[3dem] Re: [Microscopy] Ice contamination

Bob Grassucci bob.grassucci at wadsworth.org
Wed Nov 7 09:45:20 PST 2007


Peiyi,
    The sort of ice that comes from a poor transfer is not subtle.  It 
is large multi-micron sized boulders (high contrast) of crystilline 
ice.  It is obvious if this sort of contamination is present.  The sort 
of ice that slowly builds up because of a poor vacuum is what David and 
Angel are testing for.  Hope this helps.
    Regards,
    Bob

P Wang wrote:
> Dear David and Angel,
>
> Many thanks for the reply. I might not state very clearly for the proposed of
> this test. The suggestion of this method is to be used to find out whether
> there is ice contamination during the cold transfer or not. On other word is
> that can we know where the ice contamination came from if there is any when we
> just open the gun valves by this method without knowing previous condition of
> the carbon film.
>
> Cheers.
>
> Peiyi
>
>   
> Quoting Angel Paredes <Angel.Paredes at uth.tmc.edu>:
>
>   
>> Hi Peiyi,
>>
>> Better yet, if you have a gatan holder.  Put the grid in the holder at 
>> room temperature.  Put it in the scope and then cool the holder down while 
>> it is in the scope.  When it is cold, let it sit in the scope for a while. 
>> When its been there for a while, go to a higher mag and put the beam on 
>> the carbon with the beam expanded to just the size of the viewing screen. 
>> Let it sit for a while, then go down in mag.  If there is contamination, 
>> you will see a round foot print of the beam used at the higher mag on the 
>> lower mag image you see on the screen.  The suggestion you have below 
>> would also work but if contamination is slow or very little, the 
>> contamination would be gone fast after the beam exposes the area before 
>> you see burning.
>>
>> angel
>>
>> On Wed, 7 Nov 2007 P.Wang at sheffield.ac.uk wrote:
>>
>>     
>>>
>>>
>>>       
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>>     
>>> Dear all,
>>>
>>> May I have your guys options about the test method of ice contamination. I
>>>       
>> have
>>     
>>> been suggested to use following way to test whether there is an ice
>>> contamination or not during the cryoTEM session:
>>>
>>> Cooling down a plain carbon film grid in LN2. Cold transfer it into
>>>       
>> microscope
>>     
>>> and focus the beam at lower magnification (5000X). It shall be able to see
>>>       
>> a
>>     
>>> burning area on the carbon film and then brings the temperature up. This
>>>       
>> area
>>     
>>> would disappear during the temperature up so this is suggestion that there
>>>       
>> is
>>     
>>> an ice contamination.
>>>
>>> Your options are highly appreciated.
>>>
>>> Peiyi
>>>
>>>       
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>   


-- 
********************************

-Robert Grassucci-
Howard Hughes Medical Institute
Wadsworth Center Empire State Plaza
Albany, NY 12201-0509
bobg at wadsworth.org
Phone: (518)474-5821
Fax: (518)486-2191




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