Far-field optical nanoscopy
Prof.Dr. Stefan Hell (Max Planck Institute for Biophysical Chemistry, Gottingen) 2014 Nobel Laureate
The resolution of a far-field optical microscope is usually limited to d=l/(2n sina) > 200 nm, with 2n sina denoting the numerical aperture of the lens and l the wavelength of light. While the diffraction barrier has prompted the invention of electron, scanning probe, and x-ray microscopy, the 3D-imaging of the interior of (living) cells requires the use of focused visible light. Here, I will discuss lens-based fluorescence microscopy concepts that feature a resolving power on the nanoscale. All these concepts share a common basis: exploiting selected (pairs of) states and transitions of the fluorescent marker to neutralize the limiting role of diffraction[1, 2]. Specifically, the marker is switched between a bright (i.e. signal-giving) state and a dark state. The first viable concept of this kind was Stimulated Emission Depletion (STED) microscopy.