Stefan W. Hell gives Kavli Prize Laureate Lecture in Berlin

In 2014 Stefan W. Hell was awarded the Kavli Prize in nanoscience. He went on later in the year to win the Nobel Prize in chemistry as well. On 30 September 2015 he will give a Kavli Prize Laureate Lecture titled "Sharpness without limits: Light microscopy in the 21st century"at the Nordic Embassies in Berlin. The lecture is organized by the Norwegian Embassy, the Norwegian Academy of Science and Letters and Max Planck Society.

Ambassador Elisabeth Walaas will give the opening address, followed by a speech by Prof. Dr. Martin Stratmann, President of the Max Planck Gesellschaft. Professor Kirsti Strøm Bull, President of the Norwegian Academy of Science and Letters will then introduce Stefan Hell on behalf of the three partners behind the prize, which in addition to the Academy are The Kavli Foundation and the Norwegian Ministry of Education and Research.

Kavli Prize winners in nanoscience 2014. From left: Sir John B. Pendry, Stefan W. Hell og Thomas W. Ebbesen. Foto: ScanpixKavli Prize winners in nanoscience 2014. From left: Sir John B. Pendry, Stefan W. Hell og Thomas W. Ebbesen. Foto: Scanpix

Stefan W. Hell received the Kavli Prize in Nanoscience in 2014 "for ground-breaking developments that have led to fluorescence microscopy with nanometre scale resolution, opening up nanoscale imaging to biological applications."

Ernst Abbe demonstrated in 1873 that optical microscopy should not be able to discern features that are closer than half the wave-length of light. The Abbe limit became a cornerstone of optics that was not questioned for the next 120 years.

Hell met this challenge and overcame the diffraction limit by more than an order of magnitude. He accomplished this through understanding both the imaging mechanisms and the nature of what is being imaged. A key issue in the clarity of an image has always been distinguishing signal from a broad background of noise. By deeply understanding the composition of what is being imaged, be it biological or non-biological in nature, Hell showed how to control the background noise by strategically 'shutting off' molecular transitions at the appropriate time.

He calls this 'shutting off' Stimulated Emission Depletion (STED): a technique that has now become accessible through instruments which he has helped to make commercially-available. Not only has STED enabled imaging at dimensions far smaller than optical wavelengths for a broad class of materials, it has in particular made this a viable option for the life sciences. Remarkably, Hell's techniques have made possible direct observation of dynamical processes in living cells at nanoscale resolution.

Optical microscopy: the resolution revolution

Throughout the 20th century it was widely accepted that a light microscope relying on conventional optical lenses cannot discern details that are much finer than about half the wavelength of light (200-400 nm), due to diffraction. However, in the 1990s, the viability to overcome the diffraction barrier was realized and microscopy concepts defined, that can resolve fluorescent features down to molecular dimensions. In this lecture, I will discuss the simple yet powerful principles that allow neutralizing the limiting role of diffraction1,2. In a nutshell, feature molecules residing closer than the diffraction barrier are transferred to different (quantum) states, usually a bright fluorescent state and a dark state, so that they become discernible for a brief period of detection. Thus, the resolution-limiting role of diffraction is overcome, and the interior of transparent samples, such as living cells and tissues, can be imaged at the nanoscale.

1. Hell, S.W. Far-Field Optical Nanoscopy. Science 316, 1153-1158 (2007)
2. Hell, S.W. Microscopy and its focal switch. Nature Methods 6, 24-32 (2009)

Stefan W. Hell was born in Romania in 1962. After moving to West Germany as a teenager and finishing high school, he studied physics at the University of Heidelberg from where he received a diploma in 1987 and a doctoral degree in 1990. During his postgraduate work, he became interested in whether it is possible to overcome the resolution limits of light microscopy, which became the focus of his activities in the following years. From 1991 to 1993 he worked at the European Molecular Biology Laboratory in Heidelberg. In 1993 he moved to Finland to continue his research at the University of Turku until 1996, interrupted by brief stints to Oxford as a visiting scientist. 1997 saw him back in Germany, taking a position as a research group leader at the Max Planck Institute for Biophysical Chemistry in Göttingen. Following his appointment as a director in 2002, Hell established the Department of NanoBiophotonics at the Göttingen Max Planck Institute. Since 2003 he also leads the Optical Nanoscopy division at the German Cancer Research Center (DKFZ) in Heidelberg. Hell is also affiliated with the physics faculties at the universities of Heidelberg and Göttingen.

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