Electron Microscopy

Microscopy Methods in Microbiology
Microroscopy Methods in Microbiology Part 2
Microroscopy Methods in Microbiology - Introduction
Observation of Microbes in the Living State
Observation of Microbes in Smears
Dyes and Staining
Useful pH Range and Colour Change of Some Indicator Dyes
Factors Affecting Staining
Microscopy and Micrometry
Microscopy and Micrometry - Introduction
Behaviour of Light
Light Theories
Resolving Power
Refraction and Reflection
Bright Field Microscopy
Use of Bright Field Microscope

Electron Microscopy

	Electron Microscopy It was realised that the resolving power of light microscope cannot be increased more than 0.2μm because of the limitations with light as the source of illumination. Max Knoll and Ernst Ruska in 1931, at the Technical university in Berlin, constructed and demonstrated the use of electron microscope which had much higher resolving power than the light microscope. After that the instrument has undergone many modifications to improve the quality of image produced. Although, the source of illumination in electron microscope is electron beam and not light, the optical principles and its constriction are closely related to those of light microscope as explained in Figure 2-9. Electron gun generates electron
Diagrammatic comparision of image formation in electron microscope and light microscope beam. These electrons are concentrated of electron gun, producing a fast mo electrons. Electrons are focused by electromagnetic lenses. Electromagnetic lens consists of wire encased in soft iron casing. When electric current is passed through the coil, it generates an electromagnetic field, through which they are focused. There are three general types of electromagnetic lenses. The one is placed between the source of illumination and the specimen. This focuses the beam of and functions in a similar manner as the condenser in light microscope. The other two lens systems are on the opposite side of specimen which magnify the image in similar fashion as objective and ocular in light microscope.
The final image is made visible on screen coated with a phosphorus compound which fluoresces upon irradiation by electrons. Permanent record of an image is possible to make on photographic plates films. Air molecules in the microscope interfere with the movement of electrons. To prevent this, the interior of the microscope is needed to keep in the state of high vacuum, around 10^-4 to 10^-6 mm Hg. It is also necessary to have specimen ultrathin. These requirements do not allow observation of living material through electron microscope. However, dry dormant spores have been observed for the demonstration of surface details.
More comprehensive and detailed informations regarding the design of microscope and its use can be obtained from Sjostrand (9) and Kay (10). The electron beam has very poor the before, only small objects or very thin sections of the specimen can be examined under the electron microscope. If the objective of the study is to reveal the intracellular details, the usual mode of approach involves preparation of thin sections of fixed material.

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