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Pedantic note: they're not really imaging individual atoms directly; it's a composite view of the structure based on averaging thousands of different images of

Pedantic note: they're not really imaging individual atoms directly; it's a composite view of the structure based on averaging thousands of different images of copies of the molecule in different orientations. This is true of other structure determination methods such as crystallography of course. The breakthrough here is that these are exceptionally accurate measurements; when I tried learning EM in the early 2000s it was still mostly just vague blobs.

steve_adams_86 6y ago
I remember when those vague blobs were a monumental achievement. It’s very cool to see these kinds of technologies break through and get refined like this.
- chrisbrandow 6y ago
  In terms of either sample prep or data processing, how time consuming is this relative to X-ray crystallography? Setting aside entirely the enormous benefit of not needing crystals. I’m a (former) chemist that has only ever had to use X-ray crystallography for small molecules. I’m just trying to get a sense of what the practice of doing this is like?
  - natechols 6y ago
    I do not know what it's like in practice now, but on a purely theoretical basis, if you are trying to solve a completely novel structure with no known homologs, especially if it's something on the scale of a ribosome, direct imaging is always going to be easier than trying to solve the phase problem, both experimentally and computationally.
MayeulC 6y ago
I don't do much experimentation, but I am pretty sure that you can very easily distinguish individual atoms with electron beam microscopy, and get pretty close using atomic force microscopy. And I am not sure what exactly is the resolving power of synchrotron radiation, but I expect if to be pretty high. However, the breakthrough here seems being able to do so using a low-energy electron beam. All the methods I quoted above are probably impractical or damaging with biological samples.
- natechols 6y ago
  With hard xrays you can visualize interatomic densities and lone pairs. I know there are structures down to 0.5Å resolution now but that must have required careful setup. I've seen diffraction out to 0.75Å but I could never collect complete data at that resolution.
  - thechao 6y ago
    I’m imagining a collector plate the size of my dining room table, with a staff of crazy-haired scrawny physicists clambering around some sort of neo-Victorian rube-Goldbergesque X-ray source — like a wine-barrel-sized copper anode and a small nuclear power plant for the arc.
    - natechols 6y ago
      This is not far from the truth, except the detectors are actually relatively small (and very expensive), there's more aluminum foil than the Victorians used, and we have slightly better hair on average. The last time I used one of these facilities, it looked like this (and still does): https://lcls.slac.stanford.edu/sites/lcls.slac.stanford.edu/files/styles/basic_page_large_image/public/cxi-banner01.jpg https://lcls.slac.stanford.edu/sites/lcls.slac.stanford.edu/... Compared to this electron microscopy is downright boring - and a couple of orders of magnitude cheaper to set up.
- jtaillon 6y ago
  That's pretty much correct. Single-atom imaging is possible using aberration-corrected scanning TEM, but the beam doses used will typically obliterate anything organic through radiolysis or ionization damage (although there are emerging ways around that using some interesting compressive sensing techniques). Most "atomic resolution" EM images you see are actually images of columns of atoms, since the imaging mode is transmission, so necessarily the image is summed through the plane of the sample (so atomic resolution is only in the perpendicular plane). The techniques used in this paper get around the dose issue by taking many images of very many presumably identical proteins (called dose fractionation) at very low dose. Computer algorithms are then used to stitch together a 3D model based on the low-dose individual images. Making it really cold also helps things from breaking down under the beam.
__MatrixMan__ 6y ago
Pedantic note: At this scale, a particle is nothing more than a distribution of the probability of making some kind of measurement. So composites of multiple samples aren't a suboptimal means of imaging atomic structure, they're the only way. To do anything else would be to show only part of the probability field that is the atom. (Right? I've been going back and forth about this since I saw those "videos" in 2015 of "individual photons". My gut reaction was that those aren't videos, they're simulations that cleverly represent the probability of measuring a photon as the brightness of of the "photon", but since we're measuring inherently probabilistic things maybe that's the only honest way to do it, in which case perhaps we ought to accept them as images.)

steve_adams_86 6y ago

I remember when those vague blobs were a monumental achievement. It’s very cool to see these kinds of technologies break through and get refined like this.

chrisbrandow 6y ago
In terms of either sample prep or data processing, how time consuming is this relative to X-ray crystallography? Setting aside entirely the enormous benefit of not needing crystals. I’m a (former) chemist that has only ever had to use X-ray crystallography for small molecules. I’m just trying to get a sense of what the practice of doing this is like?
- natechols 6y ago
  I do not know what it's like in practice now, but on a purely theoretical basis, if you are trying to solve a completely novel structure with no known homologs, especially if it's something on the scale of a ribosome, direct imaging is always going to be easier than trying to solve the phase problem, both experimentally and computationally.

MayeulC 6y ago

I don't do much experimentation, but I am pretty sure that you can very easily distinguish individual atoms with electron beam microscopy, and get pretty close using atomic force microscopy. And I am not sure what exactly is the resolving power of synchrotron radiation, but I expect if to be pretty high. However, the breakthrough here seems being able to do so using a low-energy electron beam. All the methods I quoted above are probably impractical or damaging with biological samples.

natechols 6y ago
With hard xrays you can visualize interatomic densities and lone pairs. I know there are structures down to 0.5Å resolution now but that must have required careful setup. I've seen diffraction out to 0.75Å but I could never collect complete data at that resolution.
- thechao 6y ago
  I’m imagining a collector plate the size of my dining room table, with a staff of crazy-haired scrawny physicists clambering around some sort of neo-Victorian rube-Goldbergesque X-ray source — like a wine-barrel-sized copper anode and a small nuclear power plant for the arc.
  - natechols 6y ago
    This is not far from the truth, except the detectors are actually relatively small (and very expensive), there's more aluminum foil than the Victorians used, and we have slightly better hair on average. The last time I used one of these facilities, it looked like this (and still does): https://lcls.slac.stanford.edu/sites/lcls.slac.stanford.edu/files/styles/basic_page_large_image/public/cxi-banner01.jpg https://lcls.slac.stanford.edu/sites/lcls.slac.stanford.edu/... Compared to this electron microscopy is downright boring - and a couple of orders of magnitude cheaper to set up.
jtaillon 6y ago
That's pretty much correct. Single-atom imaging is possible using aberration-corrected scanning TEM, but the beam doses used will typically obliterate anything organic through radiolysis or ionization damage (although there are emerging ways around that using some interesting compressive sensing techniques). Most "atomic resolution" EM images you see are actually images of columns of atoms, since the imaging mode is transmission, so necessarily the image is summed through the plane of the sample (so atomic resolution is only in the perpendicular plane). The techniques used in this paper get around the dose issue by taking many images of very many presumably identical proteins (called dose fractionation) at very low dose. Computer algorithms are then used to stitch together a 3D model based on the low-dose individual images. Making it really cold also helps things from breaking down under the beam.

__MatrixMan__ 6y ago

Pedantic note: At this scale, a particle is nothing more than a distribution of the probability of making some kind of measurement. So composites of multiple samples aren't a suboptimal means of imaging atomic structure, they're the only way. To do anything else would be to show only part of the probability field that is the atom. (Right? I've been going back and forth about this since I saw those "videos" in 2015 of "individual photons". My gut reaction was that those aren't videos, they're simulations that cleverly represent the probability of measuring a photon as the brightness of of the "photon", but since we're measuring inherently probabilistic things maybe that's the only honest way to do it, in which case perhaps we ought to accept them as images.)