Can a simple sweat sensor replace blood tests? – Physics World

Physics

Senior author Wei Gao monitors a volunteer wearing flexible sweat sensors while exercising. (Courtesy: Caltech)

An international team of scientists has developed an affordable microfluidic-based sensor able to track variations in levels of metabolites and nutrients in a patient’s blood simply by analysing their sweat. The device could be used to diagnose and monitor a wide spectrum of conditions, with an emphasis on gout (Nature Biotechnol. 10.1038/s41587-019-0321-x).

If you suffer from trypanophobia (the fear of needles), then fear not, as technological help is on the way. While blood sampling used to be the only accurate way to monitor key metabolites such as tyrosine and uric acid (UA), important indicators of metabolic disorders and gout respectively, it might soon be possible to obtain the same information from a wearable sensor. No need to have a needle stuck in your arm anymore.

The device is the result of a cooperation between American and Chinese researchers from Caltech, Peking University, Santa Clara University, Princeton University and UCLA. It contains microfluidic channels and graphene biosensors engraved onto plastic sheets by a low-cost carbon dioxide laser.

Yiran Yang and Wei Gao

This design makes the sensor easy to manufacture and enables the monitoring of small concentrations of sweat compounds. In contrast, existing prototypes can only target compounds appearing in high concentration in sweat, such as electrolytes, glucose and lactate. The sensor can also record respiratory rate, heart rate and temperature and transfer all data via Bluetooth.

“Such wearable sweat sensors have the potential to rapidly, continuously and noninvasively capture changes in health at molecular levels,” lead author Wei Gao says. “They could enable personalized monitoring, early diagnosis and timely intervention”.

A battery of tests

To see how well the sensor performed, the researchers compared data collected in healthy individuals and patients. For example, since tyrosine is influenced by physical fitness, they compared their levels in five trained athletes and five physically untrained subjects, and observed that the sensors showed lower levels of tyrosine in the sweat of the athletes.

The team was particularly interested in using the device to monitor gout, which is characterized by high levels of UA in the body that begin to crystallise in joints, causing irritation and inflammation. By monitoring UA levels in six healthy individuals initially subjected to fasting conditions and later fed with a meal rich in purines – compounds that metabolise into UA – the researchers observed that UA levels peaked in all of them after eating.

They similarly found that four subjects with hyperuricemia and six untreated patients with gout had higher sweat UA levels two hours after a regular meal than five healthy subjects, confirming the sensor’s ability to pick up variations in UA. Its accuracy also proved excellent, as UA levels derived from sweat were very closely related to those found in the blood serum in 46 biologically independent samples.

Informing patients’ health

Although the sensor has only been used in small samples and needs to be tested prospectively to noninvasively monitor disease development, the study holds promise. With its high sensitivity, ease of manufacture and Bluetooth connectivity, the sensor offers the potential to mass-produce a reliable alternative to needles that will allow patients to have real-time information about their health. Ideally, this would even allow them to adjust their own medication levels and diet as required.

“Considering that abnormal circulating nutrients and metabolites are related to a number of health conditions, the information collected from such wearable sensors will be invaluable for both research and medical treatment,” Gao concludes.

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