Abstract
1. Introduction
Flexible and stretchable sensors can be uniformly attached to the surface of skin or organs due to exceptional features such as light weight, stretchability, low modulus, high flexibility and ultrathinness, thus enhancing the sensing properties of personal healthcare and human activity detection[
Nanofibers/nanowires, as a typical one-dimensional (1D) nanostructured material, has been widely concerned in recent years due to their good mechanical flexibility, with remarkable tolerance against mechanical bending and exceptionally low flexural rigidities, which make them a promising active material for flexible and stretchable sensors[
Here, we focus on latest developments in the nanofibers/nanowires-based flexible and stretchable sensors with enhanced mechanical performance. First, we summarize the main advantages of using various types of 1D nanofibers/nanowires in flexible and stretchable sensors (Fig. 1). Then, we also comprehensively introduce some typical works of flexible and stretchable sensors applications of nanofiber/nanowires, involving pressure sensor and strain sensor. Finally, the future perspectives of flexible and stretchable sensors and the challenges and opportunities for future research directions are briefly discussed.
Figure 1.(Color online) Schematic of nanofibers/nanowires-based flexible and stretchable sensors.
2. 1D nanostructure nanofiber/nanowire and their advantages
Nanofibers/nanowires materials as a typical one-dimensional nanostructured material, have two kinds of external dimensions: 1) nanoscale (less than or equal to 100 nm) and 2) larger three-dimensional dimensions[
Figure 2.(Color online) Graphical summaries of advantages of possible flexible and stretchable sensors application of 1D nanofibers/nanowires materials.
1) Relatively higher carrier mobility and size-dependent physical properties: because of the above properties, 1D nanofibers/nanowires have a wide range of potential applications in high-performance flexible devices. For example, the 1D single-walled carbon nanotube (SWCNT)-based sensor has aroused researcher’s enthusiasm. As a result, SWCNT is expected to become a candidate for high-performance electronic devices because of its good mechanical flexibility, high mobility (> 100 000 cm2 V–1s–1) and excellent optical transparency[
2) Large specific surface area: Compared with bulk materials, nanofibers show a larger specific surface area, which makes the adhesion of target objects, gases and external stimuli enhanced. For example, the surface area of the fiber with direct 5–500 nm is about 10 000–100 000 m2/kg[
3) 1D wire-shape structure, nanofiber or nanowire flexible electron reliable and effective conductive channel, can provide 1D path carrier. In addition, the effective mobility of flexible electronic devices is greatly improved because the carriers do not have to cross many boundaries between adjacent nanocrystals.
4) Large length–diameter ratio, 1D nanofibers and nanowires are more mechanically relaxed in their natural growth direction. Under a given bending radius, the linear structure has a strong stress recovery ability. Compared with other nanostructures, the diameter of the linear structure is very small, and the deformation process is difficult to lead to the transverse formation of cracks.
5) Small size, the size of the nanofiber/nanowire has a key influence on the response time of the system to external stimuli (e.g. gas, humidity, light, temperature, force and electricity). Based on NaBEt[
3. Flexible and stretchable sensor applications of 1D nanofibers/nanowires
The response of flexible and stretchable electronic devices to different external stimuli mainly depends on the active materials[
3.1. 1D nanofibers/nanowires for flexible pressure sensor
The application of next generation pressure sensor is gradually expanding to intelligent artificial limb, humanoid robot, wearable devices and electronic skin (e-skin)[
Figure 3.(Color online) (a) Illustration of the preparation and structure of the Au nanowires-based flexible pressure sensor. (b) Optical image of the Au nanowires-based flexible pressure sensor. Inset show the SEM image of Au nanowires (scale bar, 100 mm). (c) Optical image of device attached on the wrist. (d) pulse change records of device attached on the wrist. (e) Schematic illustration of the setup for acoustic vibration sensing. (f) The current responses to the acoustic vibrations from a piece of music. Reproduced from Ref. [
In addition to the metal NWs, polymer nanofibers have also been used as the sensing materials for flexible pressure sensor. Recently, Lou et al.[
