[3dem] Electron dense contamination on cryo grids

[Sabrina Pospich]

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)

[cid:115172A7-0078-461B-88F7-50ABF840BA2F]
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