Methylene Blue

Methylene Blue is a phenothiazine derivative dye that produces a blue color when dissolved in water. It is used as a nucleic acid stain for its ability to bind DNA and RNA. Unlike ethidium bromide which intercalates with the nucleic acids, methylene blue acts as a cationic dye, merely binding electrostatically to negatively charged moieties. This reversible staining minimizes interference when nucleic acids are transferred to hybridization membranes for blotting. Also known as methylthioninium chloride, methylene blue has also been used as a redox indicator.