Percolating Network of Ultrathin Gold Nanowires and Silver Nanowires toward “Invisible” Wearable Sensors for Detecting Emotional Expression and Apexcardiogram

• Published in: Advanced functional materials Vol. 27; no. 25
• Main Authors: Ho, My Duyen, Ling, Yunzhi, Yap, Lim Wei, Wang, Yan, Dong, Dashen, Zhao, Yunmeng, Cheng, Wenlong
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc 05-07-2017
• Subjects: apexcardiogram; Electric potential; Electrical resistivity; Face recognition; Gold; gold nanowires; High aspect ratio; Materials science; Nanowires; Respiration; Sensors; silver nanowires; Strain gauges; strain sensors; Stretchability; stretchable sensors; Wearable technology
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.201700845

2 nm thin gold nanowires (AuNWs) have extremely high aspect ratio (≈10 000) and are nanoscale soft building blocks; this is different from conventional silver nanowires (AgNWs), which are more rigid. Here, highly sensitive, stretchable, patchable, and transparent strain sensors are fabricated based on the hybrid films of soft/hard networks. They are mechanically stretchable, optically transparent, and electrically conductive and are fabricated using a simple and cost‐effective solution process. The combination of soft and more rigid nanowires enables their use as high‐performance strain sensors with the maximum gauge factor (GF) of ≈236 at low strain (<5%), the highest stretchability of up to 70% strain, and the optical transparency is from 58.7% to 66.7% depending on the amount of the AuNW component. The sensors can detect strain as low as 0.05% and are energy efficient to operate at a voltage as low as 0.1 V. These attributes are difficult to achieve with a single component of either AuNWs or AgNWs. The outstanding sensing performance indicates their potential applications as “invisible” wearable sensors for biometric information collection, as demonstrated in applications for detecting facial expressions, respiration, and apexcardiogram.
The AgNWs/AuNWs percolation networks are optically transparent, electrically conductive, and mechanically stretchable, enabling their use as novel skin‐like “invisible” and “unfeelable” strain sensors for various biometric information monitoring, including heart beats, apexcardiograms, respiration, and facial expressions. The sensors are potentially useful for future practical applications in the medical health care system.