Thiazole orange as an everyday replacement for ethidium bromide and costly DNA dyes for electrophoresis

DNA gel electrophoresis is a standard tool of biochemistry and molecular biology laboratories. The common dye ethidium bromide suffers from toxicity concerns and requires the use of damaging ultraviolet light. We observe that exposing plasmid DNA to a UV transilluminator for only 1 s results in detectable loss of colonies following transformation, suggesting rapid accumulation of DNA damage. SYBR Safe, a commercial product, is marketed as a safe alternative to ethidium bromide and has excellent sensitivity with nondamaging blue light, but suffers from prohibitively high costs. We show that thiazole orange, the parent compound of SYBR Safe, is an excellent, simple, and inexpensive alternative to these dyes. It is excitable with safe blue light or UV light, with DNA detection limits in agarose gels similar to ethidium bromide and SYBR Safe (1-2 ng/lane). Thiazole orange safely allows the use of nondamaging blue light at the same cost as ethidium bromide.