Following textbook wisdom, the resolution of light microscopy is limited by diffraction to about half the wavelength of light, which is why conventional light microscopes fail to distinguish object details that are closer together than ~200 nanometers. Stefan Hell and his group have broken this century-old barrier by developing, since the early 1990's, novel fluorescence microscopes featuring diffraction-unlimited spatial resolution. Thus, they also laid the foundation of a new scientific field: superresolution fluorescence microscopy, also called fluorescence nanoscopy.
Stefan Hell's group is developing light microscopes with a spatial resolution down to a few nanometers, particularly, but not exclusively, for imaging cells and tissue of a living organism. Prominent methods include STED and RESOLFT microscopy as well as concepts based on stochastic single-molecule switching such as GSDIM microscopy. To surpass the diffraction barrier, all these methods utilize a reversible transition or switch of fluorescent labels between a bright and a dark state. In combination with 4Pi microscopy, which is another concept developed by this group that uses two opposing lenses, the resolution can be increased in all spatial dimensions down to the nanometer scale. Since these superresolution concepts fundamentally rely on transitions between molecular states, novel labels are required that can be optically prepared in at least two different states. Consequently, the group also pioneers the chemical synthesis and application of new labeling methods and techniques to improve the performance of the labels’ switching behavior to separate close-by molecules.
The novel superresolution methods are destined to become primary tools for imaging living biological samples ranging from cells and tissues to small animals, having the potential to transform the life sciences.