I am trying to extract DNA from bat tissue samples (2mm biopsy punches) collected from 2002 to 2005 using the Qiagen Blood and Tissue Kit. These samples have been stored in 96% ethanol, at 4 degrees. So far I haven't had any success for samples collected > 10 years ago. However, samples collected in 2010 and stored in the same manner have yielded some DNA. I was just wondering if there is another DNA extraction method that is better for extracting DNA from the older samples.
I'm afraid the DNA in your old samples has degraded.
The DNA can slowly degrade even in 95% ethanol. Especially when the sample is not stored in cold. I would recommend storing samples for DNA extraction frozen at -80 or in liquid nitrogen. If you usually store samples in 95% ethanol I would still recommend to put them at least into the regular freezer (-20C)
Hi Lizelle,
Make sure to 'wash' well your biopsies in dd water before extraction with the Qiagen kit (from our experience, it interferes with the extration procedure). Once washed, let them dry at ambient temperature (e.g. on a piece of absorbing paper) and then proceed with extraction.
Yeah I think Sebastien may be on to something. Maybe the difference is just that the ethanol has permeated the tissue and precipitated the DNA in it much more thoroughly over the years in the older samples.
But when you wash it with water, it might wash the DNA away too... You may need to optimize the exposure.
Perhaps try to let most of the ethanol evaporate, before you extract? Might take a long time, but it would probably leave your DNA in place.
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