Buckyballs All in a Row
IBM’s Molecular Abacus
INNOVATOR: James Gimzewski
Ever since scientists discovered the carbon 60 molecule--a structure shaped like two geodesic domes and also known as a Buckminsterfullerene--back in the mid-1980s, they have been struggling to find something practical to do with it. James Gimzewski, a physicist at ibm’s Zurich Research Laboratory in Switzerland, has now succeeded--sort of.
It all started when Gimzewski and his colleagues at ibm began playing around with a scanning-tunneling microscope, or stm, which has probes so microscopically thin that it can glide over a surface and record the presence of atoms like a blind person reading braille. When they learned that the tip can also be made to scrape up globs of atoms like a plow and leave behind microscopic furrows, they quickly began pushing around individual atoms for the fun of it, even going so far as to spell out the letters ibm with 35 supercooled xenon atoms. Gimzewski and a couple of his colleagues then thought of fashioning a calculating machine out of an stm and some buckyballs. Last November they unveiled the world’s first molecular abacus.
The abacus is simple--just ten buckyballs lined up along a microscopic groove on a copper surface. To make a calculation, Gimzewski uses the stm tip to drag the buckyballs back and forth. The grooves, which are actually tiny steps that occur naturally in the copper, allow Gimzewski to perform the calculation at room temperature.
In theory, Gimzewski’s abacus could store a billion times more information than the memory in a conventional computer can. In practice, however, the abacus is cumbersome. But it does demonstrate how adept scientists have become at manipulating the very small--and it may even be a first step toward building machines the size of molecules. If you watch young children, they pick things up, turn them around, put them down--very basic actions, he says. We’re at that stage now. This sort of simple device is just a demonstration of the kinds of things we hope to achieve.
The Many Shapes of a Molecule
New York University’s DNA Structures
INNOVATOR: Nadrian Seeman
If scientists ever do realize their dream of building machines the size of molecules, then someday miniature robots could roam your bloodstream and heal injuries, fight off infections, or deliver medication directly to your liver or heart or other body part in need. That day may still be far off, but chemist Ned Seeman has brought us a step closer. Working with DNA, the long, double-stranded molecules that hold the genetic code, he has constructed objects so tiny it would take several million of them to stretch across a dime.
Seeman got the idea for the microscopic building project back in 1980, when he was examining DNA strands that had arranged themselves into four-armed junctions. (The typical DNA molecule forms a straight line, but two strands occasionally intersect to make a cross-shaped junction.) There was no reason, Seeman thought, why he couldn’t design his own strands of DNA in such a way that they would automatically zip themselves up into even more complex shapes. He started making junctions with five and six arms, and eventually moved on to squares, cubes, and a truncated octahedron.
Although DNA strands are rigid enough to serve as girders in a molecular framework, the junctions, it turned out, flopped all over the place. In June 1996, however, Seeman designed and built a stiff double junction that keeps his structures from sagging. Now he thinks he’s got the basic technique down for making micromachines. We believe we know how to make almost any shape out of DNA, he says. After taking nearly two decades to reach this point, however, Seeman takes nothing for granted. I regard most of what we’re doing here as engineering, he says, but every now and then something doesn’t work as expected and we have to do some science.