A fluorometric skin-interfaced microfluidic device and smartphone imaging module for in situ quantitative analysis of sweat chemistry

Innovative biosensing smart masks: unveiling the future of respiratory monitoring

Real-time monitoring of respiratory health is increasingly critical, particularly in addressing global health challenges such as Corona Virus Disease 2019 (COVID-19). Smart masks equipped with biosensing mechanisms revolutionize respiratory health monitoring by enabling real-time detection of respiratory parameters and biomarkers. In recent years, significant advancements have been achieved in the development of smart masks based on different sensor types with high sensitivity and accuracy, flexible functionality, and portability, providing new approaches for remote and real-time monitoring of respiratory parameters and biomarkers. In this review, we aim to provide a comprehensive overview of the current state of development and future potential of biosensing smart masks in various domains. This review outlines a systematic categorization of smart masks according to diverse sensing principles, classifying them into six categories: electrochemical sensors, optical sensors, piezoelectric sensors, and others. This review discusses the basic sensing principles and mechanisms of smart masks and describes the existing research developments of their different biosensors. Additionally, it explores the innovative applications of smart masks in health monitoring, protective functions, and expanding application scenarios. This review also identifies the current challenges faced by smart masks, including issues with sensor accuracy, environmental interference, and the need for better integration of multifunctional features. Proposed solutions to these challenges are discussed, along with the anticipated role of smart masks in early disease detection, personalized medicine, and environmental protection.

Spatiotemporal molecular tracing of ultralow-volume biofluids via a soft skin-adaptive optical monolithic patch sensor

Molecular tracing of extremely low amounts of biofluids is vital for precise diagnostic analysis. Although optical nanosensors for real-time spatiotemporal molecular tracing exist, integrating them into simple devices that capture low-volume fluids on rough, dynamic surfaces remains challenging. We present a bioinspired 3D microstructured patch monolithically integrated with optical nanosensors (3D MIN) for real-time, multivariate molecular tracing of ultralow-volume fluids. Inspired by tree frog toe pads, the 3D MIN features soft, hexagonally aligned pillars and microchannels for conformal adhesion and targeted fluid management. Embedding near-infrared fluorescent single-walled carbon nanotube nanosensors in a hydrogel enables simultaneous fluid capture and detection. Softening the elastomer microarchitecture and optimizing water management promote stable adhesion on wet biosurfaces, allowing rapid collection of ultralow-volume fluids (~0.1 µL/min·cm²). We demonstrate real-time, remote sweat analysis with ≥75 nL volumes collected in 45 s, without exercise or iontophoresis, showcasing high biocompatibility and efficient spatiotemporal molecular tracing.

Electrophoretic digital colorimetry integrated with electrochemical sweat sensor

Recent advancements in wearable sweat sensors, which use standardized electrochemical and colorimetric mechanisms, offer holistic representation of health status for users. However, the constraints of standardized sweat sensors present ongoing challenges to realization of personalized health management. This study presents an electrocolorimetric (EC) platform that enables the reversible and multiple-time use of colorimetric data visualization using electrophoretic display (EPD). This platform represents the application of low-power EPD in epidermal sweat sensor, evaluated through CIELAB-based methodology which is the first systematic evaluation tool of wearable display performance. Moreover, our platform has been demonstrated in human exercise trials for its ability to detect the lactate threshold (LT). This digital colorimetric system has the potential to play a pivotal role by integrating various health monitoring biomarkers. While providing real-time, continuous, and adjustable range information with high sensitivity, this platform validates its extensive probability as a next-generation wearable epidermal sensor.

Soft, wearable, microfluidic system for fluorometric analysis of loss of amino acids through eccrine sweat

Amino acids are essential for protein synthesis and metabolic processes in support of homeostatic balance and healthy body functions. This study quantitatively investigates eccrine sweat as a significant channel for loss of amino acids during exercise, to improve an understanding of amino acid turnover and to provide feedback to users on the need for supplement intake. The measurement platform consists of a soft, skin-interfaced microfluidic system for real-time analysis of amino acid content in eccrine sweat. This system relies on integrated fluorometric assays and smartphone-based imaging techniques for quantitative analysis, as a simple, cost-effective approach that does not require electrochemical sensors, electronics or batteries. Human subject studies reveal substantial amino acid losses in sweat from working muscle regions during prolonged physical activities, thereby motivating the need for dietary supplementation. The findings suggest potential applications in healthcare, particularly in athletic and clinical settings, where maintaining amino acid balance is critical for ensuring proper homeostasis.

