Stability of labelled probes/primers

Carmen Martin mcm24 at
Thu Oct 16 12:41:25 EST 1997

I am working with a 24 mer probe labelled at the 3'end with biotin and
at the 5' with fluorescein in an ELISA assay. I capture the probe on the
microwell with an antifluorescein antibody and the detection is with
ExtrAvidine alkaline phosphatase labelled.  My test uses a standard
curve of serial dilutions of this probe.

I used to keep these serial dilutions (made in filtered ultrapure water)
in the fridge at 4oC in a BM box.  Recently this dilutions have started
to 'go off' specially for the low concentrations which have become
background reading.

I have tried to store them at -20C and -70C, in  autoclaved TE pH 7.6
and water.  Just -70C seems to keep them, but the result is not as good
as a fresh dilution from the stock. I've tried another source of tubes
and the addition of salmon sperm DNA to these dilutions and storage at

Can anyone explain what is suddently going on and how to correct it?

I'd really appreciate some light!!!

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