[3dem] Electron dense contamination on cryo grids

Stefan Bohn bohn.stefan.acc at gmail.com
Fri Sep 29 15:20:30 PDT 2017

Hello Sabrina,

these particles look remarkably similar to nanogold particles I used
before. These particles also preferred proteins (they loved the 26S) or
showed clusters similar to the ones on the lower right image. They come in
sizes from 2 to >5nm (can't see a scale-bar, but it seems your
contamination is of similar size).

Is anyone using fiudical markers of any sort in your lab? One source of
contamination would be the tweezers that hold the grid during plunging. In
case those tweezers are shared among several 'plungers' and not readily
cleaned after use of the markers, they could appear on the next grid being

Hope that helps,

On Fri, Sep 29, 2017 at 1:52 PM, Sabrina Pospich <
Sabrina.Pospich at mpi-dortmund.mpg.de> wrote:

> Dear EM community,
> we are currently struggling with an electron dense contamination on our
> cryo-EM grids (see images below - left panel volta phase plate images with
> different phase shift - right panel standard TEM images at different
> magnifications).
> The dots seem to appear almost randomly and like to stick to protein. We
> furthermore see them independently of the glow discharger (GloCube or an
> older device) and plunger (Cp3 or Vitrobot) we use and also for both C-flat
> and Quantifoils grids.
> Has anyone seen those black dots before? We appreciate any hint.
> Cheers,
> Sabrina Pospich
> (Representative for the Raunser lab, MPI Dortmund)
> _______________________________________________
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> 3dem at ncmir.ucsd.edu
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Stefan Bohn
Gladstone Institute
1650 Owens Street
San Francisco, CA. 94158
Phone: +1 (415) 476 - 2980
Fax: +1 (415) 514 - 9736
stefan.bohn at gladstone.ucsf.edu
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