Friday, October 17, 2014

The 2104 Nobel Prize in Chemistry, STED Microscopy, and the Donut of Darkness

This month I was a bit puzzled when comparing how journalists described this year’s winners of the Nobel prizes for physics and chemistry. They had an easy time with physics. For example CNET said Efficient, useful blue-light LED draws Nobel Prize in Physics. But, many fumbled on headlines for chemistry, like the Associated Press with 3 win chemistry Nobel for super-zoom microscopes, and the New York Times with Nobel Laureates Pushed Limits of Microscopes. At Wikipedia there is a jargon-laden article covering the broad topic of Super-resolution microscopy.   

The optical microscopes that won the Nobel prize were rather different from the brightfield transmitted light microscope (shown above) that you encountered in a school biology or science class. That type of microscope has a resolution of about half the wavelength of visible light. What’s different about the new ones?

First, these are fluorescence microscopes. The sample is illuminated using ultraviolet (black) light, which makes molecules glow (fluoresce) when observed.

Second, these are scanning microscopes. The sample is lit by moving a very narrow laser beam across the surface. The popular Nobel article titled How the optical microscope became a nanoscope described it as being like a nano flashlight.

One of the techniques that won the prize is Stimulated Emission Depletion (STED) microscopy, which was developed by Stefan Hell. The depletion part of the acronym describes a very clever trick, which is the third difference. The sample is scanned by two coaxial beams: an inner ultraviolet one, and an outer depletion one that prevents fluorescence and thus creates a “Donut of Darkness” as shown above. I instantly thought of donuts when I saw Figure 2 from the Nobel article on the principle of STED microscopy. Apparently that wouldn’t have occurred to those Swedish authors, since donuts aren’t as common of a breakfast food there as in America. (Sweden just got Dunkin’ Donuts shops in May 2014).

You can watch a 39-minute YouTube video from the iBiology Microscopy Course in which Stefan Hell explains Super-Resolution: Overview and Stimulated Emission Depletion (STED) Microscopy.

The image of an optical microscope came from the National Cancer Institute.

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