Congo red stain

Congo red stain is a histological stain used in biological research and medical diagnostics. It was first synthesized by the German chemist Paul Böttiger in 1883 and is named after the Congo Free State, where it was initially used as a dye for textiles.

History

The Congo red stain was first synthesized by Paul Böttiger in 1883 while he was working for the Actien-Gesellschaft für Anilin-Fabrikation (AGFA), a German chemical company. The stain was initially used as a dye for textiles, but its use in biological research and medical diagnostics was discovered later.

Properties

Congo red stain is an azo dye, which means it contains the azo group (-N=N-), a functional group that consists of two nitrogen atoms connected by a double bond. The stain has a strong affinity for amyloid proteins, which makes it useful in the diagnosis of amyloidosis, a group of diseases characterized by the abnormal accumulation of amyloid proteins in various organs and tissues.

Usage

In histology, Congo red stain is used to detect the presence of amyloid proteins in tissue samples. The stain binds to the amyloid proteins, causing them to fluoresce under polarized light. This property is known as birefringence. The stained tissue samples are then examined under a microscope to determine the presence and extent of amyloid deposition.

In addition to its use in histology, Congo red stain is also used in microbiology to differentiate between gram-positive and gram-negative bacteria. The stain binds to the peptidoglycan layer in the cell walls of gram-positive bacteria, causing them to appear red under a microscope.

Safety

Congo red stain is considered a hazardous substance. It is a potential carcinogen and can cause skin and eye irritation. Therefore, it should be handled with care and appropriate safety measures should be taken when using it.

See also

• Histology
• Amyloidosis
• Microbiology
• Azo dye