Light Microscope in Unprecedented Resolution

Prof. Dr. rer. nat. Stefan W. Hell

Prof. Dr. rer. nat. Stefan W. Hell
Max-Planck-Institut für
Biophysikalische Chemie, Göttingen

There are constraints on our view of the microscopic world through light microscopes due to a physical limitation.
Yet is it perhaps possible to trick Nature and work around this limit?

Stefan W. Hell has effectively found a way to make smaller structures visible using a light microscope than is actually possible according to the laws of physics. Stefan W. Hell is Director of the Max Planck Institute for Biophysical Chemistry in Göttingen.

A valuable instrument for cancer research
To be able to treat a disease like cancer effectively, it is first necessary to know how it affects the body. Researchers usually use a fluorescence microscope, a light microscope that renders the distribution of proteins in a cell visible to the eye. Proteins are marked with marker molecules and illuminated, causing the marker molecules to take on a fluorescent glow: they emit colored light, indicating where which proteins are present.

Yet the potentialities of this method are limited: when the distance between proteins is very small, they cannot be distinguished. Since light propagates as a wave, which is deflected by objects, under a light microscope it is only possible to recognize details that are at least a half wavelength – around 200 nanometers – apart. This phenomenon was discovered by German physicist Ernst Abbe in 1873. To date, a higher resolution has only been achieved with electron or scanning probe microscopes which cannot be used to look inside living cells.

Superimposition of a ring-shaped spot
Stefan W. Hell became the first person to overcome the Abbe Limit using a Stimulated Emission Depletion (STED) microscope. Its resolution is not limited by the light wavelength, but only by the technology. The special technique: a ring-shaped spot is superimposed onto the round spot of light used to illuminate a cell, which has an opposite effect on the marker molecules. While the light in the round focal spot excites the fluorescent glow, the light in the ring-shaped spot suppresses the fluorescence. The result: only the markers of proteins in the small space in the middle of the ring of light up. This provides a sharper image. In principle, even individual molecules can be seen.

The technology provides the means which reveal the smallest details of processes in living cells. It promises radical new insight in the molecular causes of diseases and the effects of medicines. The company Leica Microsystems GmbH in Mannheim expects that all major scientific institutions around the world will soon be equipped with STED microscopes. As the recipient of a license to the technology, the company hopes to bring the first microscopes to the market in 2007 – made in Germany.

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