Mouth guard sensor monitors saliva for signs of illness and stress

The proof-of-concept technology monitors health markers including lactate, cortisol and uric acid and could be used to non-invasively monitor patients, or provide indications of stress levels in soldiers and pilots. The research is detailed in a paper published in Biosensors and Bioelectronics.

“The ability to monitor continuously and non-invasively saliva biomarkers holds considerable promise for many biomedical and fitness applications,” said Joseph Wang, a nanoengineering professor who led the research with electrical engineering professor Patrick Mercier.

Saliva

In a study to test the sensors, engineers focused on uric acid, which is a marker related to diabetes and gout. Currently, the only way to monitor the levels of uric acid in a patient is to draw blood.

To test the mouth guard, researchers collected saliva samples from healthy volunteers and spread them on the sensor, which produced readings in a normal range.

Next, they collected saliva from a patient who suffers from hyperuricemia, a condition characterized by an excess of uric acid in the blood. The sensor detected more than four times as much uric acid in the patient’s saliva than in the healthy volunteers.

The patient also took Allopurinol to treat his condition. Researchers were then able to document a drop in the levels of uric acid over four or five days as the medication took effect. Previously, the patient would have needed to provide a blood sample to monitor levels and relied instead on symptoms to start and stop the medication.

Fabrication

To fabricate the mouth guard sensor, Wang created a screen-printed sensor using silver, Prussian blue ink and uricase, an enzyme that reacts with uric acid. Saliva is extremely complex and contains many different biomarkers, so researchers needed to make sure that the sensors only reacted with the uric acid. Nanoengineers set up the chemical equivalent of a two-step authentication system.

The first step was a series of chemical keyholes, which ensures that only the smallest biochemicals get inside the sensor. The second step involved a layer of uricase trapped in polymers, which reacts selectively with uric acid. The reaction between acid and enzyme generated hydrogen peroxide, which is detected by the Prussian blue ink.  The information was then transmitted to an electronic board as electrical signals via metallic strips that are part of the sensor.

The electronic board, developed by Mercier’s team, used small chips that sense the output of the sensors, digitises this output and then wirelessly transmits data to a smart phone, tablet or laptop. The entire electronic board occupies an area slightly larger than a penny.

The electronics will now be embedded inside the mouth guard so that it can be worn.

The researchers are yet to test the materials used for the sensors and electronics to make sure that they are indeed completely biocompatible. Mercia estimates the next iteration of the mouth guard will be ready in a year. “All the components are there,” he said in a statement. “It’s just a matter of refining the device and working on its stability.”