Amyloid is an extracellular eosinophilic substance without a fixed shape, which can be present in different tissues and organs, resulting in a disease called amyloidosis, amyloid is mainly composed of proteins, most of the protein is arranged into a reverse β-folded layer structure, under the electron microscope amyloid is arranged in a protofibrillar arrangement, in the case material is a large number of extracellular, unbranched filaments, most of which are arranged randomly; the histological methods used to The histological methods used to identify amyloid include methyl violet staining, Congo red staining, and polarized light microscopy. Current research has found that the traditional methyl violet staining method has low sensitivity and poor specificity, and the classic and effective method is Congo red staining. In 1922, Bennhold discovered that Congo red could be used for identification of amyloid in vivo, and applied it to tissue sections.

The amyloid staining solution (Bennhold Congo red method) is mainly composed of Congo red staining solution, hematoxylin staining solution, etc. The staining principle is that amyloid has a greater affinity for Congo red than other tissue structures, and its hydroxyl group combines with the amino group of Congo red, which causes amyloid to be stained into red, and the performance of this staining method is stable, and it is a very classic method of amyloid staining.