A new imaging tool tracks carbon nanotubes inside living cells and throughout the bloodstream, which could hone the particles’ usefulness in biomedical research and clinical medicine. Carbon nanotubes have potential applications in drug delivery to treat diseases and in imaging for cancer research. Two types of nanotubes are created in the manufacturing process: metallic and semiconducting. Until now, however, no technique has visualized both types in living cells and the bloodstream, said Ji-Xin Cheng, an associate professor of biomedical engineering and chemistry at Purdue University. A new imaging tool tracks carbon nanotubes in living cells and in the bloodstream, work that could aid efforts to perfect the nanostructures’ use in laboratory or medical applications. Here, the imaging system detects both metallic and semiconducting nanotubes, false-colored in red and green, in live hamster cells. (Image: Weldon School of Biomedical Engineering, Purdue University) The imaging technique, called transient absorption, uses a pulsing near-IR laser to deposit energy into the nanotubes, which then are probed by a second near-IR laser. The researchers have overcome key obstacles in using the imaging technology: detecting and monitoring the nanotubes in live cells and laboratory mice, Cheng said. “Because we can do this at high speed, we can see what’s happening in real time as the nanotubes are circulating in the bloodstream.” The imaging technique is considered label-free in that it does not require the nanotubes to be marked with dyes. Conventional imaging methods use luminescence, which is limited because it detects the semiconducting nanotubes but not the metallic ones. The nanotubes have a diameter of about 1 nm — far too small to be seen with a conventional light microscope. One challenge in using the transient absorption imaging system for living cells was to eliminate the interference caused by the background glow of red blood cells, which is brighter than the nanotubes. The researchers solved this problem by separating the signals from red blood cells and nanotubes in two separate channels. Light from the red blood cells is slightly delayed compared with light emitted by the nanotubes. The two types of signals are separated by restricting them to different channels based on this delay. “This is important for drug delivery because you want to know how long nanotubes remain in blood vessels after they are injected,” Cheng said. “So you need to visualize them in real time circulating in the bloodstream.” Cheng and his colleagues have taken images of nanotubes in the blood vessels inside the ears of mice, as well as in the liver and other organs, and they are using the imaging technique to study other nanomaterials such as graphene. The group’s findings were published online Dec. 4 in the journal Nature Nanotechnology. For more information, visit: www.purdue.edu