The 2014 Nobel Prize in Chemistry could mean a lot to all of us

(from left: Eric Betzig, Stefan W. Hell, and
William E. Moerner; source)
Dr. Bhanu Neupane

The 2014 Nobel Prize in Chemistry has been announced today (on Oct 8th 2014). The recipients are: William E. Moerner (Stanford University, Stanford, CA, USA), Stefan W. Hell (Max Planck Institute, Göttingen and German Cancer Research Center, Heidelberg, Germany), and  Eric Betzig (Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, VA, USA) working in area of super-resolution far field fluorescence microscopy and spectroscopy. The three scientists will share total prize money of $1.5 million. Special congratulation to these great minds from “NepaChem”!  

Nobel Prize, established by a Swedish inventor Alfred Nobel in 1895 and announced by Royal Swedish Academy of Sciences, is awarded in recognition of someone whose work contributes significantly in the area of chemistry, physics, literature, peace, and physiology or medicine.

I have also been involved in super-resolution microscopy reasearch (see my publications here). In addition, we have assembled one of such kind of microscopes in North Carolina State University. With my experience in this field, let me describe this years Nobel prize to you. 

The traditional form of optical microscopy, that needs some sort of light source for illumination and aberrations corrected lens for focusing the light in a specimen/sample, because diffraction cannot  provide resolution better than  ~λ/2 laterally (in –X and –Y directions) and ~ λ in axial (Z direction. It means if 500 nm light is used for illumination then one cannot resolve two objects that are spaced smaller than 250 nm (1 nm=10-9 m) in lateral and 500 nm in axial directions. If we want two objects spaced closer than 250 nm to be resolved, then traditional microscope cannot do it. The above three scientist applied two types of concept to break the diffraction limited resolution which was never possible before 1990. Both concepts use the fluorescence property of molecule and provide super-resolution (resolution much better than diffraction limit); known as super-resolution fluorescence microscopy or nanoscopy. Super-rsolution has also been achieved in other forms of microscopy, for example near field microscopy and electron microscopic methods. Although these methods provide resolution in the range of 1-20 nm for dry and/or conductive sample, they find limited application in imaging biological specimen (a cell or tissue). Near field methods require very small distance (few 10th of nanometers) between sample and probe which cannot image deep into the 3D specimen (almost all biological specimens are 3D objects). On the other hand, electron microscopy requires sample to be conductive and dried. Almost all biological specimens contain significant amount of water, so imaging in the intact (intact means fixed and wet, or live) form is impossible.

In 1994, Stefan Hell proposed the concept of stimulated emission depletion (STED) microscopy/nanoscopy that can provide super-resolution in a fluorescently labeled specimen down to 20 nm even in live specimen. This microscope needs two lasers one having intensity distribution of Gaussian (which looks like a circular in –XY plane) type and the other donut type (i.e. circle having no light in the center). If these two lasers are overlapped (in -XYZ directions) in focal plane of objective lens, signal comes only from the narrow center portion where stimulated emission depletion does not takes place (please see the schematic). The key publications that awarded S. Hell the Nobel prize are:

Ground-state-depletion fluorscence microscopy: A concept for breaking the diffraction resolution limit.

Fluorescence microscopy with diffraction resolution barrier broken by stimulated emission.

Eric Betzig and William E. Moerner proposed different version of super-resolution called super localization fluorescence microscopy. In their approach, the fluorescent dye molecules (that is used to label a biological specimen) are optically switched in on/off state one after another over the time, and the intensity profile of each molecule (which is like a illuminating Gaussian beam) is fitted by a model to find the center position. The localization precision (which is also a form of resolution), depends on the number of photons one can collect form each molecule. If the position of all dyes in the specimen are localized, that gives highly resolved (super-resolved) image. This approach gives resolution equal to or better than STED approach but is very slow; so has limited application for live specimen. STED is a direct imaging method (does not require and processing), but super localization is model based method. The key publications that awarded Nobel Prize to these scientists are:

Recent imaging tools used in medicine have resolution in the range of few millimeter to hundredths of micrometer. This means wrongly functioning structures in tissue/organ of a patient cannot be identified on time or patient is diagnosed very late.  Although tools developed by above scientist, in current forms, need lot of improvements before implementing in clinics, day will certainly come that these tools finding great application in medicine; for example looking a tissue of cancerous patient at much details then what can be done now. Having said that, let’s hope, these new methods of imaging will save thousands of lives.   

Dr. Neupane is a postdoctoral scholar at Biomedical Engineering Department
(Joint Department of University of North Carolina and North Carolina State University)
He is also affiliated with Kathmandu Institute of Applied Sciences, Kathmandu, Nepal.

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