Tufts researchers develop dental floss sensor for real time stress monitoring

Chronic stress can lead to increased blood pressure and cardiovascular disease, decreased immune function, depression, and anxiety. Unfortunately, the tools we use to monitor stress are often imprecise or expensive, relying on self-reporting questionnaires and psychiatric evaluations. 

Now a Tufts interdisciplinary engineer and his team have devised a simple device using specially designed floss that can easily and accurately measure cortisol, a stress hormone, in real time.

It started in a collaboration with several departments across Tufts, examining how stress and other cognitive states affect problem solving and learning. We didn't want measurement to create an additional source of stress, so we thought, can we make a sensing device that becomes part of your day-to-day routine? Cortisol is a stress marker found in saliva, so flossing seemed like a natural fit to take a daily sample."

Sameer Sonkusale, professor of electrical and computer engineering

Their design of a saliva-sensing dental floss looks just like a common floss pick, with the string stretched across two prongs extending from a flat plastic handle, all about the size of your index finger. The saliva is picked up by capillary action through a very narrow channel in the floss. The fluid is drawn into the pick handle and an attached tab, where it spreads across electrodes that detect the cortisol. 

Cortisol recognition on the electrodes is accomplished with a remarkable technology developed almost 30 years ago called electropolymerized molecularly imprinted polymers (eMIPs). They work similarly to the way you might make a plaster cast of your hand. A polymer is formed around a template molecule, in this case cortisol, which is later removed to leave behind binding sites. These sites have a physical and chemical shape "memory" of the target molecule so they can bind free-floating molecules that are coming in. 

The eMIP molds are versatile, so one can create dental floss sensors that detect other molecules that can be found in saliva, such as estrogen for fertility tracking, glucose for diabetes monitoring, or markers for cancer. There is also potential for detecting multiple biomarkers in saliva at the same time, for more accurate monitoring of stress, cardiovascular disease, cancer, and other conditions. 

"The eMIP approach is a game changer," said Sonkusale. "Biosensors have typically been developed using antibodies or other receptors that pick up the molecule of interest. Once a marker is found, a lot of work has to go into bioengineering the receiving molecule attached to the sensor. eMIP does not rely on a lot of investment in making antibodies or receptors. If you discover a new marker for stress or any other disease or condition, you can just create a polymer cast in a very short period of time."

Accuracy of the cortisol sensors is comparable to the best-performing sensors on the market or in development. Bringing this device into the home and in the hands of individuals without need for training will make it possible to fold stress monitoring into many aspects of health care. Currently Sonkusale and his colleagues are creating a startup to try and bring the product to market.

He points out that while the dental floss sensor is quantitatively highly accurate, the practice of tracking markers in saliva is best for monitoring, not for the initial diagnosis of a condition. That's in part because saliva markers can still have variations between individuals.

"For diagnostics, blood is still the gold standard, but once you are diagnosed and put on medication, if you need to track, say, a cardiovascular condition over time to see if your heart health is improving, then monitoring with the sensor can be easy and allows for timely interventions when needed," he says.

The new research, published in the journal ACS Applied Materials and Interfaces, adds to a number of thread-based sensor innovations by Sonkusale and his research team including sensors that can detect gases, metabolites in sweat, or movement when embedded in clothing and transistors that can be woven into flexible electronic devices.