Have you ever seen a drop of water ? Well … I guess you will be amazed by the question, but have you really seen a drop of natural pond water??? Just take a look……
In addition to the light microscope, the electron microscopes have opened a great pasture for the biologists as well as other fields who need to work on the minutest details like the aircraft structure that should not have a microscopic scratch or the structural consolidation of an alloy so as to say.
In case of electron microscopes, the basic pattern of operation is same, there are the power source, lenses, objectives, specimens but the components differ. Like in an EM, the power source are beam of electrons produced from a tungsten filament at very high temperatures that are guided by electromagnets in the body of the microscope to be incident on the specially prepared specimen. The specimen is coated with heavy metals like osmium or old so that the electrons are reflected off the surface to form secondary electrons. The secondary electrons are captured and processed to form an image on a fluorescent screen as a negative which is converted by a software into a positive image. This is the Scannimg Electron Microscopy. IN case of transmission Electron MIcroscopy, the specimen sections by making hard resin blocks and then subjected to the electron beam. Some of the eletrons are deflected from the surface while others pass through and eventually an image of the interior of the cell is produced..
The different types of microscopes used are
Stereo Microscope, Comparison Microscope, Confocal Microscope, USB Microscope<span MICroscope, Dark Fields MIcroscope, Scanning Tunnelling MIcroscope, Pterographic Microscope, Polarizing microscope, Epifluorescence microscope, Confocal microscope etc.
LIMIT OF RESOLUTION:
Limit of resolution of a microscope refers to its ability as to how much it can clearly distinguish between two closely placed points <span and how close they are. . Here , there is an inverse relationship between the limit of resolution and what is actually resolved since the resolution increases as the distance decreases. In order to change it into a direct correlation, the increase of the limit of resolution is used.
Limit of resolution = (0.61 x λ) / N A ( Numerical aperture), resolution = NA / (0.61 x λ).The Scanning Electron MIcroscope has a resolving power of (30 -100) Angstrom while that of TEM it is ( 3-10) Angstrom .The limit of Resolution in a light microscope is about 300 times less than SEM.
The use of microscopes help us to get magnified images, but how does it do that ? Actually f you remember , the microscope has 2 lenses, the objective lens and the optical lens. Boh these lenses act together to create a virtual image of the object , that is much larger than the original one. A look at the ray diagram will hell you clear the idea.
IN ORder that the cells may be visible under the microscope with all the necessary details up to a certain magnification, we need to color them with specific dyes that change the transparency of the specimen and blocks the photons from the light source to penetrating the transparent specimen. That produces a differential dark and lighted area corresponding to the organelles that has taken absorbed the stain. The stain is is the compound that is obtained either chemically or can be obtained from natural sources like haematoxylin is obtained from the plant Caesalpinia spinosa and there are different types of hematoxylin, like Mayers Hematoxylin, Delafield’s HEmatoxylin etc. However , haematoxylin cannot be used directly as it is not actually a dye but has to be ripened (or oxidized to hematin ) by different processes.The section after bluing is counter stained with eosin.