Flexible sensors that efficiently detect various stimuli relevant to specific environmental or biological species have been extensively studied due to their great potential for the Internet of Things and wearable electronics applications. The application of flexible and stretchable electronics to device-engineering technologies has enabled the fabrication of slender, lightweight, stretchable, and foldable sensors. Here, recent studies on flexible sensors for biological analytes, ions, light, and pH are outlined. In addition, contemporary studies on device structure, materials, and fabrication methods for flexible sensors are discussed, and a market overview is provided. The conclusion presents challenges and perspectives in this field.

Recently, skin sensors have obtained considerable attentions for potential applications in skin prosthetics, healthcare monitoring, and humanoid robotics. In order to further extend the practical applications, a dynamic broad range response with excellent sensitivity is important for skin sensors in sensing pressure, which eventually simplify the sensing system devoid of extra signal processing. On the other aspect, skin sensors with multifunctional sensing

The crystal structure, magnetic and electrical transport properties of the sodium-doped lanthanum manganites La1-xNaxMnO3 (0.07⩽x⩽0.40) have been studied in detail using x-ray powder diffraction, atomic absorption spectroscopy, a SQUID (superconducting quantum interference device) magnetometer and the four-probe resistivity measurement technique. A rhombohedrally distorted perovskite structure has been observed in the range 0.07⩽x⩽0.20. Both the lattice parameter and unit-cell volume decrease with increase in the Na content. A ferromagnetic-to-paramagnetic phase transition associated with a metal-insulator transition is observed for all the La1-xNaxMnO3 compounds. There is a systematic change in both the Mn-O-Mn bond angle and the tolerance factor with Na content. The compositional variation of the magnetic and metal-insulator transition temperatures is explained as due to the distortion of the MnO6 octahedron and increase in the tolerance factor that controls the hopping interaction. In the metallic region a ρ~AT2 behaviour is observed due to the magnon excitation effect. The resistivity shows a field-dependent minimum at low temperature that has been explained as due to the intergrain transport phenomenon.

The miniaturization of integrated fluidic processors affords extensive benefits for chemical and biological fields, yet traditional, monolithic methods of microfabrication present numerous obstacles for the scaling of fluidic operators. Recently, researchers have investigated the use of additive manufacturing or “three-dimensional (3D) printing” technologies – predominantly stereolithography – as a promising alternative for the construction of submillimeter-scale fluidic components. One challenge, however, is that current stereolithography methods lack the ability to simultaneously print sacrificial support materials, which limits the geometric versatility of such approaches. In this work, we investigate the use of multijet modelling (alternatively, polyjet printing) – a layer-by-layer, multi-material inkjetting process – for 3D printing geometrically complex, yet functionally advantageous fluidic components comprised of both static and dynamic physical elements. We examine a fundamental class of 3D printed microfluidic operators, including fluidic capacitors, fluidic diodes, and fluidic transistors. In addition, we evaluate the potential to advance on-chip automation of integrated fluidic systems via geometric modification of component parameters. Theoretical and experimental results for 3D fluidic capacitors demonstrated that transitioning from planar to non-planar diaphragm architectures improved component performance. Flow rectification experiments for 3D printed fluidic diodes revealed a diodicity of 80.6 ± 1.8. Geometry-based gain enhancement for 3D printed fluidic transistors yielded pressure gain of 3.01 ± 0.78. Consistent with additional additive manufacturing methodologies, the use of digitally-transferrable 3D models of fluidic components combined with commercially-available 3D printers could extend the fluidic routing capabilities presented here to researchers in fields beyond the core engineering community.

Piezoresistive microsensors are considered to be essential components of the future wearable electronic devices. However, the expensive cost, complex fabrication technology, poor stability, and low yield have limited their developments for practical applications. Here, we present a cost-effective, relatively simple, and high-yield fabrication approach to construct highly sensitive and ultrastable piezoresistive sensors using a bioinspired hierarchically structured graphite/polydimethylsiloxane composite as the active layer. In this fabrication, a commercially available sandpaper is employed as the mold to develop the hierarchical structure. Our devices exhibit fascinating performance including an ultrahigh sensitivity (64.3 kPa), fast response time (<8 ms), low limit of detection of 0.9 Pa, long-term durability (>100 000 cycles), and high ambient stability (>1 year). The applications of these devices in sensing radial artery pulses, acoustic vibrations, and human body motion are demonstrated, exhibiting their enormous potential use in real-time healthcare monitoring and robotic tactile sensing.

Layered serpentine Ni3Ge2O5(OH)4 is compositionally active and structurally favorable for adsorption and diffusion of reactants in oxygen evolution reactions (OER). However, one of the major problems for these materials is limited active sites and low efficiency for OER. In this regard, a new catalyst consisting of layered serpentine Ni3Ge2O5(OH)4 nanosheets is introduced via a controlled one‐step synthetic process where the morphology, size, and layers are well tailored. The theoretical calculations indicate that decreased layers and increased exposure of (100) facets in serpentine Ni3Ge2O5(OH)4 lead to much lower Gibbs free energy in adsorption of reactive intermediates. Experimentally, it is found that the reduction in number of layers with minimized particle size exhibits plenty of highly surface‐active sites of (100) facets and demonstrates a much enhanced performance in OER than the corresponding multilayered nanosheets. Such a strategy of tailoring active sites of serpentine Ni3Ge2O5(OH)4 nanosheets offers an effective method to design highly efficient electrocatalysts.

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Recently, flexible organic field-effect transistor (OFET)-based pressure sensors have been attracting significant interest for promising applications in electronic skin (e-skin) and wearable healthcare monitoring systems. However, it is still challenging to achieve the low-power flexible OFET-based pressure sensors by a simple and costeffective approach. Herein, high-k Al 2 O 3 dielectrics on aluminum foil have been developed by a simple printing approach, and their applications in flexible low-power organic field-effect transistors (OFETs) and pressure sensor are presented. The high-k Al 2 O 3 dielectric films prepared by our method are robust and large-area compatible, leading to a high areal capacitance and low leakage current density. Furthermore, the flexible OFET devices based on the printed Al 2 O 3 dielectric film exhibit a field-effect mobility of 0.65 cm 2 /(V s), current on/off ratio up to 10 5 , and good mechanical stability. Additionally, the OFET devices exhibit excellent uniformity, indicating the printed Al 2 O 3 dielectric is a promising candidate to fabricate the OFETs on a large scale. The extended gate OFET-based pressure sensor achieves a high pressure sensitivity of 8 kPa −1 at an operation voltage as low as −2 V and a fast response time of <100 ms. On the merits of the high-k dielectric constant, low leakage current, and large-area compatibility, the printed Al 2 O 3 prepared by our method will boost the development of the flexible low-power transistor-based pressure sensors for e-skin and heath monitoring applications.