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S C HW E R P U N K T 29 04 | LICHT GEDANKEN Biophysicist Prof. Dr Christian Eggeling is dedicated to super-resolution fluorescence microscopy. He uses it to observe proteins and other molecules interacting within living cells. He owes many fascinating insights to this technology—as well as an invitation to the 2014 Nobel Prize in Stockholm. »We want to be able to visualize it!« INTERVIEW: UTE SCHÖNFELDER Mr Eggeling, why is microscopy so important to science? Humans are visual creatures. We want to see something; we like to have a pic- ture of something in our minds. It is only then that we believe it. And this is, of course, also true of research. You can use the most precise measuring methods to obtain detailed informa- tion and attain knowledge—but we can only really convince other people of something when we can create a visual representation of the findings. What can researchers discover with the fluorescent microscopes of today? Proteins and other molecules in living cells, for example. Until a few years ago, this wasn’t possible. Now we can for example watch live as human im- mune cells identify and attack cancer cells. Above all, we can directly ob- serve the molecular defence mecha- nisms and processes, by mapping the participating proteins and their struc- tures. What made these advancements pos­ sible? The lenses for fluorescence microsco- py have continued to improve over re- cent years, as have the lasers and the technology as a whole. But it was not physics but chemistry that gave us the decisive leap we needed to super-reso­ lution microscopy: thanks to the new fluorescence dyes. Stefan Hell initiated these advancements with his ideas that the resolution limit of an optical mi- croscope, as postulated by Ernst Abbe, could be transcended through the use of suitable fluorescence markers. This has now been established as standard practice. What was the resolution limit? At the end of the 19th century, Abbe stated that two points that were less than 200 nanometres apart were not discernible by a conventional optical microscope. This is due to the wave properties and the convergence of the light used for the observation, and the resulting diffraction. Molecules and cell components smaller than this can, therefore, not be represented with a normal optical microscope. But they can with super-resolution fluorescence microscopy? Yes, the protein structures that we are interested in are significantly smaller than 100 nanometres. In order to make these visible, we use laser beams to switch the fluorescence of dyes, used to mark the molecules under study, on and off. This reduces the effective fluo­ rescent scope of observation to scales of less than 200 nanometres and thus improves the resolution according- ly. This was a real breakthrough, and Hell received the 2014 Nobel Prize for Chemistry as a result. And you played a part too! Yes, luckily ( laughs )! I was part of Hell’s working group in Göttingen between 2003 and 2012, and worked with him and other researchers to develop the methodology and brought it into usage. When he heard about the Nobel Prize, he invited me to attend the ceremony in Stockholm with him. And, when he received the medal from the Swedish king, I was a little proud myself! It was a very touching moment. Prof. Dr Christian Eggeling wants to apply the so- called super-resolution STED microscopy (Stimulated Emission Depletion) to new areas, for example for the direct diagnosis of illnesses in patients. During his time in the laboratory of Stefan Hell, who later won the Nobel Prize, in Göttingen, he was involved in the development of the super-resolution procedure. Eggeling has contributed a photograph taken using STED microscopy to the photo gallery on the following pages (No. 10 on p. 31). F E AT U R E