As recreational marijuana legalization becomes more widespread in the U.S., so has concern about what that means for enforcing driving-under-the-influence (DUI) laws. Unlike a breathalyzer used to detect alcohol, police do not have a device that can be used in the field to determine if a driver is under the influence of marijuana.

Researchers have developed a breathalyzer device that can measure the amount of tetrahydrocannabinol (THC), the psychoactive compound in marijuana, in the user's breath. Current drug testing methods rely on blood, urine, or hair samples and cannot be done in the field. They also only reveal that the user has recently inhaled the drug, not that they are currently under the influence.

The breathalyzer was developed using carbon nanotubes. The THC molecule, along with other molecules in the breath, binds to the surface of the nanotubes and changes its electrical properties. The speed at which the electrical currents recover then signals whether THC is present. Nanotechnology sensors can detect THC at levels comparable to or better than mass spectrometry, which is considered the gold standard for THC detection.

Machine learning was used to teach the breathalyzer to recognize the presence of THC based on the electrical currents’ recovery time, even when there are other substances like alcohol present in the breath.

The prototype looks similar to a breathalyzer for alcohol with a plastic casing, protruding mouthpiece, and digital display. It was tested in the lab and shown to detect the THC in a breath sample that also contained components like carbon dioxide, water, ethanol, methanol, and acetone.

For more information, contact Deborah Todd at This email address is being protected from spambots. You need JavaScript enabled to view it.; 412-624-6687.

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This article first appeared in the February, 2020 issue of Tech Briefs Magazine.

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