New skin patch for on-the-spot sweat monitoring

Scientists have developed a first-of-its-kind soft, flexible microfluidic device that easily adheres to the skin and measures the wearer's sweat to show how their body is responding to exercise.
The simple, low-cost device analyses key biomarkers to help a person decide quickly if any adjustments, such as drinking more water or replenishing electrolytes, need to be made or if something is medically awry, researchers from Northwestern University in the US said.
Designed for one-time use of a few hours, the device, placed directly on the skin of the forearm or back, even detects the presence of a biomarker for cystic fibrosis. In the future, it may be more broadly used for disease diagnosis.

"The intimate skin interface created by this wearable, skin-like microfluidic system enables new measurement capabilities not possible with the kinds of absorbent pads and sponges currently used in sweat collection," said John A Rogers, who led the team that created the 'lab on the skin.'
"Sweat is a rich, chemical broth containing a number of important chemical compounds with physiological health information.
"By expanding our previously developed 'epidermal' electronics platform to include a complex network of microfluidic channels and storage reservoirs, we can perform biochemical analysis of this important biofluid," he said.

"The sweat analysis platform we developed will allow people to monitor their health on the spot without the need for a blood sampling and with integrated electronics that do not require a battery but still enable wireless connection to a smartphone," said Yonggang Huang, who worked on the device's design and optimisation.

The device was tested on two different groups of athletes: one cycling indoors in a fitness centre under controlled conditions and the other participating in a long-distance bicycle race in arid and complex conditions.
The researchers placed the device on the arms and backs of the athletes to capture sweat.
During moderate or vigorous exercise, sweat winds through the tiny microscopic channels of the device and into four different small, circular compartments.
In the compartments, reactions with chemical reagents result in visible colour changes that quantitatively relate to pH and concentrations of glucose, chloride and lactate.
When a smartphone is brought into proximity with the device, the wireless electronics trigger an app that captures a photo of the device and analyses the image to yield data on the biomarker concentrations.

In the group that cycled indoors, researchers compared the new device's biomarker readouts to conventional laboratory analysis of the same sweat and found the two sets of results agreed with each other.
With the long-distance cyclists, the researchers tested the durability of the device in the complex and unpredictable conditions of the desert.
They found the devices to be robust: They stayed adhered to the athletes' skin, did not leak and provided the kind of quality information the researchers sought.