Fibers/Textiles-Based Flexible Sweat Sensors: A Review

Abstract

With the rise of smart textiles, fibers/textiles-based sensors are being applied in various situations, such as healthcare, green energy, and environmental monitoring. The field of health monitoring mainly involves the detection of human secretions (such as sweat, saliva, urine, and excrement). Among them, sweat is extensive and closely related to human health, so it is receiving more and more attention. Various sensors are used for sweat detection, but fiber/textile-based flexible sensors have unique advantages and thus have emerged as an important branch. So, this Review aims to 1) explain the physiological mechanism of sweating and metabolites; 2) introduce the advantages of fibers/textiles as the substrate of sweat sensors; 3) outline different kinds of fibers/textiles-based flexible sweat sensors (enzymatic biosensors, non-enzymatic biosensors, ion-selective sensors, and others) and explain their working principle; 4) summarize the applications of such sensors in different fields (physical condition monitoring, power supply, drug monitoring, mental state monitoring, etc.). Moreover, the opportunities and challenges of flexible fiber/textile-based sweat sensors will also be discussed. This Review will help promote the diversified development of sweat sensors, which is significant for manufacturing advanced sweat detection and diagnostic systems.

Hygroscopic MXene/Protein Nanocomposite Fibers Enabling Highly Stretchable, Antifreezing, Repairable, and Degradable Skin-Like Wearable Electronics

“…With the gradual increase of interdisciplinary convergence and technological convergence, many new areas of development have emerged, such as implantable medical devices, soft robots, wearable devices, electronic fabrics, etc. − Particularly, the rise of personalized healthcare has spurred the development of flexible wearable and implantable electronic devices for monitoring physiological signals. Compared to conventional 3D and 2D electronic devices, fiber-based electronic devices have the advantages of high aspect ratio, lightweight, high flexibility, and weavability. − When applied to the skin, it can achieve a high degree of adaptability to the skin, thereby improving the comfort of the human body and enhancing signal fidelity during motion. , In health monitoring, fiber-based flexible sensors can monitor large-scale (such as the fingers, arms, and legs) and small-scale (such as emotional expression of face, breathing, and swallowing) human body movements to diagnose vocal cord damage, respiratory disorders, angina pectoris, etc. , Typically, the reported fiber-based sensors use stretchable elastomers, such as polydimethylsiloxane (PDMS), Ecoflex, and polyurethane (PU), as substrates with the conductive materials coated on the surface or embedded in the matrix to realize a close fit with the human body. − For instance, Seyedin et al prepared a fiber-based wearable strain sensor with Ti 3 C 2 T x MXene embedded in PU by wet spinning, which exhibited high sensitivity and could be used to monitor elbow joint movement. However, these polymers display poor air permeability and biocompatibility, which will cause skin discomfort during long-term usage.…”

Porous Conductive Textiles for Wearable Electronics

“…Alternatively, other biofluids (e.g., sweat, interstitial fluid, tear, saliva) also contain a wealth of biomolecules including electrolyte ions (e.g., Na + , Cl – , K + ), metabolites (e.g., glucose, lactate, urea), minerals (e.g., Ca 2+ , Mg 2+ , Fe 2+ ), nutrients, hormones, amino acid, and proteins, etc . Wearable sweat biosensors emerge as a new platform for monitoring these biomolecules through a noninvasive, real-time, and continuous manner. ,− Textiles are ideal substrates for fabrication of wearable biosensors due to their high flexibility and porosity, which are favorable for immobilizing active materials of biosensors such as bioreceptors (e.g., enzyme, antibody). , Moreover, textiles are conducive for absorption of sweat due to their high surface capillary effect . Currently, electrochemical principles are usually adopted for making biosensors, due to their high sensitivity and continuous monitoring ability compared to others such as colorimetric ones.…”

