Expertise in EM – Virus imaging at University of Pittsburgh’s Center for Biologic Imaging
With cold and flu season upon us, we wanted to spotlight how researchers use electron microscopy to learn more about viruses. In recent years, our applications team has worked with universities to obtain images of viruses by using samples that their labs already prepared. Among the studies we’ve seen or assisted with, the Watkins Lab at the University of Pittsburg Division of Cell Biology used SEM to produce images of cells infected with Covid-19. They also used Correlative Light and Electron Microscopy (CLEM).
We asked Lab Manager Jonathan Franks at the Center for Biologic Imaging (CBI) for his insight on the methods used when investigating viruses.
“SEM isn’t usually the first modality we would use for imaging viruses by themselves. TEM (specifically negative staining) is usually the first step in imaging any virus sample. SEM is important when it comes to understanding the behavior of the virus with cellular tissue,” he said.
Large area scan made with the JSM-7800F SEM using SEM Supporter. Inset shows the resolution in the regions of interest.
To prepare a sample for SEM, Jonathan says, “We dehydrate and embed the cells and viruses in a TEM resin and either section or polish into the tissue and use Backscatter EM on our SEM to take TEM-like images of the samples.” The main thing is ensuring the preparation of a good section and a smooth surface for imaging. “This technique has some advantages over TEM because we don’t have to deal with the loss of samples on the grid mesh, but the resolution isn’t quite as good as standard TEM.”
“We work with many labs that study viruses on a variety of imaging modalities, so we’ve seen a variety of sizes,” says Jonathan. “We have worked with HIV, Eastern Equine Encephalitis, Covid-19, and large Bacteriophages to name a few,” Jonathan says.
The lab at CBI has 6 faculty and 10 full-time staff members. “The diverse talents of our faculty and staff allows us to utilize our various imaging modalities and so we can image almost any and all biological samples and a variety of bioengineering and material science samples”. In the EM division of the CBI lab they utilize two 120kV TEMs and two Field-Emission SEMs. Specifically in the EM division they can look at everything from cells and tissue samples to carbon nanotubes and bioengineered scaffolds. Outside of EM, they use several other techniques for their studies.
“Techniques vary depending on the sample and we have been utilizing the large area scanning of both sections and block faces much more to get a bigger area of study than the TEM can provide us. We have also been exploring the technique of serial block imaging with the SEM using backscatter. We have several CLEM projects right now. The current challenge is getting this technique to work on slices of tissue,” Jonathan says. Most of the work at the CBI is for research, not clinical use, unless it is to help improve techniques used in the medical field.
Covid19 infected cells imaged with JSM-6335F SEM