A device may change the way police in Tennessee and around the country test for impaired driving. Researchers at Stanford University have used magnetic biosensors to test for the presence of THC in saliva. THC is the most potent psychoactive chemical in marijuana. Law enforcement screening for THC had been dependent upon urine or blood tests, but both pose problems in terms of proving intoxication at the time the sample is drawn.

Some states have already established limits of zero to five nanograms per milliliter of blood and more than 20 states allow cannabis use in some form. Several other states are scheduled to vote on the issue of marijuana legalization in November 2016. The Stanford research team is hopeful the device, sometimes referred to as the potalyzer, will gauge marijuana intoxication as effectively, noninvasively and efficiently as a breathalyzer measures alcohol intoxication.

Studies have indicated an intoxicated-driving cutoff of between two and twenty-five nanograms of THC per milliliter of saliva. The potalyzer device, using a process called immunoassay, can detect the presence of THC in saliva from zero to fifty nanograms per milliliter. Immunoassays measure the concentration of a particular molecule by using an antibody that binds only to that molecule. In the case of the potalyzer, the antibody binds to THC.

In the future, law enforcement may use the potalyzer or other devices equipped with magnetoresistive sensors to screen for the presence of marijuana or other drugs. The Stanford team has already reported promising results screening for morphine, for example. Individuals who have been charged with operating under the influence of marijuana may want to speak with their attorneys to see if the test results produced by the device can be subjected to a challenge.