Police dogs in the US could soon be out of work, replaced by an electronic ‘dog-on-a-chip’ that sniffs out cocaine and other narcotics.
Scientists at the Georgia Institute of Technology (Georgia Tech) have created a new detection tool that is portable, inexpensive, and doesn’t require feeding or grooming. They say it is superior to previous ‘electronic noses’ designed for this purpose.
‘Our technology provides a hand-held sensing device capable of real-time detection, reducing the time between drug seizure and laboratory analysis,’ said 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 has 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 is said to make the sensor superior to previous ‘electronic noses.’
The US government will spend 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 because 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 odours, 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 said.
The new device reportedly addresses all of these issues.
Two key features of any vapour-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.
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, which are cloned copies of proteins (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 vapour 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 vapour 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 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 vapour through our prototype device, we got a positive detection in a matter of seconds.’