Sensors monitor chemical activity in exhaled breath

The nanofiber sensor developed at IITMadras can easily be integrated onto the base for wearables (IIT Madras).

Scientists at the Indian Institute of Technology (IIT) Madras have developed a nanofiber sensor that can detect minute variations in relative humidity levels in exhaled breath. The sensor, fabricated by a team led by Professor T. Pradeep from the Department of Chemistry at IIT Madras, can be integrated into wearable electronics and could help to assess human metabolism and calorie burn rates.

The sensor can also detect traces of ethanol and acetone, two major components present in the oral breath of alcoholics and diabetics, respectively.

The sensors respond in about one second and can detect a range of relative humidity from 0-95%. The sensor was found to be highly stable.

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“Even after exposing the sensor to ambient conditions for a week, we still found the response time to be about one second and could match the breathing rates quite effectively,” says Sathvik Ajay Iyengar, a member of the research team, in a statement. Iyengar was a short-term student with Professor Pradeep’s team and is one of the first authors of a paper published in the journal ACS Applied Electronic Materials.

The breath rate was measured for one-two hours prior to and after exercise. The heart rate is higher soon after exercise and this is reflected in higher breath rate. “We intend collecting breath rate over a period of few days to establish the relationship between heart and breath rate and metabolism,” says Pillalamarri Srikrishnarka from IIT Madras, the other first author of the paper.

The nanofiber mat is fabricated by electrospinning poly (vinylidene fluoride) and reduced graphene oxide. Coating the mat with polyaniline turns the mat into a sensor.

The moisture in the breath reduces the resistance of the sensing material, thereby allowing more current to flow. So, when a fixed voltage (1-2 volts) is applied to the sensor, there is more current that is detected when the sensor comes in contact with moisture in the breath.

When there are traces of ethanol and acetone in the breath, the resistance of the sensor increases, and conductivity reduces. Hence, there is a dip in the current measured from the baseline. “The reduction in conductivity is because of the absence of moisture — the hydrogen bond between the sensor and analyte [ethanol and acetone] is less likely to form,” Srikrishnarka says.

To make the sensor truly portable, the researchers are using the popular Arduino prototyping platform coupled with Bluetooth module to collect data wirelessly.

“We initially tested the sensor performance using an Arduino Uno, and we observed a good response. We intend to team up with other departments to recognize patterns by using machine learning and to develop mobile-friendly apps to monitor health,” says IIT Madra’s Professor Pradeep. The team plans to take the work forward via startup initiatives.

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