When choosing a DNA or RNA stain for agarose gels, some features to consider are convenience, sensitivity, and safety. For many years, the decision was pretty easy since the only option was ethidium bromide. Ethidium bromide is convenient to use, reasonably sensitive, but not so good as far as safety goes. In fact, 90 ug of ethidium bromide is as mutagenic as the smoke from one cigarette and solutions containing the stain must be detoxified before disposal (1). When you take disposal into account, it’s anything but convenient to use.
Fortunately, many alternatives to ethidium bromide are now available and I’ve tried several. The most recent stain I’ve tried, GelRed from Biotium (Hayward, CA), is turning out to be one of the best on several counts. For one thing, it is extremely convenient to use. GelRed is available as a 10,000x solution, which is how most other gel stains are sold. However, unlike most other gel stains, it can be stored at 4C. So, no thawing is necessary. Although it’s not usually a big deal to thaw a gel stain, it can be if your molten agarose has cooled to pouring temperature and you’ve forgotten to thaw it. An additional convenient feature is that GelRed is not susceptible to degradation by heat. This means you can add it immediately after melting the agarose or even add it to the mix before heating. Biotium also claims that it is more photostabile than other gel stains, so you don’t have to worry about the stain losing sensitivity while your gel sits on the lab bench.
Nucleic acids can be visualized in GelRed-stained gels using a standard UV transilluminator with an ethidium bromide filter or a SYBR filter. It works with ssDNA, dsDNA, and RNA. Since it is also stable in aqueous solutions, a 1x solution for post-staining can be made in bulk and stored without loss of sensitivity.
Although I haven’t compared it to ethidium bromide, the company’s product webpage shows it to be much more sensitive. I did compare it to GelStar from Cambrex (Rockland, ME) and found it to be marginally less sensitive when visualized with an ethidium bromide filter. For me, the many convenient features and improved stability, however, make up for the slightly lowered sensitivity.
The product webpage also goes into some detail about tests for mutagenicity. Information is based on the Ames test, which basically measures a compound’s ability to revert a known mutation back to the wild-type. With this test, GelRed gave no indication of being mutagenic when evaluated at seven doses from 0 to 60 nmoles/plate. However, it did cause a dose-dependent increase in revertants when subjected to metabolic activation with a rat liver extract. The number of revertants, the company claims, was “greatly reduced” compared to ethidium bromide. The details are available by request. Although these results suggest that GelRed is safer than ethidium bromide, it’s metabolites can cause mutation. So, you still must use care when handling it.
GelRed is available in units of 0.5 ml. Depending on how many you purchase at one time, the price per 50 ml mini-gel varies from about 75 cents/gel to just under a dollar/gel. In contrast, GelStar costs around $1.30/gel. For routine nucleic acid gel staining, GelRed is an excellent choice. It’s economical, very convenient, and quite sensitive.
Michael Campa, Ph.D.
Assoc. Research Professor of Radiology
Duke University Medical Center
1.UC Davis Environmental Health and Safety. Ethidium Bromide Solutions Detoxification. 2003 Available from: http://ehs.ucdavis.edu/sftynet/sn-53.cfm