alumhematoxylin

Alum hematoxylin is a nuclear staining reagent used in light microscopy for histology and pathology. It is prepared by combining hematoxylin with alum (potassium aluminum sulfate), which acts as a mordant to anchor the dye to tissue. Hematoxylin is oxidized to hematein and then complexed with aluminum to form a stable dye that binds to nuclei, yielding a blue to purple color. It is commonly used as the nuclear stain in many staining protocols, including H&E variants.

Mechanism: The aluminum mordant enables hematein to bind to nuclear material such as DNA and RNA, producing a hematein-aluminum complex that stains basophilic nuclear components. The resulting color is blue to violet after a blueing step in an alkaline solution; staining intensity is controlled by oxidation state, pH, and differentiation steps.

Preparation and use: Solutions may be prepared fresh or purchased. Hematoxylin is dissolved in water or alcohol, oxidized, then combined with alum. Tissue sections are stained, washed, differentiated with a weak acid or alcohol to remove excess color, and blueed in alkaline water or buffer. A counterstain such as eosin is often applied to provide contrast. Various commercial formulations (Harris, Mayer, Gill variants) differ in solvent, oxidizer, and pH, but share the same basic mechanism.

Safety and storage: Reagents are generally stable when stored in tightly closed containers away from light. Handle with appropriate PPE; dispose of waste per institutional guidelines. As with many dyes, inhalation or skin contact should be minimized.