Figure 4.(Color online) (a) Illustration of fabrication process of rGO/PVDF nanofibers-based flexible pressure sensor. (b) SEM image of rGO/PVDF nanofibers. (c) Illustration of a flexible pressure sensor structure. (d) Sensitivity of rGO/PVDF nanofibers-based flexible pressure sensor under different force conditions. (e) dynamic response curves of rGO/PVDF nanofibers-based flexible pressure sensor for different objects. (f, g) Response curves of rGO/PVDF nanofibers-based flexible pressure sensor attached on the wrist under different condition. Reproduced from Ref. [
Oxide NWs with piezoelectric properties have also been used in flexile self-powered pressure sensors. A pressure display and recording (PVR) system is developed by Han et al. as shown in Figs. 4(h)–4(k)[
3.2. 1D nanofibers/nanowires for flexible strain sensor
Highly sensitive and stretchable flexible strain sensor can test the whole range of human motion, which is an important part of many specific fields, such as soft robot and human–machine, real-time record of human daily physical activity and personalized health care monitoring[
Figure 5.(Color online) (a) Schematic structure and (b) high-magnification SEM image of the P(VDF-TrFE)-based conductive fiber. (c) Pulse and (d) spoke response curves of the P(VDF-TrFE)-based fibrous sensor. (e) A data glove fixed with ten-fiber strain sensors. Reproduced from Ref. [
CNT represents the basis of most traditional tensile strain sensors because its performance far exceeds that of known organic semiconductor and metal/metal oxide-based flexible sensors[
Figure 6.(Color online) (a) Illustration of fabrication process of SWCNT-based strain sensor. (b) Optical image of the SWCNT-based strain sensor under strain. (c) SEM image of SWCNT. (d) Stretchable wearable sensors on the human body. (e) Finger motion detection of stretchable wearable sensors. Reproduced from Ref. [
4. Conclusion
In this review, we summarized the latest research work of 1D nanofiber/nanowire in this field of flexible and stretchable sensors (such as flexible pressure sensor and strain sensor). The exciting results highlighted in this paper confirm that their unique one-dimensional structure and good mechanical toughness and flexibility have strong advantages in the field of flexible and stretchable sensors. We also summarize the application of one-dimensional nanofibers and nanowires in flexible sensors and the performance of advanced flexible and stretchable sensors made of this kind of nanomaterials. The exciting results obtained so far can arouse researchers' interest in the research of new high performance flexible electronic devices.
To further improve the performance of flexible and stretchable sensors, the rationalization and design of one-dimensional nanofibers and nanowires should be paid more attention. Although one-dimensional nano materials have been widely used in the field of flexible sensors, there are still some challenges in improving their performance. 1) The effects of structure graphing and controllability on device performance are obvious. Therefore, it is urgent to adjust the assembly and orientation device of one-dimensional structure more precisely, so that it has high deformation performance. 2) In order to manufacture and integrate flexible and stretchable sensors, the yield of one-dimensional nanostructures is still significantly insufficient. At present, one-dimensional nanostructure assembly technology has advantages and disadvantages. In this case, printing one-dimensional nanostructures on flexible substrates will bring some problems. Therefore, a more suitable one-dimensional nanostructure assembly method is needed to provide high-quality one-dimensional nanofibers and nanowires for flexible and stretchable sensors.
Acknowledgements
The authors sincerely acknowledge financial support from the National Natural Science Foundation of China (NSFC Grant No. 61625404), the Science and Technology Development Plan of Jilin Province (20190103135JH) and Young Elite Scientists Sponsorship Program by CAST (2018QNRC001).
References
[1] L L Wang, D Chen, K Jiang et al. New insights and perspectives into biological materials for flexible electronics. Chem Soc Rev, 46, 6764(2017).
[2] L Zhao, K Wang, W Wei et al. High-performance flexible sensing devices based on polyaniline/MXene nanocomposites. InfoMat, 1, 407(2019).
[3] K Wang, Z Lou, L Wang et al. Bioinspired interlocked structure-induced high deformability for two-dimensional titanium carbide (MXene)/natural microcapsule-based flexible pressure sensors. ACS Nano, 13, 9139(2019).
