Engineering Design,Implementation, and Sensing Mechanisms of Wearable Bioelectronic Sensors in Clinical Settings

Wearable sensing devices have transformed the hourly analysis of events such as body signals and environmental risks into real-time monitoring in minutes or seconds. Wearable sensors have facilitated the ability to obtain useful data by monitoring the physiological parameters and activities of an aided and a healthy individual. Wearable devices employ detectable biomarkers in the human body, such as in tears, saliva, interstitial fluid, sweat, and so on. These can deliver relevant information on human health, online activity monitoring, and therapeutic treatments. This section outlines the significance of sample types and associated biomarkers as indicators in the development and manufacturing of wearable biosensors. We have emphasized the most recent advances of wearables based on skin-like and textile, giving attention to personalized health monitoring to record signals of motion and physiological and body fluid investigation. Furthermore, this review categorizes wearable biosensors based on the sensing mechanism, electrochemical, optical, and mechanical. Additionally, the recent wearables related to the detection of the newly havoc-causing pandemic, COVID-19, and the future perspective for the development of much more advanced and potent wearable biosensors have been highlighted. The final section highlights unmet difficulties and gaps in wearable sensors in personalized therapy.     

Sensing nanomaterials of wearable glucose sensors

The metabolic disorder of glucose in human body will cause diseases such as diabetes and hyperglycemia.Hence the determination of glucose content is very important in clinic diagnosing.In recent years,researchers have proposed various non-invasive wearable sensors for rapid and real-time glucose monitoring from human body fluids.Unlike those reviews which discussed performances,detection environments or substrates of the wearable glucose sensor,this review focuses on the sensing nanomaterials since they are the key elements of most wearable glucose sensors.The sensing nanomaterials such as carbon,metals,and conductive polymers are summarized in detail.And also the structural characteristics of different sensing nanomaterials and the corresponding wearable glucose sensors are highlighted.Finally,we prospect the future development requirements of sensing nanomaterials for wearable glucose sensors.This review would give some insights to the further development of wearable glucose sensors and the modern medical treatment.     

柔性印刷可穿戴电化学传感器

实现对人体的健康监测和慢性病监测是包括材料科学、信息技术、电子技术、分析化学等科学领域在内的世界前沿课题。通过连续获取温度、压力、应力等物理信号来实现对人体活动情况和心率、血压、脑电图、心电图等实时监测的可穿戴设备已实现商业化,但连续监测人体体液、呼出气中的各类化学物质的可穿戴传感器仍面临许多问题,比如传感器的柔韧性、灵敏度、准确性以及与人体皮肤的贴合性等。针对这些问题,本文以柔性印刷技术为出发点,综述了各类柔性基底在电化学传感器/生物传感器领域的应用,同时对可穿戴传感器的发展方向提出了建议。     

An Overview of Wearable and Implantable Electrochemical Glucose Sensors

Electrochemical glucose sensors have garnered considerable attention because of their attractive prospect in point-of-care testing (POCT). In this review, we firstly introduce the principles and challenges of electrochemical glucose sensors. Subsequently, we present an overview of the application of electrochemical glucose sensors and discuss their advantages and drawbacks. Wearable and implantable devices based on diverse target biofluid and platforms provide a considerable prospect of accurate and continuous monitoring. Thus, we believe that the future development direction of electrochemical glucose sensors is non-invasive, wearable devices and implantable devices with minimally invasive for continuous glucose monitoring in real time.     

