Fiber-based organic electrochemical transistors (FECTs) provide a new platform for the realization of an ultrafast and ultrasensitive biosensor, especially for the wearable dopamine (DA)-monitoring device. Here, we presented a fully filament-integrated fabric, it exhibited remarkable mechanical compatibility with the human body, and the minimum sensing unit was an organic electrochemical transistor (OECT) based on PVA-co-PE nanofibers (NFs) and polypyrrole (PPy) nanofiber network. The introduction of NFs notably increased the specific surface area and hydrophilicity of the PA6 filament, resulting in the formation of a large area of intertwined PPy nanofiber network. The electrical performance of PPy nanofiber network-modified fibers improved considerably. For the common FECTs, the typical on/off ratio was up to two orders of magnitude, and the temporal recovery time between on and off states was shortened to 0.34 s. Meanwhile, the device exhibited continuous cycling stability. In addition, the performances of FECT-based dopamine sensors depending on different gate electrodes have also been investigated. The PPy/NFs/PA6 filament-based dopamine sensor was more superior to the gold and platinum (Pt) wires, and the sensor presented long-term sensitivity with a detection region from 1 nM to 1 μM, rapid response time to a set of DA concentrations, remarkable selectivity in the presence of sodium chloride, uric acid, ascorbic acid and glucose, and superior reproducibility. Moreover, it could also be woven into the fabric product. The novel and wearable FECT device shows the potential to become the state-of-the-art DA-monitoring platform.

Flexible pressure sensors have attracted tremendous research interests due to their wide applications in wearable electronics and smart robots. The easy-to-obtain fabrication and stable signal output are meaningful for the practical application of flexible pressure sensors. The graphene/polyurethane foam composites are prepared to develop a convenient method for piezo-resistive devices with simple structure and outstanding sensing performance. Graphene oxide was prepared through the modified Hummers method. Polyurethane foam was kept to soak in the obtained graphene oxide aqueous solution and then dried. After that, reduced graphene oxide/polyurethane composite foam has been fabricated under air phase reduction by hydrazine hydrate vapor. The chemical components and micro morphologies of the prepared samples have been observed by using FT-IR and scanning electron microscopy (SEM). The results predicted that the graphene is tightly adhered to the bare surface of the pores. The pressure sensing performance has been also evaluated by measuring the sensitivity, durability, and response time. The results indicate that the value of sensitivity under the range of 0–6 kPa and 6–25 kPa are 0.17 kPa−1 and 0.005 kPa−1, respectively. Cycling stability test has been performed 30 times under three varying pressures. The signal output just exhibits slight fluctuations, which represents the good cycling stability of the pressure sensor. At the same stage, the response time of loading and unloading of 20 g weight turned out to be about 300 ms. These consequences showed the superiority of graphene/polyurethane composite foam while applied in piezo-resistive devices including wide sensitive pressure range, high sensitivity, outstanding durability, and fast response.

The tremendous progress of the wearable intelligent system has brought an urgent demand for flexible pressure sensors, especially for those possessing high sensing performances, simple manufacture technology, and efficient integration. In this work, hierarchical core−shell piezoresistive yarns (HCPYs), which contain internal silver-plated nylon electrodes and surface microporous structured carbon nanotubes (CNTs)/thermoplastic polyurethane (TPU) sensing layer, are designed and manufactured via facile wet-spinning accompanied by a water vapor coagulating bath. The obtained HCPY can either be inserted into traditional textiles to assemble a single-pressure sensor, or be woven into a textile-based flexible pressure sensors array with expected size and resolution, without compromising their comfort, breathability, and three-dimensional (3D) conformability. Simultaneously, to further enhance the sensing performance, the surface microporous structures of HCPYs are optimized by altering the treatment humidity and exposure time during the process of water vapor-induced phase separation. The wearable pressure sensors assembled by the optimal HCPY achieved a high sensitivity up to 84.5 N −1 , a good durability over 5000-cycle tests, a fast response time of 2.1 ms, and a recovery time of 2.4 ms. Moreover, the wearable pressure sensors have been successfully used to monitor physical signals and human motions. The textile-based flexible pressure sensors array has also been seamlessly integrated with sportswear to detect movements of the elbow joint and map spatial pressure distribution, which makes HCPY a promising candidate for constructing next-generation wearable electronics.

Wearable piezoresistive sensors have attracted wide attention for application in human activities monitoring, smart robots, medical detection, etc. However, most of the sensing signals collected from the piezoresistive sensor are triggered by coupling forces, such as the combination of tension and pressure. Thus, the piezoresistive sensor would be incapable of accurately monitoring and evaluating specific human motion due to the mutual interference from tension and pressure, as the tension is difficult to be decoupled or eliminated from the coupling forces. Herein a prestretchable conductive yarn (PCY) sensor with pressure sensitivity but tension insensitivity was introduced to remove the disturbance from tension. The PCY-based piezoresistive sensor is tension insensitive (gauge factor of 0.11) but pressure sensitive (sensitivity of 187.33 MPa–1). The fabric-based pressure sensor assembled with cross-arranged PCY weft and warp revealed magnified pressure sensitivity compared with the single PCY yarn sensor, as well as tension insensitivity to strain and tensile angle. Moreover, it possessed benign cyclicity during 5000 cycles of pressing/releasing. Therefore, the fabric piezoresistive sensor based on weaved conductive yarns is suitable for highly accurate and large area pressure detection, such as monitoring massage intensity of acupuncture points.

The rapid development of wearable electronics, humanoid robots, and artificial intelligence requires sensors to sensitively and stably detect external stress variations in large areas or on three-dimensional (3D) irregularly shaped surfaces while possessing the comfort. Most importantly, the flexibility and 3D compliance of sensors, and the fitting state of the interface between the sensor and the object are of great significance to the sensing accuracy and reliability. The ordered or random stacking and entangling of flexible and electrically conductive fiber materials can form a highly porous and mechanically stable fiber assembly. The changes in external stress can lead to the air trapped in the fiber assembly to flow in and out rapidly and repeatedly, as well as the reversible mechanical deformation of fiber materials. Correspondingly, the contact areas between electrically conductive fibers in the fiber assembly are reversibly changed, which makes the conductive and flexible fiber assembly be an ideal candidate for piezoresistive sensing material. It can be further expected that the statistical stability of contact points between conductive fibers under the stress may significantly increase with the decrease in fiber diameters. Herein, a new method to make a flexible piezoresistive sensor with conductive and porous fiber assembly was proposed. An ultrasensitive piezoresistive material was facilely prepared by fabricating conductive poly(vinyl alcohol-co-ethylene) (EVOH) nanofiber assemblies. The sensing performance of the piezoresistive sensor was optimized by regulating the nanofiber morphology, electrical conductivity, and mechanical properties. The flexible piezoresistive sensor exhibited a sensitivity of 2.79 kPa −1 , a response time of 3 ms, and a recovery time of 10 ms. The sensing performance at different working frequencies was stable and durable within 4500 cycling tests. The flexible sensor showed good pressure-sensing accuracy and reliability when used on irregular surfaces and therefore was further applied in the static monitoring of large-area spatial pressure distribution and the wearable intelligent interactive device, demonstrating great application potential.