Gold, known for its stability, excellent electrical conductivity, and biocompatibility, is widely used in the medical and energy sectors. It is also becoming increasingly popular in advanced wearable technology. Wearable devices, which come in various forms like attachments and patches, are crucial for monitoring physical, chemical, and electrophysiological signals for disease diagnosis and management. Recent research has been focusing on creating wearables that can simultaneously measure multiple bio-signals. However, this poses challenges due to the need for different materials for each signal, leading to complex fabrication, interface damage, and decreased stability of the device. Moreover, analyzing these diverse signals typically requires additional processing systems and algorithms. Researchers have now made a breakthrough by utilizing gold (Au) nanowires in different shapes to create an integrated wearable sensor capable of measuring and processing two bio-signals at the same time.

At Pohang University of Science and Technology (POSTECH, Gyeongbuk, Korea), researchers have innovatively combined gold with silver (Ag) nanowires which are recognized for their extreme thinness, lightness, and conductivity, and are generally used in wearable devices. They first developed bulk gold nanowires by coating silver nanowires with gold, thus preventing the galvanic reaction. Then, they created hollow gold nanowires by selectively etching away the silver from the gold-coated nanowires. The bulk gold nanowires demonstrated high sensitivity to temperature changes, while the hollow gold nanowires were particularly responsive to the slightest variations in strain.

These nanowires were then arranged on a substrate made of styrene-ethylene-butylene-styrene (SEBS) polymer, ensuring a seamless integration without separations. By using two types of gold nanowires, each with unique properties, the researchers were able to make an integrated sensor that simultaneously measures temperature and strain. They also developed a logic circuit for signal processing, employing a negative gauge factor achieved by adding micrometer-scale corrugations to the pattern. This innovation resulted in a smart wearable device system capable of capturing and analyzing signals using a single material of Au.

The sensors displayed excellent performance in detecting subtle muscle movements, identifying heartbeats, recognizing speech from vocal cord tremors, and monitoring body temperature changes. Remarkably, these sensors remained highly stable without damaging the material interfaces. Their flexibility and stretchability allowed for perfect adherence to the contours of the skin.

“This research underscores the potential for the development of a futuristic bioelectronics platform capable of analyzing a diverse range of bio-signals,” said Professor Sei Kwang Hahn who led the research team. “We envision new prospects across various industries including healthcare and integrated electronic systems.” 

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