Scientists at the Technion - Israel Institute of Technology demonstrated for the first time how a DNA molecule can form a basic transistor. The research results, published yesterday in Science magazine, are a breakthrough in molecular electronics, a field in which scientists have been trying to harness molecules to assemble electric circuits.
"We've succeeded in proving that electronics based on DNA is not fictional," said Professor Erez Braun of the Technion's physics department, under whose guidance the research was conducted.
The research is part of Dr. Kinneret Keren's doctorate work with the participation of Professor Uri Sivan, Dr. Evgeny Buchstab and Rotem Berman.
Speaking to Haaretz, Professor Braun explained that assembling the transistor is part of a six-year project. "Our goal is to take advantage of the natural characteristics of the DNA molecules, so the encoded information enables a self-assembling transistor."
The first stage of the project was carried out in 1998, when the scientists developed - together with Professor Yoav Ishan of the Technion's chemistry faculty - a way to turn the DNA molecules into a cable that can conduct electricity, by coating it with silver and gold.
But producing a transistor that works as a logic circuit required additional development. The tests used a basic biological process that enables mixing genes and creating new ones in nature. "We took the RecA protein from a germ whose job is to attach itself to a segment of DNA molecules and change it to a segment from another DNA molecule," explains Braun. "On the protein we mounted a short DNA strand. The protein turns into a `driver' that takes the short strand and mounts it at a certain point onto the long strand."
Braun says the scientists found that the protein protects the site it attaches itself to. "This protection prevented the production of metal on this site. This is how we achieved a metal strand whose middle consists of the protein with no metal on it. This is significant progress because it enables using the information in the DNA continuum," Braun says.
But this too was not sufficient to create a logic circuit. The protein does not serve as a semi-conductor and it was necessary to use the material that adheres to a "protein site" and will know how to transfer electricity on order. In the article published in Science the scientists explain how they overcame the problem.
They decided to used a carbon nano-tube of many characteristics, which can be used inter alia as a semi-conductor. "The problem is how to make the tube mount the protein - we wouldn't want to do it manually," says Braun. The scientists used another natural mechanism - antibodies. An antibody is a protein that knows how to join another protein to neutralize it. The researchers used an antibody that knows how to attach itself to the protein on the DNA and attached the antibody to the carbon tube with the help of another auxiliary protein. Thus they created for the second time a `driver' that drives the tube to exactly the right spot.
"Now we have a metal strand with protein in its middle, to which a carbon tube has attached itself," says Braun. "When we put the wire on a silicon bedding and passed electric current through it, we succeeded in making the DNA strand with the carbon tube on it serve as a logic circuit. When the switch is closed, it conducts electricity, and when it is open it does not."
The achievement is especially impressive considering that until now, scientists in the world have managed to produce a molecular electronic transistor only by accident. They spread a solution in which carbon tubes lay on a surface, hoping that by chance a few tubes would join in a way that would enable using them as an electric circuit.
"We are doing something completely different," stresses Braun. "We are pouring the components into the solution - a long DNA strand, a short DNA strand with protein, a carbon tube and so forth and in a few minutes the electric circuit is created in the solution, by using the special characteristics of all the components we put into the solution."
Braun said that creating a basic logic circuit that assembles itself from proteins and carbon tubes is the first step toward building more sophisticated electric circuits and electronic systems. "Scientists have been talking of molecular electronics for about for 30 years. We started working on it six years ago and only now managed to produce the first logic circuit on the basis of biological molecules. These are long processes but it seems we succeeded in overcoming the first hurdle on the way to electronic circuits that arrange themselves. Now we will try to produce more complex circuits and networks of transistors made of DNA and get another DNA molecule to be responsible for switching the transistors, rather than the silicon bedding through which the electric current is now transferred. If we succeed in doing that, that will be real progress."
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