Speaking of radiation damage in the Cryo-EM, I dont understand the concept behind this dose rate.
For example in this line "The total exposure time for producing one image composed of 70 frames was 14s and required a dose rate of 2 e-/Å2/sec"
Can some one explain this one image of 70 frames and this dose rate.
For X-ray diffraction, a larger crystal can tolerate a high total dose and often diffracts to high resolution because more molecules contribute to the diffraction. For single-particle cryo-EM, the total electron dose used to image each molecule is set to a very low level to preserve structural information at the subnanometer-resolution level. The consequence of such low-dose imaging is that individual images have a very poor signal-to-noise ratio (SNR).
In the above lines very low level of electron dose here is defining the time limit or what?
Dear Aamir,
as you mentioned one is trying to reduce radiation damage by imaging biological samples under low dose conditions.
The new DEDs as the Gatan K2 or the FEI Falcon II or III offer a very fast read out.
That means that one can collect "movies" of a target composed of for example 70 frames / individual Images. These Images can now be summed up and corrected for beam induced motion. This summ of images is then treated as an individual images (one image , 70 frames). 5 frames were taken in 1 sec. The dose rate was set to 2 e-/Å2/sec, means in 1 sec 2e- are detected per Å2 of the detector . The summed Images suffered from a electrone dose of 28 e-/Å2.
If one later realizes that the beam damage is to high one can kick out the late frames and reduce the total dose.
Generally spoken a higher dose leads to better contrast but destroys the specimen.
Best
Thiemo
Hi Aamir Iqbal , One more thing: It may sound very counter intitutive but the initial frames in the movies also are not very good due to ethane contamination etc. Last frames as pointed out above are bad because they suffer radiation damage the most. Hence, generally people discard some initial and final frames when trying to attain high resolution.
Thiemo explained it very well. Just another point that in most cases the highiest information are usually not in the first few frames anyway. Even though they are not damaged but still experience beam induced motion. This could be caused by warming of ice and movement of water molecules.
- Badges
- Science topic
- Similar topics
- Engineering
- Electrical Engineering
- Electrodes