PHILADELPHIA -- Nano-sized carbon tubes coated with strandsof DNA can create tiny sensors with abilities to detect odors andtastes, according to researchers at the University of Pennsylvania andMonell Chemical Sciences Center. Their findings are published in thecurrent issue of the journal Nano Letters, a publication of theAmerican Chemical Society.
According to the researchers, arraysof these nanosensors could detect molecules on the order of one partper million, akin to finding a one-second play amid 278 hours ofbaseball footage or a single person in Times Square on New Years' Eve.In the report, the researchers tested the nanosensors on five differentchemical odorants, including methanol and dinitrotoluene, or DNT, acommon chemical that is also frequently a component of military-gradeexplosives. The nanosensors could sniff molecules out of the air ortaste them in a liquid, suggesting applications ranging from domesticsecurity to medical detectors.
"What we have here is a hybridof two molecules that are extremely sensitive to outside signals:single stranded DNA, which serves as the 'detector,' and a carbonnanotube, which functions as 'transmitter,'" said A. T. CharlieJohnson, associate professor in Penn's Department of Physics andAstronomy. "Put the two together and they become an extremely versatiletype of sensor, capable of finding tiny amounts of a specific molecule."
Giventhe size of such sensors each carbon nanotube is about a billionth of ameter wide, Johnson and his colleagues believe arrays of these sensorscould serve as passive detection systems in almost any location. Thesensor surface is also self-regenerating, with each sensor lasting formore than 50 exposures to the targeted substances, which means theywould not need to be replaced frequently.
The specificity ofsingle-stranded DNA is what makes these sensors so capable. Thesebiomolecules can be engineered, in a process called directed evolution,to recognize a wide variety of targets, including small molecules andspecific proteins.
Likewise, the nanotubes are ideal forsignalling when the DNA has captured a target molecule. Single-wallednanotubes are formed from a single sheet of carbon molecules connectedtogether and then rolled. It is a unique material in which every atomis on both the surface and the interior. Although nanotubes have manyapplications, they are extremely sensitive to electrostatic variationsin their environment, whether the nanotube is in a liquid or in air.
"Whenthe DNA portion of the nanosensor binds to a target molecule, therewill be a slight change in the electric charge near the nanotube,"Johnson said. "The nanotube will then pick up on that change, turningit into an electric signal that can then be reported."
Accordingto Johnson, an array of 100 sensors with different responsecharacteristics and an appropriate pattern recognition program would beable to identify a weak known odor in the face of a strong and variablebackground.
"There are few limits as to what we could build thesesensors to detect, whether it is a molecule wafting off an explosivedevice or the protein byproduct of a cancerous growth," Johnson said.
Researchersinvolved in the project include Cristian Staii, a graduate student inthe Department of Physics and Astronomy in Penn's School of Arts andSciences; Michelle Chen, a graduate student in the Department ofMaterial Science and Engineering in Penn's School of Engineering andApplied Science; and Alan Gelperin of the Monell Chemical Senses Center.
Fundingfor this research was provided by the U.S. Department of Energy, grantsto Penn's Laboratory on the Research of the Structure of Matter throughthe National Science Foundation and Monell.
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