November 2006

This article is the first of a two-part series on methylene blue. Methylene blue has important uses in both biology and chemistry. The first of these articles addresses its use in biology.


The chemical structure of Methylene blue, C16H18N3ClS,
includes three joined rings of atoms. Each unlabeled corner
(vertex) of each hexagonal ring represents the location of a
carbon atom--can you locate all 16 carbon atoms in the structure?

Methylene blue is a handy, colorful compound that biologists use as a dye to help them see life under the microscope. This article will explore the advantages of methylene blue and the chemistry that is responsible for its wide use as a biological dye.

Methylene Blue Dye: Helping Us See Life in Brilliant Color

Methylene blue-stained yeast bacteria as seen
through a microscope, magnified 1,000 times.
Credit: David B. Fankhauser, University of Cincinnati

A fascinating world of life, normally invisible to the eye, comes alive with the help of two essential tools: microscopes and dyes. Microscopes magnify very tiny life forms, such as bacteria, using cleverly positioned glass lenses. Being practically colorless, however, bacteria would be hard to see without the help of specialized dyes-called stains.

Methylene blue is a commonly used stain that helps us see microscopic life in brilliant color. Biologists often add a drop or two of methylene blue to bacteria on a glass slide before placing the slide under the microscope. The blue color that stains the bacteria helps biologists see their shapes. Bacteria come in a variety of shapes, ranging from tiny rods to spheres, spirals or twigs. The methylene blue-stained yeast bacteria in the photo are rod-shaped.

Stain Chemistry

The structure of DNA resembles a
twisted ladde
(partial image from ).

Dyes and stains are colorful substances that bind to biological tissue as a result of chemical attractions. For example, when in contact with acids, methylene blue is at its deepest shade of blue, indicating a strong attraction to acids. Cell nuclei, which contain the acid deoxyribonucleic acid--also known as DNA--are easily identified under the microscope as the darkest areas of the cells stained with methylene blue.

DNA is the genetic information each organism inherits from its parents. Human DNA contains the chemical code that determines a person's height, hair and eye color, for example. The chemical structure of DNA looks like a long, twisted ladder, or double helix. The ladder has a negative charge. In water, methylene blue has a positive charge. When DNA comes in contact with methylene blue, their opposite charges attract, causing methylene blue's "rings" to slide in between the "rungs" of the DNA "ladder." The result: a rich blue stain that identifies the location of the cell nucleus.

Follow-up Questions:

  1. Find examples of rod, spherical and spiral-shaped bacteria. Sketch the shapes and label them.

  2. Use the atomic weights found on the Periodic Table of the Elements to calculate the percentage of chlorine in methylene blue.

Check The Science Center on December 1st to see how chemists use methylene blue. Can you make some predictions?

For a list of previous "Chlorine Compound of the Month" features, click here.


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