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Microwire discovery

Eric Kaler

NEWARK, DE.--University of Delaware researchers have discovered a new class of self-assembling microwires that can conduct electricity, according to the Nov. 2 issue of Science magazine.

The principal investigators for the project were Eric Kaler, dean of the College of Engineering and Elizabeth Inez Kelley Professor of Chemical Engineering, and Orlin Velev, formerly a research assistant professor in the University’s Department of Chemical Engineering and Center for Molecular and Engineering Thermodynamics, who has since joined the faculty of North Carolina State University.

The investigators were Simon Lumsdon, a postdoctoral researcher in the Department of Chemical Engineering; Kevin Hermanson, a chemical engineering graduate student; and Jacob Williams, a summer research student from Carnegie Mellon University.

The research team reports in Science that is has found a new method for the assembly of a novel class of colloidal structures – porous metallic microwires, which are wires of diameter on the order of a micron, or one one-thousandth of a millimeter.

“This work opens up a new approach to materials synthesis,” Kaler said, “and will allow researchers to assemble nanoparticles into a variety of useful structures.”

The structures grow from aqueous suspensions of metallic nanoparticles. The assembly is performed by dielectrophoresis, the application of alternating electric fields across the nanoparticle suspension.

Once assembled, the microwires can conduct electricity, hence the process can be seen as the self-assembly of electrical circuits inside small volumes of liquid containing nanoparticles.

“There has been quite a bit of interest and research in nanowires, ultra-small carbon or semiconductor cylinders chemically grown in solution,” Velev said. “On the other hand, there is electrical engineering, which operates with wires on a more macroscopic scale. Our microwires fill in the size gap between the nanowires and the conventional wires. It is important that we can grow them in a controllable manner and actually link metallic or conductive islands inside water suspensions.”

It has been shown that these wires can be used as microscopic sensors for certain chemicals, such as thiols and cyanides.

The UD researchers also have demonstrated the concept of making electrical connections through aqueous droplets by assembling rudimentary circuits.

“One very interesting, albeit yet remote, possibility is to use these wires for electronic-biology interfacing,” Velev said. “All living cells live in water environments, and our process of spontaneous growth on microwires in water can be used to connect electrical electrodes to living cells and tissues by growing wires between them.”

Where several decades ago it was commonly assumed that “bigger is better,” much of the future in science rests in the world of the small.

“There is lots of exciting research going on in miniaturization and self-assembly to make microscopic structures and devices,” Velev said. “However, there is a very large gap between the imaginary marvels that can be done by nanotechnology and the things that we do now in the lab, which we like to refer to as nanoscience. Finding new assembly tools, such as dielectrophoresis, and new structures, such as the microwires, are a small step in the direction of being able to do more on the microscale and eventually advance in the direction of nanotechnology.”

Contact: Neil Thomas, (302) 831-6408,
Nov 1, 2001