Sweat chloride can be measured with miniaturized wearable device

The device was compared to standard methods on 7 infants with CF

Steve Bryson, PhD avatar

by Steve Bryson, PhD |

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A doctor examines a child who's sitting on his mother's lap.

A miniaturized wearable device is able to measure chloride levels in sweat, the gold standard tool for diagnosing cystic fibrosis (CF).

In infants with CF, tests showed the device’s accuracy matched standard methods without the need for trained personnel in hospital settings. It also measured sweat levels of zinc and iron after food intake to monitor nutritional status, which can be compromised in people with CF.

“We have not only addressed the limitations of existing methods for inducing sweat, but also achieved success in clinical research, bringing us one step closer to commercialization,” Kim Joohee, PhD, study first author at the Korea Institute of Science and Technology, said in a press release. Details of the device’s development were published in Biosensors and Bioelectronics in “A skin-interfaced, miniaturized platform for triggered induction, capture and colorimetric multicomponent analysis of microliter volumes of sweat.”

Due to the dysfunction or absence of the CFTR protein, people with CF have abnormally high levels of chloride in their sweat. For this reason, testing sweat chloride is considered the best approach for diagnosing CF.

During a sweat test, two electrodes are attached to the forearms with straps. One contains a disc with pilocarpine gel, which triggers sweat production. A weak electrical current is sent through the electrode to push the medicine through the skin. Sweat is then collected using filter paper, gauze, or a separate device attached to the skin surface and is then tested.

This approach relies on rigid, bulky hardware, and the cost and complexity, along with the need for trained technicians, limit its use to specialized hospital facilities. The tests are only measure chloride.

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A sweat test, minus the stress

Here, researchers from the Republic of Korea and the U.S. developed a miniaturized wearable sweat-monitoring device.

The platform combines a manual switch, electrodes, hydrogels with pilocarpine, biosensors, tubes, and micro-reservoirs, all within a soft, flexible structure. It also includes separate micro-reservoirs and tests to measure chloride, along with zinc and iron to monitor CF-related nutritional deficiencies.

“A key advantage of the device is in its ability for use outside of hospital settings, without the need for trained personnel,” wrote the researchers, who confirmed its ability to measure chloride, zinc, and iron over physiologically relevant ranges. The readings were also stable at different temperatures, especially body temperature, and various pH values because sweat is usually slightly acidic.

Because CF patients often face challenges digesting and absorbing nutrients, the researchers tested the device on healthy people before and after a meal to examine changes in chloride, zinc, and iron. Results showed each sweat biomarker increased after a meal and the levels strongly matched those using a highly sensitive technique called mass spectrometry. The accuracy between the two methods was 97.6% for chloride, 98.8% for zinc, and 89.1% for iron.

The device was then compared to standard testing methods on seven infants with CF. Using the standard procedure, with wired electrodes and tight straps on the right arm, the technician initiated sweat stimulation, removed the electrodes, and collected sweat for 30 minutes.

The new device was attached to the skin and activated with the switch. Sweat was immediately collected in the microfluidic channels and micro-reservoirs, which were filled in under 30 minutes due to their small volumes. The device’s microvalves also directed excess sweat to outlet ports to ensure that “measurements can be performed at any time after the reservoir fills,” the researchers wrote.

One patient complained of pain and another didn’t produce enough sweat, both with the standard method. Of the five remaining patients, the results with the device was consistent with those obtained by the standard procedure, with an accuracy of 98%. On a pain scale of 0 (no pain) to 10 (high pain), the average pain levels were about 2, which was “a factor of [2] less than those of the clinical standard product,” wrote the researchers, who said future studies will “examine the use of similar concepts for evaluating other sweat biomarkers of interest to additional classes of patients.”

John A. Rogers, PhD, the study’s senior author at Northwestern University said “large-scale clinical studies and commercialization” that will include adults are planned.