Electron microscopy

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The electron microscope (EM) is a type of microscope that uses a beam of electrons to create an image of the individual you are experimenting on. It uses higher magnifications and has a greater focusing power than a light microscope, which allows it to see smaller objects at a higher quality with more detail. They are expensive, large pieces of equipment and training must be given to use them correctly. 

Electron microscopes offer an image resolution of up to 200 times stronger than light microscopes. This is because they use radiation of much shorter wavelengths in the form of an electron beam. The electrons are produced by a tungsten filament operating in a vacuum and are focused by electromagnets[1]. There are two types of electron microscopes; scanning electron microscope (SEM) and transmission electron microscope (TEM), which contrast in the way in which the electron beam interacts with the individual. In TEM, the beam passes through the individual and is reflected from the surface. SEM works by scanning an electron beam over the surface of the sample and the electrons in the beam interact with the sample. Then a secondary electron beam then scans the signals caused by the first beam, thus producing an image[2]. In both cases, the beam must fall on a fluorescent screen before the image can be viewed. Permanent images known as electron micrographs are produced after focusing the beam on the photographic film[3].

Electron microscopy is exceptionally important and useful in understanding cellular and subcellular structures[4]. It is mainly used to demonstrate cell ultrastructure (TEM), to show surface features of organisms (SEM), to investigate changes in the number, size, shape and condition of each and organelles (TEM) and to carry out quantitative studies of cell and organelle disposition (TEM)[5].

However there are quite a number of disadvantages of electron microscopes too, such as; they are expensive to build and to maintain. They are dynamic rather than static in their operation and are extremely sensitive to vibrational movements and external magnetic fields[6]. A significant amount of training is required in order to operate an electron microscope successfully and it is considered to be a specialised skill[7]

References

  1. Reed R., Holmes D. et al. (2013) Chapter 28; Introduction to microscopy. Practical Skills in Biomolecular Sciences (Fourth edition).
  2. https://www.nanoscience.com/technology/sem-technology/
  3. Reed R., Holmes D. et al. (2013) Chapter 28; Introduction to microscopy. Practical Skills in Biomolecular Sciences (Fourth edition).
  4. Microsopy (No date specified). http://www.jic.ac.uk/microscopy/intro_em.html [Last accessed on 23/11/13]
  5. Reed R., Holmes D. et al. (2013) Chapter 28; Introduction to microscopy. Practical Skills in Biomolecular Sciences (Fourth edition).
  6. Microsopy (No date specified). http://www.jic.ac.uk/microscopy/intro_em.html [Last accessed on 23/11/13]
  7. Microsopy (No date specified). http://www.jic.ac.uk/microscopy/intro_em.html [Last accessed on 23/11/13]
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