Smart Wearable Sensor Fuels Noninvasive Body Fluid Analysis

The advancements in wearable sensor technology have revolutionized noninvasive body fluid monitoring, offering new possibilities for continuous and real-time health assessment. By analyzing body fluids such as sweat, saliva, tears, and interstitial fluid, these technologies provide painless diagnostic alternatives for detecting biomarkers such as glucose, electrolytes, and metabolites. These sensors play a crucial role in early disease detection, chronic condition management, and personalized healthcare. Recent innovations in flexible electronics, microfluidic systems, and biosensing materials have significantly improved the accuracy, reliability, and integration of sensors into everyday textiles. Moreover, the convergence of artificial intelligence and big data analytics has enhanced the precision and personalization of health monitoring systems, transforming wearable sensors into powerful tools for health holographic inspection. Despite significant progress, challenges remain, including improving sensor stability in dynamic environments, achieving real-time data transmission, and covering a broader range of biomarkers. Future research directions focus on enhancing material sustainability through green synthesis, optimizing sampling techniques, and leveraging machine learning to further improve sensor performance. This Review highlights the transformative potential of wearable sensors in medical applications, aiming to bridge gaps in healthcare accessibility and elevate the standards of patient care through noninvasive continuous monitoring technologies.

Smartphones as a platform for molecular analysis: concepts, methods, devices and future potential

Over the past 15 years, smartphones have had a transformative effect on everyday life. These devices also have the potential to transform molecular analysis over the next 15 years. The cameras of a smartphone, and its many additional onboard features, support optical detection and other aspects of engineering an analytical device. This article reviews the development of smartphones as platforms for portable chemical and biological analysis. It is equal parts conceptual overview, technical tutorial, critical summary of the state of the art, and outlook on how to advance smartphones as a tool for analysis. It further discusses the motivations for adopting smartphones as a portable platform, summarizes their enabling features and relevant optical detection methods, then highlights complementary technologies and materials such as 3D printing, microfluidics, optoelectronics, microelectronics, and nanoparticles. The broad scope of research and key advances from the past 7 years are reviewed as a prelude to a perspective on the challenges and opportunities for translating smartphone-based lab-on-a-chip devices from prototypes to authentic applications in health, food and water safety, environmental monitoring, and beyond. The convergence of smartphones with smart assays and smart apps powered by machine learning and artificial intelligence holds immense promise for realizing a future for molecular analysis that is powerful, versatile, democratized, and no longer just the stuff of science fiction.

Trends and Advances in Wearable Plasmonic Sensors Utilizing Surface-Enhanced Raman Spectroscopy (SERS): A Comprehensive Review

Wearable sensors have appeared as a promising solution for real-time, non-invasive monitoring in diverse fields, including healthcare, environmental sensing, and wearable electronics. Surface-enhanced Raman spectroscopy (SERS)-based sensors leverage the unique properties of SERS, such as plasmonic signal enhancement, high molecular specificity, and the potential for single-molecule detection, to detect and identify a wide range of analytes with ultra-high sensitivity and molecular selectivity. However, it is important to note that wearable sensors utilize various sensing mechanisms, and not all rely on SERS technology, as their design depends on the specific application. This comprehensive review highlights the recent trends and advancements in wearable plasmonic sensing technologies, focusing on their design, fabrication, and integration into practical wearable devices. Key innovations in material selection, such as the use of nanomaterials and flexible substrates, have significantly enhanced sensor performance and wearability. Moreover, we discuss challenges such as miniaturization, power consumption, and long-term stability, along with potential solutions to address these issues. Finally, the outlook for wearable plasmonic sensing technologies is presented, emphasizing the need for interdisciplinary research to drive the next generation of smart wearables capable of real-time health diagnostics, environmental monitoring, and beyond.

Advances in Photonic Materials and Integrated Devices for Smart and Digital Healthcare: Bridging the Gap Between Materials and Systems

Recent advances in developing photonic technologies using various materials offer enhanced biosensing, therapeutic intervention, and non-invasive imaging in healthcare. Here, this article summarizes significant technological advancements in materials, photonic devices, and bio-interfaced systems, which demonstrate successful applications for impacting human healthcare via improved therapies, advanced diagnostics, and on-skin health monitoring. The details of required materials, necessary properties, and device configurations are described for next-generation healthcare systems, followed by an explanation of the working principles of light-based therapeutics and diagnostics. Next, this paper shares the recent examples of integrated photonic systems focusing on translation and immediate applications for clinical studies. In addition, the limitations of existing materials and devices and future directions for smart photonic systems are discussed. Collectively, this review article summarizes the recent focus and trends of technological advancements in developing new nanomaterials, light delivery methods, system designs, mechanical structures, material functionalization, and integrated photonic systems to advance human healthcare and digital healthcare.

