Anyone who has ever gotten irritated eyes or a mild burn from leaning over a UV transilluminator to cut out DNA bands from a gel does not have to be told that UV irradiation can be dangerous. Viewing fluorescently labeled DNA using even long-range UV irradiation can cause damage to the face and eyes of the researcher as well as the DNA samples. Now, Clare Chemical Research, a Colorado company started just 12 months ago, offers an alternative to UV transilluminators: the Dark Reader product line.
Dark Reader hand lamp and transilluminators use only visible light. Mark Seville, president of Clare Chemical Research, noted that "standard office lighting puts out more UV than any of the Dark Reader products." These products make use of two filters and a lamp that emits light with a wavelength greater than 400 nm. Between the lamp and the gel is a filter that removes light above approximately 500 nm (the red and green-yellow components of visible light) allowing light in the range of 400 to 500 nm (the blue-green light) to be emitted. This wavelength range corresponds with the optimal excitation peaks of the popular SYBRTMGreen, SYBRTM Gold, and SYPROTM Orange dyes from Molecular Probes and also significantly excites ethidium bromide. A researcher looks at the gel through an amber filter, (or with some cool amber colored glasses) which screens out the blue-green background light coming directly through the gel and makes it easy to visualize green through red fluorescence.
Seville notes several advantages offered by the use of visible light. First and foremost, the visible light eliminates the danger to researchers and damage to DNA caused by UV irradiation. Seville mentioned that just a 5 second exposure of plasmid DNA to light from a standard transilluminator results in a detectable amount of pyrimidine dimer formation (the most common DNA damage from UV irradiation), whereas no significant amount of dimer was detected with even a 30-minute exposure of DNA to light emitted from the Dark Reader transilluminator. Vicki Singer, who is the product manager for the molecular biology reagents at Molecular Probes and is evaluating the Dark Reader line, believes the use of visible light "makes the Dark Reader ideal for classroom use and for researchers cutting bands out of gels." There is also an added safety benefit of using the Dark Reader systems with the Molecular Probes dyes, which produce the best results. In addition to being approximately 10-fold more sensitive than ethidium bromide, some of the dyes appear to be much safer than ethidium bromide. Extensive testing of the SYBR Green I reagent determined it has virtually no mutagenic activity in the Salmonella reverse mutation Ames test.
| Dark Reader Transilluminator from Clare Chemicals. DNA gel illuminated with Clare Chemical's Dark Reader. Photo submitted by Aaron Chen of the Agricultural Research Service Unit in College Station, Texas.|
Another benefit of the Dark Reader system is the ability of visible light to penetrate transparent plastics quite well, unlike UV light. This makes it very easy for researchers to visualize samples in a gel while it is running. Dr. James McManaman, a researcher at the Webb-Waring Biomedical Research Institute and Director of the Protein Chemistry Laboratory at the University of Colorado Cancer Center, has found this feature very useful in his research. In the course of developing techniques for digestion of proteins in gels, Dr. McManaman visualizes the migration of fluorescein-labeled proteins during electrophoresis. Dr. McManaman also noted another advantage that influenced his decision to purchase: "The cost of the Dark Reader was only about one-third to one-half the price of standard UV transilluminators."
For more information on the Dark Reader products, please contact Clare Chemical Research at 303-321-0815 or www.clarechemical.com
For more information on the SYBR and SYPRO dyes, please contact Molecular Probes at 541-465-8353 or www.probes.com
Paul Diehl is a free lance writer based in Perth Amboy, N.J. He can be reached at firstname.lastname@example.org.