Electron Microscope

The electron microscope, first built by Ernst Ruska in 1931 and substantially advanced by Gerd Binnig and Heinrich Rohrer in 1981, replaced visible light with a beam of accelerated electrons as its illuminating source. Because electrons have a far shorter effective wavelength than visible light, an electron microscope's resolving power is roughly 100,000 times better than that of a light microscope, which is exactly what makes it possible to see a cell's 'ultrastructure' - the fine internal architecture of organelles that light microscopy simply cannot resolve. Before viewing, a specimen has to be carefully dehydrated and then coated or impregnated with an electron-dense heavy metal such as gold or palladium; this coating lets the delicate specimen withstand bombardment by the electron beam and also gives the final image contrast, since the metal scatters electrons differently from the biological material itself. There are two distinct electron microscope designs. The Transmission Electron Microscope (TEM) is the more commonly used type: a focused beam of electrons is passed straight through an extremely thin section of the specimen and captured on a fluorescent screen as a flat, two-dimensional image, giving magnifications of roughly one to three lakh times and a resolving power of 2-10 angstroms - ideal for studying the fine structure of viruses, mycoplasma and cell organelles. The Scanning Electron Microscope (SEM), by contrast, fires a finely focused electron beam over the surface of a gold-coated specimen; the interaction knocks loose various radiations (secondary electro …