Carbon nanotubes have already found many valuable applications in nanotechnology. Now researchers are adding yet another potential use for these unique nanomaterials: as a detector for specific sequences of DNA. The work suggests that carbon nanotubes could be the basis for ultrasensitive devices for detecting pathogens such as anthrax and DNA mutations that cause genetic diseases, as well as leading to a more precise tool for understanding genetic mechanisms inside cells.
The technology, developed at the University of Illinois at Urbana-Champaign, and published in Nano Letters, relies on the fact that carbon nanotubes glow when exposed to light. Michael Strano, the lead researcher on the project, and his coworkers begin by attaching single strands of DNA to nanotubes. If the complementary DNA sequence is present in the test sample, binding occurs; as a result of the binding, the color of the nanotubes changes markedly – a clear signal that a match has been found. In the future, Strano says, it may be possible to use the nanotubes to screen for more than 50 different DNA sequences at once by tuning the colors emitted by nanotubes, which would enable quick screenings for multiple pathogens or specific genes.
The research is part of a growing effort to use nano tools – including carbon nanotubes, nanowires, and other nanoparticles – to make devices that could serve as fast, ultrasensitive detectors of DNA and other biological molecules. Such devices might be used in a quick test, for instance, to distinguish a cold from pneumonia or to catch the earliest stages of cancer by measuring an array of protein biomarkers. Unlike existing detection methods, these nano sensors do not require an amplification of the number of DNA molecules or modification with a fluorescent tag.
Alexander Star, a professor of chemistry at the University of Pittsburgh, who recently used nanotubes to detect DNA electrically, says the University of Illinois work with glowing nanotubes stands out because it could be used to study genetic interactions in research animals. The light emitted by the nanotubes travels easily through biological tissue, so the nanotubes can be observed even as they travel freely inside cells, Star says. “You can actually perform these measurements in vivo.”
Strano says he’s beginning to talk with companies about developing the technology to the next stage, but it could be several years before it is widely available. One important next step is demonstrating single-molecule sensitivity with the detection method. Strano is also working to increase the color shift in order to make the signal easier to read and to speed up the reaction time to make the testing time faster.
Chad Mirkin, a Northwestern University chemist whose work on nanosensors is being commercialized by Nanosphere in Northbrook, IL, says it’s still too early to know whether the new nanotube-based method has an advantage that will give it a commercial edge over other nanotech sensors being developed. In part because there are so many new approaches, “the bar is extremely high,” he says.