Methylene blue

Methylene blue is a synthetic blue dye that can reversibly accept electrons. It is used to stain biological specimens, indicate redox conditions, and treat methemoglobinemia.

Redox reaction: A chemical reaction involving the transfer of electrons between substances. Methylene blue changes between colored and colorless forms as it gains or loses electrons.
Biological staining: The use of dyes or other markers to make biological structures visible under examination. Methylene blue colors cells and tissues for microscopy.
Heinrich Caro: A German chemist associated with the development of synthetic aniline dyes. Caro synthesized methylene blue in 1876 while working at BASF.
Toluidine blue: A basic thiazine dye used in histology and clinical staining, chemically related to methylene blue. Toluidine blue is a related stain with different staining properties and diagnostic uses.
Leucomethylene blue: The reduced, nearly colorless form of methylene blue. This form appears when methylene blue accepts electrons in reducing conditions.
Nissl stain: A histological staining method that highlights RNA-rich structures in neurons, especially rough endoplasmic reticulum. Methylene blue is among the basic dyes used to reveal Nissl substance.
BASF: A German chemical company founded in 1865, originally focused on dyes and related chemicals. Methylene blue emerged from the synthetic-dye industry in which BASF was a major early producer.
Indigo carmine: A blue dye used as a redox indicator and medical diagnostic agent. Unlike methylene blue, indigo carmine is an alternative redox dye with distinct chemistry and clinical uses.
Methemoglobinemia: A blood disorder in which hemoglobin iron is oxidized, impairing oxygen transport. Methylene blue helps restore oxidized methemoglobin to its oxygen-carrying form.
Vital staining: The staining of living cells or tissues without first killing them. Methylene blue can be used to assess living cells, though its toxicity and concentration matter.

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