Sensitive, specific, yet multifunctional tattoo‐like electronics are ideal wearable systems for “any time, any where” health monitoring because they can virtually become parts of the human skin, offering a burdenless “unfeelable” wearing experience. A skin‐like, multifunctional electronic tattoo made entirely from gold using a standing enokitake‐mushroom‐like vertically aligned nanowire membrane in conjunction with a programmable local cracking technology is reported. Unlike previous multifunctional systems, only a single material type is needed for the integrated gold circuits involved in interconnects and multiplexed specific sensors, thereby avoiding the use of complex multimaterials interfaces. This is possiblebecause the programmable local cracking technology allows for the arbitrary fine‐tuning of the properties of elastic gold conductors from strain‐insensitive to highly strain‐sensitive simply by adjusting localized crack size, shape, and orientations—a capability impossible to achieve with previous bulk cracking technology. Furthermore, in‐plane integration of strain/pressure sensors, anisotropic orientation‐specific sensors, strain‐insensitive stretchable interconnects, temperature sensors, glucose sensors, and lactate sensors without the need of soldering or gluing are demonstrated. This strategy opens a new general route for the design of next‐generation wearable electronic tattoos.

The noninvasive continuous analysis of human sweat is of great significance for improved healthcare diagnostics and treatment in the future, for which a wearable potentiometry-based ion-selective electrode (ISE) has attracted increasing attention, particularly involving ion detection. Note that traditional solid-state ISE electrodes are rigid ion-to-electron transducers that are not conformal to soft human skin and cannot function under stretched states. Here, we demonstrated that vertically aligned mushroom-like gold nanowires (v-AuNW) could serve as stretchable and wearable ion-to-electron transducers for multiplexed, in situ potentiometric analysis of pH, Na+, and K+ in sweat. By modifying v-AuNW electrodes with polyaniline, Na ionophore X, and a valinomycin-based selective membrane, we could specifically detect pH, Na+, and K+, respectively, with high selectivity, reproducibility, and stability. Importantly, the electrochemical performance could be maintained even under 30% strain and during stretch-release cycles without the need of extrinsic structural design. Furthermore, our stretchable v-AuNW ISEs could be seamlessly integrated with a flexible printed circuit board, enabling wireless on-body detection of pH, Na+, and K+ with fast response and negligible cross-talk, indicating considerable promise for noninvasive wearable sweat analysis.

We have recently demonstrated that Enokitake mushroom-like gold with nanoparticles as the "head" and nanowires as the "tail" could grow directly on elastomeric substrates, which are extremely stretchable electrodes that can be used as wearable sensors for detecting strain and pressure. In this work, we show that such electrodes can also be used as intrinsically stretchable glucose biosensors. By modifying the vertical gold nanowire electrodes with glucose oxidase and Prussian blue nanoparticles, a limit of detection of 10 μM, sensitivity of 23.72 μA•mM −1 •cm −2 , and high selectivity can be achieved. The as-obtained glucose biosensors were able to maintain a high sensing performance under various mechanical deformations. Even for 30% strain, a sensitivity of 4.55 μA•mM −1 •cm −2 toward glucose detection in the artificial sweat was possible. Furthermore, it was found that strains could be simultaneously detected with a gauge factor of 2.30 (strain 0−10%) and 22.64 (strain 10−20%), demonstrating the potential of such bimodal sensors to allow simultaneous monitoring of physical and biological signals.

Traditional electrochemical biosensing electrodes (e.g., gold disk, glassy carbon electrode, etc.) can undergo sophisticated design to detect chemicals/biologicals from cells. However, such electrodes are typically rigid and nonstretchable, rendering it challenging to detect cellular activities in real-time and in situ when cells are in mechanically deformed states. Here, we report a new stretchable electrochemical cell-sensing platform based on vertically aligned gold nanowires embedded in PDMS (v-AuNWs/PDMS). Using H2O2 as a model analyte, we show that the v-AuNWs/PDMS electrode can display an excellent sensing performance with a wide linear range, from 40 μM to 15 mM, and a high sensitivity of 250 mA/cm2/M at a potential of −0.3 V. Moreover, living cells can grow directly on our stretchable high-surface area electrodes with strong adhesion, demonstrating their excellent biocompatibility. Further cell stimulation by adding chemicals induced H2O2 generation, which can be detected in real-time and in situ using our v-AuNWs/PDMS platform for both natural and stretched states of cells. Our results indicate the v-AuNWs/PDMS electrochemical biosensor may serve as a general cell-sensing platform for living organisms under deformed states.

