Computer devices via DNA

DNA moves from biological to material to meet the speed of miniaturization. Ever had the creepy feeling that your computerized machine is taking on a life of its own, your coffeemaker is developing a personality, or your digital stereo is exhibiting its own taste in music? That day may be much closer to reality when DNA is used to build electronic process control circuits. Yes, that's right, deoxyribonucleic acid, known as DNA and long held in awe as the wonder molecule of life, the software of choice for most living organisms, now shows promise for use in creating tiny electronic devices. Building on earlier work: with carbon nanotubes, Swiss physicists Hans-Wemer Fink and Christian Schonenberger, working at the University of Basel in Switzerland, modified a low-energy electron point source (LEEPS) microscope to measure electrical conductivity across a few strands of DNA. In a "Eureka!" moment, they discovered that DNA conducts electricity as well as being a good semiconductor.

The ability to measure DNA's conductance, coupled with existing technology able to make DNA strands of specified length, moves DNA

from the biological world into the materials world. The conductance discovery also represents a big step forward in the current push to find ways to build ever-smaller electronic devices. Self-assembly, a manufacturing process whereby wires, switches, and memory elements are chemically synthesized and connected to form working computers or other electronic circuits, is a promising alternative to standard silicon-based semiconductor manufacturing methods, which are reaching a practical limit of miniaturization. And DNA promises to help make self-assembly a reality.

DNA's power lies in directing the assembly, not necessarily in serving as a semiconductor. As reviewed by Dutch physicist Leo Kouwenhoven of the University of Delft, the Netherlands, much better semiconductors already exist. As in the cellular machinery of living things, DNA in nanodevices will be the brain of the outfit. The high fidelity with which the base pairing occurs is the main reason DNA is so promising in electronic self-assembly. By attaching single-stranded short pieces of DNA, called oligomers, to nanocrystals and then allowing the single strand to seek another single strand with its complementary sequence and perhaps with a different type of nanocrystal attached, it is possible to assemble circuits in solution.

It is believed that the immediate next step will be to find appropriate switching functions and then build an integrated circuit structure using DNA molecules with anchors at their ends to assemble a micro-structured chip automatically.

Stan Williams, head of basic research at Hewlett, Packard (HP) Laboratories in Palo Alto, CA, reports DNA will be used to create structure in self-assembly, probably more as a tool than a main player. Williams and his colleagues at HP tested principles of self assembly in building their experimental Teramac computer, which operates 100 times faster that a high end single processor workstation. While DNA was not used to create this computer, he believes it will take a minimum of a decade before DNA is incorporated. Williams sees the use of DNA in nanodevices, although in need of more experimental work, as a step forward in finding ways to create many devices within a device that needs to talk to each other. The favored software of life could soon become the favored software of machines, further blurring the disappearing distinctions between the living and the nonliving worlds.

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