One lab I was in was paranoid about keeping it in a foil-wrapped conical tube; my current lab leaves it out on the bench (and it works fine for staining gels). It's the same company/concentration in both cases, but this second lab uses it up much faster.


Good question.

I found this reference in "Molecular Biology: A Project Approach"

A phenomenon called photobleaching occurs when ethidium bromide (EtBr) -stained DNA is illuminated by ultraviolet light.... This decreased fluorescence is presumably due to the dissociation of ethidium bromide from the DNA.

Ethidium bromide fluoresces when it is in a hydrophobic environment, such as when its stuck between two base pair stacks in DNA- water quenches its fluorescence.

I also found this article citing the fact that sunlight can break down EtBr but only when a catalyst of iron and titanium dioxide is there to catalyze the reaction.

A lot of the original characterization of EtBr as a stain is very old, so I couldn't access it directly online... It looks like the compound itself is pretty stable, but UV can, somehow interact with it when its bound to DNA to bleach it out.

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    $\begingroup$ Thanks. So on the bench in its bottle, ethidium bromide shouldn't be light-sensitive, unless there's iron and titanium dioxide contamination (or some hydrophobic substance)? (also, could you link to the article? I'm pretty sure I found it earlier but I can't find it anymore) $\endgroup$ – blep Jun 5 '13 at 23:57
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    $\begingroup$ I should think not. Eppendorf tubes are UV absorbant anyway. I added a link to the article - thought I had it there.. (UV reference: eppendorfna.com/int/…) $\endgroup$ – shigeta Jun 6 '13 at 5:22

In my current lab we just leave the bottle out (but use it up pretty quickly as we have 20+ people). But we do buy 5 bottles at a time and leave them in the same spot as the bottle that is in use (inside a hood, with the light always turned on) and we've never had a problem with degradation/expiration


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