California Institute of Technology researchers led by Wei Gao, assistant professor of medical engineering, have developed a mass-producible wearable sensor that can monitor metabolites and nutrients in a person's blood by analyzing their sweat. Unlink previously developed sweat sensors which target compounds that appear in high concentrations, Gao’s sweat sensor can detect sweat compounds of much lower concentrations, in addition to being easier to manufacture, said the researchers.
According to the researchers, these sensors would allow doctors to continuously monitor the condition of patients with illnesses like cardiovascular disease, diabetes, or kidney disease, all of which result in abnormal levels of nutrients or metabolites in the bloodstream. Patients would benefit from having their physician better informed of their condition, while also avoiding invasive encounters with hypodermic needles.
"Such wearable sweat sensors have the potential to rapidly, continuously, and noninvasively capture changes in health at molecular levels," Gao said in an article appearing on California Institute of Technology’s website. "They could enable personalized monitoring, early diagnosis, and timely intervention."
Gao's work focuses on developing devices based on microfluidics, technologies that manipulate tiny amounts of liquids, usually through channels less than a quarter of a millimeter in width. Microfluidics minimize the influence of sweat evaporation and skin contamination on sensing accuracy. The sensor can make more accurate sweat measurements and can capture temporal changes in concentrations.
Previously, microfluidic-based wearable sensors were mostly fabricated with a costly, complicated lithography-evaporation process. Gao’s team instead made their biosensors out of graphene, a sheet-like form of carbon. Both the graphene-based sensors and the tiny microfluidics channels are created by engraving the plastic sheets with a carbon dioxide laser.
The researchers opted to have their sensor measure respiratory rate, heart rate, and levels of uric acid and tyrosine. Tyrosine was chosen because it could indicate 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 gauge sensor performance, the researchers ran a series of tests on two groups of healthy individuals and patients, one group trained athletes and the others of average fitness. The sensors showed lower levels of tyrosine in the sweat of the athletes. To check uric acid levels, the researchers monitored the sweat levels of healthy individuals while they were fasting, as well as after they ate a meal rich in purines, food compounds that are metabolized into uric acid. The sensor showed uric acid levels rising after the meal. Gao's team also performed a similar test with gout patients, finding that their uric acid levels were much higher than those of healthy people.
To check the sensors' accuracy, the researchers also drew blood samples from the gout patients and healthy subjects. The sensors' measurements of uric acid levels strongly correlated with levels of the compound in the blood.
Gao noted 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 allow patients to adjust their own medication levels and diet as required.