综述-石墨烯在柔性可穿戴传感器的设计与应用

研究背景

柔性传感器的类型通常要求器件具有灵活性、可拉伸性、轻量级、无毒性和出色的器件性能。石墨烯是一种二维层状材料，具有非常独特的结构特性和电、光、热特性。这些特性使得石墨烯可被用于柔性电子设备、薄膜涂层和其他领域。特别是，石墨烯拥有新的柔性和可穿戴技术所需的材料特性，并已成为开发轻型和柔性传感设备的重要候选材料。在这篇综述中，作者主要关注用于物理信号传感的柔性石墨烯结构和装置的设计。一般来说，基于石墨烯的传感器可以根据被测信号的应用情况分为物理传感器(如光、电、力、温度等)、化学传感器(如气体、分子、离子、PH值、化学电位等)、生物传感器(如生物组织、微生物、生物分子、蛋白质、细菌、病毒等)以及相关的集成智能系统。在此，作者回顾了如何设计一个实现特定功能的灵活的物理信号传感器，并展示其相关性能和应用。物理传感器的核心技术是围绕被测物理信号设计电子器件，控制载流子的传输和相关的电器件特性，从而实现特定的传感功能。基于这种器件设计技术，本文介绍了目前基于石墨烯的柔性物理传感器件，并将指出该领域的开放性问题、挑战和未来方向。

成果简介

人机互动和物联网技术的兴起，需要开发机械灵活和神话般的可穿戴的功能化传感器。因此,新材料和新设备的出现对技术的设计和发展尤为重要。石墨烯具有原子级的厚度、机械灵活性、重量轻、高导电性和透明度。特别是，石墨烯的大比面积使其对外部刺激的感知具有高灵敏度，有望用于柔性传感器技术。华南师范大学李昕明、香港理工大学柴扬教授联合在2D Materials期刊上发表相关综述“Design and applications of graphene-based flexible and wearable physical sensing devices”，介绍了石墨烯在柔性物理信号传感器方面的研究进展，包括器件结构设计和这些器件在可穿戴技术中的应用。同时概述了传感器的新发展方向，如小型化、智能化和多模式。还重点介绍了相关传感设备的最新技术进展，并指出可穿戴传感器未来发展的挑战和方向。

图文导读

Figure 1. Graphene-based devices for physical signal sensing.

Figure 2. (a) The flexible graphene/Si photodetector. (b) The schematic illustration of the flexible graphene/MoS2 photodetector gated by polymer electrolyte. (c)The photocurrent as a function of bending radius. (d) The flexible graphene/AuOx photodetector. (e) The schematic illustration of the band diagram of the graphene/AuOx heterojunction under the illumination. (f) The logarithmic scale of the excess current related to the incident power under various wavelengths of light.

Figure 3. (a) The wrinkled graphene-AuNPs hybrid structure based photodetector integrated on contact lenses and its photoresponse. (b) Position-sensitive detection. The rGO devices have a photovoltaic response related to the position of the laser spot, when the laser spot illuminates the area of rGO between the electrodes. (c) The image and schematic illustration of the flexible graphene/semiconducting quantum dots photodetector. (d) The schematic illustration and (e) photographic image of photoplethysmogram (PPG) in reflectance mode and transmission mode based on the photodetector. (f) Normalized PPG results for transmission and reflectance modes of the photodetector. (g) The schematic illustration and photographic image of the flexible graphene photodetector which is constructed of pentacene organic semiconductor sand gold nanoparticles (AuNPs). (h) Memory performance of graphene photodetector. (i) The schematic illustration and photographic image of the flexible graphene/perovskite photodetector array (24 × 24 pixels). (j) The schematic illustration and corresponding output image of the flexible graphene/perovskite photodetector for color discrimination.

Figure 4. (a) Flexible temperature sensor array based on rGO/polyorganosiloxane aerogel. (b) and (c) The sensor array attached to the surface of the glass filled with hot water and its associated temperature signal response. (d) The schematic illustration of the PVDF/rGO sensor array which is sandwiched by the electrode. (e) Resistance change mapping for the human palm temperature distribution. (f) The schematic illustration and SEM of the interlocked micro dome array structure. Scale bar, 10 µm. (g) Relative resistance change and sensitivity of planar PVDF/rGO sensor and interlocked micro dome structure sensor . (h) The schematic illustration of integrated temperature and strain sensors. (i) Monitor the resistance changes in skin temperature and muscle movements of the neck when drinking hot water. Infrared imaging shows the results of changes in neck temperature before and after drinking hot water.

Figure 5. (a) The plot of the relative change in resistance as a function of strain for suspended graphene; Inset: The schematic illustration of the suspended graphene NEMS device. (b) Pressure and voltage measurements for the suspended graphene NEMS devices with and without cavity. (c) The voltage change relative to the pressure for the two kinds of devices. (d) The accelerometers of suspended graphene with attached proof masses. (e) The schematic illustration of the construction of the microphone. (f) Suspended Graphene diaphragm and assembled speaker.

