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Headway On Next-Gen Skin Gas Sensing For Metabolic Diseases

By Deborah Borfitz

May 5, 2022 | An interdisciplinary team of researchers at The Ohio State University (OSU) is creating a “new paradigm for personalized medicine” with a skin gas sensing device for monitoring metabolism and managing weight, according to lead scientist Pelagia-Iren (Perena) Gouma, professor of materials science and engineering. The work is being funded by the National Science Foundation’s Smart and Connected Health program seeking to catalyze scientific and engineering innovations.

The novel sensor, recently described in an article published in PLOS ONE (DOI: 10.1371/journal.pone.0267311), meets all the must-have performance criteria, says Gouma. It’s highly sensitive and selective for gaseous acetone—known to be related to blood sugar levels and fat-burning rates—as well as easy and inexpensive to make.

“There’s nothing comparable on the market because all the other technologies under development for studying metabolites are looking for enzymes or measure electrolytes,” she says. “For skin gas sensing in the absence of sweat there is hardly any portable standalone detection technology available.” The widely used SCRAM (secure continuous remote alcohol monitoring) system, which is a sensor in an ankle bracelet worn by some newly released prisoners, is old and unrelated technology that tests both sweat and gas over the skin.

One of the first envisioned applications for the new skin gas sensor is to monitor metabolic rate changes to indicate when individuals are, for example, burning fat or muscle during exercise or have a metabolic disorder such as heart disease or diabetes, Gouma says. The best part is that the device is noninvasive and nonintrusive. “You don’t have to think about it, you don’t have to cautiously follow it, it is just going to let you know you need to take medication or stop this exercise so you can regulate the calories you burn effectively for this week.”

In the latest study, the sensor was found to be much more sensitive to acetone than ethanol (alcohol). The addition of water (sweat) also variably affected the sensitivity, selectivity, and repeatability of device readouts, making it best suited to low-sweat body locations such as behind the ear or on the nails.

As envisioned, the next-gen health sensor will adhere to the skin as a strip to continuously monitor the concentration of acetone in people with metabolic disorders. “Although the skin is not breath, it has good quantification of these gases,” she notes.

Bending Response

Components of the wearable sensor most notably include a patented chemo-mechanical actuator, a polyaniline-cellulose acetate (PANI-CA) composite film that bends upon exposure to gaseous acetone, Gouma continues. PANI is known to exhibit intrinsic electrical conductivity and is combined with CA to give the sensing material more robust mechanical properties and to fine tune the sensing response.

Scientists have previously used conducting polymers, such as PANI, to create artificial muscles, she notes. But until now, “nobody has used that to make chemical actuators for the selective detection of gases that can be biomarkers of disease or metabolic disorders.”

The research team plans to interface the sensor with a transducer to correlate the bending response with an electrical signal that can be sent wirelessly to a smartphone or other device where individuals could track changes to these metabolites over time based on their preferred threshold, says Gouma. For a person with diabetes, for example, an acetone level over 500 parts per billion would signal the need for insulin. 

OSU colleagues outside of her lab and collaborators at Rutgers are developing the electronics for wirelessly transmitting the signals, and the packaging to keep out environmental interferences, respectively, she explains. Co-principal investigator Manoj Srinivasan, OSU associate professor of mechanical and aerospace engineering, contributed the machine learning tools to expedite validation of the testing methodology offering new metrology.

Anthony Annerino, lead author of the latest study and an OSU graduate student in materials science and engineering, is credited with making and validating the sensing material as well as optimizing the process.

Fast Track To Market

Clinical testing of the device, expected to begin within the next six months, will initially focus on obesity, says Gouma. Study participants will be people intending to lose weight via diet and exercise who will be wearing the sensor to monitor changes to their metabolism and receiving personalized feedback from a facilitator about their specific metabolic pattern (including carbon dioxide and oxygen as well as acetone) to individualize their experience.

For up to one year, the study will track 20 subjects who have been fitted with a continuous acetone monitor and Fitbit-like activity monitor, she says. Their diet will be followed based on self-reporting and a smartphone app (MyFitnessPal), and before-and-after body fat will be measured. Eligibility criteria includes being between the ages of 18 ad 60 and excludes pregnant women and anyone with a movement disorder or cardiovascular issues.

The sensor will thereafter be similarly used in the study of different diseases, simply by modifying the material to target the analyte of interest, Gouma says. In addition to acetone, the OSU research team is looking at applications of the device for sensing ethanol (biomarker for liver disease), isoprene (biomarker for sleep apnea), and ammonia (biomarker for renal diseases) ambiently emitted from the skin. “Skin odor is cleaner than breath print,” she notes, “as it is filtered through the dermal layer and skin gas is released in amounts controlled by the autonomous nervous system so its concentration in not under the subject’s control.”  

Gouma has been working on personalized diagnostics for about two decades now and was the first to develop a breathalyzer test to diagnose COVID-19 in critically ill patients (PLOS ONE, DOI: 10.1371/journal.pone.0257644). It was the first such device to seek Emergency Use Authorization from the U.S. Food and Drug Administration, and her team continues to work on meeting the agency’s specifications for the technology, she says.

Most of her previous work has involved tracking the concentration of organic compounds in the breath as indicators of health, including breathalyzers for measuring the amount of alcohol in the blood or to detect viruses. But unlike the new skin gas sensing device, such gadgets require active intent and only provide a momentary snapshot of the body. The also operate on the much larger volume of chemicals released with breathing.

Gouma says she expects the device will quickly make its way to market. In the spirit of open science, she and her colleagues have transparently published all their discovered biomarkers, machine learning algorithms, and study methodologies so they can be reproduced. “Our intent is to spread knowledge and promote science and technology,” she says. 

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