Ever since its invention in the 17th century, the light microscope has served as a key instrument to the advancement of knowledge. For biology, this statement is true even today, since focused light is the only way to examine living cells non-invasively. However, because of the wave nature of light, focused light is subject to diffraction. As early as 1873, Ernst Abbe recognized that this fact imposes an absolute limit on resolution in microscopy. Abbe, whose 100th year death anniversary was in February, captured this limit in a formula (Fig. 1), which states that objects at distances that are smaller than a certain limit cannot be separated in a light microscope. This resolution limit can be largely ascribed to the fact that light cannot be focused to a smaller spot due to diffraction. It seemed impossible to image details smaller than a distance where delta d is equal to 200nm using conventional lenses and visible light.
For a long time, Abbe's law was regarded as being insurmountable. For higher resolution, the textbook knowledge was that a complicated and costly electron or scanning tunneling microscope would be required. However, over the past few years, researchers from the Max Planck Institute for Biophysical Chemistry in Göttingen, Germany, have developed with Stimulated Emission Depletion (STED) microscopy, a physically consistent concept for breaking the diffraction limited resolution li
Contact: Prof. Stefan W. Hell