Conductive Film with Flexible and Stretchable Capability for Sensor Application and Stealth Information Transmission

Flexible and wearable strain sensors for human-computer interaction, health monitoring, and soft robotics have drawn widespread attention to promising applications in the next generation of artificial intelligence devices. However, conventional semiconductor sensors are difficult to meet the requirements of flexibility and stretchability. Here, we reported a kind of novel and simple sensor based on layer-by-layer(LBL) method. Carbon nanotubes (CNTs) layer provides high ductility and stability in the process of tension sensing, while silver layer provides low initial resistance and fast reflecting in the process of tension sensing. LBL method ensures the uniformity of the conductive layer. The sensor has superior sheet resistance of 9.44Ω/sq., high elongation at break of 104%. For sensing capability, the sensor has wide reflecting range of 60%, high gauge factor (GF) of 1000 up to 60%strain, fast reflecting time of 165 ms. Excellent reliability and stability have also been verified. It is also worth mentioning that the entire process does not require any expensive equipments, complicated processes or harsh experimental conditions. The above features provide an idea for large-scale application of flexible stretchable sensors.     

Wearable electrochemical sensors for noninvasive monitoring of health—a perspective

Global problems today such as aging society and rising health costs have made preventive care and health monitoring increasingly important, so research on wearable electrochemical sensors for noninvasive monitoring of health has become very popular during the past several years. But the new technologies cannot be some dues ex machine who wrought changes overnight. Problems about fundamentals of electrochemistry under wearable conditions, software algorithms to treat signal artifacts in the real wearable detection, reliable sensors for prolonged wearable sensing in body fluid, platforms for tests of newly developed sensors, validation of test results, reproducible and standardized sampling methods, as well as clinical significance of wearable testing data still require to be addressed. The short review is not to include all important works recently published or reach any conclusion but to focus on the challenges as well as some of the promising approaches that help to overcome these challenges.     

Paper-based Wearable Electrochemical Sensors: A New Generation of Analytical Devices

Over the past few years, the emergence of electrochemical wearable sensors has attracted considerable attention because of their promising application in point-of-care testing due to some features such as high sensitivity, simplicity, miniaturization, and low fabrication cost. Recent developments in new fabrication approaches and innovative substrates have resulted in sensors able to real-time and on-body measurements. Wearable electrochemical sensors have also been combined with paper-based substrates and directly used on human skin for different applications for non-invasive analyses. Furthermore, wearable electrochemical sensors enable monitoring analytes in different biofluids without complex procedures, such as pre-treatment or sample manipulation. The coupling of IoT to various wearable sensors has also attracted attention due to real-time data collection and handling in remote and resource-limited conditions. This mini-review presents the significant advances in developing wearable electrochemical devices, such as sampling, data collection, connection protocols, and power sources, and discusses some critical challenges for higher performance in this field. We also present an overview of the application of paper as an intelligent substrate for electrochemical wearable sensors and discuss their advantages and drawbacks. Lastly, conclude by highlighting the future advances in wearable sensors and diagnostics by coupling real-time and on-body measurements to multiplexed detection of different biomarkers simultaneously, reducing the cost and time of classical analysis to provide fast and complete overall physiological conditions to the wearer.     

OLED器件新型应用研究进展

有机发光二极管(organic light-emitting diodes,OLED)具有可柔性制备、低驱动电压、低功耗等优点,近年来技术上的突飞猛进及其广泛的应用前景,使之成为平板显示、新型照明、可穿戴,以及智能电子产品开发中最热门的研究课题之一.作为新一代的显示及照明技术,小尺寸OLED显示器已实现商业化,大尺寸O...     

Environmental significance of wearable sensors based on MXene and graphene

Conductive layered materials such as MXenes (e.g., transition metal carbides, nitrides, and carbonitrides), graphene and their derivatives have attracted tremendous research interests in diverse fields of research for their unique structured merits and outstanding physical and chemical properties. Benefitting from their unique layered structures and fascinating multifunctional characteristic, MXenes and graphene serve as vital components in a variety of wearable devices. Especially, due to their large surface area and high electrocatalytic activity, these materials have also demonstrated great promise in biophysical and biochemical sensing systems. Following an introduction into the field, we summarize the recent progress in wearable sensors that can be accomplished by using layered materials, with a specific focus on kinematic, mechanical, thermal, pressure and strain sensors. A further large section underscores the recent progress in MXenes and graphene based wearable biochemical sensors including electrolyte monitoring, glucose monitoring, micro/mcromolecular organics metabolite, volatile gases monitoring and humidity sensors. The next section covers the sensing of small biomolecules serving as biomarkers, which are of great significance for early diagnosis and treatment of a spectrum of diseases. This review underscores the recent progress in wearable sensors to be used in different physiological and environmental signals. Finally, the review concludes with a debate on current challenges being faced and future perspectives.     

