35S contamination while cycle sequencing

Johannes Winkler J.Winkler at uni-bonn.de
Fri Aug 1 08:30:11 EST 1997

Black, Michael wrote:
> Hello Everyone,
>    I run between 3 or 4 sets of cycle-sequencing reactions per week in a
> Cetus cycler (the model which pre-dated the 480 - just called DNA Thermo
> Cycler I think), using 35S-ATP as label.  Given the warnings about
> volatility of 35S which have been out for several years now, I set up the
> reactions in a hood but had thought that by the time the reactions were
> sealed in their tubes with an oil overlay the risk of air-borne
> contamination would be eliminated.  Recently our technician was doing a
> wipe test while I had a reaction running, and he lifted the lid on the
> cycler and wiped the underside - sure enough, the count was disturbingly
> high (the previous week he had wiped the block itself and it was clean).
>    My question is, does anyone have any further information about the risk
> of contamination from air-borne 35S while a cycler is running?

Hello Michael,

I'm not quite sure it's airborne contamination. At least one
manufacturer of 
plasticware claims that 0.05 to 0.1 ul of a given reaction volume will
be lost
during one cycle in a thermal cycler, regardless of the absolute volume.
The loss is said to take place by diffusion through the reaction tube's


Johannes Winkler
Institut fuer Zoologie
Roemerstr. 164
53117 Bonn, Germany

Tel. +49-228-734338
FAX. +49-228-734555

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