A new carbon-nanotube-based sensor shows promise for detecting nitric oxide in biological environments, in real time, and with spatial resolution. NO plays a vital role in biology as a signaling molecule. But NO decomposes rapidly to form other species, and thus tracking it through a biological system has proved difficult. Now, chemical engineering professor Michael S. Strano and colleagues at MIT have functionalized single-walled carbon nanotubes (SWNTs) with a 3,4-diaminophenyl-functionalized dextran (shown) to sense NO (Nat. Chem. 2009, 1, 473). Scientists have been exploring use of SWNTs, with their sensitive and unusual charge-conducting properties, as near-infrared biological sensors for a number of years. Strano’s SWNT-based NO sensor also fluoresces under near-IR light. The light is bleached when it encounters NO—but not other cellular nitrogen or oxygen species, the authors say. The sensor would therefore be able to signal the presence of NO selectively and in real time. And because near-IR light penetrates animal tissues, the presence of NO could be detected in live animal experiments. The group also tested the sensor, which is not toxic to cells, in the abdomen of a dead mouse, setting the stage for future studies in live mice.