If a police officer suspects you're drink-driving, they can simply use a breathalyzer to get an accurate picture of your blood alcohol level right there and then. However, if a cop spots you driving suspiciously slow with half-closed red eyes, there's often no reliable and instantaneous method to see if you're stoned and potentially impaired.
But now, scientists from the University of Pittsburgh have developed a breathalyzer, just like a breathalyzer for alcohol, that can tell if a person is under the influence of marijuana with more accuracy than ever.
As reported in the journal ACS Sensors, the prototype device uses nanotechnology and machine learning to detect levels of tetrahydrocannabinol (THC), the psychoactive component of marijuana, left lingering in the user's breath.
A series of carbon nanotubes, some 100,000 times smaller than a human hair, pick up on volatile breath components, such as carbon dioxide, water, ethanol, and THC. If one of these components is blown down the nanotubes, it binds to their surface and changes their electrical properties. By analyzing the way the nanotubes react to electrical currents using machine learning, the device can detect the concentration of THC in a person's breath.
According to the team, the results are more accurate than mass spectrometry, which is considered “the gold standard” method for THC detection.
"The semiconductor carbon nanotubes that we are using weren't available even a few years ago," Sean Hwang, lead author from the Department of Chemistry at the University of Pittsburgh, said in a statement.
"We used machine learning 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."
Law enforcement agencies currently rely on blood, urine, or hair samples, often taken at a police station, to determine if a driver is under the influence of marijuana or any illegal substance. Currently used "roadside" marijuana detection tests have come under fire for providing grossly inaccurate results.
Conversely, this new technology could be used in the field to provide instant results. The device is currently just a prototype and requires some fine-tuning, but the researchers hope to make the breathalyzer available for real-world use soon.
Regardless of the technology’s accuracy, THC breathalyzers are still likely to cause contention if they're ever rolled out. As one study pointed out in February 2018, marijuana can affect people in totally different ways and the amount of THC in the body doesn’t necessarily correlate with how impaired a person's behavior is. While the same is also true for alcohol to some extent, the debate is much more complicated with marijuana.
"In legal states, you'll see road signs that say 'Drive High, Get a DUI', but there has not been a reliable and practical way to enforce that," added lab leader Dr Alexander Star, professor of chemistry. "There are debates in the legal community about what levels of THC would amount to a DUI, but creating such a device is an important first step toward making sure people don't partake and drive."