$2.5 Million Initiative To Develop Chameleon-Like Nanoshells

The Defense Department has chosen to fund a new five-year Multidisciplinary University Research Initiative (MURI) headed by Rice University, and including Oklahoma State University and the University of Houston, to study and develop the nanoshells, their optical and electromagnetic responses and properties, and commercial applications.

A number of industries could potentially benefit from the development of this technology, including electronics, energy conservation, construction materials, biomedicine and cosmetics.

"The wonderful thing about metal nanoshells is that we can tailor them to have specific optical properties at different wavelengths of light," said Naomi Halas, professor of electrical and computer engineering at Rice and principal investigator of the project. "The particles themselves have these properties, an overwhelming advantage over other optical structures, which require multilayer films or nanoparticle arrays to give rise to similar effects. Nanoshells can be easily and directly incorporated into coatings and responsive devices."

Metal nanoshells are tiny particles, ranging from about 50-1,000 nanometers in diameter, with an insulating core, such as silica, coated by a thin shell of conductive metal--resembling nano-sized malted milk balls.

Metal nanoshells can absorb light or scatter light, both in the visible and infrared regions of the spectrum. Varying the thicknesses of the shell and the core changes the way in which light is manipulated. Variations in thickness and particle composition extend the controlled electromagnetic wave response from visible light into the far-infrared and submillimeter-wave spectral regions.

Nanoshells can be chemically attached to a wide variety of materials, including plastics, liquids, aerosols, epoxies, glasses and even fibers. New products could include energy-efficient smart windows, powerful solar collection and solar cells, coatings for cars, airplanes or buildings, biomedical sensors, and optical switches, steering light to different points in futuristic computer architecture.

When incorporated into device structures, nanoshells are capable of responding to an applied electric current and producing a voltage-dependent optical response. For instance, by changing the voltage to a visual display panel built with nanoshell technology, the panel could change colors or transparency.

Led by Halas, the research team is working to design and create the metal nanoshells, and to fully understand their properties and abilities. They will develop arrays, coatings, films and ultrathin films. The researchers are also studying different types and combinations of materials to improve upon current inorganic nanoshells and to develop completely organic nanoshells.

Jennifer West, Rice assistant professor of bioengineering, is working to develop nanoshell-based all-optical biosensors and biotests. Because near-infrared light can pass harmlessly through the human body, an implantable sensor that uses light to monitor chemicals could be used to instantly monitor a range of different chemicals in the body. In addition, such nanoshell biotesting devices could be used to check proteins in whole blood, providing a big advantage over current methods, which are difficult and time consuming. Customized nanoshell monitors could allow doctors to look at small amounts of antigens or antibodies and determine rapidly the health of a patient.

Peter Nordlander, Rice professor of physics, is a theoretical physicist and is studying the electrical transport properties of nanoshells and how they behave in a variety of environments.

Alex Rimberg, Rice assistant professor of physics, is studying the way electrons flow around the nanoshells and how the internal structure affects its electrical transport properties.

Dan Grischkowsky and Alan Cheville, professors in electrical engineering at the University of Oklahoma, are experts in making measurements in the terahertz region--the range between infrared light and microwaves--and at using the unique spectroscopy for probing chemical content of materials. They characterize the particles that are made and provide insight into how to design strongly absorbing particles in this region of the spectrum.

As part of the synthetic effort, Randy Lee, a professor of organic chemistry at the University of Houston, is using synthetic techniques to grow organic nanoshells, and exploring new methods for the uniform growth of nanoshell structures.