An ultramicroscope is a microscope with a system that lights the object in a way that allows viewing of tiny via light scattering, and not light reflection or absorption. When the diameter of a particle is below or near the wavelength of visible light (around 500 ), the particle cannot be seen in a light microscope with the usual methods of illumination. The ultra- in ultramicroscope refers to the ability to see objects whose diameter is shorter than the wavelength of visible light, on the model of the ultra- in ultraviolet.
Synopsis
In the system, the particles to be observed are dispersed in a liquid or gas
colloid (or less often in a coarser suspension). The colloid is placed in a light-absorbing, dark enclosure, and illuminated with a convergent beam of intense light entering from one side. Light hitting the colloid particles will be scattered. In discussions about light scattering, the converging beam is called a "
Tyndall cone". The scene is viewed through an ordinary microscope placed at right angles to the direction of the lightbeam. Under the microscope, the individual particles will appear as small fuzzy spots of light moving irregularly. The spots are inherently fuzzy because light scattering produces fuzzier images than light reflection. The particles are in
Brownian motion in most kinds of liquid and gas colloids, which causes the movement of the spots. The ultramicroscope system can also be used to observe tiny nontransparent particles dispersed in a transparent solid or gel.
Ultramicroscopes have been used for general observation of aerosols and colloids, in studying Brownian motion, in observing tracks in , and in studying biological ultrastructure.
History
In 1902, the ultramicroscope was developed by Richard Adolf Zsigmondy (1865–1929) and
Henry Siedentopf (1872–1940), working for Carl Zeiss AG.
Applying bright sunlight for illumination they were able to determine the size of 4 nm small
in
cranberry glass. Zsigmondy further improved the ultramicroscope and presented the immersion ultramicroscope in 1912, allowing the observation of suspended nanoparticles in defined fluidic volumes.
In 1925, he was awarded the Nobel Prize in Chemistry for his research on colloids and the ultramicroscope.
Later the development of electron microscopes provided additional ways to see objects too small for light microscopy.
See also
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Dark-field microscopy, a different technique that leverages light scattering against a dark background
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Light sheet fluorescence microscopy
