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Scientists Observe Strong Spectral Signals From Spikes On Gold Particles
New optics research from Rice University's
Laboratory for Nanophotonics suggests that tiny gold particles called
nanostars could become powerful chemical sensors.
The findings are available online and due to appear in an upcoming issue of the journal Nano Letters.
New optics research from Rice University's Laboratory for Nanophotonics suggests that tiny gold particles called nanostars combine some unique qualities with some of the best properties of oft-studied photonic particles like nanorods and quantum dots. Like other particles, nanostars deliver strong spectral peaks that are easy to distinguish with relatively low-cost detectors, but unlike other particles, each spike on a nanostar has a unique spectral signature that could be useful for 3-D molecular sensing. The findings were published online by the journal Nano Letters on March 28, 2006.
Nanophotonics is a rapidly growing field of study that looks at ways to
generate and manipulate light using ultrasmall, engineered structures. The
virus-sized nanostars, so named because of their spiky surface, are one of a
growing number of intricately shaped particles that are increasingly drawing
the attention of experts at LANP and other leading photonics labs.
"Just a few years ago, everyone's attention was on the size of nanoparticles because altering size was a straightforward way to change the wavelength of light that the particle reacted with," said lead researcher Jason Hafner, associate director of LANP and assistant professor of physics and astronomy and of chemistry. "Today, researchers are increasingly interested in intricate shapes and the specific ways that those shapes affect a particlešs interaction with light."
Most nanophotonic research at LANP involves the study of plasmons, waves of electrons that flow like a fluid across metal surfaces. Light can be used to amplify plasmon waves on metal nanoparticles. Like a child in a bathtub, rhythmically building waves until they slosh out of the tub, the plasmons on the particles dramatically amplified with wavelengths of light that correspond to the rhythm of the electron waves. The study of plasmonics is one of the fastest growing fields in optics because it could prove useful for a wide range of applications in biological sensing, microelectronics, chemical detection, medical technology and others.
"LANP is building a broad-based plasmonics research program at Rice, and our recent cutting-edge work on novel structures like nanostars and nanorice is a clear indication of leadership we're building in this field," said LANP Director Naomi Halas, the Stanley C. Moore Professor of Electrical and Computer Engineering and professor of chemistry.
Nanostars incorporate some of the best properties of oft-studied photonic particles like nanorods and quantum dots. For example, they deliver strong spectral peaks that are easy to distinguish with relatively low-cost detectors. But Hafner's team found unique properties too. A painstaking analysis revealed that each spike on a nanostar has a unique spectral signature, and preliminary tests show that these signatures can be used to discern the three-dimensional orientation of the nanostar, which could open up new possibilities for 3-D molecular sensing.
"We are just getting started with our follow-up work, but nanostars clearly offer some exciting possibilities," said Hafner, assistant professor of physics and astronomy and of chemistry. "Their extreme sensitivity to the local dielectric environment is a particularly attractive quality for molecular sensing."
Co-authors of the study include physics and astronomy graduate student Colleen Nehl and chemistry graduate student Hongwei Liao. The research was supported by the Army Research Office, the National Science Foundation and the Welch Foundation.
About Rice University:
Rice University is consistently ranked one of America's best teaching and research universities. It is distinguished by its: size: 2,850 undergraduates and 1,950 graduate students; selectivity: 10 applicants for each place in the freshman class; resources: an undergraduate student-to-faculty ratio of 6-to-1, and the fifth largest endowment per student among American universities; residential college system, which builds communities that are both close-knit and diverse; and collaborative culture, which crosses disciplines, integrates teaching and research, and intermingles undergraduate and graduate work. Rice's wooded campus is located in the nation's fourth largest city and on America's South Coast.
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