Revamping ultracold liquid helium microscopy to produce high-resolution images of proteins
A team of researchers at the Medical Research Council Laboratory of Molecular Biology, in the U.K., has re-examined an old liquid-helium-cooled electron microscope, discovered the reason for the lack of improvement in the resolution of molecular protein imaging, and found a workaround to the problem. Their study is published in the Proceedings of the National Academy of Sciences.
Several decades ago, researchers began using helium-cooled electron microscopes to image protein specimens near absolute zero in hopes of creating sharper images. The assumption was that the extreme cold would reduce damage due to the radiation from the microscope. Unfortunately, the approach did not work as hoped—the method produced blurry images, so the approach was abandoned. In this new study, the research team took a new look at the older technology.
The team analyzed an electron microscope built 20 years ago for experiments to image proteins. To find the problem, they replaced the protein being studied with gold nanoparticles, allowing them to track the electron beams as they were bounced around after firing. Images of the particles at 77 K and 13 K were fuzzy as expected, but by tracking the paths of the electrons, the team found that the cause was the expansion of ice during the chill, which forced specimens upward and blurred the images.
To solve the problem, the research team replaced the copper plate used to hold the specimens with a gold one. The specimens were held in place within holes drilled into the plate. By using gold, repulsive charges were reduced, reducing the buildup of ice. They also made the holes smaller to prevent undesirable movement of the ice.
With the changes in place, the team added protein specimens, chilled the microscope and began firing electrons. They found that the changes they made improved resolution at either 77 K or 13 K by approximately 1.5 times, which they describe as a "big deal." The improvement, they claim, is enough to provide useful imagery of proteins that have been imaged in other ways, and also to image some that are much smaller—perhaps even including those found on cell membranes.
More information: Christopher J. Russo et al, Reducing the effects of radiation damage in cryo-EM using liquid helium temperatures, Proceedings of the National Academy of Sciences (2025).
Journal information: Proceedings of the National Academy of Sciences
© 2025 Science X Network
