Month: January 2002

According to a press release (3 January 2002), researchers at the University of Illinois at Urbana-Champaign and the University of Pennsylvania have discovered that carbon nanotubes packed with fullerene spheres, like so many peas in a pod, have tunable electronic properties. They reported their work in the 3 January 2002 issue of Science.

"Our measurements show that encapsulation of molecules can dramatically modify the electronic properties of single-wall nanotubes," said Ali Yazdani, a professor of physics at UI. "We also show that an ordered array of encapsulated molecules can be used to engineer electron motion inside nanotubes in a predictable way."

To explore the properties of these novel nanostructures, Yazdani and coworkers used a low-temperature scanning tunneling microscope to image the physical structure of individual peapods and to map the motion of electrons inside them. The encapsulated fullerenes modify the electronic properties of the nanotube without affecting its atomic structure. "In contrast to unfilled nanotubes, peapods exhibit additional electronic features that are strongly dependent on the location along the tube," Yazdani said. Because the local electronic properties of single-wall nanotubes can be selectively modified by the encapsulation of a single molecule, the technique might one day be used to define on-tube electronic devices.

Update: An article on the Wired website ("Nanotech Fine-Tuning", by Mark K. Anderson, 4 January 2002) provides some additional coverage, with some perspective from Yazdani, as well as Cees Dekker and Calvin Quate.

from the A-new-twist dept.
According to a press release (2 January 2002), Nadrian Seeman and his co-workers at New York University have been able to create a more robust, controllable version of the rudimentary DNA-based device that Seemanís group first reported they had created in January 1999 (see report in Foresight Update 36).
According to the release, the new device "improves upon previously developed nano-scale DNA devices because it allows for better-controlled movement within larger DNA constructs. The researchers say that the new device may help build the foundation for the development of sophisticated machines at a molecular scale, ultimately evolving to the development of nano-robots that might some day build new molecules, computer circuits or fight infectious diseases." Their research is reported in the 3 January 2002 issue of Nature.

The January 1999 version of the device constructed from DNA molecules had two rigid arms that could be rotated from fixed positions by adding a chemical to the solution. However, the chemical affected all molecules within a structure uniformly. The most recent findings demonstrate how movement can be manipulated within molecule pairs without affecting others within a larger structure. This is done by inserting DNA ìsetî and ìfuelî strands into individual molecule pairs. Scientists used special DNA molecule pairs and produced a half-turn rotation by converting them from one configuration into a second configuration by removing the set strands with fuel strands and replacing them with new set strands that reconfigure the structure of the device.

Update: An illustration of the new DNA-based device, along with a not particularly lucid explanation of the change in configuration that produces the rotation, is available on this page of the Seeman groupís website.

Dr. Seeman was awarded the 1995 Feynman Prize in Nanotechnology (see Foresight Update 23) in recognition of his pioneering work to synthesize complex three-dimensional structures with DNA molecules.