No limit

“Ingenious.” That is how the Royal Swedish Academy of Sciences described the work of Eric Betzig of the Howard Hughes Medical Institute, Virginia, USA; Stefan W. Hell of the Max Planck Institute for Biophysical Chemistry, Göttingen, Germany; and W. E. Moerner from Stanford University, USA, who have shared the 2014 Nobel Prize in Chemistry. The prize was awarded for the development of fluorescence techniques with nanometre 'super-resolution' that have enabled scientists to observe chemistry occurring in unprecedented detail. These techniques sidestep a fundamental physical law — first described by Ernst Abbe in the late nineteenth century — that limits standard optical microscopy to a resolution of roughly 200 nm.

Hell (pictured right) developed a technique known as stimulated emission depletion (STED) microscopy. It works by using a laser to stimulate fluorescence in a sample of labelled molecules and a second laser beam that prevents fluorescence from a doughnut-shaped region around the point of interest. Only the fluorescence from the central area is detected. The microscope can then be swept across the sample, nanometre-by-nanometre, until a large picture is built up. Hell first published the concept in 1994, but it was not demonstrated experimentally until 2000.