[4] Z Lou, L Wang, K Jiang et al. Programmable three-dimensional advanced materials based on nanostructures as building blocks for flexible sensors. Nano Today, 26, 176(2019).
[5] Z N Bao, X D Chen. Flexible and stretchable device. Adv Mater, 28, 4177(2016).
[6] D Ye, Y Ding, Y Duan et al. Large-scale direct-writing of aligned nanofibers for flexible electronics. Small, 14, 1703521(2018).
[7] J H Jin, D Lee, H G Im et al. Chitin nanofiber transparent paper for flexible green electronics. Adv Mater, 28, 5169(2016).
[8] K Wang, W Wei, Z Lou et al. 1D/2D heterostructure nanofiber flexible sensing device with efficient gas detectivity. Appl Surf Sci, 479, 209(2019).
[9] K Wang, J Li, W Li et al. Highly active co-based catalyst in nanofiber matrix as advanced sensing layer for high selectivity of flexible sensing device. Adv Mater Technol, 4, 1800521(2019).
[10] L Wang, S Chen, W Li et al. Grain-boundary-induced drastic sensing performance enhancement of polycrystalline-microwire printed gas sensors. Adv Mater, 31, 1804583(2019).
[11] Z Lou, G Z Shen. Flexible photodetectors based on 1D inorganic nanostructures. Adv Sci, 3, 1500287(2016).
[12] L Wang, J Deng, Z Lou et al. Cross-linked p-type Co3O4 octahedral nanoparticles in 1D n-type TiO2 nanofibers for high-performance sensing devices. J Mater Chem A, 2, 10022(2014).
[13] J Li, L Wang, L Li et al. Metal sulfides@carbon microfiber networks for boosting lithium ion/sodium ion storage via a general metal–aspergillus niger bioleaching strategy. ACS Appl Mater Interfaces, 11, 8072(2019).
[14] X J Zhuang, C Z Ning, A Pan. Composition and bandgap-graded semiconductor alloy nanowires. Adv Mater, 24, 13(2012).
[15] A Menzel, K Subannajui, F Güder. Multifunctional ZnO-nanowire-based sensor. Adv Funct Mater, 21, 4342(2011).
[16] B M Wen, J E Sader, J J Boland et al. Mechanical properties of ZnO nanowires. Phys Rev Lett, 101, 175502(2008).
[17] Z Liu, J Xu, D Chen et al. Flexible electronics based on inorganic nanowires. Chem Soc Rev, 44, 161(2015).
[18] S A Chowdhury, M C Saha, S Patterson et al. Highly conductive polydimethylsiloxane/carbon nanofiber composites for flexible sensor applications. Adv Mater Technol, 4, 1800398(2019).
[19] N Nan, J He, X You et al. A stretchable, highly sensitive, and multimodal mechanical fabric sensor based on electrospun conductive nanofiber yarn for wearable electronics. Adv Mater Technol, 4, 1800338(2019).
[20] L F Chen, Y Feng, H W Liang et al. Macroscopic-scale three-dimensional carbon nanofiber architectures for electrochemical energy storage devices. Adv Energy Mater, 7, 1700826(2017).
[21] S J Choi, L Persano, A Camposeo et al. Electrospun nanostructures for high performance chemiresistive and optical sensors. Macromol Mater Eng, 302, 1600569(2017).
[22] R Rasouli, A Barhoum, M Bechelany. Nanofibers for biomedical and healthcare applications. Macromol Biosci, 19, 1800256(2019).
[23] A Camposeo, L Persano, D Pisignano et al. Light-emitting electrospun nanofibers for nanophotonics and optoelectronics. Macromol Mater Eng, 298, 487(2013).
[24] L T H Nguyen, S Chen, N K Elumalai et al. Biological, chemical, and electronic applications of nanofibers. Macromol Mater Eng, 298, 822(2013).
[25] J Wang, C Lu, K Zhang. Textile-based strain sensor for human motion detection. Energy Environ Mater, 0, 1(2019).
[26] T J Sill, H A Recum. Electrospinning: applications in drug delivery and tissue engineering. Biomaterials, 29, 1989(2008).
