Quantum dots – a supernova in nano-size – Niels Bohr Institute - University of Copenhagen

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13 October 2008

Quantum dots – a supernova in nano-size

A quantum dot is a very small crystal bead that is extremely bright. It is the supernovae of the nano world (exploding star) and researchers from the Niels Bohr Institute have succeeded in trapping an individual quantum dot with an Optical Tweezer and manipulating it. The research results are published in the prestigious scientific journal, Nano Letters.

It was not many years ago that it was discovered how to produce quantum dots, which are small semiconducting nano-crystals between 2 and 10 nanometers and about ten times the size of an atom. They are used to visualize biological systems on the level of individual molecules. At the same time, they are extremely difficult to study due to their extremely small size and many research laboratories around the world have tried for years to do so.

The Danish research group lead by Lene Oddershede from the Niels Bohr Institute at the University of Copenhagen has succeeded in trapping a quantum dot with an Optical Tweezer, which is a special instrument that uses laser light to trap a subject.

Researchers have succeded in
trapping an individual quantum dot
with an Optical Tweezer

A wealth of new possibilities
“We have trapped a quantum dot and manipulated it with laser light in three dimensions and manipulated it with physical forces”, explains Lene Oddershede, and this gives a wealth of new possible applications, because one can use quantum dots to both visualize and manipulate biological systems on a nanometer-scale (equal to a billionth of a meter).

Biomolecules are everywhere in living cells, where they take care of the transportation of matter internally in the cells. But biomolecules are far too small to be trapped optically. For that reason one typically sets a handle on the biomolecules in the form of relatively large plastic spheres, which are easy to see and manipulate under a microscope. The problem though is that the large plastic spheres can have a significant influence on the biomolecules’ function.

With an optically trapped quantum dot it will be possible to manipulate a molecule and see it at the same time without setting a large plastic sphere on the molecule. When a laser illuminates the molecule the quantum dots emit light at a frequency that depends upon the surroundings and can show both the size and position of the quantum dots. Consequently they can be used to track extremely small objects like biomolecules of nanometer size.

New knowledge about physical characteristics
Lene Oddershede and her research group trapped and manipulated a quantum dot by using a laser of only 100 milliwatts for the test. Their measurements provide information about the interaction of the quantum dot with the electromagnetic field and furthermore have given completely new knowledge about the quantum dot’s physical characteristics.

Read the article:
http://pubs.acs.org/cgi-bin/article.cgi/nalefd/2008/8/i10/pdf/nl801962f.pdf