Toward fluorescence nanoscopy

TLDR: A family of concepts has emerged that overcomes the diffraction barrier altogether and, relying on saturated optical transitions, these concepts are limited only by the attainable saturation level.

Abstract: For more than a century, the resolution of focusing light microscopy has been limited by diffraction to 180 nm in the focal plane and to 500 nm along the optic axis Recently, microscopes have been reported that provide three- to sevenfold improved axial resolution in live cells Moreover, a family of concepts has emerged that overcomes the diffraction barrier altogether Its first exponent, stimulated emission depletion microscopy, has so far displayed a resolution down to 28 nm Relying on saturated optical transitions, these concepts are limited only by the attainable saturation level As strong saturation should be feasible at low light intensities, nanoscale imaging with focused light may be closer than ever