[27] Y Zhang, S Yuan, X Feng et al. Preparation of nanofibrous metal–organic framework filters for efficient air pollution control. J Am Chem Soc, 138, 5785(2016).
[28] X T Shuai, P L Zhu, W J Zeng et al. Highly sensitive flexible pressure sensor based on silver nanowires-embedded polydimethylsiloxane electrode with microarray structure. ACS Appl Mater Interfaces, 9, 26314(2017).
[29]
[30] F K Ko, V Kuznetsov, E Flahaut. Formation of nanofibers and nanotubes production. Nanoeng Nanofibrous Mater(2004).
[31] B Nabet. When is small good? on unusual electronic properties of nanowires. ECE Department, Philadelphia, 19104(2002).
[32] A El-Aufy, B Nabet, F Ko. Carbon nanotube reinforced (PEDT/PAN) nanocomposite for wearable electronics. Polym Prepr, 44, 134(2003).
[33] L Wang, K Wang, Z Lou et al. Plant-based modular building blocks for “green” electronic skins. Adv Funct Mater, 28, 1804510(2018).
[34] L Wang, J A Jackman, W B Ng et al. Flexible, graphene-coated biocomposite for highly sensitive, real-time molecular detection. Adv Funct Mater, 26, 8623(2016).
[35] L Wang, J A Jackman, J H Park et al. A flexible, ultra-sensitive chemical sensor with 3D biomimetic templating for diabetes-related acetone detection. J Mater Chem B, 5, 4019(2017).
[36] G Y Ren, F Y Cai, B Z Li et al. Flexible pressure sensor based on a poly(VDF-TrFE) nanofiber web. Macromol Mater Eng, 298, 541(2013).
[37] J H Lee, J Kim, D Liu et al. Highly aligned, anisotropic carbon nanofiber films for multidirectional strain sensors with exceptional selectivity. Adv Funct Mater, 29, 1901623(2019).
[38] Q Wang, M Q Jian, C Y Wang et al. Carbonized silk nanofiber membrane for transparent and sensitive electronic skin. Adv Funct Mater, 27, 1605657(2017).
[39] G R Zhao, B S Huang, J X Zhang, at et. Electrospun poly(l-lactic acid) nanofibers for nanogenerator and diagnostic sensor applications. Macromol Mater Eng, 302, 1600476(2017).
[40] Q Gao, H Meguro, S Okamoto et al. Flexible tactile sensor using the reversible deformation of poly(3-hexylthiophene) nanofiber assemblies. Langmuir, 28, 17593(2012).
[41] J Wang, R Suzuki, M Shao et al. Capacitive pressure sensor with wide-range, bendable, and high sensitivity based on the bionic komochi konbu structure and Cu/Ni nanofiber network. ACS Appl Mater Interfaces, 11, 11928(2019).
[42] K Roy, S K Ghosh, A Sultana et al. A self-powered wearable pressure sensor and pyroelectric breathing sensor based on GO interfaced PVDF nanofibers. ACS Appl Nano Mater, 2, 2013(2019).
[43] G R Zhao, X D Zhang, X Cui et al. Piezoelectric polyacrylonitrile nanofiber film-based dual-function self-powered flexible sensor. ACS Appl Mater Interfaces, 10, 15855(2018).
[44] K Qi, J X He, H B Wang et al. A highly stretchable nanofiber-based electronic skin with pressure-, strain-, and flexion-sensitive properties for health and motion monitoring. ACS Appl Mater Interfaces, 9, 42951(2017).
[45] M Lou, I Abdalla, M M Zhu et al. Hierarchically rough structured and self-powered pressure sensor textile for motion sensing and pulse monitoring. ACS Appl Mater Interfaces, 12, 1597(2020).
[46] S Y Wu, J Zhang, R B Ladani et al. Novel electrically conductive porous PDMS/Carbon nanofiber composites for deformable strain sensors and conductors. ACS Appl Mater Interfaces, 9, 14207(2017).
[47] S Garain, S Jana, T Kumar et al. Design of in situ poled Ce3+-doped electrospun PVDF/graphene composite nanofibers for fabrication of nanopressure sensor and ultrasensitive acoustic nanogenerator. ACS Appl Mater Interfaces, 8, 4532(2016).
