NANOTECHNOLOGY
Current Research - SYNTHESIS OF QUANTUM DOTS
Quantum dot is a generic term applied to a small particle, a few nanometers in diameter (a nanometer is a billionth of a meter or to get a sense of scale, there are about 25 million nanometeres in an inch). At that level of dimension matter acquires properties not usually seen in bulk objects that one sees or touches. An unusual characteristic of nanometer particles, and thus the term quantum dot, is that they behave like an atom in their interaction with electrical charges and can hold a single electron in addition to their usual complement that balances the overall nuclear charge and therefore acquire a single charge. This property mimics, although in a much smaller scale, what transistors and memory elements do in conventional silicon based computer chips. It is this connection that drives interest in the creation and manipulation of quantum dots. The successful implementation of computing based on quantum dots will lead to tremendous gains in speed and at the same time a considerable shrinking in size and power consumption of the computer hardware.
 GEL ELECTROPHORESIS OF GOLD CLUSTERS Gold clusters that are being purified in a gel by the passage of electricity to select a narrow distribution of particle sizes prior to reaction with the DNA. |
The fundamental aspects of how to make very small particles date back to the previous century to work of the British scientist Michael Faraday ((1791-1867) who experimented with very small particles of gold. Not surprisingly, there have been advances in synthetic techniques, so that nowadays it is possible to produce particles as small as one nanometer. There are a number of materials that lend themselves to preparation in the nanometer scale but gold continues to be very useful because of its stability and versatility.
A simple preparation procedure for gold nanoparticles involves the dissolution of a gold salt in a solvent mixture, which contains an organic sulfur compound. This mixture is treated with a chemical that converts the gold salt into metallic gold. Molecules of the sulfur compound initially present in the mixture form an envelope surrounding completely the gold particle and act as a protective coating that prevents particles from sticking to each other (a normal process that would take place in the absence of the sulfur compound).
There is a large number of sulfur compounds that could be used as described above and judicious choice enables the preparation of gold particles that are not only coated and protected but that can also be manipulated chemically to combine with other chemical compounds.
One of the greatest challenges in dealing with quantum dots, associated with their size, is the difficulty of positioning them in a controlled location but this might be overcome by exploiting an assembly strategy involving the use of DNA (the genetic material in all living matter). It is possible to direct gold clusters with an appropriate coating to combine with DNA that has been previously assembled and which contains connecting points complementary to the gold at predetermined distances so to produce an array that can function as a device.
[