Transmission electron microscopy
Transmission electron microscopy (TEM) forms images using electrons that pass through a thin specimen. Electromagnetic lenses direct and magnify the beam, and differences in electron transmission reveal features within the material. It differs from scanning electron microscopy, which commonly records signals generated near a specimen's surface.[1]
Image formation
An electron source, lenses, specimen holder and detector operate within the microscope column. A specimen must be sufficiently thin for useful transmission. In biological work, differences in electron scattering can be enhanced with electron-dense stains. The resulting image can show internal structures such as membranes and organelles that cannot be distinguished with an ordinary light microscope.[1]
Preparation and interpretation
Conventional biological TEM often involves chemical fixation, dehydration, embedding in resin and cutting very thin sections with an ultramicrotome. The sections are placed on supporting grids and stained to increase contrast. These operations preserve and expose structures, but they can also remove material or distort it. Preparation artefacts must therefore be considered when interpreting a micrograph.[2]
Serial sections allow a structure to be followed through adjacent parts of a specimen. Electron tomography instead combines images taken at different specimen tilts to reconstruct a three-dimensional volume. Cryogenic methods preserve samples in vitreous ice and can avoid some chemical fixation and staining steps, although low contrast creates other imaging difficulties.[2]
The method is used to answer structural questions rather than merely to obtain a highly magnified picture. The choice of preparation, section thickness and imaging method depends on the feature under investigation. Conventional TEM, tomography and cryogenic imaging can provide complementary evidence, with different compromises between preservation, contrast and the volume sampled.[2]
References
- ↑ 1.0 1.1 OpenStax. Instruments of Microscopy. Microbiology.
- ↑ 2.0 2.1 2.2 Mark Winey, Janet B. Meehl, Eileen T. O’Toole and Thomas H. Giddings Jr (2014). Conventional transmission electron microscopy. Molecular Biology of the Cell.
Attribution
Adapted with reference to English Wikipedia, revision 1373216485 (contributors and history), under CC BY-SA 4.0. The prose has been rewritten and checked against the cited sources; changes have been made.