[48] W L Deng, T Yang, L Jing et al. Cowpea-structured PVDF/ZnO nanofibers based flexible self-powered piezoelectric bending motion sensor towards remote control of gestures. Nano Energy, 55, 516(2019).
[49] J F Gao, B Li, X W Huang et al. Electrically conductive and fluorine free superhydrophobic strain sensors based on SiO2/graphene-decorated electrospun nanofibers for human motion monitoring. Chem Eng J, 373, 298(2019).
[50] T Yan, Z Wang, Y Q Wang et al. Carbon/graphene composite nanofiber yarns for highly sensitive strain sensors. Mater Des, 143, 214(2018).
[51] M F Lin, J Q Xiong, J X Wang et al. Core-shell nanofiber mats for tactile pressure sensor and nanogenerator applications. Nano Energy, 44, 248(2018).
[52] D W Jiang, Y Wang, B Li et al. Flexible sandwich structural strain sensor based on silver nanowires decorated with self-healing substrate. Macromol Mater Eng, 304, 1900074(2019).
[53] M Kang, J H Park, K I Lee et al. Fully flexible and transparent piezoelectric touch sensors based on ZnO nanowires and BaTiO3-added SiO2 capping layers. Phys Status Solidi A, 212, 2005(2015).
[54] Y Wang, L P Zhu, C F Du. Flexible difunctional (pressure and light) sensors based on ZnO nanowires/graphene heterostructures. Adv Mater Interfaces, 7, 1901932(2000).
[55] T Lee, W Lee, S W Kim et al. Flexible textile strain wireless sensor functionalized with hybrid carbon nanomaterials supported ZnO nanowires with controlled aspect ratio. Adv Funct Mater, 26, 6206(2016).
[56] X Q Shi, M Z Peng, J Z Kou et al. A flexible GaN nanowire array-based schottky-type visible light sensor with strain-enhanced photoresponsivity. Adv Electron Mater, 1, 1500169(2015).
[57] Y Kim, J W Kim. Silver nanowire networks embedded in urethane acrylate for flexible capacitive touch sensor. Appl Surf Sci, 363, 1(2016).
[58] Y Y Peng, M L Que, H E Lee et al. Achieving high-resolution pressure mapping via flexible GaN/ZnO nanowire LEDs array by piezo-phototronic effect. Nano Energy, 58, 633(2019).
[59] X J Xu, R R Wang, P Nie et al. Copper nanowire-based aerogel with tunable pore structure and its application as flexible pressure sensor. ACS Appl Mater Interfaces, 9, 14273(2017).
[60] M Amjadi, A Pichitpajongkit, S Lee et al. Highly stretchable and sensitive strain sensor based on silver nanowire–elastomer nanocomposite. ACS Nano, 8, 5154(2014).
[61] C Lou, N S Liu, H Zhang et al. A new approach for ultrahigh-performance piezoresistive sensor based on wrinkled PPy film with electrospun PVA nanowires as spacer. Nano Energy, 41, 527(2017).
[62] S Y Xu, Y W Yeh, G Poirier. Flexible piezoelectric PMN–PT nanowire-based nanocomposite and device. Nano Lett, 13, 2393(2013).
[63] L Wang, J A Jackman, E L Tan et al. High-performance, flexible electronic skin sensor incorporating natural microcapsule actuators. Nano Energy, 36, 38(2017).
[64] Z Lou, S Chen, L Wang. Ultrasensitive and ultraflexible e-skins with dual functionalities for wearable electronics. Nano Energy, 38, 28(2017).
[65] L Q Tao, K N Zhang, H Tian et al. Graphene-paper pressure sensor for detecting human motions. ACS Nano, 11, 8790(2017).
[66] Y Ren, Y D Zou, Y Liu et al. Synthesis of orthogonally assembled 3D cross-stacked metal oxide semiconducting nanowires. Nat Mater, 19, 203(2020).
[67] L Wang, X Luo, X Zheng et al. Direct annealing of electrospun synthesized high-performance porous SnO2 hollow nanofibers for gas sensors. RSC Adv, 3, 9723(2013).