Flexible strain sensor with ridge-like microstructures for wearable applications

The flexible stretchable sensors have great potential for implementation in various applications, such as intelligent soft robots, health monitoring, and motion detection. However, most of the flexible stretchable sensors with microstructures and high sensitivities are fabricated by expensive templates and complex processes. In consideration of large-scale fabrication, a low cost and efficient way is in great demand. Herein, electroless plating on Nafion films with decent swelling ratios are proposed to fabricate stretchable sensors with wrinkle-structured electrodes. By adding isopropanol (IPA) to the electroless plating process, the H₂O-IPA sensor with larger swelling ratio shows deeper surface wrinkles, higher surface roughness, and better sensitivity to strain. At the same time, the H₂O-IPA sensor exhibit good durability (500 cycles). By mounting the sensor on the joint of human finger, the motion of the finger bending and even the bending degree can be accurately detected, indicating the potential use in the field of wearable devices and soft electronic skins.     

Sponge-inspired multisensory hydrogel

The preparation of smart sensors with multiple sensory systems, reusable property, and high sensitivity remains a challenge. Here, inspired by a sponge, we develop a multisensory PCA–poly(vinyl alcohol) (PVA)/borax–LiCl hydrogel (named PPL hydrogel) with low cost and simple fabrication process using sodium polyacrylate (PAAS), PVA, and lithium chloride (LiCl) to address this challenge. PPL hydrogel has a sponge-like porous structure and can repeatedly “absorb” and “drain” water, while maintaining good tensile (strain up to 1442%) and electrical conductivity. PAAS builds the main skeleton of PPL hydrogels and provides the basis for building the pore structure, PVA enhances the mechanical properties of the crosslinked network, while LiCl ionic solution further improves the conductivity, which can reach 8.8 s m⁻¹ and be increased nearly 42 times better than without LiCl. Therefore, this makes PPL hydrogel a very sensitive sensing system for wearable devices that can be used to detect signals from the human body. Additionally, PPL hydrogel is also capable of detecting temperature due to its temperature-sensitive properties. Moreover, PPL hydrogel can also roughly identify the basic properties of different solvents. Our simple, low-cost and multisensory PPL hydrogel offers promising opportunities for multisensory sensors, even functional/smart materials, flexible/wearable devices, and medical care.     

Facile and Large-scale Fabrication of Self-crimping Elastic Fibers for Large Strain Sensors

Stretchable conductive fibers offer unparalleled advantages in the development of wearable strain sensors for smart textiles due to their excellent flexibility and weaveability.However,the practical applications of these fibers in wearable devices are hindered by either contradictory properties of conductive fibers(high stretchability versus high sensing stability),or lack of manufacturing scalability.Herein,we present a facile approach for highly stretchable self-crimping fiber strain sensors based on a polyether-ester(TPEE)elastomer matrix using a side-by-side bicomponent melt-spinning process involving two parallel but attached components with different shrinkage properties.The TPEE component serves as a highly elastic mechanical support layer within the bicomponent fibers,while the conductive component(E-TPEE)of carbon black(CB),multiwalled carbon nanotubes(MWCNTs)and TPEE works as a strain-sensitive layer.In addition to the intrinsic elasticity of the matrix,the TPEE/E-TPEE bicomponent fibers present an excellent form of elasticity due to self-crimping.The self-crimping elongation of the fibers can provide a large deformation,and after the crimp disappears,the intrinsic elastic deformation is responsible for monitoring the strain sensing.The reliable strain sensing range of the TPEE/E-TPEE composite fibers was 160％-270％and could be regulated by adjusting the crimp structure.More importantly,the TPEE/E-TPEE fibers had a diameter of 30-40 μm and tenacity of 40-50 MPa,showing the necessary practicality.This work introduces new possibilities for fiber strain sensors produced in standard industrial spinning machines.     

