Wearable Device Tracks Gases From Just Above the Skin

The skin is the largest organ of the human body. It plays an essential role, protecting all of your internal organs. But it can also be a source of valuable information about your health. Many wearables such as smartwatches and fitness trackers monitor biometrics using sensors that are in contact with the skin to track optical, thermal, mechanical, and fluid data—mostly about blood flow beneath the skin. However, current devices cannot detect the gases that are emitted and absorbed by the skin itself.

This movement of several gases through the skin provides important health data. Measuring water vapor gives insights about hydration, which can be vital for patients, athletes, and people working in hazardous settings. Carbon dioxide emissions can track a variety of metabolic functions, such as skin health and wound healing. Some volatile organic compounds (VOCs) can be environmental health hazards, so monitoring their absorption by the skin can help with risk assessment. VOCs are also emitted by the skin, which can be related to bacterial infection of a wound.

A team of researchers at Northwestern University in Evanston, Ill., have developed a wearable device that can measure the gases flowing in and out of the body with a sensor positioned just above the skin but not touching it. The device, called an epidermal flux sensor (EFS), measures the changes in gas concentrations adjacent to the subject’s skin.

While the sensor itself does not make contact with the wearer’s body, the device does form a circular seal on the skin to create a space that isolates an air sample. That sample is monitored by several discrete sensors designed to measure the concentration of different gases: water vapor, CO₂, and VOCs. The device also has sensors for skin temperature and electrical impedance where it is attached to the subject’s skin.

The system records the sensor’s readings for the concentration of target gases at specific time intervals, revealing how they change due to exchange through the skin. A valve between this air-sample chamber and a vent can be put in an open or closed position using an electromagnet, which allows the vent to provide a new sample of ambient air periodically.

How could tracking skin gases help your health?

This system makes it possible to monitor both the emission and absorption of gases by the skin over time. Data from the device is transmitted wirelessly using a Bluetooth connection for analysis and reporting using a smartphone or tablet. This provides health professionals with real-time results, along with time series data that shows trends rather than just an isolated snapshot. That data in turn supports remote patient monitoring in an outpatient setting, which can be more efficient and convenient for both health care professionals and patients.

The device could be used to help monitor diabetic ulcers and other wounds.John A. Rogers/Northwestern University

The device can placed on the body using an adhesive similar to those used in smart patches and continuous glucose monitors. “Nearly any body location works, so long as the surface is not highly curved or time dynamic (fingers, elbows, knees),” according to John A. Rogers, a professor at Northwestern University, who co-led the study. “Hair doesn’t seem to be a problem, and the inner forearm tends to be a convenient location.”

One of the key applications for the device is wound management, especially diabetic ulcers. Contact with a wound can interfere with the healing process, but that healing needs to be closely monitored. If a wound becomes infected, it might require treatment with antibiotics. The bacteria that cause such infections produce VOCs that can be detected and used to indicate an infection. This can be especially important when a wound has formed a scab but has not healed completely. Detecting the VOC markers of infection can lead to early intervention to avoid further damage.

The device could also assess the effectiveness of insect repellents. Blood-sucking insects such as mosquitoes can be vectors for disease in humans, including malaria. The skin gives off carbon dioxide and VOCs that attract mosquitoes. The EFS can provide precise measurements of these gases from different individuals, revealing the levels that are most attractive to the insects. This can also be used to measure the changes that result from the use of different repellents. That data could be used to create artificial skin that mimics the gas-emission profiles of human subjects, making it easier to create repeatable experiments that eliminate the variability of live subjects.