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The National University of Singapore Demonstrates the Benefit of Oximeters For Medical Applications and Wearables

January 27, 2020 by Luke James

A team of researchers from the National University of Singapore has created a new low-power, responsive, and reusable sweat pH monitor that they have prototyped as a ‘pH Watch’ add-on for wearable health monitors.

Researchers from the National University of Singapore (NUS) have developed a low-power, responsive, and reusable upgrade to wearable health monitors that is capable of reading the pH of sweat produced by its wearers. 

Named the pH Watch, it can be incorporated into current smartwatches, fitness trackers, and other devices to track the acidity or alkalinity of wearers’ sweat, along with blood oxygen concentration and heart rate in real-time. To do this, the researchers integrated their custom pH sensor and sensing algorithm into gadgets that feature pulse oximeters. 


Flexible and Highly Responsive

Pulse oximeters, which are found in many smartwatches and fitness devices, consist of red and infrared light sensors and sit between the skin and the device. They emit visible red and invisible infrared lights onto the wearers’ skin. By doing this, they are able to calculate the difference between the two lights’ wavelengths to determine blood oxygen content. 

A classic example of pulse oximeters being used outside smartwatches and fitness tech includes the small white clips that are placed on the top of patients’ index fingers in hospitals. 

To create more use cases for these oximeters, the NUS team created a flexible and responsive pH sweat sensor. It is made using a material that changes color when it comes into contact with a different sweat pH, just like litmus paper does. However, the sensor’s color changes are designed to match the recording capabilities of the pulse oximeter. By integrating their custom-made pH sensor and algorithms into existing devices with pulse oximeters, it can monitor the pH values of the end-users sweat, along with heart rate and blood oxygen saturation, with around 90% accuracy.

Designed and fabricated using polyaniline polymer, the pH sensor is inexpensive and durable while also being very flexible, allowing it to conform to the skin. It requires only 20KB of RAM for data processing and is power efficient, not requiring a power source, while the pH sensing algorithm uses under 0.01% of the total power consumption of a standard smartwatch. 


National University of Singapore researchers.

National University of Singapore (NUS) researchers responsible for developing the 'pH Watch', an add-on to wearable health monitoring gadgets. Image Credit: The National University of Singapore. 


Potential Applications for the Medical Field

Mr. Ananta, the developer of the pH sensing algorithm, said, “The pH sensor can be readily mounted atop any wearable with a pulse oximeter. It can take any form — an armband, chest strap or headband — but we have developed a watch-like wearable prototype because of the popularity of wrist-worn wearables among users. The potential use of our pH Watch is not only limited to athletes; it could be used by any user as we would sweat during daily activities like walking or running. Also, because of its non-invasive nature, it could be used as a personal health monitoring device for seniors and children.”

The NUS sensor and its easy integration into a wide range of devices, both fitness, and non-fitness related, pave the way for ubiquitous sensing of biomarkers. Medical devices especially could benefit from their use, and there is potential for the technology demonstrated here to lead to the development of various wide-reaching monitoring solutions in medicine. 

The team is currently investigating other biomarkers in sweat and exploring the use of other existing sensors to detect more sweat biomarkers.

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