可穿戴光学汗液传感器的研究进展

“…可穿戴传感器在健康监测领域中发挥着重要作用。 随着人民生活水平日益提高和人口老 龄化趋势日益严峻，人们越来越重视自身的健康状况。传统的健康监测方法往往依赖于大型 医疗机构的设备和专业人员，而可穿戴传感器则打破了这种局限性。近些年来，许多非侵入 式可穿戴体液监测系统快速崛起 [1,2] ，为人体健康监测开辟了新途径。 与其他体液(如泪液、唾液等)相比 [1] ，汗液易获取，且含有丰富的生物标志物(如盐 离子、乳酸、葡萄糖以及皮质醇等) [3][4][5] ，这些物质的代谢量同人体健康息息相关 [6][7][8][9] 。因此， 汗液可作为理想的人体健康监测对象 [10] ，无创、便捷的可穿戴汗液传感器也具有巨大的研 究应用价值，其能够与人体皮肤紧密贴合，具有较强的灵活性、舒适性与便携性，为健康监 测、疾病诊断与医疗护理等领域带来了无限的可能性 [11] 。 近年来，汗液电化学传感器取得了一定的进展 [12,13] ，但其电信号抗干扰能力仍有提升空 间。而光学传感不需要像电化学传感那样复杂的连接线结构及电子元件，其作为一种快速、 简便的检测技术 [14] 较低的固有荧光背景。近年来，制备可穿戴光学汗液传感器常用的材料主要有纸基 [15] 、聚 合物 [16] 、织物 [17] 以及柔性微纳米材料 [18] 等。 2.1 纸基 在可穿戴光学汗液传感器中，纸基是一种取材方便、成本低廉且具有良好便携性的柔性 界面材料。Xiao 等 [19] 将氧等离子体处理后的棉线用于汗液的输送，将功能化滤纸作为汗液 传感元件，制备出一种用于人体汗液中葡萄糖比色检测的分析装置。此外，由于纸基材料本 身的特性，它可以被折叠和裁切成各种形状和结构以满足不同传感器的不同功能需求，这也 为传感器的设计提供更大的灵活性。Weng 等 [20] 采用丝网印刷和折叠技术设计出一种便携式 三维微流控折纸光学传感器(图 2a)。该传感器的吸汗层、输送层和覆盖层均由滤纸制成， 反应层由硝酸纤维素膜构成。通过简单的折叠就能有效避免光学与化学污染，有利于人体汗 液中皮质醇的荧光检测。Jain 等 [21] 设计出一种用于实时监测排汗量的纸基放射状贴片，不同 长度通道的终端均沉积有水性染料。 当排汗过程中通道被填充至饱和状态时， 终端就会变色， 进而能够可视化监测人体脱水水平。Vaquer 等 [22] 制备出一种基于滤纸的集汗液体积传感器 和乳酸传感器为一体的一次性可穿戴分析平台。通过微调该分析平台的形状等参数，还可将 其用于汗液中葡萄糖浓度的测定 [23] ，检测限低至 10 -2 mM，可用于检测低血糖。此外，该团 队还设计出一种基于滤纸的能够实现汗液成分持续、精确测定的多路传感装置(图 2b) [24] 。 该传感装置的制作方法简单，按照设定的规格形状进行裁剪即可，支持个性化定制。Gao 等 [25] 制备的具有高拉伸性的纸基鱼形可穿戴传感器可用于汗液中乳酸、尿素的荧光传感，同 时还可用于监测人体的运动过程。该装置中的可伸缩鳞状纸基网络是可调的，不同的裁切方 式可以得到不同拉伸长度的纸基网络。 2.2 聚合物 相较于纸基的易变形、易破损性质，聚合物更加结实牢固，并且通过改变聚合物的化学 结构可以增强其生物相容性、柔韧性等 [26] 。用于构建可穿戴光学汗液传感器的聚合物主要 F o r R e v i e w O n l y 中国科学: 化学 http://chemcn.scichina.com 有 PDMS、水凝胶等。…”