Some cutting-edge types of light microscopy (beyond the techniques we discussed above) can produce very high-resolution images. However, if you want to see something very tiny at very high resolution, you may want to use a different, tried-and-true technique: electron microscopy.Electron microscopes differ from light microscopes in that they produce an image of a specimen by using a beam of electrons rather than a beam of light. Electrons have much a shorter wavelength than visible light, and this allows electron microscopes to produce higher-resolution images than standard light microscopes. Electron microscopes can be used to examine not just whole cells, but also the subcellular structures and compartments within them.One limitation, however, is that electron microscopy samples must be placed under vacuum in electron microscopy (and typically are prepared via an extensive fixation process). This means that live cells cannot be imaged.
Images of Salmonella bacteria taken via light microscopy and scanning electron microscopy. Much more detail can be seen in the scanning electron micrograph.Image credit: OpenStax Biology. Credit a: modification of work by CDC/Armed Forces Institute of Pathology, Charles N. Farmer, Rocky Mountain Laboratories; credit b: modification of work by NIAID, NIH; scale-bar data from Matt Russell.In the image above, you can compare how Salmonella bacteria look in a light micrograph (left) versus an image taken with an electron microscope (right). The bacteria show up as tiny purple dots in the light microscope image, whereas in the electron micrograph, you can clearly see their shape and surface texture, as well as details of the human cells they’re trying to invade.
Image of an electron microscope. It is very large, roughly the size of an industrial stove.Image credit: OpenStax Biology. Modification of work by Evan Bench.There are two major types of electron microscopy. In scanning electron microscopy (SEM), a beam of electrons moves back and forth across the surface of a cell or tissue, creating a detailed image of the 3D surface. This type of microscopy was used to take the image of the Salmonella bacteria shown at right, above.In transmission electron microscopy (TEM), in contrast, the sample is cut into extremely thin slices (for instance, using a diamond cutting edge) before imaging, and the electron beam passes through the slice rather than skimming over its surface^55start superscript, 5, end superscript. TEM is often used to obtain detailed images of the internal structures of cells.Electron microscopes, like the one above, are significantly bulkier and more expensive than standard light microscopes, perhaps not surprisingly given the subatomic particles they have to handle!