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Nanorods' Assembly Could Spur Nanodevice Creation

Photonics.com
Mar 2007
HOUSTON, March 12, 2007 -- Chemists have discovered that tiny building blocks known as gold nanorods spontaneously assemble themselves into ring-like superstructures. The finding could potentially lead to the development of novel nanodevices like highly sensitive optical sensors, superlenses and even invisible objects for military use.goldnanorod.jpg
Transmission electron microscopy (TEM) image of a circular superstructure of Rice University hybrid nanorods templated by a water microdroplet (Image courtesy of Bishnu Khanal)
"Finding new ways to assemble nano-objects into superstructures is an important task because at the nanoscale, the properties of those objects depend on the arrangement of individual building blocks," said principal investigator Eugene Zubarev, the Norman Hackerman-Welch Young Investigator and assistant professor of chemistry at Rice University.

Although ring-like assemblies have been observed in spherical nanoparticles and other symmetrical molecules, until now such structures had not been documented with rod-shaped nanostructures. Like many nanoscale objects, gold nanorods are several billionths of a meter, or 1000 times smaller than a human hair.

Zubarev used hybrid nanorods for this research because attached to their surface are thousands of polymer molecules, which are flexible chainlike structures. The central core of the nanorods is an inorganic crystal, but the polymers attached to the outside are organic species. The combination of the inorganic and organic features resulted in a hybrid structure that proved to be critical to the study.

Working with Rice graduate student Bishnu Khanal, Zubarev placed the nanorods in a solution of the organic solvent chloroform. As the chloroform evaporated, its surface temperature dropped low enough to cause condensation of water droplets from the air, much like how dew forms. As thousands and thousands of microdroplets of water formed on the surface of the liquid chloroform, the nanorods that had been suspended in the solution started to press up against the round droplets and form rings around them. The polymer coating prevented the rods from being absorbed into the droplets because it is insoluble in water. After the droplets evaporated, the nanorods remained in their ring formation.

"When nanorods are organized into a ring, significant changes in their optical and electromagnetic properties occur," Zubarev said. "These can have technological applications in the area of metamaterials, which have enormous potential in optoelectronics, communications and military applications."

Zubarev said thousands of well-defined rings can be produced in a matter of seconds using the approach from his study. "This method is surprisingly simple and can be used for organizing nanocrystals of various shapes, size and chemical composition into circular arrays."

The study will be published in the March 19 international edition of the chemistry journal Angewandte Chemie. The research was funded by the National Science Foundation and the Welch Foundation.

For more information, visit: www.rice.edu


GLOSSARY
nanoparticle
A small object that behaves as a whole unit or entity in terms of it’s transport and it’s properties, as opposed to an individual molecule which on it’s own is not considered a nanoparticle.. Nanoparticles range between 100 and 2500 nanometers in diameter.  
photonics
The technology of generating and harnessing light and other forms of radiant energy whose quantum unit is the photon. The science includes light emission, transmission, deflection, amplification and detection by optical components and instruments, lasers and other light sources, fiber optics, electro-optical instrumentation, related hardware and electronics, and sophisticated systems. The range of applications of photonics extends from energy generation to detection to communications and...
rod
The light-sensitive cells on the retina of the eye that are responsible for low-resolution, peripheral vision.
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