According to a study published in ACS Nano, researchers led by Prof. HUANG Xingjiu from the Hefei Institutes of Physical Science of the Chinese Academy of Sciences have developed a unique wristwatch, and several modules, including a sensor array, a microfluidic chip, signal processing, and a data display system, have been packed into this advanced watch to monitor chemicals in human sweat.

"It can continuously and accurately monitor the levels of potassium (K⁺), sodium (Na⁺), and calcium (Ca²⁺) ions," said Prof. HUANG, "providing both real-time and long-term tracking capabilities."

Tremendous progress has been made in sweat sensors based on electrochemical methods, making it easier to track changes in the body. The stability of the sensor chip is crucial to its application effectiveness and lifetime, which is the key to ensuring the long-term reliable operation of the sensor.

Therefore, the researchers focused on designing a stable solid contact interface as core components, while fully integrating multiple modules of the sweat sensor to achieve enable simultaneous and dependable monitoring of multiple target ions.

In this study, the researchers developed mass-manufactured sensor arrays based on hierarchical multilayer pore cross-linked N-doped porous carbon coated with reduced graphene oxide (NPCs@rGO-950) microspheres with high hydrophobicity as core solid contact. This enabled highly selective monitoring of K⁺, Na⁺, and Ca²⁺ ions in human sweat.

Using computed tomography and solid-solid interface potential diffusion simulation, they found that the diffusion of substances between solid interfaces is very low, and the ability to store electrical charge at these interfaces is high. This ensures the excellent potential stability, reversibility, repeatability, and selectivity of the sensor arrays.

The long-term reliability of this watch is remarkable. It can consistently monitor the three ions in human sweat for over 6 months, surpassing the stability of many other sensors that have been reported.

This study represents a comprehensive approach to material design, interface mechanism research, mass production of sensor chips, and modular full integration, providing more possibilities for wearable electrochemical sweat sensors.

A wristwatch is used for monitoring electrolyte ions in sweat. (Image by CAI Xin)

A student is showing the wristwatch that can monitor levels of several chemicals in sweat. (Image by ZHAO Weiwei)