By discreetly measuring the concentration of key chemicals in our sweat, thin, pliable sensors could play a huge role in how wearable devices track our health and wellbeing in the future. Scientists at the University of California, Los Angeles (UCLA) have developed a new type of double-sided, disposable film that opens up some interesting possibilities in this area, by working with a smartwatch to present a real-time picture of body chemistry. Analyzing the biochemicals in our perspiration can reveal a wealth of information about our health, and in the past few years we’ve seen quite a few experimental technologies designed to tap into the secrets of our sweat. Some track cortisol as a way of monitoring stress levels, some track lactate to forewarn athletes when they are running out of energy, and some could even power themselves by the sweat that they analyze. The new film developed at UCLA is similar to a sweat-sensing wristband from UC Berkeley we looked at back in 2016, but is a significantly streamlined version. It also measures glucose and lactate, but is thin enough to slip beneath the body of a watch and rest against the skin. Here, the side of the film in contact with the skin analyzes sweat, while the other side converts those chemical signals into electrical signals. To demonstrate its capabilities, the team built a custom smartwatch loaded with an app that then processes those electrical signals and displays the data on its face. “By making our sensors on a double-sided adhesive and vertically conductive film, we eliminated the need for the external connectors,” Zhao says. “In this way, not only have we made it easier to integrate sensors with consumer electronics, but we’ve also eliminated the effect of a user’s motion that can interfere with the chemical data collection.” Through testing, the team even found the adhesiveness of the film to be strong enough to hold the watch in place for an entire day without the need for a wrist strap. With this successful proof-of-concept under their belts, the researchers imagine that with further work their double-sided film could make its way into a new generation of wearable devices that offer an intricate, real-time picture of our health. “The inspiration for this work came from recognizing that we already have more than 100 million smartwatches and other wearable tech sold worldwide that have powerful data-collection, computation and transmission capabilities,” says study leader Sam Emaminejad. “Now we have come up with a solution to upgrade these wearables into health monitoring platforms, enabling them to measure molecular-level information so that they give us a much deeper understanding of what’s happening inside our body in real time.” The research was published in the journal Science Advances.