November 2, 2010, Updated September 13, 2012

A new Star of David-shaped nanoparticle may have important implications for medicine and clean energy.

Star of David nanoparticle

Photo courtesy of the Hebrew University of Jerusalem.
A magnified computer image of the new Star of David-shaped nanoparticle.

A new type of nanoparticle resembling the six-pointed Star of David, the symbol on Israel’s blue and white national flag, has been discovered by researchers in Israel. They say the discovery may lead in such diverse directions as new ways to sense glucose when diagnosing diabetes and providing a catalyst to capture the sun’s energy and transform it into clean fuel.

The scientists at the Hebrew University (HU) of Jerusalem further believe that their work greatly contributes to an understanding of how hybrid nanoparticles form. (One nanometer is a billionth of a meter.) Hybrid nanoparticles are systems that combine two or more different materials on the same particle, in which the combination provides multi-functionality to the particle.

The HU discovery, which joins other impressive finds by Israel’s nanotech scientists and engineers, is described in an article published both online and in the October issue of the journal Nature Materials.

The new Star of David-shaped particles, with sizes 10,000 times smaller than the width of a human hair, were discovered by the research group of Uri Benin, the Alfred and Erica Largish Memorial Professor and the director of the Harvey M. Kruger Family Center for Nan science and Nanotechnology at HU.

Creating new Nano particles

The researchers have been working to try and develop new nanoparticles made of two kinds of materials joined together. So far, scientists have only been aware of nanoparticles in which one material encapsulates the other (resembling an egg and a yolk), or where an island of one material forms on the other (much like the head of the match on a matchstick). This was not the case with the Star of David shapes.

Dr. Janet Macdonald, a postdoctoral fellow in Banin’s group, worked on synthesizing nanoparticles combining copper sulfide, a common mineral with semiconducting properties, and ruthenium, a metal with exceptional chemical-catalytic properties.

Instead of the expected ruthenium islands on the seed particles, what she saw in the pictures from the electron microscope were particles with surprising striped patterns and Star of David shapes.

What followed was the difficult task of determining the three-dimensional shape of the particles that could provide such images. The mystery took months to solve and confirm by careful analysis and with the aid of Dr. Maya Bar Sadan and Dr. Lothar Houben of the Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons in Juelich, Germany.

The researchers generated a three-dimensional image of the tiny nanoparticles using a powerful electron microscope and found that, remarkably, the shapes are Star of David “nano-cages.” The particles are nano-sized, hexagonal crystals, each with a tiny metal frame wrapping around and encasing them just like a bird’s cage, but 100 million times smaller.

Because the nano-cage is hexagonal, when looking at pictures of them from above, they appear as Stars of David. No one had ever seen hybrid nanoparticles form with such a cage structure before.

Beautiful, and useful for medicine and clean energy

Exploration into the possible applications for the nano Stars of David has just begun, but scientists have already shown that they are not just beautiful; the composition and the unique cage shape makes them useful.

The first application demonstrated was in the use of the nano-cages as sensors. The researchers coated an electrode with the Star of David nano-cages and proved that with the new device it is possible to detect minute quantities of hydrogen peroxide.

Un-caged copper sulfide particles alone were not sensitive, and remarkably, the addition of the metal frame boosted the electrical signal of detection 200 fold. Sensing peroxide is a first step toward new and better sensors for glucose, which has important medical implications, including for diabetes diagnostics.

Banin and his researchers have even wider aspirations for the nano Stars of David. They plan to test these materials as sensors for other medical and environmental applications, and explore whether they can be used as photocatalysts to take sunlight and create “green fuel.”

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Jason Harris

Jason Harris

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