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

Abstract

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 ORCID identification number(s) for the author(s) of this article can be found under http://dx.

Surface coatings of silver nanowires lead to effective, high conductivity, high-strain, ultrathin sensors

“…As an alternative material, silver nanowires (AgNWs) have been of great interest [25][26][27][28][29][30][31][32][33][34][35][36][37][38] due to the ability to form highly conductive percolative networks. [38][39][40][41] AgNW based sensing composite materials, formed exclusively by layer deposition, consist of a percolative network of the nanowires adhered to a flexible polymer substrate. Similar to carbon nanotube (CNT)…”

One‐component waterborne in vivo cross‐linkable polysiloxane coatings for artificial skin

“…Sara EI‐Molla (El‐Molla et al, ) and Nam‐Joon Cho (Wang et al, ) both presented high‐performance electronic skin sensors by integrating a thin PDMS‐based film into their sensors. Cheng and co‐workers (Ho et al, ) fabricated an invisible and unfeelable wearable strain sensor by encapsulating the percolating network of soft gold nanowires and rigid silver nanowires with a layer of PDMS. Nevertheless, all these PDMS‐based artificial skins involve toxic raw materials or need harsh film‐forming conditions.…”

Dual‐Mode Wearable Strain Sensor Based on Graphene/Colloidal Crystal Films for Simultaneously Detection of Subtle and Large Human Motions

“…[13][14][15][16] Large human joint motions usually result in about 55% strain, [7] and often require that the sensing material has a broad range of strain deformations and excellent stretchability to keep its structural connections at large strains. [13][14][15][16][17][18][19][20][21][22][23] Designing the geometric structures and controlling the connection types of graphene-sensing materials are the main approaches to realizing these goals. However, the strain sensors with high sensitivity easily lead to drastic structural changes at small deformation, and usually suffer a restricted strain range, whereas the strain sensors with high stretchability to detect large strain usually have poor sensitivity and cannot detect the subtle strains.…”