ultramicroscope
What is an ultramicroscope used for?
How does an ultramicroscope work?
Who invented the ultramicroscope and when?
How did the ultramicroscope inspire future developments?
ultramicroscope, microscope arrangement used to study colloidal-size particles that are not visible in an ordinary light microscope because they are smaller than the wavelengths of visible light. The particles, usually suspended in a liquid, are illuminated with a strong light beam perpendicular to the optical axis of the microscope. These particles scatter light, and their movements are seen as flashes against a dark background. Since visible light wavelengths are also larger than the distance between colloidal-size particles, the particles can only be rendered visible, but their structure cannot be resolved by an ultramicroscope.
Invention and evolution
The Austrian chemist Richard Zsigmondy invented the ultramicroscope in 1903. Zsigmondy was researching colloidal gold, especially the colloidal pigment called purple of Cassius used to stain ceramics and glass. At the time, many thought it was a chemical compound or a suspension, but Zsigmondy proposed that it was a colloidal system. (Colloids and suspensions are both made up of particles mixed into another medium. Suspension particles will eventually settle, but colloidal particles are smaller and will not.)
When his chemical experiments failed to convince fellow scientists that his gold solutions were colloidal, Zsigmondy tried using physical methods to prove it. However, the available ordinary light microscopes could not make these particles visible. To overcome the microscopes’ limitations, Zsigmondy devised a new technique—he directed light onto the object at a right angle (from the side) rather than from below. This led to the invention of the ultramicroscope. He developed the prototype of the ultramicroscope in collaboration with the German optical physicist Henry Siedentopf.
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Zsigmondy and Siedentopf worked together to improve the design of the ultramicroscope, creating the slit-ultramicroscope. This device made it easier to observe Tyndall cones—the light rays scattered by colloidal particles in a solution. Using this, Zsigmondy was able to determine the size of gold particles in solutions with known concentrations of gold. Several contemporaries of Zsigmondy, including Siedentopf, continued to improve on the design of the ultramicroscope, which led to the development of paraboloid, cardioid, mirror, and concentric ball condensers. In collaboration with the German microscope manufacturing company Rudolf Winkel, Zsigmondy developed the immersion ultramicroscope in 1912. With it, he studied colloids in liquid systems. The concept of the ultramicroscope inspired the later development of light sheet fluorescence microscopy and its variant, selective plane illumination microscopy.
Application and importance
The invention of the ultramicroscope and its subsequent application in research led to three Nobel Prize awards.
- Austrian chemist Richard Zsigmondy received the 1925 Nobel Prize for Chemistry for his work on colloids and the methods developed to study them (which included the invention of the ultramicroscope).
- French physicist Jean Perrin received the 1926 Nobel Prize for Physics for his studies of Brownian motion (which was done using the ultramicroscope).
- Swedish chemist Theodor H.E. Svedberg received the 1926 Nobel Prize for Chemistry for his studies in the chemistry of colloids and for his invention of the ultracentrifuge (which was named in analogy to the ultramicroscope).
The invention of the ultramicroscope made it possible to visualize gold particles as small as 4 nm (1 nm = 10-9 meter) in diameter. It was also used to study the Brownian motion of particles in solution. Together, these developments helped shape the growing discipline of colloidal chemistry.
The ultramicroscope and its later modifications advanced research across disciplines as diverse as physics, medicine, agriculture, biology, biochemistry, and bacteriology. It helped shed light on fundamental questions such as the existence of atoms. By enabling the study of colloids, which form the basis of many pharmaceutical products and cosmetics, the ultramicroscope also aided in the development of commercially important products such as shampoos and shaving creams.