![]() Previously, sections need to be treated with heavy metals like osmium, lead and uranyl, which have a similar function as dyes in light microscopy, and make cellular structures visible. That is why they are called ultrathin sections. Tissue sections have to be very thin, about tens of nanometers, to get sharp images and allow the electrons to cross the whole tissue thickness. The electron beam is concentrated by electromagnets and focused on the tissue. In this type of electron microscopes, a beam of electrons is produced from a tungsten filament that works as a cathode (Figure 1). Tow types of electron microscopes are commonly used in histology: transmission electron microscopes and scanning electron microscopes. That is why they have large cylinders where the electron beam is formed and manipulated with magnets, and where the sample has to be introduced. Otherwise, the electrons would hit the particles present in the air. The changes in magnification power are set by modulating the speed of the electrons, which also modifies the wavelength frequency.Įlectron microscopes are very large apparatuses because electrons must travel in vacuum. Nowadays, there is an intense research for deciphering the 3D organization of molecules by using electron microscopes.Įlectron microscopes do not have glass lenses, they use magnets instead, that work as magnetic lenses by concentrating the electron beam emitted by an electron gun. In fact, what limits the sharpness of the images is the sample preparation more than the electron microscope itself. ![]() The current electron microscopes are capable of distinguishing atoms in molecules and can reach 50 10 6 magnifications. Electrons have shorter wavelength than visible light and therefore permit several million times magnification. The resolution power of electron microscopes may be as small as 1 nm because they use electron beams, instead of visible light. ![]() Thus, observing cell ultrastructure means visualizing the cell with an electron microscope. Very small cellular components could be studied, which are commonly called cell ultrastructures. The first electron microscope was made in 1933 by Ruska, and was adapted to study biological samples shortly after. When very small tissular structures are going to be visualized, smaller than the light microscope resolution power, such us some organelles, membranes, macromolecular complexes or viruses, we need to make use of electron microscopes. ![]()
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