Research Assists Cancer Tests

Harvard researchers have found new ways of assembling nanowires—ultra-thin wires that have the potential to revolutionize electronics—and a new application of the technology that may make over-the-counter cancer tests available in drugstores in the near future.

Ritesh Agarwal, a former Harvard postdoctoral associate, published a paper this week in Optics Express on a new technique for assembling and arranging nanowires, which are smaller than any circuitry currently available, even on microchips.

The ability to construct specific, three-dimensional, nano-scale devices at the whim of a researcher has until this week been elusive.

Because nanowires also have the ability to direct light, they have potential applications in “optoelectronic” devices, which use light instead of electricity to do computations.

Agarwal, working with Professors David G. Grier ’84 at New York University and Hyman Professor of Chemistry Charles M. Lieber at Harvard, among others, found a way to cut, rotate, and fuse hundreds of nanowires in precise patterns.

Agarwal’s discovery uses a mechanism called the Holographic Optical Trap, or HOT, invented by Grier’s group in 1997. According to Grier, a HOT “use[s] forces exerted by light to grab and move microscopic objects.”

The HOT technology improves on previous methods to arrange nanowires by stochastic methods—like the use of fluid pressure to coax nanowires into place.

Grier wrote in an e-mail that applications of the HOT technique “range from performing surgery within living cells to fundamental investigations of many-body statistical physics”—the investigation of large-scale motion of many small particles.

“HOT micromanipulation provides unprecedented access to and control over the microscopic world,” he wrote.

While no one is yet sure how to build a new generation of microchips from nanowires, chips with some nanoelectronic components may be available in the foreseeable future.

Still, the HOT technique is insufficient to build highly intricate devices.

“Currently we can manipulate hundreds of wires, not millions,” said Agarwal.

Another recent advance from Harvard nanoengineers may have more immediate applications.

In an article in the October issue of Nature: Biotechnology, Lieber published a paper explaining how nanowires can be used to help diagnose cancer. Lieber’s idea was to attach each of the wires to numerous antibodies. When the antibodies bind to enzymes known to be associated with cancer, their conductivity changes. A patient’s diagnosis is obtained by measuring the electric current across the grid.

According to Lieber, these nanowire devices have numerous advantages over current techniques for diagnosing cancer: they are cheap to produce, can test for a number of different cancer markers in parallel, and can be easily updated when new markers are discovered.

Professor Lieber was not available for comment about his research.