The report will appear in the Nov. 15 edition of Analytical Chemistry, a peer-reviewed journal of the American Chemical Society, the world's largest scientific society.

"Our technology provides a hand-held sensing device capable of real-time detection, reducing the time between drug seizure and laboratory analysis," says Desmond Stubbs, a doctoral candidate in chemistry working under the direction of William Hunt, Ph.D., a professor of electrical engineering at Georgia Tech in Atlanta.

The sensor, which performed well in the lab and in a field test with the Georgia Bureau of Investigation, is "an elegant fusion of biotechnology and microelectronics," according to Hunt. This combination of disciplines makes the sensor superior to previous "electronic noses." The U.S. government will spesnd more than $19 billion this year in the war on drugs, according to the Office of National Drug Policy. Police dogs are important tools in this battle; their highly developed olfactory systems can detect small molecules in the part-per-billion range.

But using dogs has its drawbacks. They require expensive handlers to train and care for them, and the seized drugs must still be sent to the lab for further analysis ¿ adding trained technicians and costly lab equipment to the tab.

Plus, scientists still don't know exactly what chemicals the dogs are sensing, allowing for significant variations from one dog to the next. Dogs also have trouble detecting specific drug targets in the presence of other odors, such as coffee grounds. "Unfortunately, the illicit drug traffickers are aware of this and invariably mask their product with different chemicals to evade authorities," Stubbs says.

The new device addresses all of these issues.

Two key features of any vapor-sensing tool are sensitivity and specificity. Sensitivity is the ability to detect very small amounts of a chemical. Specificity is the ability to differentiate a certain chemical from a group of many similar ones (e.g., cocaine from coffee grounds).

The dog-on-a-chip can sense cocaine at a few trillionths of a gram. This sensitivity is achieved through surface acoustic wave (SAW) electronics, a method of detecting a chemical by measuring the disturbance it causes in sound waves across a tiny quartz crystal. This is a fairly common analytical method, and it has been used in other electronic noses, but by itself it does not address the problem of specificity.

The new chip goes a step further by incorporating monoclonal antibodies ¿ cloned copies of proteins called antibodies that the immune system produces to fight foreign invaders. The researchers used anti-benzoylecgonine (anti-BZE) in the device because it differs only slightly in structure from cocaine, allowing it to bind preferentially to that molecule.

The SAW sensor is coated with a thin layer of anti-BZE. When a vapor sample passes through, cocaine molecules attach to anti-BZE molecules, causing a disturbance in the sound waves on the quartz crystal that is detected as an electrical signal.

"We are the first group to use specific antibodies to differentiate similar sized molecules in a complex vapor sample," Hunt says. This gives the dog-on-a-chip an advantage over its canine competitors and other electronic devices. It will also be significantly cheaper and less time-consuming by removing many of the steps from the current detection protocol.

The new device was carefully calibrated in a laboratory setting, and then it was put to the test in the field. "In field tests conducted at the Georgia Bureau of Investigation, we were able to detect cocaine obtained during an actual drug seizure," Stubbs says. "By simply drawing the vapor through our prototype device, we got a positive detection in a matter of seconds."

The ability to detect and identify small, non-volatile molecules like cocaine based on their electronic vapor signature could also be used in airports and other locations to detect explosives and chemical warfare agents, according to the researchers.

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