaCl. Add a saturating amount of Congo Red, stir, and filter to obtain thefinal working solution.
What are the diseases associated with Congo red stain?
Common diseases for Congo red stain include primary amyloidosis, AL amyloid seen in plasma cell dyscrasias, AA amyloid associated with inflammatory conditions Amyloidosis is a rare disease characterized by the deposition of insoluble misfolded proteins in various tissues and organs
Is the Congo red capsule stain Gram positive or negative?
The Gram positive control should be purple and the Gram negative control should be pink. Discard your used slide in the disinfectant bucket. The Congo Red Capsule stain is a modification of the nigrosin negative stain you may have done previously.