Krista D. Zanolli, email@example.com
HOUSTON – Just as generations of children have enjoyed stacking
and building with plastic Lego toys, scientists are now using light-activated nanoshells
as Lego-like building blocks for both 2- and 3-D structures that could be used in
chemical sensors, metamaterials and nanolasers.
In a collaborative effort, scientists from Rice University, Harvard
University, the University of Texas at Austin and the University of Houston are
using this self-assembly method to build complex structures that can trap, store
and bend light.
“We used the method to make a seven-nanoshell structure
that creates a particular type of interference pattern called a Fano resonance,”
said Peter Nordlander, professor of physics and astronomy at Rice. “These
resonances arise from peculiar light wave interference effects, and they occur only
in man-made materials. Because these heptamers are self-assembled, they are relatively
easy to make, so this could have significant commercial implications.”
The research team was led by Harvard University applied physicist
Federico Capasso, whose efforts to fabricate the structure were spurred by Nordlander’s
2008 prediction that a heptamer of nanoshells would produce Fano resonances.
Artist’s rendition of two types of optical circuits: The three-particle
trimer functions as a nanoscale magnet, while the seven-particle heptamer exhibits
almost no scattering for a narrow range of wavelengths, due to interference. Courtesy
of the laboratory of Federico Capasso, Harvard School of Engineering and Applied
Coated with polyethylene glycol, the nanoshells are assembled
into clusters when a droplet of particles is dried on a hydrophobic substrate. When
the initial droplet evaporates, it breaks down on the surface of the substrate into
smaller droplets, some of which contain three or seven nanoshells. As the droplets
completely evaporate, capillary forces pack the nanoshells together into a cluster,
and they remain held together by van der Waals forces.
Because of the Fano resonance pattern, the new materials can manipulate
light in bizarre ways that no natural material can. According to Nordlander, the
new materials are ideally suited for making ultrasensitive biological and chemical
sensors. He added that they also might lend themselves to nanolasers and integrated
photonic circuits that run off of light rather than electricity.
The spherical nanoshells, which are roughly one-twentieth the
size of red blood cells, consist of a glass center and are coated with gold. By
varying the size of the glass center and the thickness of the gold shell, researchers
can create nano-shells that interact with specific wavelengths of light.
“Nanoshells were already among the most versatile of all
plasmonic nanoparticles, and this new self-assembly method for complex 2-D and 3-D
structures simply adds to that,” said nanoshell inventor Naomi Halas, Rice’s
Stanley C. Moore professor of electrical and computer engineering. She has also
helped develop a number of biological applications for nanoshells, including diagnostics
and a minimally invasive procedure for treating cancer.
Halas’ extensive work in the field of photonics has led
to human trials for cancer treatment involving near-infrared light heating gold
nano-shells, which target and destroy cancerous tumors without affecting the surrounding
Halas and collaborator Jennifer West, the Isabel C. Cameron professor
of bioengineering, founded Nanospectra Biosciences Inc., a Houston company based
on the patented light-activated gold nanoshell technology.
“It has been highly gratifying to see our discovery move
from the research laboratory into the commercial sector, where it is now helping
cancer patients,” West said.
In early June, the State Bar of Texas designated the two “Inventors
of the Year” for their patented process. Halas and West are the first women
to win the award since its inception in 1983. Theirs is also the first nanotechnology-based
invention to win.