Furthermore, the nanotube sensors can detect very small molecules that would be difficult to identify with other technologies, and at very low concentrations. In this study, the researchers could identify a single molecule of hydrogen peroxide, a small and volatile molecule. "In terms of sensitivity, we've reached the limit," Strano says. And the optical signal of the nanotubes does not fade over time, a property called photobleaching that limits the effectiveness of fluorescent dyes.

James Heath, a chemist at Caltech who was not involved in the study, says that while questions remain about how these sensors compare with other approaches, they represent an impressive achievement. "A single platform that can be delivered into cells and then optically report on chemical events within the cell is very original, and it is amazing that this system works as well as it does," he says.

The most immediate application of the technology is as a research tool, allowing scientists to find and study the behavior of chemical signals that were difficult to study before, because of size or low concentration. The sensors can be used to study the effects of antioxidants in cells, or could also be extended to tissues--for example, to study chemical reactions in cancer cells within a tumor.

However, Ravi Kane, a chemical and biological engineer at Rensselaer Polytechnic Institute, says that this class of sensors "could have numerous diagnostic applications." Strano says that the technology could eventually be used in humans to give doctors a way to track the effectiveness of chemotherapy regimens and tailor dosages for individual patients. Although this study focuses on chemicals that interact with DNA, the sensors can be adapted for other purposes, depending on what is wrapped around the carbon nanotube. Strano's lab has been using similar sensors to study glucose and brain neurotransmitters in cells and tissues.