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(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”!
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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