Three scientists who devised ways to bypass the resolution limits of traditional optical microscopy have been awarded the Nobel Prize in Chemistry. One of the scientists, Stefan W. Hell, Ph.D., of the Max Planck Institute for Biophysical Chemistry and the German Cancer Research Center, developed a technique called stimulated emission depletion (STED) microscopy. The other two scientists, Eric Betzig, Ph.D., of the Howard Hughes Medical Institute and William E. Moerner, Ph.D., of Stanford University, independently developed single-molecule microscopy.
Both STED and single-molecule microscopy bring optical microscopy into the nanodimension, and so these methods are sometimes referred to as nanoscopy. More properly, they are called super-resolved fluorescence microscopy.
Whatever they are called, the methods allow scientists to visualize the pathways of individual molecules inside living cells. For example, scientists can see how molecules create synapses between nerve cells in the brain; they can monitor how proteins aggregate in Parkinson’s, Alzheimer’s, and Huntington’s diseases; and they follow individual proteins in fertilized eggs, tracking the proteins’ movement as the eggs initiate rounds of cell division culminating in embryonic development.
Before nanoscopy, optical microscopy faced a hard limit: It was unable to obtain a better resolution than half the wavelength of light, and so it seemed unlikely that scientist would ever be able to observe living cells in the tiniest molecular detail. For example, a typical protein has a size of about one or two nanometers—some 200 times smaller than what can be seen with an ordinary light microscope. Even near-field microscopy can do no better than to discriminate structures of about 30 nanometers.
Breaking past traditional microscopy limits, the developers of STED and single-molecule microscopy have brought optical microscopy into the nanodimension.
In STED microscopy, which dates back to 2000, two laser beams are utilized. One stimulates fluorescent molecules to glow, another cancels out all fluorescence except for that in a nanometer-sized volume. Then, when the sample is scanned, nanometer for nanometer, an image emerges that has a resolution better than that obtainable with traditional optical microscopy.
Single-molecule microscopy, which was used for the first time in 2006, relies on a different approach: turning the fluorescence of individual molecules on and off. Scientists image the same area multiple times, letting just a few interspersed molecules glow each time. Superimposing these images yields a dense, super-image resolved at the nanolevel.