Figure 6. (a) The relationship between the adhesion degree to the skin and the thickness of the graphene field effect transistors(70 nm, 220 nm, and 430 nm). (b) The schematic illustration of the sensor array on the skin. (c) Formation of patterned graphene design on tape. (d) The schematic illustration of the rGO/PDMS structure formation with micro-cracks and hierarchical surface textures.

Figure 7. (a) The untreated and the treated cotton fabric filled with rGO through padding bath and rollers. (b) Unwashed cotton yarn and cotton yarn dyed with rGO. Based on such cotton yarn, the concept of smart clothing can be proposed. (c) The schematic illustration and characterizations of the a-PAN/graphene films which can be used for pulse detection. (d) The schematic illustration and characterizations of the piezoelectric nanowires and piezoelectric nanowires/graphene sensors for press detection. (e) The schematic illustration and characterizations of the palladium nanoisland/graphene sensors and its application for monitoring the swallowing function in patients.

Figure 8. (a) and (b) The graphene-based electrodes attached to the left and right forearms and left legs. (c) The ECG signal measured by graphene-based electrodes and a commercially Ag/AgCl electrode using adhesive hydrogel. (d) The graphene-based electrodes attached to the forehead and earlobe. (e) The EEG signal measurement by detecting the alpha-rhythm. (f) The power spectrum density when the eyes are closed and open. (g) and (i) The graphene-based electrodes attached to the different positions on the arm. (h) and (j) the EMG signals measured by the graphene-based electrodes and commercial Ag/AgCl electrodes.

Figure 9. (a) The graphene-based electrodes attached to the skin when it is stretched or compressed. (b)–(d) Measurement of the EEG, ECG, EMG signal of the alpha rhythm, the heart and muscle activity. (e) Graphene sensor system with an imperceptible electrooculogram and (f) the different voltage signals through the movement of the eye. (g) The motion control of the airplanes remotely.

Figure 10. (a) The schematic illustration of the graphene multi-electrode array. (b) Graphene electrode array in contact with the rabbit eyes. Scale bar, 5 mm. (c) The position of the recording channel on the rabbit’s eye. (d) A set of multi-electrode ERG responses under stimulus intensity with 0.3 cd s m⁻² . Cross marked with a and b wave locations. (e) The electrode impedance values at 100 Hz and a and b wave amplitudes of EEG signals recorded on different channels . (f) Spatial distribution of b-wave amplitude at different stimulus intensities. 0 dB corresponds to 3.0 cd s m⁻² .

总结展望

总之，基于石墨烯的柔性传感器有着巨大的应用潜力，随着智能社会和物联网的到来，将面临重要的发展机遇。同时，基于石墨烯的电子器件的产业化应用又将刺激石墨烯生产工艺的提升。围绕着石墨烯的电学特性和结构特点，有针对性的器件设计是该领域的研究重点。本综述介绍了基于石墨烯的柔性器件对物理信号的传感，重点介绍了器件结构的设计和功能。与目前的传感器技术相比，基于石墨烯的传感器体现了柔性和智能化的发展趋势。单原子层结构实现了材料的柔性，而石墨烯的大表面积和带状结构决定了其对外部环境信号的敏感性，从而实现了传感性能。

尽管柔性传感设备的研究发展迅速，但其实际应用仍存在许多挑战，这也是该领域未来发展的机遇。基于目前的研究进展，作者提出了未来应该注意的几个方面。(a)传感器的信号精度。目前，基于石墨烯的柔性传感器的精度还难以与传统传感器相比。毕竟，新技术的发展还处于初级阶段，需要后续研究，应更加关注信号的采集和分析。(b)传感器的环境影响。传感器容易受到外部环境因素的影响，如温度、湿度的变化和其他干扰信号。由于石墨烯的超高表面积，传感器更容易耦合不同的干扰信号。因此，基于石墨烯的传感器需要专门设计器件结构,并针对待测信号的特性指定测试条件。同时，当温度等条件发生变化时，应该对传感器进行校准。(c)传感器的接口电子电路。接口电路对传感器的系统集成非常重要，它将主要在信号提取和处理方面发挥关键作用。目前，基于石墨烯的柔性传感器在技术上面临着与典型的接口电路整合的挑战。同时，电路的灵活设计也将促进基于石墨烯的柔性传感器系统的实际应用。(传感器的无线通信。柔性传感技术的重要应用是可穿戴和便携式传感器和设备。无线通信技术的实现和应用是必不可少的。这不仅包括不同传感器之间的信息交互，也包括传感器和其他设备之间的信息通信。目前，射频(RF)无线技术在可穿戴式传感器中得到了广泛的应用，在新型柔性传感器的集成开发方面还有待改进。传感器的能源供应。目前，许多传感器是由电池供电的。虽然近年来柔性电池取得了许多进展，但商业电池的性能仍有许多不足之处，限制了柔性传感器的应用。这些问题.涉及多个学科，如材料装置、电子电路、信息通信和能源管理。同时，这一领域的发展也需要学术界和工业界之间更积极的互动。随着技术的发展,基于石墨烯的柔性传感器有望取得更大的突破。

文献链接

Design and applications of graphene-based flexible and wearable physical sensing devices, 2D Mater. 8 (2021) 022001.

https://doi.org/10.1088/2053-1583/abcbe6.