Wearable Electrochemical Sensors Based on Nanomaterials for Healthcare Applications

Wearable electrochemical sensors have attracted great interest in health care applications because of their flexibility, biocompatibility, low cost and light weight. This review briefly focuses on the main concepts and methods that are related to the application of nanoparticles (NPs) in wearable electrochemical sensors. Moreover, attempts to bring together different perspectives and terms that are commonly used in NPs-based wearable electrochemical sensors along with the introduction and discussion of common manufacturing methods and recent achievements. In the end, future challenges and prospects are also discussed on the development of wearable electrochemical sensors based on nanoparticles.     

Advances in Medical Wearable Biosensors: Design,Fabrication and Materials Strategies in Healthcare Monitoring

In the past decade, wearable biosensors have radically changed our outlook on contemporary medical healthcare monitoring systems. These smart, multiplexed devices allow us to quantify dynamic biological signals in real time through highly sensitive, miniaturized sensing platforms, thereby decentralizing the concept of regular clinical check-ups and diagnosis towards more versatile, remote, and personalized healthcare monitoring. This paradigm shift in healthcare delivery can be attributed to the development of nanomaterials and improvements made to non-invasive biosignal detection systems alongside integrated approaches for multifaceted data acquisition and interpretation. The discovery of new biomarkers and the use of bioaffinity recognition elements like aptamers and peptide arrays combined with the use of newly developed, flexible, and conductive materials that interact with skin surfaces has led to the widespread application of biosensors in the biomedical field. This review focuses on the recent advances made in wearable technology for remote healthcare monitoring. It classifies their development and application in terms of electrochemical, mechanical, and optical modes of transduction and type of material used and discusses the shortcomings accompanying their large-scale fabrication and commercialization. A brief note on the most widely used materials and their improvements in wearable sensor development is outlined along with instructions for the future of medical wearables.     

Metallized electrospun polymeric fibers for electrochemical sensors and actuators

Electrospun polymeric fibers present an emerging alternative for the development of flexible electronics, enabling applications in wearable sensors and biosensors for continuous monitoring, and actuators for tissue engineering. The possibility to prepare sub-micrometric polymeric scaffolds, their processing for increasing the conductivity, their modification with different materials, conductive polymers and biomolecules in order to obtain functional flexible electrodes, allows the development of innovative devices for healthcare, and biomedical applications. In this review, the impact of metallized electrospun polymeric fibers in electrochemical (bio)sensors and actuators is discussed. A relation between their structure and functionality is provided, alongside with an overview of the different methods to obtain functional conductive fibers.     

Sensing at Your Fingertips: Glove‐based Wearable Chemical Sensors

In this review, we detail the evolution and recent progress of glove‐based wearable electrochemical sensors with focus on forensic, security, and defense applications. Glove‐based wearable sensors offer the ability to have rapid, on‐site chemical and biological threat assessment, ranging from explosive and gunshot residues to drugs of abuse and pesticides, critical for timely and informed incident management and investigation. Additionally, these field deployable systems offer the ability for law enforcement to complete on‐the‐spot qualitative chemical testing for immediate forensic evidence collection in connection to mechanical ‘swipe’ sampling. Recent advances have been made for translation of this class of wearable electrochemical sensors to increase the sensory perspective of robotics, demonstrating the progression to robotic skin with chemical analysis capability suitable for translation to remote chemical analysis in hazardous scenarios. Critical to such progress have been advances in flexible electrochemically‐compatible materials and design, with increasing functionality, leveraging from advances in wearable biosensors and electronic miniaturization. Indeed, the customization potential of these wearable systems is great, yet challenges remain for advancing these systems from prototypes to more ubiquitous devices readily deployed in the field. With significant attention these challenges can be overcome, creating new opportunities for further decentralization of electrochemical analyses using these flexible and intuitive glove‐based wearable sensing systems for significant impact on fields such as forensics, defense, biomedical, robotics and beyond.     

