A three-dimensional cage-shaped, artificial nanoparticle that looks from above like a six-pointed Star of David has been created by Hebrew University of Jerusalem researchers. They believe that it could eventually lead to better glucose sensors to diagnose diabetes or a more efficient catalyst using sunlight to turn water into hydrogen for clean fuel.

The achievement by Prof. Uri Banin and Canadian postdoctoral student Dr. Janet Macdonald is an advance because while there were previous existing soccer-ball-shaped molecules, they are so tiny that they cannot hold other things. Nanometers are one-billionth of a meter in size.

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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 nanocage is hexagonal, when looked at from above, the images appear as Stars of David. No one had ever seen hybrid nanoparticles form with such a cage structure before.

Banin and Macdonald -- who worked with Israeli post-doctoral student Dr. Maya Bar Sadan and Dr. Lothar Houben of the Ernst Ruska-Center for Microscopy and Spectroscopy with Electrons in Juelich, Germany -- published details of their work Sunday evening in the latest (October) issue of the prestigious journal Nature Materials.

The new star-shaped particles, with sizes 10,000 times smaller than the width of a human hair, is very different from existing 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 match-stick). Instead of viewing ruthenium islands on the seed particles, what they saw in electron microscope images were particles with surprising striped patterns and six-pointed star shapes.

Banin, the Alfred and Erica Larisch Memorial Professor and the director of HU’s Harvey M. Kruger Family Center for Nanoscience and Nanotechnology, said he and Macdonald worked on the project for two years. "It took a long time to repeat the accomplishment, understand how it worked and think of possible ways to implement it," he said. "We created a new particle combining a semiconductor [copper sulfide] and a metal [ruthenium] with the characteristics of each appearing in the new nanoparticle," Banin said. The next hurdle was figuring out the three-dimensional shape of the particles that could give such images. The mystery took months to solve and confirm, with help from the German team.

Banin and Macdonald believe their work greatly contributes to scientific understanding of how hybrid nanoparticles combining two or more different materials on the same particle form. Although they are not yet at the stage of application and have not consulted a diabetes expert, they understood that the cage-like structure could be used as a glucose sensor for the blood to detect diabetes. Because the resulting nanoparticle is not organic it has a longer shelf life and is more stable than existing sensors. "It may be a solution for the instability problem. There are no other inorganic cases of this size in the scientific literature," Banin added.

The researchers coated an electrode with the nanocages and proved that it is possible to detect with the new device minute quantities of hydrogen peroxide. Uncaged copper sulfide particles alone were not sensitive, and amazingly, the addition of the metal frame boosted the electrical signal of detection 200 times. Sensing peroxide is a first step towards new and better sensors for glucose, which has important medical implications, including for diabetes diagnostics, Banin said.

The cage-like receptacle could be used to change light to chemical energy, even efficiently separating hydrogen out of water to produce clean fuel instead of petroleum, Banin said. The researchers found that the nanoparticle could be created with other semiconductors as well.

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