In spite of advances in electronics and internet technologies, current healthcare remains hospital‐centred. Disruptive technologies are required to translate state‐of‐art wearable devices into next‐generation patient‐centered diagnosis and therapy. In this review, recent advances in the emerging field of soft wearable materials and devices are summarized. A prerequisite for such future healthcare devices is the need of novel materials to be mechanically compliant, electrically conductive, and biologically compatible. It is begun with an overview of the two viable design strategies reported in the literatures, which is followed by description of state‐of‐the‐art wearable healthcare devices for monitoring physical, electrophysiological, chemical, and biological signals. Self‐powered wearable bioenergy devices are also covered and sensing systems, as well as feedback‐controlled wearable closed‐loop biodiagnostic and therapy systems. Finally, it is concluded with an overall summary and future perspective.

Depending on the scale involved, there are different challenges in contemporary energy research. At the large scale, the main challenge lies in the environmental issues involved in powering cities in a sustainable manner; at the medium scale, the main challenge lies at simultaneously high energy and power density to drive electrical vehicles; at the small scale, the main challenge is how to power wearable and implantable devices anytime and anywhere without the need of external power supply of bulky connecting wires. To realize this latter goal, energy conversion/storage devices need to be ultrathin yet highly functional when being bent, twisted, and stretched. [1][2][3][4][5] However, current energy devices remain bulky and rigid. Despite the development of commercial paper batteries, these devices are not stretchable. [6,7] Therefore, it is highly desirable to develop thinner, softer, more biocompatible, and skin-conformal energy technologies to power future medical devices.It is encouraging to witness recent growing interest in stretchable devices including battery, [8,9] photovoltaics, [10,11] triboelectric generator, [12,13] supercapacitor, [14,15] and fuel cells. [16,17] To date, some biofuel cell based stretchable energy devices have been developed to power wearable electronic devices. [16][17][18][19] Nevertheless, their performance depends largely on the enzyme or bacteria, [16,[19][20][21] and their activity is affected by many factors, including the temperature and pH. [22,23] In contrast, methanol or ethanol based fuel cells have been shown to offer a much higher efficiency and reliability [24] because they are not influenced by external biological environments. To fabricate flexible fuel cells, specially designed electrodes or catalysts are required. In this context, carbon fiber paper or carbon cloth, [25,26] graphene paper, [27] and nickel foam [28] have been successfully utilized to fabricate flexible methanol or ethanol fuel cells. It is possible to design bendable on-chip fuel cells by imprinting Au on cycloolefin polymer films. [29] Ultralong Ag nanowires have been deposited onto polydimethylsiloxane (PDMS) forming percolation network, which can be used as current collectors for bendable fuel cells. [30] Despite the encouraging progress made so far, it remains highly challenging to fabricate stretchable fuel cells, which require new design of the electrodes and electro-catalysts. Conventional fuel cells are based on rigid electrodes, limiting their applications in wearable and implantable electronics.Here, it is demonstrated that enokitake-like vertically-aligned standing gold nanowires (v-AuNWs) can also serve as powerful platform for stretchable fuel cells by using ethanol as model system. Unlike traditional fuel cell electrodes, the v-AuNWs have "Janus Morphology" on both sides of the film and also are highly stretchable. The comparative studies demonstrate that tail side exposed v-AuNWs based stretchable electrodes outperform the head-side exposed v-AuNWs toward the electro-oxidation of eth...

In parallel to the burgeoning field of soft electronics, soft plasmonics focuses on the design and fabrication of plasmonic structures supported on elastomers and to understand how their properties respond to mechanical deformations. Here, we report on a partial ligand-stripping strategy to fabricate elastomer-supported gold nanobipyramid (NBP) plasmene nanosheets. Unlike spherelike building blocks, NBP-building blocks display complex orientation-dependent plasmonic responses to external strains. By collecting polarized plasmonic resonance spectra in conjunction with electrostatic eigenmode modeling, we reveal simultaneous changes in interparticle spacing and spatial orientations of NBP building blocks under mechanical strains. Such changes are directly related to initial NBP packing orders. Further analysis of strain sensitivities for various NBP plasmenes indicated that plasmonic spectra of ∼45°oriented samples are mostly susceptible to strain at acute polarized angles. The results presented may enable novel applications in future soft optoelectronic devices in sensing, encryption, and data storage.

In bioelectronics, gold thin films have been widely used as sensing electrodes for probing biological events due to their high conductivity, chemical inertness, biocompatibility, wide electrochemical window, and facile surface modification. However, they are intrinsically not stretchable, which limits their applications in detecting biological reactions when a soft biological system is mechanically deformed. Here, we report on a nanosphere lithography-based strategy to generate ordered microhole gold thin-film electrodes supported by elastomeric substrates. Both experimental and theoretical studies show that the presence of microholes substantially suppresses the catastrophic crack propagationthe main reason for electrical failure for a continuous gold film. As a result, the holey gold film achieves a ∼94% stretchable limit, after which the conductivity is lost, in contrast to ∼4% for the nonstructured counterpart. Furthermore, the pinhole gold electrode is successfully used to monitor the H 2 O 2 released from living cells under dynamic stretching conditions.