Nanoscale alloys that are 100 times brighter than those currently being used could have potential applications in medicine, demonstrations conducted at the University of Pittsburgh (Pitt) have shown. Alloys such as bronze and steel have been transformational for centuries, yielding machines necessary for industry, but as scientists move toward nanotechnology, the focus has shifted toward creating alloys at the nanometer scale — producing materials with properties unlike their predecessors. Those demonstrated at Pitt have properties drastically different from those of their predecessors — including near-infrared (NIR) light emission — depending on their size, surface chemistry and shape. “We demonstrate alloys that are some of the brightest, near-infrared-light-emitting species known to date,” said Jill Millstone, principal investigator of the study and assistant professor of chemistry at Pitt’s Kenneth P. Dietrich School of Arts and Sciences. “Think about a particle that will not only help researchers detect cancer sooner, but be used to treat the tumor, too.” NIR is an important region of the light spectrum and is integral to technology found in science and medical settings, she said. Take a laser pointer, for example. “If you put your finger over a red laser [which is close to the NIR light region of the spectrum], you’ll see the red light shine through,” Millstone added. “However, if you do the same with a green laser [light in the visible region of the spectrum], your finger will completely block it. This example shows how the body can absorb visible light well, but doesn’t absorb red light as well. That means that using NIR emitters to visualize cells and, ultimately, parts of the body, is promising for minimally invasive diagnostics.” The experiment also demonstrated, for the first time, a continuously tunable composition for nanoparticle alloys, meaning the ratio of materials can be altered based on need. Materials such as steels can be highly tailored toward the application — for example, as an airplane wing versus a cooking pot — in traditional metallurgical studies, but alloys at the nanoscale follow different rules, Millstone said. Because the nanoparticles are so small, the components quickly separate, like oil and vinegar. To ensure that the components stay mixed, Millstone used a small organic molecule to “glue” an alloy in place. This strategy led to the discovery of NIR luminescence and could pave the way for other types of nanoparticle alloys that are useful for applications such as catalysis for the industrial-scale conversion of fossil fuels into fine chemicals. These observations, Millstone said, provide a new platform to investigate the structural origins of small metal nanoparticles’ photoluminescence and of alloy formation in general for applications ranging from health to energy. The research — supported by the university’s Central Research Development Fund and administered by the Office of Research and University Research Council — appeared in the Journal of the American Chemical Society (doi: 10.1021/ja400569u). For more information, visit: www.pitt.edu