Magazine article Science News

Speed Bump: Tip's Tricks Sort DNA, Write at Nanoscale

Magazine article Science News

Speed Bump: Tip's Tricks Sort DNA, Write at Nanoscale

Article excerpt

Using an old tool in surprising new ways, scientists in California are making molecules race down the sloping sides of a minuscule silicon spike ordinarily reserved for poking at atoms. The novel role for the spike, which is the tip of an instrument known as an atomic-force microscope, or AFM, could lead to advances in DNA sequencing, nanofabrication of devices, and other technologies, the scientists say.

About 10 micrometers long, an AFM's tip protrudes from the end of a cantilever. Scientists usually drag it or tap it on a surface to discern an objects topography down to the atomic level (SN:2/18/06,p.101). Now, H. Kumar Wickramasinghe and his colleagues at IBM Almaden Research Center in San Jose, Calif., have demonstrated that DNA molecules separate according to their lengths as they move along a spike's wetted surface. Moreover, the scientists have used the spike's point to lay down a nanoscale pattern of molecules.

For both feats, the IBM researchers first wired an AFM tip to accept up to 10 volts. The electric fields thus produced then made molecules move up or down the spike's surface inside the thin film of water that forms naturally in humid air.

In their experiments, the scientists showed that a voltage propels a strand of DNA made of 16 chemical building blocks, or bases, more quickly than a strand that's only 5 bases long. In this way, the electrified spike separated the molecules by size and electric charge--a process known as electrophoresis.

Automated machines today decipher the genomes of people and other organisms by carrying out electrophoresis of DNA pieces within fine glass tubes (SN:8/6/05 p. …

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