Wiring up molecules.

Researchers in Illinois have devised a new type of microscopic wire that they say will accelerate the development of sensors, circuit components, and other devices made from single molecules. What make the wire so versatile are gaps as small as 2.5 nanometers, the diameter of a DNA strand. The broken wire is held together by a backing of silica or another material, a team at Northwestern University in Evanston reports in the July 1 Science.

To create the wires, Chad A. Mirkin and his colleagues infused gold vapor into deep pores that had been electrochemically bored into an alumina block. During the gold deposition, the team switched briefly to either nickel or silver to create segments of wire made of those metals. The researchers then dissolved the alumina block and coated one side of the freed wires with silica or another material. Finally, the team doused the wires with a corrosive liquid that ate away the silver or nickel stretches. Because the scientists could control how much of these sacrificial metals were inserted, the process yielded gold wires with precisely determined gaps.

The team has already used a gap in a wire as a site for measuring the electronic properties of a speck of conductive polymer. To make sensors for biological or chemical agents, researchers would fill gaps with substances whose chemical reactions with target agents would modify electric signals in the wires, Mirkin explains. Although the Northwestern team has yet to use the wires in this way, the ease with which the researchers can fabricate and manipulate the new wires "bodes well" for molecular-scale electronics, comment Charles R. Martin and Lane A. Baker of the University of Florida in Gainesville in the same issue of Science.--P.W.