Researchers Create New Nanoparticle

By Jade Boyd

Who better to invent “nanorice” than researchers at Rice University? But marketing and whimsy weren’t what motivated the team of engineers, physicists, and chemists from Rice’s Laboratory for Nanophotonics (LANP) to make rice-shaped particles of gold and iron oxide.

“On the nanoscale, the shape of a particle plays a critical role in how it interacts with light,” says Naomi Halas, the Stanley C. Moore Professor in Electrical and Computer Engineering, professor of chemistry, and director of LANP. “We were looking for a new shape that would combine the best properties of the two most optically useful shapes—spheres and rods. It’s just a coincidence that that shape turned out to look exactly like a grain of rice.”

Nanorice

The new particles, which are being examined for possible applications in molecular imaging, cancer treatment, medical diagnostics, and chemical sensing, are similar in structure to nanoshells, spherical nanoparticles invented by Halas in 1998. Both are made of a nonconducting core that is covered by a metallic shell—in the case of nanorice, a nonconducting iron oxide called “hematite” covered with gold. The core size and shell thickness vary slightly, but the nanorice particles described in the Nano Letters paper were about 360 nanometers long and about 80 nanometers in diameter—1/20th the size of a red blood cell.

Research over the past decade has shown that some nanoscale structures—like nanoshells and nanorice—act as superlenses that can amplify light waves and focus them on spots far smaller than a wavelength of light. When light of a specific frequency strikes plasmons—ripples in the ocean of electrons that flow constantly across the surface of metals—that oscillate at a compatible frequency, the light is converted into electrical energy that propagates, as plasmons, though an adjacent nanostructure. This allows scientists and engineers to examine minute details of the adjacent surfaces with greater accuracy.

Halas and her colleagues plan to capitalize on this by moving grains of nanorice next to proteins and unmapped features on the surfaces of cells, hoping to get a far clearer picture of them than is possible with current technology. The researchers already have shown, for example, that nanoshells are about 10,000 times more effective at surface-enhanced Raman scattering than traditional methods. Raman scattering is a type of spectrographic technique used by medical researchers, drug designers, chemists, and others to determine the precise chemical makeup of materials. Nanorice possesses a far greater ability to change the shape of a metal at the nanoscale than even nanoshells and another commonly studied optical nanoparticle, the nanorod, indicating that nanorice is the most sensitive surface plasmon resonance nanosensor yet devised.

The research appeared in the April 12 issue of Nano Letters. The co-authors include Peter Nordlander, professor of physics and astronomy and in electrical and computer engineering, and graduate students Hui Wang, Daniel Brandl, and Fei Le. It was funded by the National Science Foundation, the U.S. Army Research Office, the U.S. Air Force Office of Scientific Research, NASA, and the Robert A. Welch Foundation.