Our world is made up of moving, vibrating and leaping molecules. However, it is not an easy task to capture their movement. IBS Scientists at the Center for Soft and Living Matter, within the Institute for Basic Science (IBS), were able to observe the movement of molecules stored within a graphene pocket without having to stain them.
This research is published in Advanced Materials, and presents new possibilities for exploring the dynamics of life building blocks, such as DNA and proteins, and also the self-assembly of other materials.
One third of the diameter of a human hair is roughly the smallest size that can be seen by human eyes without any help. Thus, microscopes are required for distinguishing tinier objects. While bacteria and cells are visible under optical microscopes, molecules and viruses can be seen only under an electron microscope.
Images are formed by electrons shot onto a sample in the case of an electron microscope. Since electrons have a much shorter wavelength than light, electron microscopy offers a much higher magnification when compared to optical microscopy. The sample, however, is destroyed by the electron beam and if water is present, it might decompose into bubbles. Thus, electron microscopy is ideal for visualizing inert, dead samples, while living material is chemically protected in place.
Breaking this rule, the Scientists visualized non-fixed chains of atoms, known as polymers, swimming in a liquid within graphene pockets. These include two graphene layers on the top and 3-5 graphene layers on the bottom. Besides being impermeable to tiny molecules, these sheets also prevent the electron beam from immediately damaging the sample: the dynamic movement of individual polymer molecules was admired by the Researchers for an average of 100 seconds, before the electron beam destroyed them. Molecules change position, rearrange or “jump around” during these important seconds.
It was amazing to watch these flexible organic macromolecules dancing around. Molecules move much more quickly in bulk. We were surprised to see that they are moving more slowly here. We believe that attachment to the surface of the pocket worked in our favor to slow them down, without that we would probably see just a blurred image.
Hima Nagamanasa, First Co-Author of the Paper
Earlier, Scientists had to stain samples with dye or metal molecules so that the samples were visible within the graphene pocket. Metal shines as it has high reflexibility, and thus can be used to get good images. However, the characteristics of the sample molecule change due to the chemical bonds between the sample and the dye or metal. In this work, the graphene pocket is thin enough that its content can be seen in real time without the need for staining.
The Scientists worked with two specific polymers: one with polystyrene sulfonate, sulfur and one without, polyethylene oxide. This enabled them to explain that the contrast under the microscope is due to the polymer structure - made of hydrogen and carbon atoms – and not from the sulfur.
Most molecules produced by living organisms have a backbone made of carbon and hydrogen, and that's why we hope to extend this research to the study of interactions between DNA and proteins.
Huan Wang, First Co-Author
In addition, as a standard electron microscope was used, the Scientists believe that other laboratories will make use of this technique.
Dancing inside a graphene pocket
(Credit: Institute for Basic Science)