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Cortisol is well-suited for measurement through wearable devices, according to study co-author Sam Emaminejad, because its concentration levels in sweat are similar to its circulating levels. (Credit: Yichao Zhao and Zhaoqing Wang/UCLA)

A research team has developed a device that could be a major step forward: a smartwatch that assesses cortisol levels found in sweat — accurately, noninvasively, and in real time. The technology could offer wearers the ability to read and react to an essential biochemical indicator of stress.

In the new smartwatch, a strip of specialized thin adhesive film collects tiny volumes of sweat, measurable in millionths of a liter. An attached sensor detects cortisol using engineered strands of DNA, called aptamers, which are designed so that a cortisol molecule will fit into each aptamer like a key fits a lock. When cortisol attaches, the aptamer changes shape in a way that alters electric fields at the surface of a transistor.

One challenge in using cortisol levels to diagnose depression and other disorders is that levels of the hormone can vary widely from person to person — so doctors can’t learn very much from any single measurement. But the authors foresee that tracking individual cortisol levels over time using the smartwatch may alert wearers, and their physicians, to changes that could be clinically significant for diagnosis or monitoring the effects of treatment.

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