Lighting the Path to Precision Healthcare: Advances and Applications of Wearable Photonic Sensors

Recent advancements in wearable photonic sensors have marked a transformative era in healthcare, enabling non-invasive, real-time, portable, and personalized medical monitoring. These sensors leverage the unique properties of light toward high-performance sensing in form factors optimized for real-world use. Their ability to offer solutions to a broad spectrum of medical challenges - from routine health monitoring to managing chronic conditions, inspires a rapidly growing translational market. This review explores the design and development of wearable photonic sensors toward various healthcare applications. The photonic sensing strategies that power these technologies are first presented, alongside a discussion of the factors that define optimal use-cases for each approach. The means by which these mechanisms are integrated into wearable formats are then discussed, with considerations toward material selection for comfort and functionality, component fabrication, and power management. Recent developments in the space are detailed, accounting for both physical and chemical stimuli detection through various non-invasive biofluids. Finally, a comprehensive situational overview identifies critical challenges toward translation, alongside promising solutions. Associated future outlooks detail emerging trends and mechanisms that stand to enable the integration of these technologies into mainstream healthcare practice, toward advancing personalized medicine and improving patient outcomes.

Recent Advances in Wearable Sweat Sensor Development

Wearable sweat sensors for detecting biochemical markers have emerged as a transformative research area, with the potential to revolutionize disease diagnosis and human health monitoring. Since 2016, a substantial body of pioneering and translational work on sweat biochemical sensors has been reported. This review aims to provide a comprehensive summary of the current state-of-the-art in the field, offering insights and perspectives on future developments. The focus is on wearable microfluidic platforms for sweat collection and delivery and the analytical chemistry applicable to wearable devices. Various microfluidic technologies, including those based on synthetic polymers, paper, textiles, and hydrogels, are discussed alongside diverse detection methods such as electrochemistry and colorimetry. Both the advantages and current limitations of these technologies are critically examined. The review concludes with our perspectives on the future of wearable sweat sensors, with the goal of inspiring new ideas, innovations, and technical advancements to further the development and practical application of these devices in promoting human health.

Optical sensors for transdermal biomarker detection: A review

This review has explored optical sensors and their important role in non-invasive transdermal biomarker detection. While electrochemical sensors have been thoroughly studied for biomarker tracking, optical sensors present a compelling alternative due to their high sensitivity and selectivity, multiplex capabilities, cost-efficiency, and small form factor. This review examines the latest advancements in optical sensing technologies for transdermal biomarker detection, such as colorimetry, fluorescence, surface plasmon resonance (SPR), fiber optics, photonic crystals, and Raman spectroscopy. These technologies have been applied in the analysis of biomarkers present in sweat and skin gases, which are essential for non-invasive health monitoring. Furthermore, the review has discussed the challenges and future perspectives of optical sensors in in transdermal biomarker detection. The analysis of various sensor types and their applications highlights the transformative potential of optical sensors in enhancing disease diagnostics and promoting proactive health management.

Advanced Wearable Devices for Monitoring Sweat Biochemical Markers in Athletic Performance: A Comprehensive Review

Wearable technology has advanced significantly, offering real-time monitoring of athletes' physiological parameters and optimizing training and recovery strategies. Recent developments focus on biosensor devices capable of monitoring biochemical parameters in addition to physiological ones. These devices employ noninvasive methods such as sweat analysis, which reveals critical biomarkers like glucose, lactate, electrolytes, pH, and cortisol. These biomarkers provide valuable insights into an athlete's energy use, hydration status, muscle function, and stress levels. Current technologies utilize both electrochemical and colorimetric methods for sweat analysis, with electrochemical methods providing higher precision despite potential signal interference. Wearable devices such as epidermal patches, temporary tattoos, and fabric-based sensors are preferred for their flexibility and unobtrusive nature compared to more rigid conventional wearables. Such devices leverage advanced materials and transmit real-time data to computers, tablets, or smartphones. These data would aid coaches and sports medical personnel in monitoring athletes' health, optimizing diets, and developing training plans to enhance performance and reduce injuries.

