[3DEM] Resin sections in a cryo instrument

[Bill Tivol]

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On May 22, 2007, at 6:42 AM, David Bhella wrote:

> I am trying to formulate a policy for a new 200 keV FEG cryo TEM we 
> are installing, with regards to what should and should not be 
> permitted in the column. The instrument is intended primarily for cryo 
> and 3D reconstruction by both single particle and tomographic methods.
> I have canvassed several opinions, particularly with regards to resin 
> sections, and received a very polarised response. Many have indicated 
> that they do not believe there is any danger of increasing 
> contamination, while others are equally adamant that cryo-instruments 
> should be used for that purpose only.
>
> Does anyone have any concrete evidence in support of one or other 
> viewpoint?
> It seems that opinions on this are firmly held, it would be good to 
> know if someone has conducted an in-depth investigation.
>
Dear David,
	The answer will depend on the anticontaminator.  Irradiation of 
plastic sections will produce organic fragments, and these can end up 
on the column; however, an anticontaminator that surrounds the specimen 
with only holes above and below the specimen to allow the beam through 
(and, of course, the hole that the stage must pass through to get the 
specimen into the scope) will capture almost all these fragments, so 
the column will remain very clean.  The presence of a few resin 
sections in the pipeline will not cause too much contamination over a 
decade, but, of course, the level will never be zero.  Our Tecnai T12 
has had a few plastic sections in it, and our F30 had a handful during 
the first year it was running, but none since, and there has been no 
noticeable contamination in either instrument.  Frequent cryo-cycling 
and other necessary maintenance is, of course, necessary to keep any 
instrument clean.  Finally, since biological material within the 
cryo-specimens can also be a source of organic fragments, there is a 
ratio of plastic to cryo- specimens for which the major source of 
contamination will be the cryo-specimens.
Yours,
Bill Tivol, PhD
EM Scientist
Electron Cryo-Microscopy Facility
Broad Center, Mail Code 114-96
California Institute of Technology
Pasadena CA 91125
(626) 395-8833
tivol at caltech.edu

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