HEFEI -- Smart wearable devices have evolved with advanced features for a holistic health and fitness experience, monitoring heart rate, tracking step count, calculating calorie intake, and now notifying users when they need electrolyte drinks during exercise with just a flick of the wrist.

Scientists from the Hefei Institutes of Physical Science (HIPS) under the Chinese Academy of Sciences have designed a wristwatch that can measure essential chemicals in body sweat. Their findings were published in the journal ACS Nano.

Sweat contains electrolytes, primarily potassium, sodium and calcium. The balance of these essential minerals is crucial for supporting muscle function, nerve health and regular heartbeat, said Yang Meng, an associate professor at the institute and one of the authors of the study.

Sweating leads to the loss of both water and electrolytes. "Excessive loss of potassium, for instance, can impact heart function and neuromuscular activity. Similarly, the depletion of sodium ions may result in symptoms such as fatigue, dizziness and muscle cramps," Yang said, explaining the importance of maintaining a balanced electrolyte level.

The wristwatch designed by Yang's team collects sweat from the skin and analyzes it in real time using a sensor chip with an ion-sensitive membrane.

When sweat enters the device, it will come into contact with the membrane that contains three tubules capable of measuring sodium, potassium and calcium levels, respectively.

Although they are not the first to invent sweat sensors, the Chinese researchers emphasized the wristwatch's solid interface for long-term reliability.

"It surpasses the stability of many other sensors by consistently monitoring the three ions in human sweat for over six months," said lead researcher Huang Xingjiu, of the Institute of Solid State Physics under the HIPS.

Since endurance athletes use electrolyte drinks to counteract the loss of energy and replenish it, researchers in the study measured the sweat composition of these chemicals in athletes running long distances on a treadmill.

The accuracy reached approximately 95 percent when compared to the standard detection method.

"When there are electrolyte abnormalities, the device will remind users to supplement them promptly," said the co-first author Cai Xin. "The aim of developing this device is to provide warnings for electrolyte loss and reduce exercise-related injury risks."

For ordinary people, the conventional electrolyte test requires samples of body fluids taken in hospitals. The new wristwatch has the potential to serve as an alternative to needles for measuring electrolytes.

In addition to offering a non-invasive test, the device allows for real-time monitoring of electrolytes, "which is undoubtedly a significant advancement in human health monitoring," said Xu Han, a physician at the Central Hospital of Bengbu, who was not involved in the study.

The next goal of the research team is to design various sensitive membrane materials for monitoring more physiological information, such as glucose and chloride ions.

The researchers noted that compared to popular fitness watches on the market, the device they designed is larger and heavier, making it less comfortable to wear. However, they expect to develop wearable sweat sensors suitable for market applications in the next five years.

Yang said that the team of researchers also aims to adapt the device for environmental monitoring to measure heavy metals in the future.