Electron Microscopy

Electron microscopy is a technology for examining the extremely fine detail or ultrastructure of biological specimens. This methodology opened a totally new vista to the human eyewhenbiological ultrastructurewas revealed as a dynamic and architecturally complex arrangement of macromolecules under the direction of genetic units termed genes. Complex subcomponents of the cell, termed organelles, were clearly visualized and biochemical activities associated with each structure. Pathogenic microorganisms, the viruses, were finally captured on film and the simple, yet beautiful, structures of these infectious subunits provided the first step to organizing them into major taxonomic categories, or virus families. The structural organization of DNA into the chromosome was elucidated using electron microscopy and the electron microscope provided insight into many disease processes. Electron microscopy is routinely used as a tool in such diverse areas as anatomy, anthropology, biochemistry, cell biology, forensic medicine, microbiology, immunology, pathology, physiology, plant biology, toxicology and zoology. The two basic types of electron microscopy are scanning electron microscopy, for viewing surfaces of bulk specimens, and transmission electron microscopy, for scrutinizing internal as well as external features of extremely thin specimens. The scanning electron microscope is so named because a fine probe of electrons is scanned across the surface of a specimen to generate an image with a three-dimensional appearance. In the transmission electron microscope, the electrons are transmitted through the specimen to reveal a two-dimensional image of the interior of cells. Although these instruments operate in completely different ways, both use accelerated electrons and electromagnetic lenses to generate images. Both types of electron microscope require high vacuum so that electrons, having little mass, can travel down the column of the microscope without being scattered by air molecules. Images are recorded either on photographic films or captured digitally using computer interfaces. In order to appreciate the types of information obtainable with these instruments, it is important to understand their basic design and operational principles. The Transmission Electron Microscope