Stefan Hell

STED microscope

Lifetime Achievement
Technical field
Max Planck Institute for Biophysical Chemistry
Throughout history, medicine has benefited dramatically from groundbreaking technologies at seemingly regular intervals. One of the latest contributions to clinical microbiology came in 2001 with the revolutionary Stimulated Emission Depletion (STED) microscope, developed by Professor Stefan Hell of the Max Planck Institute in Göttingen, Germany.

The arrival of the first microscopes in the 17th century proved nothing short of a revolution for the field of medicine. Overnight, scientists could investigate concepts behind biological processes far too miniscule to be seen by the naked eye. But microscopy had its limits, and for almost 130 years the so-called Abbé Limit postulated that the wavelength of light posed an insurmountable barrier to the ability of light microscopes to magnify ever smaller structures.

In 2001, Stefan Hell, director of the Max Planck Institute for Biophysical Chemistry in Göttingen, presented his Stimulated Emission Depletion (STED) Microscope which not only magnified beyond the Abbé Limit, but surpassed it tenfold. In 2005, Hell and his colleagues introduced a new law to replace the Abbé Limit. Named after RESOLFT (reversible saturable optical fluorescence transition), its premise is that the wavelength of light is no longer an issue. Only the technical design of a microscope, they postulate, can determine the limits of magnification - which are practically infinite.

At first, his efforts met with considerable doubt from colleagues, as the Abbé Limit was a maxim carved in stone for all light-based microscopy. At the same time, other approaches, including the scanning-tunnelling electron microscope (STM) were proving far more promising and powerful. However, Hell insisted on pursuing his light optics approach, as light microscopy is the only method for imaging the inside of living cells and organisms; the gorgeous images generated by scanning-tunnelling microscopes reveal surface structures only.

With researchers now able to look deep inside living cells, scientists can launch new studies into the origins of diseases and develop new insights into the principles of life at a molecular level. Hell's invention has advanced the research of cancer and infectious diseases tremendously, a field to which he himself has contributed directly since 2003 as head of the High Resolution Optical Microscopy Division at the German Cancer Research Centre in Heidelberg. Little wonder STED has quickly proven an essential tool in everyday clinical research since Leica Microsystems started shipping the technology in 2007.

How it works

The Stimulated Emission Depletion (STED) microscope is based on the principle of fluorescence, where molecules are targeted with light of a certain wavelength that the molecule then radiates back in a different colour. Fluorescent molecules can be used to mark biological material such as proteins, DNA and other cellular components, allowing for very detailed and precise imaging. The STED microscope then uses two synchronised lasers to achieve fluorescence in the marked focus spot.


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