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Electron Microscopy

Séverine Kunz


With a resolution down to less than one nanometer, electron microscopy provides an open view deep into biological samples. It even allows exploring the structure of molecular machines in the cell.

Electron microscopy is an indispensable tool in many fields of cell biology and medicine to study subcellular structures in the normal and diseased states. However, since the electron beam is only stable in high vacuum (a vacuum with very low pressure) it is impossible to image living cells or tissues. Samples have to be chemically fixed and embedded or immobilized through very low (cryogenic) temperatures – while aiming to retain biological structures in a close-to-native state. Recent developments in cryo-electron microscopy in particular, such as highly sensitive electron detectors, allow visualizations at unprecedented resolution.

Our tools

  • Transmission electron microscopes:
    • Talos L120 C (120 kV) with long duration dewar, 16M Ceta CMOS camera and 2 Gatan cryo holders (FEI)
    • Morgagni (80 kV) with 11M Morada CCD camera (FEI)
    • EM 910 (120 kV) with 11M Quemesa CCD camera (Zeiss)
  • 4 ultramicrotomes, one with a cryo chamber for Tokuyasu technique
  • Freeze substitution device AFS2, grid plunger and grid stainer AC20 (Leica)
  • Carbon coater, GloCube glow discharge system, trimming device and others

Service and Technology

Deploying the electron beam

Our group offers a range of electron microscopic methods to explore manifold specimens from humans as well as model organisms, such as mice, zebrafish or fruit flies. In many cases, immunolabeling of the sample with specific antibodies is required for identifying the cellular structures of interest. Usually, we then deploy a routine preparation procedure known as Tokuyasu cryosectioning technique, in combination with a special in-house developed contrasting method. The approach allows clearly depicting cellular membranes and the inner structure of mitochondria, for example. Another important technique that we perform is the negative contrast, in which the background (instead of the target structure) is stained. Immunolabeling and negative contrast can also be combined.

Such structures are formed in neuronal brain cells of Huntington’s disease patients. This fibril was produced in the test tube for experimental investigation. (negative contrast)

Using these tools, our group has been investigating heart and muscle cell disorders, stem cells and myelin defects in the brain. We have visualized neurodegenerative proteins as well as nanoparticles for drug development, and characterized various cell cultures. We also compared the well-known mouse model with the naked mole rat, a unique species, on an ultrastructural level. For many projects, available protocols had to be adapted or new sample preparation strategies developed. Recently, we started using a technique known as high pressure freezing, which is particularly suited for preserving the subcellular architecture. Our facility is available for all types of collaborations.



A 3D dive into the cell

Since 2017, we have a new transmission electron microscope (Talos L120C) at our disposal, opening the door to the future practice of cryo-electron microscopy. We have started optimizing sample preparation approaches and obtaining initial results in structural and cell biology. The device allows electron tomography, in which detailed 3D structures are assembled from microscopic series. Thus, we will be able to visualize small cell compartments such as vesicles and membrane structures and even biological macromolecules in 3D.

Additionally, we envisage a tight collaboration with the Charité university clinic that will establish a new facility for high-end cryo-electron microscopy on the campus in Berlin-Buch.