Thread/fabric-based microfluidic device for sweat sensing and monitoring.

According to the sensing mechanism, pressure sensors can be divided into five types: piezoelectric, [1,2] piezoelectric resistivity, [3][4][5][6] capacitance, [7,8] triboelectric, [9,10] and transistor. [11] Piezoresistive sensors have attracted much attention in recent years due to their simple design, low manufacturing cost, good signal repeatability, low power consumption, low working voltage, and simple measurement scheme. [12][13][14][15][16][17][18] The elastic pressure sensor is usually composed of sensing material, substrate material, and electrode. The sensing material can be filled or coated on the substrate material to activate the conductive path. Under the external pressure, the contact area between the surface conductive elements increases significantly, resulting in a significant decrease in the path resistance or contact resistance. The change of resistance is due to the deformation of the microstructure under pressure, which leads to the change of the contact area. The traditional rigid material pressure sensor has been eliminated due to its poor reliability and low applicability. As an optional piezoresistive material, nanomaterials have been proved to be potential components of novel strain sensors with enhanced performance. High-performance sensor devices based on several typical nanostructures, such as carbon nanotubes [19,20] and graphene, have been developed. [21] However, the sensors based on these materials have some defects, such as complex manufacturing processes and unknown toxicity.Sensing material is the essential component of a pressure sensor. In terms of sensing materials, metal nanomaterials, as one of the most popular multifunctional conductive materials, have been widely used in chemistry, biomedical, optical, and other fields. [22] Specifically, gold nanowires (AuNWs) are a flexible filamentous structure in the nanoscale and behave like polymer chains because of their ultrathin nature (2 nm in width and >10 000 in aspect ratio). [23] AuNWs have the advantages of high chemical inertness, good biocompatibility, wide electrochemical window, high conductivity, and easy surface modification that depends on thiol gold chemistry. Zhang and co-workers reported a pulse monitoring sensor based on AuNWs and polyacrylamide

Textile-based flexible electronic devices have attracted tremendous attention in wearable sensors due to their excellent skin affinity and conformability. However, the washing process of such devices may damage the electronic components. Here, a textile-based piezoresistive sensor with ultrahigh sensitivity was fabricated through the layered integration of gold nanowire (AuNW)-impregnated cotton fabric and silver ink screen-printed nylon fabric electrodes, sealing with Parafilm. The prepared piezoresistive sensing patch exhibits outstanding performance, including high sensitivity (914.970 kPa–1, <100 Pa), a fast response time (load: 38 ms, recovery: 34 ms), and a low detection limit (0.49 Pa). More importantly, it can maintain a stable signal output even after 30 000 s of loading–unloading cycles. Furthermore, this sensing patch can efficiently detect breathing, pulse, heart rate, and joint movements during the activities. After five cycles of mechanical washing, the piezoresistive performance keeps 90.3%, demonstrating the high feasibility of this sensor in practical applications. This sensor has a simple fabrication, with good fatigue resistance and durability due to its all-fabric core element. It provides a strategy to address the machine-washing issues in textile electronics. This washable textile sensor is expected to show significant potential in future applications of health monitoring, human–machine interfaces, and artificial skin.

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