Nanoparticles that fluoresce to enable tracking in the body can also be precisely manipulated with magnetic fields. Manipulating the particles with electromagnets is key to using them in biological research because the tiny particles could otherwise get lost in the jumble of molecules circulating within a cell, according to MIT chemistry professor Moungi Bawendi. “Without a magnetic ‘handle,’ it’s like a needle in a haystack,” he said. “But with the magnetism, you can find it easily.” A technique developed by Bawendi and colleagues involves magnetic nanoparticles that cluster together while fluorescent quantum dots form a uniform coating around them. These “supernanoparticles” can also be coated with a silica to seek out and bind to particular molecules, such as markers for tumor cells or other disease agents. In addition to multiphoton microscopy techniques, the supernanoparticles can also be used in magnetic resonance imaging, the researchers said. TEM images of increasing magnification show the structure of the core-shell supernanoparticles. Fluorescent quantum dots form a shell around a core of magnetic nanoparticles. Courtesy of MIT. Other research groups have been able to achieve different combinations of fluorescence and magnetism, but a nanomaterial that incorporates both has long evaded scientists. Such particles have typically been too large to make practical probes of living tissue, Bawendi said, noting that “compactness is critical for biological and a lot of other applications.” The nanoparticles could be used to probe basic biological functions within cells. The researchers said future experiments could involve attaching additional materials to the particles’ coating so that they interact in specific ways with molecules or structures within the cell, either for diagnosis or treatment. “We’ve made the material,” said Ou Chen, a postdoctoral researcher at MIT. “Now we’ve got to use it, and we’re working with a number of groups around the world for a variety of applications.” The work was supported by the National Institutes of Health, the U.S. Army Research Office through MIT’s Institute for Soldier Nanotechnologies and the U.S. Department of Energy. The research was published in Nature Communications (doi: 10.1038/ncomms609). For more information, visit www.mit.edu.