[68] Z Lou, L Wang, R Wang et al. Synthesis and ethanol sensing properties of SnO2 nanosheets via a simple hydrothermal route. Solid-State Electron, 76, 91(2012).
[69] S J Han, C R Liu, H H Xu et al. Multiscale nanowire-microfluidic hybrid strain sensors with high sensitivity and stretchability. npj Flex Electron, 2, 16(2018).
[70] S Gong, W Schwalb, Y Wang et al. A wearable and highly sensitive pressure sensor with ultrathin gold nanowires. Nat Commun, 5, 3132(2014).
[71] B Zhu, Y Ling, L W Yap et al. Hierarchically structured vertical gold nanowire array-based wearable pressure sensors for wireless health monitoring. ACS Appl Mater Interfaces, 11, 29014(2019).
[72] Z Lou, S Chen, L Wang et al. An ultra-sensitive and rapid response speed graphene pressure sensors for electronic skin and health monitoring. Nano Energy, 23, 7(2016).
[73] G Wang, T Liu, X C Sun et al. Flexible pressure sensor based on PVDF nanofiber. Sens Actuators A, 280, 319(2018).
[74] X Han, W Du, M Chen et al. Visualization recording and storage of pressure distribution through a smart matrix based on the piezotronic effect. Adv Mater, 29, 1701253(2017).
[75] Z Chen, Z Wang, X Li et al. Flexible piezoelectric-induced pressure sensors for static measurements based on nanowires/graphene heterostructures. ACS Nano, 11, 4507(2017).
[76] Y Q Li, Y Samad, T Taha et al. Highly flexible strain sensor from tissue paper for wearable electronics. ACS Sustain Chem Eng, 4, 4288(2016).
[77] J Oh, J C Yang, J O Kim et al. Pressure insensitive strain sensor with facile solution-based process for tactile sensing applications. ACS Nano, 12, 8, 7546(2018).
[78] J Zhang, J Liu, R Zhuang et al. Single MWNT-glass fiber as strain sensor and switch. Adv Mater, 23, 3392(2011).
[79] Y Peng, J Lu, D Peng et al. Dynamically modulated GaN whispering gallery lasing mode for strain sensor. Adv Funct Mater, 29, 1905051(2019).
[80] W Zhou, Y Li, P Li et al. Metal mesh as a transparent omnidirectional strain sensor. Adv Mater Technol, 4, 1800698(2019).
[81] J Ren, W Zhang, Y Wang et al. A graphene rheostat for highly durable and stretchable strain sensor. InfoMat, 1, 396(2019).
[82] S Chen, Y Song, D Ding et al. Flexible and anisotropic strain sensor based on carbonized crepe paper with aligned cellulose fibers. Adv Funct Mater, 28, 1802547(2018).
[83] B M Lee, J Y Oh, H Cho et al. Ultraflexible and transparent electroluminescent skin for real-time and super-resolution imaging of pressure distribution. Nat Commun, 11, 663(2020).
[84] Q J Sun, W Seung, B J Kim et al. Active matrix electronic skin strain sensor based on piezopotential-powered graphene transistors. Adv Mater, 27, 3411(2015).
[85] S Chen, Z Lou, D Chen et al. Polymer-enhanced highly stretchable conductive fiber strain sensor used for electronic data gloves. Adv Mater Technol, 1600136(2016).
[86] E Roh, B U Hwang, D Kim et al. Stretchable, transparent, ultrasensitive, and patchable strain sensor for human–machine interfaces comprising a nanohybrid of carbon nanotubes and conductive elastomers. ACS Nano, 9, 6252(2015).
[87] T Yamada, Y Hayamizu, Y Yamamoto et al. A stretchable carbon nanotube strain sensor for human-motion detection. Nat Nanotechnol, 6, 296(2011).
[88] G Choi, H Jang, S Oh et al. A highly sensitive and stress-direction-recognizing asterisk-shaped carbon nanotube strain sensor. J Mater Chem C, 7, 9504(2019).
Set citation alerts for the article
Please enter your email address