For most people, sweat is an unwelcome part of their day. In Jan Halamek’s laboratory, it’s an important biometric research tool and sample.
The Halámek Lab at the University of Albany is well-known for its contributions to forensic science. The lab has been funded through numerous fellowships and a three-year grant from the Department of Justice and National Institute of Justice to develop non-invasive sensing concepts for law enforcement. The latest two sweat-based innovations do just that.
First, Halámek and his colleagues developed strips that can test the ethanol levels in a person’s sweat to detect their blood alcohol content (BAC)—essentially, a sweat-testing strip that works like a breathalyzer.
The chemistry of the strip relies on two enzymes, alcohol oxidase and horseradish peroxidase. Once the strip comes into contact with an individual, the chemical reaction of the two enzymes to the ethanol in sweat produces a visible color change. The higher concentration of alcohol present, the darker the color intensity.
“There's a direct relationship between ethanol in blood and sweat," Halámek told Laboratory Equipment. "Through our research, we have shown that as an individual consumes alcoholic beverages, their blood alcohol levels increase at a similar pace to sweat alcohol levels.”
As proof of concept, Halámek’s lab led a controlled drinking study with 26 volunteers. After the study participants consumed several shots of 40 percent vodka to obtain 0.08 percent BAC, more than 100 readings were compared between a professional grade breathalyzer and the sweat sensing strip. The sweat samples showed a strong correlation with the breathalyzer readings, according to results published in a paper in Analytical Chemistry.
While there is a printed color legend for use, Halámek’s lab is also working with the university’s Department of Computer Science to develop a smartphone application that would perfectly match the test strip’s color change to BAC level.
“A smartphone application will ideally take out any subjectivity from the user,” Halámek said. “Although the responses are visible by naked eye, the changes in shade of color can be difficult to distinguish. Using an app will also regulate the response from different users and record the report.”
Marijuana use test
On the heels of their sweat-based ethanol detector, researchers at the Halámek Lab created another strip that can detect a person’s marijuana use based on a small amount of perspiration that can be taken from fingerprints or any other sweat glands.
Just like the alcohol test strip, the marijuana-use strips rely on a color change to visually confirm the presence or absence of tetrahydrocannabinol, or THC, the main psychoactive component in cannabis. The analysis works by using an antibody that quantifies the THC metabolite. Less of a color change indicates a higher amount of THC metabolite present in the sweat sample.
In a proof-of-concept test, Halámek and his team of graduate students surveyed eight volunteers on their recent marijuana use. Four were users; four were non-users. The group then provided their fingerprints on a plastic wrap that was cut out and subject to analysis. Results showed a clear difference in observed color change between the two groups.
The test was designed to give a Yes/No answer on the presence of marijuana as the national law is currently zero-tolerance for marijuana use when operating machinery. As recreational marijuana continues to gain approval at the state level, those laws could change. However, Halámek said the test can be modified to be quantitative. Before it gets to that level, there is a lot science still has to figure out. For example, studies have shown that marijuana can be detected in an individual’s body long after the effects of the “high” have worn off. What if the sweat test accurately shows a person used marijuana, but it was the night before and impairment is no longer an issue? Unlike a person’s blood alcohol level, marijuana “levels” are not as straightforward.
Halámek said his lab is already looking in this direction, and is seeking collaborators regarding the pharmacokinetics of THC.
“While drugs are a new topic for the Halámek lab, it is something we plan to continue diving into,” Halámek said. “Much of the fundamentals are the same as our previous research in terms of the collection, extraction, and use of sweat as a biometric.”
Photo: The Halámek lab showcases a prototype of its sweat testing strip. Credit: Scott Freedman/UAlbany