Thursday, October 09, 2014

Nobel Prizes 2014 - Let There Be Light !

This week the Nobel laureates in chemistry and physics were determined. As usual, the scientific results of both groups of scientists seem rather complicated if appropriately dealt with. However, both fields of scientific research have something in common: They are dealing with light.


U.S. scientists Eric Betzig (Howard Hughes Medical Institute) and William Moerner (Stanford University) received the Nobel chemistry award together with German laureate Stefan Hell (Max Planck Institute for Biophysical Chemistry) for improving the imaging techniques that show us microscopic processes in action.

This means nothing else but an improvement of microscopy using visible light for the observation of molecular processes in living cells and which should be impossible in the deathly vacuum needed for the operation of electron microscopes that used to be applied in the static observation of biological cells.

STED image of a nerve cell in living mouse brain.
The dendritic protrusion of synapses [ view inset ]
marks places where information transfer happens.

An increase of resolution, necessary for the live observation of biochemical processes, then requires a modification of what scientists call Stimulated Emission Depletion (STED), and which works by directing a pulse of light towards a sample seeded with fluorescent molecules. The pulse agitates these molecules, and then a second pulse of light dims the fluorescent glow everywhere but in a specific minuscule section of the sample. For the first time, this allowed scientists to detect and study parts of cells and strands of DNA wrapped up around each other.

In 2000, Hell used this technique to capture the best image ever of an E. coli bacteria with a light microscope. At the same time, Moerner discovered that by activating the fluorescent molecules using specific wavelengths of light, scientists could use a light microcrope to see individual molecules.

Resolution limitations of traditional optical microscopes lead to blurry images of small cellular components such as mitochondria (level 1). However, if specific proteins are tagged with fluorescent molecules that can be activated one-at-a-time (between levels 1 and 2), the positions of the molecules can be determined at a much finer level. The total position data is then assembled into an image (level 2) at a resolution comparable to an electron microscope (level 4), but with the added benefit of being specific to only the desired target protein. (Image: Eric Betzig, HHMI Janelia Farm Research Campus)

In 2005, Betzig finally led that new technique to another breakthrough explained by the following source:
"Using fluorescent proteins that could be turned on and off at will, he created images of a resolution much higher than the theoretical limit. Weak pulses of light activate the proteins for a very short time, so that pieces of the subject can be illuminated bit by bit. These images are superimposed to form high-resolution images - without killing the cells being observed, or even interrupting their biological processes. The single-molecule microscopy method is now widely used."


The Japanese scientists Isamu Akasaki (Meijo University), Hiroshi Amano (Nagoya University) and Shuji Nakamura (University of California) have been awarded the Nobel Prize for physics in 2014 for developing the environmentally friendly, energy-efficient blue light-emitting diode (LED).

"Red and green LEDs have been around for a long time but blue was really missing. Thanks to the blue LED we now can get white light sources which have very high energy efficiency and very long lifetime." Therefore, it only needs to superimpose the light of red, green and blue LEDs. Varying the basic LED intensities can even generate any other colour needed.

While last year’s physics prize was awarded for the discovery of the Higgs boson particle, this year’s prize honours an entirely practical invention that’s been making its way into countless homes around the world since the turn of the century. As 20 percent of the world’s electricity is used for lighting, and because LED lighting is so efficient, that latest Japanese invention has the capacity to reduce electricity used for lighting to just 4 percent.

Structure of a Blue LED

Description of the Blue LED Structure:
The principle for light emission in a p-n junction between two differently doped semiconductor materials is as follows: In a p-n junction biased with a forward voltage, electrons are injected from the n- to the p-side, and holes are injected in the opposite direction. Electrons recombine with holes and light is spontaneously emitted. In the above structure which is characteristic for Blue LED, that process is supported by a double heterojunction between the chemical components Indium-Gallium Nitride InGaN and Aluminium-Gallium Nitride AlGaN. The basic layer of that complicated structure is crystallized Aluminium(III)Oxide (Sapphire).


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From China's first space station:
A lecture on elementary physics.
(best view in fullscreen mode)

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