T. Clark Brelje, Ph.D.
University of Minnesota
Department of Genetics, Cell Biology and Development
6-160 Jackson Hall
321 Church St SE
Minneapolis, MN 55455
Robert L. Sorenson, Ph.D.
University of Minnesota
Department of Genetics, Cell Biology and Development
6-160 Jackson Hall
321 Church St SE
Minneapolis, MN 55455
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The human eye can resolve objects separated by at least 0.250 mm. A microscope magnifies an image so smaller details can be seen by the eye.
Light Microscopy
A light microscpe forms a magnified image by focusing light with glass lenses on a thin tissue section.
Bright-field illumination is used with specimens stained with colored dyes. It has a resolution of ~0.25 µm (or ~1000x greater than the unaided eye).
ELECTRON MICROSCOPY
An electron microscope forms a magnified image of a specimen using electrons.
Transmission Electron Microscopy (TEM)
Ultrathin tissue sections (50 to 100 nm) are stained with heavy metals (such as osmium tetroxide, uranium or lead salts) to increase constrast.
TEM measures relative differences in transparency (i.e., contrast) of a specimen to electrons. The images are colorless and have a resolution of 0.1 nm (or ~1000x greater than a light microscope).
Scanning Electron Microscopy (SEM)
Specimens are coated with a thin film of metal (such as platinum).
SEM measures relative differences in the reflection of electrons to produce images of three-dimensional surfaces. The images are colorless and have a resolution of ~10 nm (or ~100x greater than a light microscope).
