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This year’s Nobel Prize in Chemistry went to three scientists whose work surpassed the long-established resolution limit for optical microscopes. The award went to Eric Betzig of the Howard Hughes Medical Institute, Stefan W. Hell of the Max Planck Institute for Biophysical Chemistry, and William E. Moerner of Stanford University “for the development of super-resolved fluorescence microscopy.”
October 8, 2014 | Michael Lucibella
Photos: HHMI, MPI, Stanford
Eric Betzig, Stefan Hell, and William Moerner
“This year’s prize is about how the optical microscope became a nano-scope,” said Staffan Normark, the permanent secretary of the Royal Swedish Academy of Sciences.
The award is for two similar but distinct techniques that overcome Abbe’s limit. First described in 1873, Abbe’s limit says the resolution of a microscope can’t be greater than approximately half the wavelength of the light used, or about 200 nanometers for visible light.
Hell developed stimulated emission depletion microscopy in 2000, which uses two concentric lasers to scan a cell’s image. The finely focused central laser excites fluorescent molecules in the sample, while the broader outer laser quenches out all other fluorescence. The detector scans back and forth, registering the fluorescent glow to create an image with resolution better than 200 nanometers.
“Light microscopy is very important to the life sciences because the use of focused light is the only way that allows you to see living things, however the resolution of light microscopy was fundamentally limited,” Hell said. “What we have found is that you can overcome this limit. You can see details at much much higher spatial resolution and that of course discloses how the cell works at the nanometer scale, so that’s at the molecular scale.”
Though Betzig and Moerner never collaborated directly, their work was instrumental in laying the groundwork for stimulated emission depletion microscopy.
After Moerner was first able to detect a single fluorescent molecule in 1989, Betzig came up with the concept of using overlaid images of individual glowing molecules to create a complete image. The process he outlined in a 1995 paper described shining different wavelengths of light on a cell to get different molecules to fluoresce and then record where light spots appeared. This way when all the images were combined, the discrete spots would resolve themselves into a coherent outline.
However to make a coherent image, many different colors from unique molecules would be needed, far more than was practical. It wasn’t until 2005 when Betzig found a specific protein identified by Moerner that the technique could be put into use. Moerner’s protein would glow briefly then, and most importantly, it turned itself off. A cell stained with this protein could be hit multiple times with a laser pulse and each time a different set of proteins would fluoresce, giving Betzig the constellation of glowing spots needed to create a coherent image.
Electron microscopes have long been able to image objects smaller than 200 nanometers, however that technique is extremely damaging to the sample. It can’t image living things and electrons can only penetrate a shallow depth into cells. “It is fluorescence that makes the miracle possible,” said Mans Ehrenberg of Uppsala University.
“We can observe E. coli …in all the glory of super resolution without having to kill them, slice them. … and subject them to intense radiation and high vacuum,” said Sven Lidin, chair of the Nobel Prize chemistry committee. “They can be studied in real time while they live long and prosper.”
Moerner is an APS Fellow and has previously been awarded the Earle K. Plyler Prize for Molecular Spectroscopy and Dynamics and the Irving Langmuir Prize in Chemical Physics for his work. Hell is a member of APS and also won the Kavli Prize this year for his work.
Image credit: Max Planck Institute (image on the APS home page)