EtBr, or ethidium bromide, is also known as 3,8-diamino-5-ethyl-6-phenylphenanthridinium bromide—a dye used in biochemical research laboratories. EtBr is a red, crystalline, nonvolatile solid that is soluble in water and is available as a powder or as a solution. 

What is the Purpose of Ethidium Bromide?

Researchers use EtBr to stain DNA, allowing them to identify and visualize nucleic acid bands. According to a post on "In the Pipeline," a science blog, it works "by slipping neatly between the base pairs [of DNA] . . . like sliding a card into a deck," which happens through a process known as intercalation.

After intercalation, researchers can visualize the DNA in a medium by illuminating it with ultraviolet (UV) light, which causes the bonded EtBr to fluoresce bright orange-red, according to "Molecular Biomethods Handbook." Because of these qualities, EtBr is often used in the electrophoresis of nucleic acids, a process that separates them by size, usually in an agarose or polyacrylamide support gel. According to manufacturer Millipore Sigma, EtBr is the most commonly used nucleic acid stain for PAGE (polyacrylamide gel electrophoresis) or agarose gel electrophoresis.

The "Handbook of Fluorescent Dyes and Probes" points to research into a number of additional applications for ethidium bromide, including:

• Counting or assessing the quality of sperms
• Counting or classifying leukocytes
• Assaying apoptosis, cytotoxicity or mitochondria toxicity
• Studying multidrug resistance
• Sensing temperature

Is EtBr Dangerous?

EtBr is often described as a mutagen, which means that it can cause genetic damage. Further, many organizations, including the University of California Santa Cruz Environmental Health and Safety Department and the University of Wisconsin–Madison Environment, Health and Safety Department, state that it should be treated as a possible carcinogen and reproductive toxin (teratogen).

For more information, the "Handbook of Fluorescent Dyes and Probes" gives references to recent scholarly research investigating the safety, toxicity and potential adverse effects of EtBR.

Because EtBr may be harmful, precautions may be warranted when disposing of EtBr solutions, cleaning up EtBr spills and cleaning contaminated equipment. Different precautions and procedures are required by different laboratories. Check with the health and safety department of your institution or organization for details on the relevant policies for your work.