A Sweat-Based On-Site Immunoassay for Monitoring Marijuana Use

A novel sweat-based skin test enables on-site testing for tetrahydrocannabinol (THC), the main psychoactive component found in marijuana plants (Cannabis).

This development was made in response to the increase in the number of states legalizing marijuana. This has left law enforcement in a situation where the use and consumption of the drug are legal, but there are no limitations for what is acceptable for driving or operating machinery. The prototype THC detector anticipates the formulation of laws restricting THC consumption by drivers and the need for the police to be able to detect abuse of the substance.

Investigators at University at Albany, State University of New York (USA) had already developed a sweat-based device for measurement of alcohol in the blood. The new device operates in a similar fashion but displays a color change when THC interacts with a specific antibody.

In the new assay system, the THC metabolite and an enzyme-labeled conjugate compete against each other as the antigens for the system. The antibody used in this assay has a greater affinity for the metabolite; so as its concentration increases, the absorbance of the system decreases due to reduced binding of the enzyme-labeled conjugate. Thus, the presence of THC in the sample inhibits the color change generated by the test, and the greater the amount of THC metabolite present in the sweat sample, the less color is produced by the test reagents.

“Currently there is a zero-tolerance policy when it comes to marijuana use and operating machinery,” said senior author Dr Jan Halámek, assistant professor of chemistry at the University at Albany. “While many states are moving to various stages of legalization, the focus is mostly on possession and in-home use. There are no reliable roadside devices being used to test for marijuana-impaired driving. What makes the use of sweat as a biometric unique is that it is non-invasive. No blood needs to be drawn for a sample. Our test can be done instantaneously, on the side of the road, which eliminates any possibility of tampering.”

“While drugs are a new topic for the Halámek lab, it is something we plan to continue diving into,” said Dr. Halámek. “Much of the fundamentals are the same as our previous research in terms of the collection, extraction, and use of sweat as a biometric.”

The THC sweat-based assay was described in the December 3, 2019, online edition of the journal ACS Sensors.

Related Links:
University at Albany, State University of New York