Wearable Electronic Sweat Sensor Detects Health Biomarkers

The landscape of modern medicine and the way we monitor our health is changing. A technological revolution has taken place over the last few decades, where electronic devices shrunk from being large – and quite ugly – apparatuses to impressively small and discreet mini devices, almost in the blink of an eye. Electronic sensors can now be miniaturized into wearable health devices (WHDs), commercialized to provide various health measures – including vital signs and sleep hygiene – at the click of a button on an accessory such as a watch.

Certain physiological conditions, such as exercise, illness or temperature cause fluctuations in the data, which can be detected in real-time via the sensor, placing an individual at the center of their health and wellness.¹ However, commercially available WHDs shed very little information on the intrinsic changes that occur within the body.

Metabolic markers, such as electrolytes and other biological molecules collected via bodily fluids, provide a more direct indicator of homeostasis. Recent advances in the suite of analytical technologies typically adopted in omics research – such as mass spectrometry – enable scientists to identify small molecular changes that occur in cells and tissues at a higher sensitivity and speed than ever before. But this data collection is not in real-time, is complex and often requires an invasive procedure to collect the sample

The insights offered by a WHD able to collect and store real-time information on biological, molecular changes are applicable to numerous areas of human health and lifestyle. In a clinical context, for example, this information could provide clinicians with a more holistic view of an individual's health. In sports training, the data could be used to personalize and tailor training programs for specific athletes.

In 2019, Technology Networks interviewed Professor Emanuel Petricoin – a pioneer of proteomics research – about the future of the field. He discussed his expectations that omics will be "less about the detection methods" and more about "stitching those detection methods into practical applications that we see in our everyday life", such as "wearable devices that can sense the environment" or nanosensors "implanted inside the body".

Petricoin's prediction was correct. Engineers at Tufts University have shared their research in developing a flexible electronic sensing patch that analyzes sweat for a variety of biological markers, including sodium, ammonium, pH and lactate, directly from sweat and in a band format that can be sewn on to clothing. The study is published today in npj Flexible Electronics.²

A unique use for a band aid

The sensor platform is built as a patch where threads are placed on to the fabric gauze of a commercial bandage, the gauze enabling sweat transport from the sensing area on the patch to the reverse side of the patch for evaporation. However, the gauze edges are sealad to prevent sweat evaporating from the sensing area.

Sweat is wicked at the sensor surface for real-time measurement, and the threads connect to wireless readout electronics that permit real-time data acquisition and collection for detection and sensing of the biomarkers. The open-access paper in npj Flexible Electronics provides a visual aid for understanding the sensor platform.

Urine and blood are bodily fluids commonly adopted for health monitoring; it's quite rare you visit a physician and are asked to provide a bottle of sweat for clinical analysis. So why is the ability to analyze sweat useful?

"Sweat is a useful fluid for heath monitoring since it is easily accessible and can be collected non-invasively," Trupti Terse-Thakoor, formerly a post-doctoral scholar at Tufts University School of Engineering and first author of the study, said in a press release. "The markers we can pick up in sweat also correlate well with blood plasma levels which makes it an excellent surrogate diagnostic fluid."

Terse-Thakoor and colleagues decided to test the patch in human subjects to monitor their electrolyte and metabolic response to exercise. A total of seven participants, including male and females that were diverse in fitness abilities and had no dietary restrictions, were involved. The sensor was applied to their skin before they underwent a minimum of 30 minutes exercise either on a stationary bike, or a treadmill run. Throughout the exercise period, the sensors detected fluctuations in the analytes within five to 30 second intervals, a time-period which aligns with commercially available real-time monitoring technologies.

The analyte levels fluctuated as a function of oxygen uptake, measured in a test of the subjects’ maximum oxygen uptake which is regarded as the "gold standard" test for physical fitness.

Part of a larger strategy

The study provides proof of feasibility, but lacks strict standardized measurements and statistically validated data at this point. The authors nod to this in their discussion write-up, and suggest that this will be the next step for development of the sensor: "The sensors can be statistically validated for their effectiveness in real-time continuous measurements of multiplexed biomarkers in the context of underlying clinical trials in lieu of sparse standardized measurements."

The sensor patch developed by the researchers is part of a "larger strategy" that will make "completely flexible thread-based electronic devices", according to Sameer Sonkusale, professor of electrical and computer engineering at Tufts' School of Engineering and corresponding author of the study.

Is electronic-based clothing as a health device futuristic, or will it be here sooner than we think? The “still emerging” technology behind it, and research projects such as Terse-Thakoor and colleagues’ study have many hurdles to overcome, but as Dias and Cunha write in their review Wearable Health Devices—Vital Sign Monitoring, Systems and Technologies: They [WHDs] are expected to "overcome their challenges" and enter in the consumer market "with a higher impact in the following years."¹

References:

1.     Dias and Cunha. (2018). Wearable Health Devices—Vital Sign Monitoring, Systems and Technologies. Sensors. DOI: 10.3390/s18082414.

2.     Terse-Thakoor et al. (2020). Thread-based multiplexed sensor patch for real-time sweat monitoring. npj Flexible Electronics. DOI: https://doi.org/10.1038/s41528-020-00081-w.