Recent Advances in Nanowire-Based Wearable Physical Sensors

Abstract

Wearable electronics is a technology that closely integrates electronic devices with the human body or clothing, which can realize human-computer interaction, health monitoring, smart medical, and other functions. Wearable physical sensors are an important part of wearable electronics. They can sense various physical signals from the human body or the surrounding environment and convert them into electrical signals for processing and analysis. Nanowires (NW) have unique properties such as a high surface-to-volume ratio, high flexibility, high carrier mobility, a tunable bandgap, a large piezoresistive coefficient, and a strong light-matter interaction. They are one of the ideal candidates for the fabrication of wearable physical sensors with high sensitivity, fast response, and low power consumption. In this review, we summarize recent advances in various types of NW-based wearable physical sensors, specifically including mechanical, photoelectric, temperature, and multifunctional sensors. The discussion revolves around the structural design, sensing mechanisms, manufacture, and practical applications of these sensors, highlighting the positive role that NWs play in the sensing process. Finally, we present the conclusions with perspectives on current challenges and future opportunities in this field.

Keywords: health monitoring; human–machine interfaces; nanowires; wearable electronics; wearable sensors.

Figure 2

NW-based wearable strain sensors. (a–c) Resistive strain sensors. (a) Schematic illustration of (I) laser direct writing process to cut the outline of sensor and (II) weld AgNW network. Adapted with permission from [51]. Copyright 2022, American Chemical Society. (b) (I) SEM image and schematic illustration of an in-plane SiNW spring-guided growth along the predesigned step edge. (II) Schematic illustration of in-plane SiNW spring networks with electrode joints on a PDMS substrate. Adapted with permission from [52]. Copyright 2017, American Chemical Society. Adapted with permission from [83]. Copyright 2019, American Chemical Society. (c) (I) Schematic illustration of the fabrication of the fibrous strain sensor with a growth ring-like spiral structure. (II) Schematic for the change in AgNW networks in growth ring-like spiral structure during stretching and releasing cycle. (III) Optical image of knit glove integrated with the fibrous strain sensor. Adapted with permission from [64]. Copyright 2021 Elsevier Ltd. (d,e) Capacitive strain sensors. (d) (I) Exploded schematic of the electrospun sandwich-structured elastic film. (II) Schematic illustration of the strain-sensing mechanism of the capacitive e-skin based on electrospun sandwich-structured elastic films. Reprinted with permission from [65]. Copyright 2022 American Chemical Society. (e) (I) Schematic illustration of the interdigitated capacitive strain sensor based on AgNW. (II) Design Schematic of the in-plane interdigitated electrode pattern. Reprinted with permission from [49]. Copyright 2017 American Chemical Society.

Figure 7

NW-based multifunctional wearable sensors. (a) Schematic structure diagram of a multifunctional sensor based on an SF/AgNW composite film (I) and schematic structure diagram of its pressure-sensing mechanism (II) and temperature-sensing mechanism (III). Reprinted with permission from [154]. Copyright 2023, Elsevier Ltd.; (b) (I) Characterization of the multifunctional sensing properties of the SiNW fabrics. (II) Photograph of a robot integrated with three photodetectors, a temperature sensor, a pressure sensor, and two strain sensors, all based on the SiNW fabrics, as a schematic of wearable applications. Reprinted with permission from [155]. Copyright 2019, Springer Nature. (c) Conceptual diagram of a multimodal force sensor based on AgNWs, carbon nanofibers, and porous PDMS. Reprinted with permission from [156]. Copyright 2020, American Chemical Society. (d) (I) Schematic illustration of a stretchable dual-parameter sensor with “Brick and mortar” structure composed of AgNW, Mxene, pp:TeNW, and PEDOT:PSS. (II) I–V curves of the multifunctional sensor measured under different ΔT and diverse applied strains. Reprinted with permission from [157]. Copyright 2020, American Chemical Society. (e) Schematic diagram of a multifunctional device with a temperature sensor, a gas sensor, and three photodetectors using NWs with diverse materials. Reprinted with permission from [159] Copyright 2020, Springer Nature. (f) Exploded schematic of a multilayer multifunctional biosensor based on AgNWs, CNTs, ZnO, and PEDOT:PSS via a supersonic cold-spraying method. Reprinted with permission from [160]. Copyright 2022, Springer Nature.

Figure 1

Schematic diagram of the structure modes and sensor types of NW-based sensors. The structure types of NWs can be mainly divided into networks, planar arrays, vertical arrays, and composite fibers. Reprinted with permission from [51]. Copyright 2022, American Chemical Society. Reprinted with permission from [52]. Copyright 2017, American Chemical Society. Reprinted with permission from [53]. Copyright 2019, Elsevier. Reprinted with permission from [54]. Copyright 2019, American Chemical Society. The representative types of NW-based wearable physical sensors for applications in the human body, including temperature sensors, photodetectors, pressure sensors, acoustic sensors, strain sensors, and humidity sensors: Reprinted with permission from [55]. Copyright 2022, The Royal Society of Chemistry. Reprinted with permission from [56]. Copyright 2022, Wiley-VCH. Reprinted with permission from [50]. Copyright 2018, Springer Nature. Reprinted with permission from [57]. Copyright 2020, Wiley-VCH. Reprinted with permission from [58]. Copyright 2018, Springer Nature. Reprinted with permission from [59]. Copyright 2020, American Chemical Society.

