The condenser lenses focus the electronic beams through the specimen and electrons are scattered depending upon the thickness or refractive index of different parts of the specimen. A large voltage is applied between the cathode (the tungsten filament) and the anode, which excites the electrons and it travels with high velocity towards the condenser lens. The electronic beam is obtained from a heated tungsten filament which generates electrons. Slices thus prepared are then mounted on a metal slide. Slicing: Specimen is cut into thin slices by an ultramicrotome knife.Embedding: Specimen is embedded in plastic polymer and then, is hardened to form a solid block.Dehydration: Specimen is then dehydrated with organic solvents (e.g.Fixation: Cells are fixed by using glutaraldehyde or osmium tetroxide for stabilization.Unlike visible light, electron beams can not penetrate even a single cell. The general flow of sample preparation is as follows: The specimen suitable for electron microscopes should be very thin (20-100 nm thickness) so the bacterial cells and any other biopsy materials should be slice into thin layers. For Transmission Electron Microscope Specimen Preparation The major differences between scanning electron microscope (SEM) and transmission electron microscope (TEM) are available here. It has low magnifying power compared to TEM. In SEM sample is prepared by coating it with a thin layer of metal such as gold or palladium. SEM scans the surface of the objects and provides three-dimensional views of the surface structures. It uses scattered electrons as the light source. It is the most commonly used type of electron microscope. Its magnifying power is very high as compared to SEM and shows a 2-dimensional image. Tissues must be cut in thin sections for viewing under TEM. It provides a detailed view of the internal structure of the prepared test samples. Transmission Electron Microscope ( TEM)Īs the name suggests, this type uses transmitted electrons as light sources. There are two types of electron microscopes with different operating styles: the transmission electron microscope (TEM) and the scanning electron microscope (SEM). In electron microscope, the entire illuminating imaging system is usually referred to as the microscope column and is constructed upside down as compared to a light microscope. Image viewing and recording system: The magnified image of the specimen is formed as a photograph (called an electron micrograph) or as an image on a TV screen.In an electron microscope, the coils bend the electron beams the same way. In an ordinary microscope, the glass lenses bend (or refract) the light beams passing through them to produce magnification. The magnetic lens of an electron microscope can have different powers (focal lengths and magnification) depending on the amount of current flowing through the electrical coils. In addition to the condenser and objective lenses, a third projector lens is also present. There are 3 sets of electromagnetic lenses in an electron microscope as compared to two in light microscopes. Electromagnetic fields (instead of lenses): The lenses that make the specimen seem bigger are replaced by a series of coil-shaped electromagnets through which the electron beam travels also known as electromagnetic lenses.These electron beams are obtained when the tungsten filament in an electron microscope, is heated by applying a high voltage current, which is used as a light beam. Source of light: The source of light is replaced by a beam of very fast-moving electrons.Like any ordinary microscope, the electron microscope also uses a light source, a combination of lenses to produce a magnified image, however, this vary slightly as compared to ordinary light microscope. Schematic diagram of Transmission Electron Microscope
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