Biosensors That Don’t Get Bent Out of Shape
This wearable biosensor uses twin transistors to cancel noise from heat and stretching for real-time, drift-free tracking of biomarkers.
Whatever problems you may have had at work this week, you can at least take comfort in knowing that you don’t have to deal with the frustration of developing wearable biosensors (unless that is your job, in which case there’s always the inevitable heat death of the universe to look forward to). These biosensors, which convert physiological signals into electrical signals, have the potential to dramatically improve human health through continuous monitoring and sharing data with medical professionals.
But before any of that can happen, people will have to actually choose to wear these devices all day long. And for that to happen, they will need to be soft and comfortable to wear. Therein lies the rub: stretchy, flexible sensors pick up lots of noise, rendering the measurements they collect of limited value. Add in the fact that the human body, with its heat and moisture, already throws off sensors, and you’ve got quite the problem.
It is a problem that a multidisciplinary group of researchers at Stanford University believes they can overcome, however. They have developed a skin-like material that can comfortably be worn against the skin for long periods of time. This material has been paired with a unique arrangement of biosensors that can continuously collect important biological data. And crucially, these measurements are not thrown off by factors like stretching, moisture, and heat.
The team designed their new sensors around organic field-effect transistors (OFETs), a class of devices made from organic semiconductors that control the flow of electric current. OFETs are attractive for wearable electronics because they are lightweight, flexible, and can conform closely to the skin. Unfortunately, these same advantages also make them susceptible to environmental interference. To solve this, the researchers engineered a twin transistor architecture that cancels out noise before it becomes a problem.
Each OFET in the new system is built to be identical, and two of them are positioned side by side. Because the two transistors experience the same environmental conditions, they drift in the same way. By electrically linking them, the shared noise signals cancel each other out, leaving behind only the true biological signal of interest. The resulting device is a soft, stretchable, drift-free biosensor capable of detecting biomarkers in real time, even as it bends and flexes with the wearer.
Tests showed that the new biosensor design reduced signal distortion by more than two orders of magnitude, even under extreme conditions such as stretching up to 100%, compression, and temperature fluctuations between 25 degrees C and 40 degrees C. In practical trials, the sensors successfully measured key biomarkers like glucose, sodium, and cortisol from human sweat.
To demonstrate real-world potential, the team integrated the biosensor into a flexible circuit that communicates wirelessly with a smartphone app. This setup allows real-time monitoring of stress and metabolism biomarkers directly from sweat, opening the door to wearable systems that can detect early signs of illness or mental distress.
Looking forward, the team hopes to go even further by creating fully integrated electronic skin systems that combine sensors, power, and wireless transmission into one package. If successful, the future of health tracking could be more of a part of you than you might think.