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Bielefeld researchers provide 3D images of coronaviruses

Scientists at Bielefeld University’s Faculty of Physics have succeeded for the first time in imaging the SARS-CoV-2 coronavirus with a helium ion microscope. In contrast to the more conventional electron microscopy, the samples do not need a thin metal coating in helium ion microscopy. This allows interactions between the coronaviruses and their host cell to be observed particularly clearly. The scientists have published their findings, obtained in collaboration with researchers from Bielefeld University's Medical School OWL and Justus Liebig University Giessen, in the Beilstein Journal of Nanotechnology.

Coronaviruses are tiny – only about 100 nanometres in diameter, or 100 billionths of a metre. So far, mainly scanning electron microscopy (SEM) has been used to examine cells infected with the virus. With SEM, an electron beam scans the cell and provides an image of the surface structure of the cell occupied by viruses. However, SEM has a disadvantage: the sample becomes electrostatically charged during the microscopy process. Because the charges are not dispersed from non-conductive samples, for example viruses or other biological organisms, the samples must be coated with an electrically conductive coating, such as a thin layer of gold.

Coronaviruses (blue) exiting a kidney cell, images captured with a helium ion microscope. Photo: Bielefeld University/N. Frese

In their study, the scientists infected cells – artificially produced from the kidney tissue of a species of monkey – with SARS-CoV-2 and studied them in dead state under the microscope. ‘Our images provide a direct view of the 3D surface of the coronavirus and the kidney cell – with a resolution in the range of a few nanometres,’ says Frese. This enabled the researchers to visualise interactions between the viruses and the kidney cell. Their study results indicate, for example, that helium ion microscopy can be used to observe whether individual coronaviruses are just lying on the cell or are bound to it. This is important in order to understand defence strategies against the virus: an infected cell can bind the viruses, which have already multiplied inside it, to its cell membrane on exit and thus prevent them from spreading further. 

A kidney cell infected with SARS-CoV-2 under the helium ion microscope (sectional magnification from left to right, a single virus is about 100 nanometres in size): the images indicate that some coronaviruses only lie loosely on the cell as they exit, while other viruses are bound to the cell. Photo: Bielefeld University/N. Frese

Helium ion microscopy is a comparatively new technology. In 2010, Bielefeld University became the first German university to acquire a helium ion microscope, which is used primarily in nanotechnology. Worldwide, helium ion technology is still rarely used to examine biological samples. ‘Our study shows that there is great potential here,’ says Gölzhäuser. The study appears in a special issue of the Beilstein Journal of Nanotechnology on the helium ion microscope.