Ultramicroscope
An ultramicroscope is a special form of a dark field microscope for the observation of very small objects that could not be seen with an imaging light microscope alone. These include B. colloidal particles , mist droplets or smoke particles. The term “ultramicroscopy” came up around 1900. He referred to the microscopic examination of so-called "ultra-micron" particles that are smaller than the resolution limit of light microscopy. In microscopy, a distinction is made between resolution and detectability. Resolution means that it can be seen whether one or two separate structures are present. With classic light microscopy, the limit of resolution is around 0.2 micrometers . Much smaller objects can be detected if they generate light signals against a dark background. This can be the case with dark field microscopy or fluorescence microscopy . However, it cannot then be determined whether the signal is coming from just one or from several neighboring objects.
One variant is the slit ultrasonic microscope that Henry Siedentopf and Richard Adolf Zsigmondy developed at the beginning of the 20th century. In 1902, when illuminated with bright sunlight, the two scientists were able to detect particles of less than 4 nanometers in size in ruby glasses . As a result, Zsigmondy's ultramicroscope was further developed into an immersion ultrasonic microscope in 1912 and enabled the observation of nanoparticles in (aqueous) solution.
Zsigmondy received the Nobel Prize in Chemistry in 1925 for his research on colloids using ultramicroscopy .
In the 21st century the term ultramicroscope is sometimes used for light disk microscopes , a variant of a fluorescence microscope in which, similar to a slit ultramicroscope , only one plane of the specimen is illuminated.
Structure of the slit ultramicroscope
The observation objects are suspended in a gas or a liquid . They are observed in the darkest possible, absorbing environment with an imaging light microscope and illuminated with a convergent light beam perpendicular to the observation axis. The scattering of the light bundle on the suspended objects to be observed corresponds to the Tyndall effect , which is why the light bundle is also called the Tyndall cone. This light bundle is focused in the field of view of the microscope and generates light scattering on each individual observed particle in the observation volume, which is then observed.
Since the objects to be observed are smaller than the resolution limit of the imaging microscope, they create diffraction rings that appear in the imaging microscope as bright spots against the dark background.
use
Ultramicroscopes were used to study Brownian molecular motion , in the Millikan experiment to determine the elementary charge and to observe particle traces in cloud chambers .
The illumination geometry of the slit ultramicroscope was taken up in fluorescence microscopy in the 1990s and 2000s and is now used in light disk microscopy .
Individual evidence
- ↑ Dieter Gerlach: History of microscopy . Verlag Harri Deutsch, Frankfurt am Main 2009, ISBN 978-3-8171-1781-9 , pp. 663-676 .
- ↑ K. Becker, N. Jahresling, S. Saghafi, HU Dodt: Ultramicroscopy: light-sheet-based microscopy for imaging centimeter-sized objects with micrometer resolution. In: Cold Spring Harbor protocols. Volume 2013, number 8, August 2013, pp. 704-713, doi : 10.1101 / pdb.top076539 , PMID 23906921 .
Web links
- Nobel Prize lecture by RA Zsigmondy (English): Properties of colloids (PDF; 108 kB), with an illustration and a brief explanation of the ultramicroscope
- Repetition of an experiment to observe the behavior of 50 nm silver particles in aqueous solution with a historical microscope and comparison with modern scientific methods: Timo Mappes, Norbert Jahr u. a .: The invention of the immersion ultramicroscope in 1912 - the beginning of nanotechnology? In: Angewandte Chemie. 124, 2012, pp. 11370-11375, doi : 10.1002 / anie.201204688 .
- Immersion ultrasonic microscope according to the patent from 1912 with application to 50 nm silver particles