Chemists at Rice University in Texas have discovered that tiny building blocks known as gold nano-rods spontaneously assemble themselves into ring-like superstructures.

The observation could help in the development of nano-devices such as highly sensitive optical sensors, super-lenses and even invisible objects for use in the military.

"Finding new ways to assemble nano-objects into superstructures is an important task because, at the nanoscale, the properties of these objects depend on the arrangement of individual building blocks," said principal investigator Eugene Zubarev, assistant professor of chemistry at Rice.

The nano-rods measure several billionths of a metre, or 1,000 times less than the width of a human hair.

Although similar ring-like assemblies have been observed in symmetrical nano-particles, such structures had not been documented with rod-shaped structures.

Professor Zubarev used hybrid nano-rods, a combination of an inorganic core and an organic surface, for his research because thousands of flexible chainlike structures called polymer molecules are attached to their surface.

The combination of the inorganic and organic features resulted in a hybrid structure that proved to be critical to the study.

"When nano-rods are organised into a ring, significant changes in their optical and electromagnetic properties occur," Professor Zubarev said.

"These can have technological applications in the area of meta-materials, which have enormous potential in opto-electronics, communications and military applications."

Professor Zubarev said that 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 organising na no-crystals of various shapes, sizes and chemical compositions into circular arrays," he concluded.