The 2014 Nobel Prize in chemistry has been awarded to an American neuroscientist, a German biochemist and an American chemist “for the development of super-resolved fluorescence microscopy.”
Image credit: Fabian Göttfert, Christian Wurm via Wikimedia Commons
The prize goes jointly to Eric Betzig, from the Howard Hughes Medical Center in Ashburn, Virginia, Stefan W. Hell, from the Max Planck Institute for Biophysical Chemistry, in Göttingen, Germany, and William E. Moerner, from Stanford University in Stanford, California.
The prize awards the three scientists for getting around a theoretical limit to the ability to magnify tiny objects, which allows scientists to use optical microscopes to observe the nanoworld with greater detail than previously possible. Whereas typical optical microscopes cannot resolve items smaller than a couple of hundred nanometers — a bit bigger than most viruses — the techniques honored today allow scientists to zoom in much, much closer, to the tens of nanometers for biological samples.
“What this year’s prize is about is beating the diffraction limit of light,” said Trisha Andrew, a chemist at the University of Wisconsin-Madison. “You can actually image directly very, very small features that are below the resolution of the visible light that everyone uses.”
Since 1873, when Ernst Abbe published an equation suggesting that the wavelength of light limited the level of detail that a traditional microscope can provide, scientists had thought that those techniques couldn’t be used to clearly see things smaller than about 200 nanometers, which is half the width of violet light’s wavelength. This means that for microscopes that use lenses and light, anything below that limit is too blurry to see. And, in reality, optical microscopes don’t resolve everything right down to that limit.
Researchers tried other approaches to observe finer details. Electron microscopes were originally developed in the 1930s, and offer incredible resolution of very small things — well over one million times magnification, versus about 2,000 times for typical light-based microscopes. But in order to look at a sample in an electron microscope, it must be prepared very carefully, and typically any living cells are killed.
These limitations — both the optical microscope resolution and the preparations required for electron microscopes and other techniques — kept researchers from observing many processes in chemistry and biology, since they happen at the molecular level, at a much finer scale than the Abbe limit. The super-resolution microscopy the new laureates developed offers a much-improved ability to see smaller and smaller objects.
“Here we can look at a single molecule as it is active in a chemical system. That means that rare events can be studied in a very different way … as they take place,” said Sven Lidin, chairman of the Nobel Committee for chemistry, during the announcement.
In order to look at very small things, scientists began lighting up portions of cells. When bombarded with light, some molecules respond by emitting light at a different wavelength. This is called fluorescence. This technique allows scientists to highlight specific molecules, and can reveal some fine details within a cell, such as where the strands of DNA are located. However, it can’t show any of the individual strings.
That idea, however, soon proved important.
Hell, working in Finland in the early 1990s, was reading a textbook on quantum optics when he read two words, stimulated emission. Those words opened the door to his findings, which can be thought of as a nano-flashlight.
His method, called stimulated emission depletion, or STED, uses a series of light pulses to simultaneously excite the fluorescent molecules in an area while also quenching, or extinguishing, the fluorescence of molecules in most of that same area, leaving a tiny illuminated bull’s eye. By then sweeping through the entire desired region, repeating the process, the technique creates a very high-resolution final image — with no theoretical limit to its resolution.
The other awarded concept is called single-molecule microscopy, and it also develops a very finely detailed image, but in a different way. It overlays numerous images from many single wavelengths of light.
In 1989, Moerner, while working at IBM, became the first person to measure light absorbed by a single molecule. By 1997 he was working in the lab of Roger Tsien, at the University of California, San Diego. Tsien won the chemistry Nobel in 2008 for discovering green fluorescent proteins. Moerner figured out that he could turn on and off one type of green fluorescent protein at will. The proteins tended to be sparsely scattered, which meant that an optical microscope could observe the glow of individual molecules, like tiny single beacons, at scales smaller than the limit Abbe defined.
Separately, Eric Betzig was working on an optical technique called near-field microscopy at Bell Labs in New Jersey. This technique can look at items smaller than the diffraction limit, but one of its drawbacks is that it can’t easily image below the cell’s surface.
In 1995, he developed an insight. Since there are molecules that glow with different colors, why not superimpose a series of images on top of each other? This enabled researchers to create images of, for example, red, yellow and green colors, then combine them, creating an image that showed molecules just nanometers apart. He wrote these ideas in a paper, and then quit academia.
Betzig began working at his father’s machine-tool company in Michigan. He kept working on microscopy, but in a non-traditional way.
His lab equipment at the time amounted to “a laptop and a couple of really good ideas,” he said in a statement. In 2005, he encountered Moerner’s fluorescent protein work, and within a year, he developed a working prototype of a super-resolution microscope.
Currently, the two types of techniques developed by the new Nobel winners are in the range of 5-10 times better than optical microscopes, reaching as fine as 20 nanometers in resolution said Jung-Chi Liao, an associate research fellow at Academia Sinica, in Taiwan.
“Both techniques are using very, very smart ideas,” he said.
There are some alternative techniques that offer similarly impressive levels of resolution to those developed by Hell, Moerner and Benzig, but many of those have limitations, said Andrew.
“Resolution-wise I think there are a bunch of competitors,” she said. “The adaptability is what gave super resolution microscopy the edge.” She explained that the awarded techniques are especially well-adopted for use in biology. Her own research reaches outside of biological applications to allow visible light to be used in semiconductors and microchips.
Hell has used them to investigate living nerve cells. Moerner studied Huntington’s disease with the techniques. Betzig watched cell division within embryos.
By: Chris Gorski, Inside Science News Service