Imaging Methods
Written by Levi Clancy
First published
December 15, 2005
Last modified
October 8, 2009
Numerical aperture is a measure of light-gathering ability.
| (Compound) Light Microscope | These use visible light. Bright-field, phase-contrast, dark-field and fluorescence are the most common light microscopes. These are 2-dimensional. |
| Bright-Field Microscopy | Visualizes via differences in density, and lacks high contrast. Staining is usually required to visual cells using bright-field microscopy, making it worthless for most applications. |
| Phase-Contrast Microscopy | Used to view wet-mount preparations. Cells slow incident light and thus differ in refractive index from surroundings. |
| Dark-Field Microscopy | Lighting hits specimen’s sides only. Light reaching lens is scattered by specimen. Specimen appears light on dark background. Best resolution of all light microscopes. |
| Fluorescence | Visualize fluorescing specimens. |
| 3-Dimensional | The most common instruments for 3-dimensional imaging are differential interference contract (DIC), atomic force and confocal scanning laser. |
| DIC | Polarized light is split by a prism. These beams traverse the specimen and enter the objective lens where they are combined into one. Since the refractive indices are different, the image looks 3-dimensional. |
| Atomic Force | A stylus is positioned extremely close to the specimen, repulsive atomic forces are established and these forced are used to generate an image. |
| Confocal Scan | Confocal Scanning Laser Microscopy (CSLM) couples laser source to light microscope. Laser is adjusted to a vertical layer and then directed at specimen. Illumination intensity is highest at plane of focus. You can see various layers by adjusting plane of focus. |
| e- Microscopy | e- microscopes use e-s, not photons, for visualization. Instead of photos, e- micrographs are produced. Cells need to be sliced into 20-60 nm slices for visualization of internal structures. |
| Transmission | In a vaccuum, electromagnets are used as lenses. This is used to view internal cell structure. |
| Scanning Microscope | Specimen is coated with heavy metal, such as gold. An e- beam goes across the specimen, and e-s scattered by the metal are collected. |
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