Buckyballs with a Surprise
Carbon cages filled with metal molecules could improve MRI diagnostics and make high-efficiency solar cells.
A Virginia-based startup called Luna nanoWorks is nearing commercialization of a novel version of buckyballs–soccerball-shaped carbon molecules–that the company says could improve magnetic resonance imaging (MRI) and lead to high-efficiency solar cells. Each buckyball is made of 80 carbon atoms with metal-nitride clusters trapped inside, creating a nanomaterial with novel electronic, optical, and magnetic properties.
The new material was first made by Harry Dorn and his colleagues at Virginia Tech, in Blacksburg, VA, by accident. Scientists typically create buckyballs–hollow spheres made of 60 carbon atoms are the most common kind–by striking an electric arc between two graphite electrodes. When the Virginia Tech researchers were making these fullerenes using metal catalyst-infused electrodes, air leaked into the electric-arc chamber. The result was a large number of 80-carbon buckyball cages, each with a metal-nitride molecule with three metal atoms trapped inside.
Researchers have enclosed metal molecules in buckyballs before, but these are the first buckyballs enclosing highly unstable metal-nitride molecules. What’s more, the 80-carbon buckyball itself was unusual: no one had ever before made one, either hollow or filled. Even though the metal-nitride molecules and the 80-carbon buckyball do not exist for long on their own, they stabilize each other in the new arrangement. Luna nanoWorks, based in Danville, VA, can make the fullerenes with various combinations of rare earth metals, such as scandium, yttrium, and lanthanum.
The buckyball has a net negative charge, while the metal cluster has a net positive one. This charge distribution of the metallic fullerene molecule gives it interesting properties, which researchers are still trying to understand. “It’s a very unusual material, not your run-of-the-mill compound,” says James Cross, professor of chemistry at Yale University. “There could easily be various practical applications,” the most promising being MRI enhancement, he says.
Luna nanoWorks, which licensed the technology from Virginia Tech, says the materials could be utilized as a more effective contrast agent in MRI, which is used to image soft body tissue such as the brain and spinal cord. Physicians currently inject gadolinium into a patient’s body right before an MRI exam. The metal improves the resolution of the scans and increases the image contrast. But gadolinium is toxic, so it is wrapped with an organic compound. This does not eliminate the toxicity risk completely, Cross says, and it limits the amount of gadolinium that doctors can inject into the patient’s body.
In contrast, the 80-carbon buckyball is a much stronger cage for trapping gadolinium nitride “for the next generation of contrast agents where you want to target them to a particular organ or disease condition,” says Robert Lenk, Luna nanoWorks’ president. Indeed, Dorn and his colleagues at Virginia Tech have shown that the metal-nitride fullerenes show 40 times better contrast than contrast agents currently on the market, although the exact mechanism behind that is not yet understood. Before the material can be used for MRI, however, it would have to undergo a battery of safety and toxicity tests, and get Food and Drug Administration approval. The company plans to do this once the material has been fully developed.
Trapping other metals in the buckyball could lead to different applications. Luna nanoWorks is planning to use these nanomaterials to make new types of highly efficient solar cells, although Lenk declined to explain how they would work. When photons hit photovoltaic materials, a negatively charged electron and a positively charged hole are created that often recombine and do not contribute to the electric current. “One of the active areas of research right now is finding more-efficient ways of separating the electron-hole pair before they can recombine, and therefore increasing the efficiency of solar panels,” Lenk says.
Luna nanoWorks already sells milligram quantities of the materials to researchers, and being able to make such relatively large quantities sets the company apart from others in the research field, Cross says. While German and Japanese groups have done significant work on metal-nitride fullerenes, none had a way to make adequate quantities of the material. “They’d get a few micrograms of these things,” Cross says. “It clearly wasn’t enough to do any kind of serious chemistry or find any applications.” Dorn’s method, on the other hand, creates grams of the material.
“There are all sorts of things you could do” with this material by putting various metal molecules inside, says Cross. “This might well be a prototype for a much more extensive series of compounds which may have their own set of interesting properties.”