Sweat excreted by the skin contains important biomarkers for a number of diseases, as well as being a critical parameter in athletic performance, overall body function, and even an early warning indicator of an oncoming illness. Measuring sweat output and its chemical composition, in an accurate and easily administered way, has been a challenge. Athletes and others would benefit from a wearable patch that can be stuck near sweat glands to continuously measure pH levels, glucose, salt content, and the overall amount of sweat produced. Making such patches has turned out to be harder than thought, even with existing microfluidic devices, because it’s hard to gather large samples and process them without substantial evaporation. Now, a team of engineers at Penn State and Xiangtan University in China have developed a microfluidic device that overcomes important sample gathering issues for skin-based sweat sensors, hopefully leading to the introduction of such devices for wider use. The new approach uses a single opening to collect a sweat sample into tiny channels inside a vial. The channels are hydrophilic, and so draw the sweat in, while the valve inside the inlet is made of hydrophobic components so that all the sweat passes through and into the channels. Because there is only a single open end of each channel, the sweat doesn’t have a chance to evaporate, resulting in substantially larger sample sizes for analysis. “The two-valve device is more complicated and requires using a clean-room technique called photolithography. Our simpler one-valve device can be made without expensive equipment utilizing micromachining,” said Huanyu “Larry” Cheng, assistant professor of engineering science and mechanics at Penn State, in a press release To analyze the sweat for certain parameters, a color-based analyte can be introduced into the sweat-holding chambers and a color change can be seen by the eye or, for particularly sensitive tests, with a smartphone that is more keen at detecting specific colors. Study in Lab on a Chip: Skin-interfaced microfluidic devices with one-opening chambers and hydrophobic valves for sweat collection and analysis Source
