I've seen a number of IHC protocols which describe that after cryosectioning of OCT frozen tissue, slides should be dried overnight at room temperature. Won't this lead to tissue degradation?
Many histochemical stains can be done on such dried tissue. And, many antigens can also be detected by IHC. But, if the antigen you are looking at is sensitive, you may have problems with its detection. A bigger problem you will have, is that your morphology/cytology will not be optimal. This can cause problems with interpretation. Therefor the appropriate fixation should be used. If your are doing in situ for RNA, you will have problems, ie low or no signal. So for such labels, you must fix as soon as possible and keep the samples RNAase free and at -70C.
The process of drying for a long time was used to insure that the tissue sticks. If you use the slides which are coated with adhesives such as the "+" slides, that problem is minimized.
In our lab it is also standard to dry the sections prior to staining. I think it was done ages ago in order to mount the section very well to the glass. The method persists even now we use poly-L-lysin coated slides (polysine of superfrost). I have tried staining without drying and found no difference. Not even in confocal IF. Drying is done here for => 15 minutes with a cool blowing hair dryer.
If morphology is a concern, drying is damaging it completely. In terms of protein preservation drying is the same as for cytology preparations - no detectable consequences. RNA detection is an issue for sure.
Anyway, immediate fixation will give superior morphology, particularly in case of snap frozen samples.
Overnight is very excessive. Adherence shouldn't be a problem with modern techniques. I either don't bother drying at all or dry for 10 minutes at most.
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