Wearable Sensors detects what's in your sweat

Needle bites not your thing? A team of scientists from the University of California, Berkeley, are developing portable skin sensors that can detect what's in your sweat.

They hope that someday, sweat monitoring could avoid resorting to more invasive procedures such as blood sampling and providing real-time updates on health issues such as dehydration or fatigue.

In an article published today (Friday, August 16) in Progress of science, the team describes a new sensor design that can be quickly fabricated using a "roll-to-roll" processing technique that essentially consists of printing the sensors onto a plastic sheet, just like the words newspaper.

They used sensors to monitor the transpiration rate, as well as the electrolytes and metabolites present in sweat, from volunteers who were exercising and from people suffering from chemical-induced sweating.

"The goal of the project is not just to make sensors, but to start doing many studies on the subject and see what sweat tells us – I always say decode the composition of sweat," said Ali Javey, professor of electrical engineering and computer science at UC Berkeley and lead author on the paper.

"For that, we need reliable, reproducible sensors that we can scale up so we can place multiple sensors in different parts of the body and apply them to many subjects," said Javey, who is also a university researcher. . at the Lawrence Berkeley National Laboratory.

The new sensors contain a microscopic spiral tube, or microfluidic tube, that wicks sweat away from the skin. By detecting the rate of perspiration through microfluidics, sensors can indicate a person's level of perspiration or its transpiration rate.

Microfluidics are also equipped with chemical sensors capable of detecting electrolyte concentrations such as potassium and sodium and metabolites such as glucose.

Javey and his team collaborated with researchers at the VTT Technical Research Center in Finland to develop a way to quickly make sensor patches using roller-like processing similar to screen printing.

"Roll-to-roll processing enables the production of large volumes of low-cost disposable patches," said Jussi Hiltunen of ATV. "Academic groups gain a significant advantage from roll-to-roll technology when the number of test devices does not limit the search. In addition, large-scale manufacturing demonstrates the potential of applying the concept of sweat detection in practical applications. "

To better understand what sweat can say about the real-time health of the human body, researchers first placed sweat sensors at various locations in the body of volunteers – including the forehead, the front -arms, underarms and upper back – and measured their transpiration rate. Sodium and potassium levels in their sweat while they were riding on an exercise bike.

They found that the local sweat rate could indicate the loss of overall body fluid during exercise, which means that tracking sweat rate could be a way to give athletes a head whip when they risk getting push too hard.

"Traditionally, people collected sweat from the body for a while, then analyzed it," said Hnin Yin Yin Nyein, a graduate student in Materials Science and Engineering at the University of Berkeley and one of the authors the paper. "So, you could not really see the dynamic changes very well with good resolution.Using these wearable devices, we can now continuously collect data from different parts of the body, for example to understand how the local sweat loss can estimate the loss of fluid throughout the body. "

They also used the sensors to compare sweat glucose levels and blood glucose levels in healthy and diabetic patients, concluding that a simple sweat glucose measurement could not necessarily tell the patient's blood glucose level. 'one person.

"There was much hope that non-invasive sweat tests could replace blood-based measures for the diagnosis and monitoring of diabetes, but we showed that there was no Simple and universal correlation between sweat and blood sugar levels, "said Mallika. Bariya, a graduate student in materials science and engineering at UC Berkeley and the other senior author of the journal. "It is important for the community to know, so that in the future we can focus on finding individualized or multi-parameter correlations."

Ali Javey describes an earlier version of his laboratory's portable perspiration sensor in this 2016 video. (UC Berkeley video by Roxanne Makasdjian and Stephen McNally)

Contributors to the article include Liisa Kivimaki, Sanna Uusitalo, Elina Jansson, Tuomas Happonen and Christina Liedert of the VTT Technical Research Center of Finland; and Tiffany Sun Liaw, Christine Heera Ahn, John A. Hangasky, Jianqi Zhao, Lin Yuanjing, Minghan Chao, Yingbo Zhao and Li-Chia Tai from UC Berkeley.

This work was supported by NSF nanofabrication systems for mobile computing and mobile energy technologies (NASCENT), the Berkeley Sensor and Actuator Center (BSAC). and the Bakar Stock Exchange.