How to get aliquots from frozen serum samples?

Dear experts,

we want to analyze about 70 serum samples which currently are stored
in cryotubes (about 2ml) and which are frozen at -80. I am looking for
suggestions on how to obtain small aliquots (sufficient for a few
ELISAs, less than 100ul in total) without actually thawing all the
material.

I thought of drilling holes into the frozen samples with a drilling
machine and pre-chilled ("-frozen") spiral drills and to collect the
chips, but am somewhat concerned of contaminating the samples with
metal abrasions or oil from the surface of the drills. I could clean
the drills in the dishwasher before and autoclave them, but that won't
solve the possibility of metal abrasions.

Has anyone out there solved a similar problem and would like to give
some recommendations?

Many thanks!

Wolfgang

If you are interseted in a few microliters for the ELISA, then imply use
the tip to scrape and transfer the scarpings to an eppi tube! That should
give you anywhere between 5 and 15uL.

On Tue, 21 Aug 2007, WS wrote:


Take the metal block out of an electric hot block and chill it in the -80
overnight. Put it on the bench; take the tubes out, and one by one, put
them in it and scrape away at the top of the slug of frozen serum with a
micropipette tip until enough is melted. Put the tip on a micropipette and
suck it up.

A caveat about the whole approach, though: when solutions freeze slowly,
soluble molecules become unevenly partitioned, getting progressively
concentrated in the fraction of the sample that remains liquid. Think
about the concentration of sugar during the making of ice wine, or of
alcohol in making applejack. Thus, if you froze the samples in the first
place by putting them in the -80, they won't be uniform throughout, so a
sample scraped from the top won't be representative. If you flash-froze
them in LN2, this should not be such a problem. Of course, it might not
matter to you anyway.

tom

--
Tom Anderson, MRC Laboratory for Molecular Cell Biology, UCL, London WC1E 6BT
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