New Technique Breaks Nano-Particle Self-Assembly Barrier

Scientists succeeded in getting three different types of nano-particles to self-assemble.

Researchers on the cutting edge of chemistry and materials science are striving to manipulate nano-particles—bits hundreds of times smaller than the diameter of a human hair—to assemble themselves into miniscule machines capable of all manner of functions.  Scientists have long been able to create nano-structures from a single particle type, but assembling sophisticated structures from multiple types of particles has never been achieved.

Now, scientists at Duke University and the University of Massachusetts, Amherst, have coaxed three different-sized particles to self-assemble into elegantly shaped structures the scientists say are “simply beautiful.” Under the microscope some look like flower petals, others resemble Saturn and its rings.

The structures are formed in a solution containing suspensions of nano-particles composed of iron-containing compounds, which can be highly magnetized by external magnets. Changing the levels of magnetization of the fluid controls how the particles are attracted to or repelled by each other. By tuning these interactions, the magnetic and non-magnetic particles form around each other much like a snowflake forms around a microscopic dust particle.

“It appears that a rich variety of different particle structures are possible by changing the size, type or degree of magnetism of the particles,” said Ben Yellen, a materials scientist at Duke who developed the magnetizing fluids with Bappaditya Samanta and Vincent Rotello at U. Mass.

Using heat and certain chemicals as “glue,” the researchers can permanently fix the structures so they won’t come apart when the magnetic field is turned off.

Yellen foresees the use of these nano-structures in advanced optical devices, such as sensors, where different nano-structures could be designed to possess custom-made optical properties. Rings composed of metal particles could be used for antenna designs, he said. The materials may also be used as building blocks for cloaking devices and data storage.

Rotello and his team say they may next test the new method in biological systems. “We may see if we can get cells to do the same kind of dance we’ve gotten the particles to do,” he notes. They also plan to test different combinations of particles types and sizes, as well as fluid composition, to see how small they can make new nanostructures.

The work, supported by the National Science Foundation, is described in the Feb. 19, 2009 issue of the journal Nature.

• Video of self-assembling particles available here.

—By Leslie Fink/NSF with material provided by Duke University and U. Mass., Amherst.

This report is provided by the National Science Foundation, an independent federal agency that supports fundamental research and education across all fields of science and engineering, in partnership with U.S. News and World Report. For more information, go to www.nsf.gov.