Wei Gao

New Wearable Sensor Detects Gout and Other Medical Conditions

Dec. 6, 2019
Sensor can pick up small concentrations of metabolites in sweat and provide readings over long periods of time.

A Cal Tech researcher team led by Wei Gao, a professor of biomedical engineering, developed a wearable sensor that monitors levels of metabolites and nutrients in a person’s blood by analyzing their sweat. Previous sweat sensors mostly targeted compounds that appear in high concentrations, such as electrolytes, glucose, and lactate. This new one is more sensitive and detects sweat compounds at much lower concentrations. It is also easier to manufacture and can be mass-produced.

The team’s goal is a sensor that lets doctors continuously monitor the condition of patients with illnesses such as cardiovascular disease, diabetes, and kidney disease, all of which put abnormal levels of nutrients or metabolites in the bloodstream. Patients would be better off if their physician knew more about their personal conditions and this method avoids tests that require needles and blood sampling.

“Such wearable sweat sensors could rapidly, continuously, and noninvasively capture changes in health at molecular levels,” Gao says. “They could make personalized monitoring, early diagnosis, and timely intervention possible.”

The sensor relies on microfluidics which manipulates small amounts of liquids, usually through channels less than a quarter of a millimeter in width. Microfluidics are well-suited ideal for an application because they minimize the influence of sweat evaporation and skin contamination on sensor accuracy. As freshly supplied sweat flows through the sensor’s microchannels, it accurately measures the composition of the sweat and captures changes in concentrations over time.

Until now, Gao and his colleagues say, microfluidic-based wearable sensors were mostly fabricated with a lithography-evaporation approach, which requires complicated and expensive fabrication processes. His team opted to make its biosensors out of graphene, a sheet-like form of carbon. Both the graphene-based sensors and microfluidics channels are created by engraving the plastic sheets with a carbon dioxide laser, a device so common it is available to home hobbyists.

The research team designed its sensor to also measure respiratory and heart rates, in addition to levels of uric acid and tyrosine. Tyrosine was chosen because it can be an indicator of metabolic disorders, liver disease, eating disorders, and neuropsychiatric conditions. Uric acid was chosen because, at elevated levels, it is associated with gout, a painful joint condition that is on the rise globally. Gout occurs when high levels of uric acid in the body begin crystallizing in the joints, particularly those of the feet, causing irritation and inflammation.

To see how well the sensors performed, researchers tested it on healthy individuals and patients. To check sweat tyrosine levels which are influenced by a person's physical fitness, they used two groups of people: trained athletes and individuals of average fitness. As expected, the sensors showed lower levels of tyrosine in the athletes’ sweat. To check uric acid levels, the researchers monitored the sweat of a group of healthy individuals that was fasting, and also after the subjects ate a meal rich in purines—compounds in food that are metabolized into uric acid. The sensor showed uric acid levels rising after the meal. Gao’s team performed a similar test with gout patients. The sensor showed their uric acid levels were much higher than those of healthy people.

To check the accuracy of the sensors, the researchers drew and checked blood samples from the gout patients and healthy subjects. The sensors’ measurements of uric acid levels strongly correlated with levels of it in their blood.

Gao says the high sensitivity of the sensors, along with the ease with which they can be manufactured, means they could eventually be used by patients at home to monitor conditions like gout, diabetes, and cardiovascular diseases. Having accurate real-time information about their health could even let patients adjust their medication levels and diet as required.

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