Smart sensors in environmental/water quality monitoring using IoT and cloud services

The growing social awareness and consequent concern for the environment has driven environmental analytical chemistry to a position of great prominence. In recent times, this position has translated into taking advantage of the great benefits provided by cloud computing and the Internet of Things (IoT), which are especially appropriate when devices such as chemical sensors are used. The use of such sensors is very common when in situ monitoring of environmental parameters is performed, but until recently, it was limited to the deployment of a small number of sensors. Currently, this approach has given way to genuine smart sensing systems (for instance, fully consolidated wireless sensor networks) that are able to provide a substantial amount of information. This type of sensor (the so-called smart sensor) is fundamentally characterized by (a) low consumption, versatility, and autonomy, (b) ease of integration with cloud solutions, (c) durability and reliability of IoT platforms and sensors, and (d) easy installation and deployment of sensor nodes. For all these reasons, and given the increasing importance and use of this type of device, a revision of the recent literature relating the development of smart sensors with environmental issues has been conducted, with major contributions being discussed, most notably those addressing the continuous in-line monitoring of water quality.     

S‐Click Reaction for Isotropic Orientation of Oxidases on Electrodes to Promote Electron Transfer at Low Potentials

Electrochemical sensors are essential for point‐of‐care testing (POCT) and wearable sensing devices. Establishing an efficient electron transfer route between redox enzymes and electrodes is key for converting enzyme‐catalyzed reactions into electrochemical signals, and for the development of robust, sensitive, and selective biosensors. We demonstrate that the site‐specific incorporation of a novel synthetic amino acid (2‐amino‐3‐(4‐mercaptophenyl)propanoic acid) into redox enzymes, followed by an S‐click reaction to wire the enzyme to the electrode, facilitates electron transfer. The fabricated biosensor demonstrated real‐time and selective monitoring of tryptophan (Trp) in blood and sweat samples, with a linear range of 0.02–0.8 mm . Further developments along this route may result in dramatic expansion of portable electrochemical sensors for diverse health‐determination molecules.     

Skin‐worn Soft Microfluidic Potentiometric Detection System

A flexible skin‐mounted microfluidic potentiometric device for simultaneous electrochemical monitoring of sodium and potassium in sweat is presented. The wearable device allows efficient natural sweat pumping to the potentiometric detection chamber, containing solid‐contact ion‐selective Na⁺ and K⁺ electrodes, during exercise activity. The fabricated microchip electrolyte‐sensing device displays good analytical performance and addresses sweat mixing and carry‐over issues of early epidermal potentiometric sensors. Such soft skin‐worn microchip platform integrates potentiometric measurement, microfluidic technologies with flexible electronics for real‐time wireless data transmission to mobile devices. The new fully integrated microfluidic electrolyte‐detection device paves the way for practical fitness and health monitoring applications.     

柔性可穿戴传感器件与储能器件的发展现状与挑战

随着人们生活质量与对可穿戴监测设备需求的提高以及物联网、人工智能和人机交互等科技水平的发展,能够对人体生命体征信号采集、转化与识别的可穿戴柔性电子装置成为连接智能生物与非智能机械装置的桥梁. 可穿戴柔性电子器件对人体生命体征信号的采集包括人体脉搏、温度、皮肤应变、呼吸和心跳等指标. 本文总结概述了近年来可穿戴柔性传感器对人体生命信号采集的现状以及存在的问题和挑战,并对可穿戴柔性供能器件做了简要的总结和展望.