Imaging of SARS-CoV-2 infected Vero E6 cells by helium ion microscopy.

Friedemann Weber,Matthias König,Natalie Frese,Holger Sudhoff,Armin Gölzhäuser,Matthias Schürmann,Patrick Schmerer,Martin Wortmann,Michael Westphal

doi:10.3762/bjnano.12.13

Abstract

Helium ion microscopy (HIM) offers the opportunity to obtain direct views of biological samples such as cellular structures, virus particles, and microbial interactions. Imaging with the HIM combines sub-nanometer resolution, large depth of field, and high surface sensitivity. Due to its charge compensation capability, the HIM can image insulating biological samples without additional conductive coatings. Here, we present an exploratory HIM study of SARS-CoV-2 infected Vero E6 cells, in which several areas of interaction between cells and virus particles, as well as among virus particles, were imaged. The HIM pictures show the three-dimensional appearance of SARS-CoV-2 and the surface of Vero E6 cells at a multiplicity of infection of approximately 1 with great morphological detail. The absence of a conductive coating allows for a distinction between virus particles bound to the cell membrane and virus particles lying on top of the membrane. After prolonged imaging, it was found that ion-induced deposition of hydrocarbons from the vacuum renders the sample sufficiently conductive to allow for imaging even without charge compensation. The presented images demonstrate the potential of the HIM in bioimaging, especially for the imaging of interactions between viruses and their host organisms.

Highlights

The last decade of helium ion microscopy (HIM) was characterized by a rapid exploration of its sub-nanometer imaging and ion-beam nanofabrication capabilities in materials science and engineering [1]
Shaped particles below 100 nm diameter on the cell membrane shown in Figure 1b4 were only abundant on the cells of the multiplicity of infection (MOI) 1 sample and were identified as SARS-CoV-2 virus particles
An effect frequently occurring during HIM imaging with charge compensation can be observed in the sequence of HIM images shown in Figure 2a1–3, where a location on a multiplicity of infection of approximately 1 (MOI 1)-infected Vero E6 sample was first imaged at a field of view (FOV) of 23 μm (Figure 2a1), followed by two higher magnification images with a FOV of 4.5 μm and a FOV of 1 μm (Figure 2a2)

Summary

Introduction

The last decade of helium ion microscopy (HIM) was characterized by a rapid exploration of its sub-nanometer imaging and ion-beam nanofabrication capabilities in materials science and engineering [1]. While TEM achieves unsurpassed resolution and can visualize macromolecular structures such as spike glycoproteins or transmembrane proteins [21], SEM provides topographic images of infected cells and virus particles distributed on their surface, albeit only after the samples have been coated with a conductive layer.

Results

Conclusion