It used to be fact, and even children at school were taught one basic principle of light microscopy: it’s impossible to see things that are smaller than 200 nanometers – that is, a 200 millionth of a millimeter. This was called the diffraction limit. So you might be able to see the shapes of very large bacteria or human cells under your microscope, but you won’t be able to see smaller structures inside of these cells or viruses and certainly no single molecules. This year three new Nobel Laureates in Chemistry – William E. Moerner, Stefan W. Hell and Eric Betzig – have turned it all on its head with the development of super-resolved fluorescence microscopy.
Stefan Hell developed a special method which makes use of two laser beams. One stimulates fluorescent molecules to glow. A second laser beam, though, cancels out any glow caused by the first beam – except for that in a nanometer-sized volume. This way, he yielded images with a resolution much better than conventional confocal light microscopes. He called the new microscopy STED – stimulated emission depletion microscopy.
Working separately Moerner and Betzig, using the same concept of fluorescence and turning individual molecules on and off with laser beam pulses, made it possible to see single molecules only one nanometer big under a microscope.
Since this technology can be used with living cells it will be an invaluable resource when studying HIV or to observe how living cancer cells react to certain cancer drugs. Biologists will even be able to study nerve synapses and the interaction between viruses and cells. This will be a rapidly expanding field in many, many branches of science.
To watch a video on the STED microscope produced by the Max Planck Institute click below.