Figure 3

NW-based wearable pressure sensors. (a,b) Resistive pressure sensors. (a) Schematic illustrations of the vertical AuNWs layer growing on micropatterned PDMS (I) and the structure of the resistive pressure sensor (II). Reprinted with permission from [94]. Copyright 2019, American Chemical Society. (b) (I) Exploded schematic of CNN-based pressure sensors. (II) Working principle schematic of the electroluminescent skin for pressure distribution imaging. Reprinted with permission from [50]. Copyright 2020, Springer Nature. (c,d) Capacitive pressure sensors. (c) Schematic illustration of fabricating processes for the capacitive pressure sensor with a wrinkled dielectric layer. Reprinted with permission from [98]. Copyright 2019, Wiley-VCH. (d) Mechanism schematic of AgNW-bacterial cellulose composite fiber-based capacitive pressure sensor. (I) At pressure-free state, two fibers are in touch within a small overlap area. (II) When pressure is applied, the overlap area significantly increases. Reprinted with permission from [99]. Copyright 2020, American Chemical Society. (e,f) Piezoelectric pressure sensors. (e) Schematic drawing of flexible self-powered piezoelectric pressure sensors based on radial p-n junction GaN NWs. Reprinted with permission from [100]. Copyright 2021, Elsevier B.V. (f) Schematic illustrations of p-GaN film/n-ZnO NW LED-based pressure sensor array for pressure distribution mapping (I), and energy band of p-GaN/n-ZnO heterostructure after applied compressive strain (II). Reprinted with permission from [53]. Copyright 2019, Elsevier Ltd. (g,h) triboelectric pressure sensors. (g) (I)Schematic illustration of the conducting-wrinkle-based pressure sensor. (II) Circuit diagram of the pressure sensor Reprinted with permission from [101]. Copyright 2019, Wiley-VCH. (h) (I)Exploded schematic of pressure sensor textile. (II) Schematic illustrations of the comparison of the triboelectric nanofibers with the smooth and rough surface. Adapted with permission from [102]. Copyright 2020, American Chemical Society.

Figure 4

NW-based wearable photodetectors. (a,b) Photoconductors. (a) Schematic illustration of biodegradable and disposable UV photodetectors for smart textiles. Reprinted with permission from [118]. Copyright 2023, Institute of Optics and Electronics, Chinese Academy of Sciences. (b) Schematic illustration of the flexible image sensor under polarized 1.55 μm light. Reprinted with permission from [122]. Copyright 2022, American Chemical Society. (c–e) photodiodes. (c) Schematic illustration of the wearable Te@TeSe photodetector textile. Reprinted with permission from [121]. Copyright 2021, Wiley-VCH. (d) Schematic illustration of the a-SiGe:H radial junction flexible photodetector and its detecting pulse at the wrist. Reprinted with permission from [56]. Copyright 2022, Wiley-VCH. (e) Schematic illustration and an optical image of the flexible UV photodetectors based on piezo-phototronic effect-enhanced photoresponse. Reprinted with permission from [124]. Copyright 2022, Elsevier Ltd.

Figure 5

NW-based wearable temperature sensors. (a) (I) Optical images of a temperature sensor based on AgNWs and PI at tensile strains of 0 and 100%, respectively. (II) Optical images of the as-established sensor attached to the skin of a male’s bicep (left). Scale bar: 10 mm. Temperature data were recorded by the sensor and an infrared thermometer during the workout on the biceps (right). Reprinted with permission from [133]. Copyright 2019, American Chemical Society. (b) (I) Schematic of a temperature sensor fabricated by printing Au@AgNW–PEG–PU nanocomposite ink on interdigitated electrodes. (II) Temperature-sensing principle diagram of the fabricated sensor. Reprinted with permission from [55]. Copyright 2022, The Royal Society of Chemistry. (c) A schematic illustration of artificial thermoreceptors (ATRs) based on aligned V₂O₅ NWs. Reprinted with permission from [134]. Copyright 2022, Wiley-VCH. (d) (I) Schematic of the sensing principle based on the thermoelectric effect of a hot-pressed Te/PEDOT:PSS composite thin film. (II) Photograph of the developed temperature sensor, which has the capability to detect finger temperature. Reprinted with permission from [135]. Copyright 2023, The Royal Society of Chemistry.

Figure 6

(a) Airflow sensor array based on single cm-SiNW. Reprinted with permission from [139]. Copyright 2021, American Chemical Society. (b) Resistive acoustic sensor with point crack on PDMS embedded with V-AuNWs. Reprinted with permission from [57]. Copyright 2020, Wiley-VCH. (c) Schematic illustration of a Fe₃O₄@AuNWs nanoparticle, which provides additional magnetic sensing functionality. Reprinted with permission from [140]. Copyright 2019, Elsevier B.V. (d) Diagrams that reveal the structure and sensing mechanism of a SAW humidity sensor based on ZnO NWs and GQDs. Reprinted with permission from [59]. Copyright 2020, American Chemical Society.