AsianScientist (Aug. 16, 2018) – Researchers in South Korea have developed a method to protect samples during electron microscopy. Their findings, published in ACS Nano, could give us insight into complex phenomena such as molecular self-assembly.
Since life is mostly based on water, molecules are constantly moving, vibrating and flipping in a liquid environment. Electron microscopy, a technique used to study static molecules at the nanometer scale, has been incompatible with the observation of moving molecules, primarily because the incident electron beam damages the samples.
In the present study, scientists at the Center for Soft and Living Matter of the Institute for Basic Science (IBS), South Korea, have discovered a ‘shield’ that protects samples from the incident beam of an electron microscope. The researchers used a tiny pocket filled with liquid sandwiched between atomically-thin sheets of graphene, within which the sample molecules are free to move and are protected from electrical charging.
After testing several types of liquids, they found that the use of heavy water, D2O, most effectively delays not only the formation of gas bubbles, but also the structural damage of individual polymer molecules. Compared to normal water, D2O has one more neutron, which means that it is heavier, more difficult to dissociate into radicals, and therefore less reactive.
“Heavy water outperforms [other liquids] by a factor of two to five at least,” said Dr. Kandula Hima Nagamanasa of IBS, who is a co-author of the study. “Since bubble formation is delayed, the molecules were visible for twice as long.”
An equally important advantage is that D2O is a harmless sunscreen. The sample, a polymer of polystyrene sulfonate in this case, showed the same pattern of dynamics and similar contrast in D2O and in water.
“In the future, we plan to extend this study to more complex macromolecules, like DNA and proteins,” explained Professor Steve Granick, director of the IBS Center for Soft and Living Matter and corresponding author of the study.
“Moreover, the study opens avenues to observe long-term phenomena in other related microscopy techniques, like cryogenic electron microscopy, and to get more statistical information about complex phenomena, like self-assembly of single molecules into more complex biological structures.”
The article can be found at: Wang et al. (2018) Longer-Lasting Electron-Based Microscopy of Single Molecules in Aqueous Medium.
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Source: Institute for Basic Science; Photo: Shutterstock.
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