DNA as a tool for nanotubes

Biological key-lock principle helps with sorting

Electronic interaction between DNA and nanotube in cross section (top) and side (bottom). For the smaller tube on the left in the picture, it can be seen in cross-section that the central tube has little involvement. The larger tube on the right, on the other hand, interacts strongly, especially with several DNA strands © A. Enyashin / TU Dresden
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Researchers have used the biological key-lock principle by using individual strands of DNA as a tool for sorting carbon nanotubes. The resulting hybrid material is a step towards a new electronic nano-device.

In DNA, the genetic information is stored by the sequence of individual proteins. It looks like a double spiral staircase. If you remove a string, the open spiral staircase offers a long chain of tiny, small keys regularly arranged around a tubular cavity.

A research team from the Technische Universität Dresden (TUD) and the Forschungszentrum Dresden-Rossendorf (FZD) requires carbon nanotubes with well-defined properties for the development of a novel nano-device. These tubes with only a few nanometers in diameter are created not least when grilling in the garden. In the industrial manufacturing process, it has not been possible, as in the case of grilling, to produce large quantities of tubes of a specific size in a pure variety. Instead, a mixture of semiconducting and metallic grades with different structures is obtained. Filtering out only the desired variety is difficult because the tubes stick together into bundles that are almost insoluble.

DNA as key for nanotube lock

TUD scientists took up the idea of ​​using DNA chains to separate nanotubes from the insoluble mixture. The size of the open DNA spiral staircase is ideal for tubes with a diameter of 0.3 to 0.4 nanometers (one millionth of a millimeter). If DNA chains obtained from bacteria or synthetic DNA are added to the previously vigorously shaken mixture of nanotubes, the DNA chains and spirals are deliberately placed around suitable tubes. The DNA keys are therefore only at certain diameters the associated locks on the tubes and it creates a new hybrid material. The advantage: the tubes are now water-soluble, which greatly simplifies further processing.

Interaction determined for the first time exactly

Theoretical calculations accompanied the experiments. For the first time, researchers from TUD and FZD systematically recorded the interaction between the biological DNA molecules and the carbon tubes at the quantum-mechanical level. For some cases, they have been able to show that the electrons of both systems interact more strongly than predicted by simpler models. This is evidence for the DNA-driven selection of certain types of tubes previously reported by American scientists. display

Carbon nanotubes alone are already widely used today, for example in sports technology or in sensors. However, as the dimensions become smaller, a well-defined manufacturing process with the potential for targeted selection of conductive carbon nanotubes is indispensable. The new calculations form an important basis for this.

Components for nano-transistor

The carbon nanotubes sorted and wrapped by DNA chains can conduct electricity in a defined manner. This makes them ideal as a central component for the planned nano-scale device, a nano-field effect transistor. At such Nanor hrchen- based transistors is currently being researched worldwide; the special feature of the Dresdner approach is that a ferroelectric carrier material is used. Such a carrier material is composed of charged particles whose arrangement can be selectively and reversibly changed by external forces.

This should make it possible for an external force on the nanometer scale to switch the electric field of the transistor on and off, which could be advantageous for computers or nano-machines of the future. Dr. Michael Mertig from TUD and his colleagues has already succeeded in producing a transistor based on DNA-encapsulated nanotubes, and in the group of Prof. Lukas Eng, individual elements of the even smaller ferroelectric nano-field effect have already been synthesized Transistor realized.

(Research Center Dresden - Rossendorf, 16.01.2008 - NPO)