[3dem] Electron dense contamination on cryo grids

Sameer K Singh sameer.singh at einstein.yu.edu
Fri Sep 29 14:11:01 PDT 2017

Hi Sabrina,

I've seen the same dots  (top and bottom right). In my case I saw them in areas where the ice was too thin and interpreted it as aggregated proteins. Perhaps you need to change the grid making conditions (reduce blotting time slightly ?)
You could also look at a different part of the the current grid where the ice may be of more optimum thickness.

Hope this helps.


Sameer Singh, PhD
Albert Einstein College of Medicine
1300 Morris Park Avenue
New York, NY - 10461
Phone: 718-430-2048
Cell: 917-848-9319
From: 3dem [3dem-bounces at ncmir.ucsd.edu] on behalf of Sabrina Pospich [Sabrina.Pospich at mpi-dortmund.mpg.de]
Sent: Friday, September 29, 2017 4:52 PM
To: 3dem at ncmir.ucsd.edu
Subject: [3dem] Electron dense contamination on cryo grids

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.

Sabrina Pospich
(Representative for the Raunser lab, MPI Dortmund)

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