Hematoxylin (Hematoxylin) and Eosin (Eosin) co-staining referred to as HE staining is one of the most commonly used staining methods in pathology and histology. Hematoxylin is an alkaline natural dye that can color the cell nucleus. The main component of chromatin in the cell nucleus is DNA, and in the double helix structure of DNA, the phosphate groups on the two nucleotide chains are outwardly oriented, which makes the outside of the double helix of DNA negatively charged and acidic, and it can easily be stained by combining with the positively charged Hematoxylin alkaline dye by ionic bonding or hydrogen bonding.

Cole hematoxylin staining solution is a chemical oxidation of mature alum hematoxylin, mainly composed of hematoxylin, potassium aluminum sulfate, glycerol, etc. The staining solution has a small content of hematoxylin, no oxidative film formation, clear staining of the nucleus of the cells, without staining the cytoplasm and fibrous components, is a progressive staining, so the staining can be used without hydrochloric acid ethanol differentiation, the staining time is about 5 to 10 min, mainly used for re-staining the nucleus of the cells.