Super-sharp video clip of the cell
Scientists in Göttingen film for the first time cellular life process on the nanoscale
For a long time, biologists have dreamed of observing life processes inside cells in real-time. However, to observe relevant details, scientists need a resolution on the nanoscale, which using a light microscope has not been achieved in living cells to date. Scientists at the Max Planck Institute for Biophysical Chemistry and the Cluster of Excellence "Microscopy at the Nanometer Range", which was established in line with the German Excellence Initiative of the University of Göttingen, have succeeded in shooting the first video ever of the inside of a living cell. Using the STED-microscope, the researchers followed the rapid movements of tiny cell building blocks with up to 28 images per second and with an up to four times better resolution compared to conventional light microscopes. For the first time, scientists could track in real-time how vesicles move within living nerve cells (Science Express, February 21th, 2008).
If one succeeds in following the life processes inside cells in close detail, it is then easy to understand what happens inside a living cell. But detailed observation has so far only been possible using electron- or scanning probe microscopes. However, these techniques do not allow views inside living cells. In contrast, lens-based optical microscopy allows non-invasive investigations but the images are not sharp enough. The light microscopy method suffers from a critical disadvantage, namely their diffraction-imposed resolution, which is limited at best to 200 nm. This diffraction barrier seemed for a long time to be an insurmountable obstacle. With his newly developed "Stimulated Emission Depletion" (STED) microscope, Stefan W. Hell, director at the Max Planck Institute for Biophysical Chemistry, could dramatically increase the resolution in fluorescence microscopy and therefore allowed light microscopy with resolution on the nanoscale. Stefan Hell and co-workers have already successfully used the STED microscope to observe single protein complexes separated only 20 to 50 nanometres from each other - structures, which are more than 1000 times smaller than a human hair. But in almost all of these snap-shots, the cells were chemically arrested - and therefore "frozen" in their physiological processes. The long exposure time required for a single image did not allow the recording of movements.
By developing special fast recording techniques for the STED microscopy, the physicists Volker Westphal, Marcel Lauterbach and Stefan Hell, in cooperation with the biologists Reinhard Jahn as well as Silvio Rizzoli from the Cluster of Excellence "Microscopy at the Nanometer Range" succeeded in recording fast movements within living cells. They reduced the exposure time for single images in such a dramatic way that they could film the movements within living nerve cells with a resolution of 65 to 70 nanometres - a 3 to 4 times better resolution compared to conventional light microscopes - in real-time.
Follow movements of tiny vesicles in nerve cells in real-time
Nerve cells communicate with other cells by releasing neurotransmitters stored in synaptic vesicles in nerve terminals. The scientists succeeded in filming movements of these tiny vesicles with up to 28 images per second. Being only 40 nanometres in size, these vesicles are tiny - about 1000 of them fit into the width of a single hair. Looking through the microscope, the researchers could follow their movements within nerve cells in until now unmatched resolution. "The vesicles do not move continuously. Rather, they bind to the cell structures and detach again", says Rizzoli, describing the events in the nerve terminals. "We have demonstrated for the first time that it is possible to film life processes in real-time. We achieved a resolution, which was until now only possible with an electron microscope", Stefan Hell summarizes the quantum leap in microscopy.
Already in November last year, Leica Microsystems introduced the first commercial STED microscope. One of these microscopes has been acquired by the research group headed by Silvio Rizzoli at the European Neuroscience Institute (ENI) in Göttingen. Rizzoli and his co-workers successfully applied it to study vesicles in the nerve cells of rats. But the STED microscope can not only be used to elucidate processes of the transmission of signals in nerve cells. In fact, the scientists expect to find answers to many open questions in biological and medical research. Stefan Hell and his co-workers now aim to further optimise the recording technique for STED microscopy. Hell sees an enormous potential for further applications. "To shoot a video of the life processes in cells on the nanoscale was an important step. It pushes open a door towards new insights into what happens on the molecular scale of life - a door which was believed for a long time to be non-existent."
Stefan W. Hell (born in 1962) received his doctorate in physics from the University of Heidelberg in 1990, followed by a research stay at the European Molecular Biology Laboratory in Heidelberg. From 1993 to 1996, he worked as a senior researcher at the University of Turku, Finland, where he developed the principle of STED microscopy. In 1996, Stefan Hell moved to the Max Planck Institute for Biophysical Chemistry in Göttingen, where he built up his current research group dedicated to sub-diffraction-resolution microscopy. He was appointed a Max Planck director in 2002 and currently leads the Department of Nano-Biophotonics there. He is an honorary professor of experimental physics at the University of Göttingen and adjunct professor of physics at the University of Heidelberg. Hell has received several national and international awards, including the Prize of the International Commission for Optics (2000), the Carl Zeiss Research Award (2002), the "Innovation Award of the German Federal President" (2006), the Julius Springer Award for Applied Physics (2007), and the Leibniz Prize (2008).