Types of microscopes

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Types of microscopes

Scanning

Uses a beam of electrons instead of light; electrons are reflected from the specimen; because of the shorter wavelength of electrons, structures smaller than 0.2 um can be resolved.

To study the surface features of cell and viruses.

Electron Transmission

Uses a beam of electrons instead of light; electrons pass through the specimen; because of the shorter wavelength of electrons, structures smaller than 0.2 um can be resolved.

To examine viruses or the internal ultra structure in thin sections of cells.

Fluorescence

Uses an ultraviolet or near-ultraviolet source of illumination that causes fluorescent compounds in a specimen to emit light.

For fluorescent-antibody techniques to rapidly detect and identify microbes in tissues or clinical specimens.

Phase-Contrast

Uses a special condenser containing an annular (ring-shaped) diaphragm. The diaphragm allows direct light to pass through the condenser, focusing light on the specimen and a diffraction plate in the objective lens. Direct and reflected or diffracted light rays are brought together to produce the image.

To facilitate detailed examination of the internal structures of living specimens.

Dark Field

Uses a special condenser with an opaque disk that blocks light from entering the objective lens directly; light reflected by specimen enters the objects lens, and specimen appears light against a black background.

To examine living microorganisms that are invisible in bright field microscopy, do not stain easily, or are distorted by staining; frequently used to detect Treponema padllidum in the dignosis of syphilis.

Light Bright Field

Uses visible light as a source of illumination; cannot resolve structures smaller than about 0.2 um; specimen appears against a bright background inexpensive and easy to use.

To observe various stained specimens and to count microbes; does not resolve very small specimens, such as viruses.