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.

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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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Such future soft wearable electronics or wearable 2.0 products [8] will not be viable unless efficient reliable and skin-conformal power sources are to be developed. Most of the current wearable electronics are powered by rigid and bulky lithium-ion battery. Although paper batteries are emerging as a thinner version candidate, [9] they are still based on conventional metallic materials, which are neither stretchable nor compressive, unable to conformally be attached onto human skin. Typical smart soft electronics including wearable glucose sensors, pressure sensors, and surface electromyography (sEMG) only require a voltage of <100 mV and a power consumption of <20 µW, which could be supplied by different types of energy devices. [10] In this context, a variety of soft energy devices based on nanomaterials including batteries, [11] supercapacitors, [12,13] solar cells, [14] triboelectric nanogenerators, [15] and fuel cells [16-18] have attracted tremendous attention as the potential replacement of the lithium-ion battery to power skin-like electronics. Each type of those energy devices has their own intrinsic pros and cons. Wearable supercapacitors cannot provide continuous long-term energy supplies; [12,13] the performance of wearable photovoltaic devices is highly dependent on the external light source; [14] and the wearable nanogenerators based on piezoelectric and triboelectric devices can only provide intermittent energy and must be integrated with energy storage devices for continuous long-term monitoring. [15] Stretchable enzymatic biofuel cell that uses glucose or lactic acid in the body fluid to generate energy has been considered as an environmentally friendly power source for the next-generation skin-like energy devices. However, its performance is largely dependent on the stability of the enzyme, which may be easily affected by body temperature, pH, and fuel concentrations. [19,20] In contrast, fuel cells that use ethanol or methanol as a model system could offer a much higher power density and stability as they are not influenced by the biological environments. [21] A number of materials including silver nanowires, [22] carbon fibers, [23] graphene paper, [24] nickel foam, [25] vertically aligned gold nanowires (V-AuNWs) [26] have been demonstrated to fabricate flexible or even stretchable fuel cells. Nevertheless, high power output, skin-like device thickness, Skin-like energy devices can be conformally attached to the human body, which are highly desirable to power soft wearable electronics in the future. Here, a skin-like stretchable fuel cell based on ultrathin gold nanowires (AuNWs) and polymerized high internal phase emulsions (polyHIPEs) scaffolds is demonstrated. The polyHIPEs can offer a high porosity of 80% yet with an overall thickness comparable to human skin. Upon impregnation with electronic inks containing ultrathin (2 nm in diameter) and ultrahigh aspect-ratio (>10 000) gold nanowires, skin-like strain-insensitive stretchable electrodes are successfully fabricated. With such designed ...

A new colorimetric aptasensor for the detection of CEA was developed. Aptamer-based colorimetric method with nanoparticles was used for the detection of CEA. The colorimetric aptasensor has potential for the detection of other proteins or nucleotides.

Electronics is evolving from rigid, flexible to ultimate stretchable electronics in which active optoelectronic materials are required to deposit onto or embedded into elastomeric materials. We have recently demonstrated a...

The past decade has witnessed growing interest in developing soft wearable pressure sensors with the ultimate goal of transforming today's hospital-centered diagnosis to tomorrow's patient-centered bio-diagnosis.