PCR with radioactive nucleotides

B.L.Cohen gbga13 at udcf.gla.ac.uk
Thu Nov 17 10:11:40 EST 1994

This problem of 35S contamination of thermal cyclers has been discussed
here several times before.   Most manufacturers are aware of it, e.g.
Hybaid Ltd.   It seems clear that whatever the contaminant may be (most
probably H35S evolved during the denaturation cycle) it escapes by
diffusion through the tube walls, not around the cap particularly.   In our
case, evidence for this is that a high level of activity became fixed to
the (silver) heater block especially in the filled wells, not in the empty
ones.   Also none was detectable on the foam lining of the lid which was in
close contact with the tube caps.   However I can imagine that this
conclusion might be invalid if the reaction with Ag could capture all the

Anyway, to be surprised at the possibility of diffusion through
polyethylene or polypropylene is to be ignorant of the properties of the
materials.   Many molecules can diffuse into them.

Another well-known situation that generates volatile 35S is that it is
released during the incubation of tissue cultures with labelled aminoacids
e.g. methionine.   This should always be done in a fume-hood or with an
efective absorbent present.   It has been reported that activated charcoal
is effective, I believe.
Dr Bernard L. Cohen          Phone (+44) (0)41 339 8855 ext. 5103/5101
Genetics Dept.,              Fax               330 5994
University of Glasgow
Church St.,
Glasgow G11 5JS
Scotland, UK.

More information about the Methods mailing list