We have recently demonstrated that vertically aligned gold nanowires (v-AuNWs) are outstanding material candidates for wearable biomedical sensors toward real-time and noninvasive health monitoring because of their excellent tunable electrical conductivity, biocompatibility, chemical inertness, and wide electrochemical window. Here, we show that v-AuNWs could also be used to design a high-performance wearable pressure sensor when combined with rational structural engineering such as pyramid microarray-based hierarchical structures. The as-fabricated pressure sensor featured a low operation voltage of 0.1 V, high sensitivity in a low-pressure regime, a fast response time of <10 ms, and high durability with stable signals for the 10 000 cycling test. In conjunction with printed electrode arrays, we could generate a multiaxial map for spatial pressure detection. Furthermore, our flexible pressure sensor could be seamlessly connected with a Bluetooth low-energy module to detect high-quality artery pulses in a wireless manner. Our solution-based gold coating strategy offers the benefit of conformal coating of nanowires onto three-dimensional microstructured elastomeric substrates under ambient conditions, indicating promising applications in next-generation wearable biodiagnostics.
facile fabrication. [15][16][17][18] Metal nanowires (gold, silver, copper, etc.) [19][20][21][22][23][24] and carbon based materials such as carbon nanotubes (CNTs) and graphene, [25][26][27][28][29][30][31] have received tremendous research attention in constructing intrinsically stretchable electrodes for organic electronics.Among those choices, raw materials cost of gold may not be the lowest, but it offers superior advantages in biomedical applications of wearable and implantable electronics, due to the attributes including high conductivity, mechanical robustness, chemical inertness, and biocompatibility. [32][33][34] For example, the conductivity of gold is two orders higher than carbon based materials. [35] Also, gold has been known to be anti-oxidative and anti-corrosive, while silver or copper fails in maintaining a long-term stability in complex body fluidic environments. Furthermore, the work function of gold is close to the HOMO levels of many p-type organic semiconductors such as poly(3-hexylthiophene) (P3HT) and pentacene, offering small hole-injection barriers and low contact resistance at metal-organic semiconductor interfaces. [36][37][38][39][40] Although little research attention had been paid to improving contact resistance in stretchable organic transistors because the state-of-the-art device performance is mostly hindered by channel resistance, advances in high mobility organic semiconductors will make contact resistance increasingly crucial in determining device performance, rendering gold materials more favorable in stretchable organic electronics. [41][42][43][44][45][46] Nevertheless, gold nanomaterials based electrodes have hitherto yet been well developed for intrinsically stretchable transistors. 2D gold nanosheets have been assembled to stretchable electrodes for P3HT fiber based stretchable organic transistors with good mechanical and electrical performance. [47][48][49] However, 2D gold nanosheets, fabricated at relatively high temperature (95 °C), are rigid in nature and the fabrication process is incompatible to the patterning processes via conventional photo lithography, and hence may limit device density, mechanical robustness, and scalability. [15] 1D gold nanowires (AuNWs) have emerged as an excellent materials candidate for serving as electrodes in stretchable electronics because of their mechanical flexibility, ease of fabrication, and Advances in large-area organic electronics for sensor arrays and electronic skins demand highly stretchable, patternable, and conformal electrodes to minimize contact resistance when sensing devices are mechanically deformed. Gold is an excellent electrode material with work function matching well with p-type organic transistors. However, it is non-trivial to fabricate highly stretchable gold electrodes for stretchable organic electronics. Here, by combining the advantages of both top-down patterning and bottomup synthesis, a new materials platform of patterned vertically grown gold nanowires (AuNWs) for constructing intrinsically stretcha...
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