Research Team at UMass Amherst Builds Something From (Almost) Nothing

AMHERST, Mass. - A team of University of Massachusetts researchers has found a way to make molecules that are too tiny to be seen, under even the strongest microscopes, behave in a predictable and orderly way. The finding should have major implications in the development of faster computers and ultra-sensitive sensors, such as electronic "noses" that locate land-mines and diseases. The team, led by professor of chemistry Vincent Rotello, reports the details in the April 13 issue of the journal Nature.

The team specializes in coaxing molecules to stick together - a process scientists call "self-assembly." While self-assembly occurs often in nature - such as when ice forms, and salt crystals congeal in the salt shaker - it''s much tougher to make synthetic molecules self-assemble in a controlled way, Rotello said. Scientists have long been able to form small molecules of a specific shape. They have also been able to form large structures. The significance of this work is the ability to form large, synthetic structures while controlling their shape, atom-by-atom.

A major part of the problem is scale: scientists are essentially trying to build Tinkertoy-like structures without being able to see the sticks and hubs. "Making things tiny is important to industry," Rotello pointed out. "If transistors fashioned from molecules could be effectively arranged, a billion to a trillion times as many transistors could fit on the same size chip as fit now."

The researchers explored ways to build molecules that would hold together until they reached a size that would allow them to be manipulated. "We start with something small and ordered, and build it up into something we can see and work with," said Rotello. "It''s a strategy scientists and engineers call ''multi-scale ordering.''"

The solution was in tiny, solid gold spheres just two nanometers across; one-fiftieth the size of a small virus. The team attached six binding molecules to each gold sphere using sulfur atoms as links. Then they essentially "glued" them together by combining them with a form of polystyrene containing complementary binding sites, so that the two mixtures fit together like puzzle pieces. What they found is that the sulfur-modified, gold particle-polystyrene combination fits together in an extremely orderly fashion, forming a perfect, tightly-packed sphere of 7,000 gold particles, 100 nanometers across. "We can then order the spheres - we can have order from molecular to macroscopic scale. If you want to do multi-scale engineering, you have to be able to order on all scales."

Conducting the same process at lower temperatures was even more successful. At minus 10 degrees Celsius, the spheres linked together in a network fashion. And at minus 20 degrees Celsius, they formed a well-formed sphere that was comparatively huge, with more than 2½ million particles measuring 1,500 nanometers across - the size of a bacterium.

"Self-assembly of nanoparticles into structured spherical and network aggregates" appears in the April13 issue of the journal Nature. Co-authors on the paper are chemistry graduate students Andrew Boal and Faysal Ilhan; polymer science and engineering graduate student Jason DeRouchey; visiting Professor Thomas Thurn-Albrecht; and polymer science and engineering Professor Thomas P. Russell.

NOTE: Vincent Rotello can be reached at 413/545-2058 or rotello@chem.umass.edu.