Transdermal Drug Delivery Systems (TDDS): Recent Advances and Failure Modes

Transdermal drug delivery systems (TDDS), commonly refered to as "patches", present a nonintrusive technique to provide medication without the need for invasive procedures. These products adhere to the skin and gradually release a specific dosage of medicine at a defined rate into the bloodstream. Compared with other methods of drug delivery, TDDS offer benefits such as reduced invasiveness, convenience for patients, and avoidance of the metabolic processes that occur when drugs are orally consumed. Throughout time, TDDS have been used to provide medications for various medical conditions (such as nicotine, fentanyl, nitroglycerin, and clonidine), and their potential for delivering biologics is currently being explored. This review investigates the current literature on the drug delivery efficacy of medical TDDS through the transdermal route. Additionally, the review addresses potential risks and failure modes associated with TDDS design and development as well as strategies for mitigating such risks. A thorough understanding of failure modes provides a blueprint to mitigate failure and produce high-quality efficacious therapeutics.

A sensor platform based on SERS detection/janus textile for sweat glucose and lactate analysis toward portable monitoring of wellness status

Herein we report a wearable sweat sensor of a Janus fabric based on surface enhanced Raman scattering (SERS) technology, mainly detecting the two important metabolites glucose and lactate. Janus fabric is composed of electrospinning PU on a piece of medical gauze (cotton), working as the unidirectional moisture transport component (R = 1305%) to collect and transfer sweat efficiently. SERS tags with different structures act as the probe to recognize and detect the glucose and lactate in high sensitivity. Core-shell structured gold nanorods with DTNB inside (AuNRs@DTNB@Au) are used to detect lactate, while gold nanorods with MPBA (AuNRs@MPBA) are used to detect glucose. Through the characteristic SERS information, two calibration functions were established for the concentration determination of glucose and lactate. The concentrations of glucose and lactate in sweat of a 23 years volunteer during three-stage interval running are tested to be 95.5, 53.2, 30.5 μM and 4.9, 13.9, 10.8 mM, indicating the glucose (energy) consumption during exercise and the rapid accumulation of lactate at the early stage accompanied by the subsequent relief. As expected, this sensing system is able to provide a novel strategy for effective acquisition and rapid detection of essential biomarkers in sweat.

Wearable Hydrogel SERS Chip Utilizing Plasmonic Trimers for Uric Acid Analysis in Sweat

Uric acid is typically measured through blood tests, which can be inconvenient and uncomfortable for patients. Herein, we propose a wearable surface-enhanced Raman scattering (SERS) chip, incorporating a hydrogel membrane with integrated plasmonic trimers, for noninvasive monitoring of uric acid in sweat. The plasmonic trimers feature sub 5 nm nanogaps, generating strong electromagnetic fields to boost the Raman signal of surrounding molecules. Simultaneously, the hydrogel membrane pumps sweat through these gaps, efficiently capturing sweat biomarkers for SERS detection. The chip can achieve saturation adsorption of sweat within 5 min, eliminating variations in individual sweat production rates. Dynamic SERS tracking of uric acid and lactic acid levels during anaerobic exercise reveals a temporary suppression of uric acid metabolism, likely due to metabolic competition with lactic acid. Furthermore, long-term monitoring correlates well with blood test results, confirming that regular exercise helps reduce serum uric acid levels and supporting its potential in managing hyperuricemia.

A physiological perspective of the relevance of sweat biomarkers and their detection by wearable microfluidic technology: A review

The great majority of published microfluidic wearable platforms for sweat sensing focus on the development of the technology to fabricate the device, the integration of sensing materials and actuators and the fluidics of sweat within the device. However, very few papers have discussed the physiological relevance of the metabolites measured using these novel approaches. In fact, some of the analytes present in sweat, which serve as biomarkers in blood, do not show a correlation with blood levels. This discrepancy can be attributed to factors such as contamination during measurements, the metabolism of sweat glands, or challenges in obtaining significant samples. The objective of this review is to present a critical and meaningful insight into the real applicability and potential use of wearable technology for improving health and sport performance. It also discusses the current limitations and future challenges of microfluidics, aiming to provide accurate information about the actual needs in this field. This work is expected to contribute to the future development of more suitable wearable microfluidic technology for health and sports science monitoring, using sweat as the biofluid for analysis.

Skin sensing and wearable technology as tools to measure atopic dermatitis severity

Wearable medical technology encompasses a range of electronic devices that act as biosensors. Atopic dermatitis (AD) is the commonest inflammatory skin disease and represents an important area of need in which to leverage the power of wearable biosensor technology, especially as the impact of COVID-19 increases the likelihood of virtual consultations becoming an integrated part of clinical practice. The aim of this review is to systematically define the published evidence for the utility of wearable biosensors in assessment and management of atopic dermatitis (AD). A systematic literature search was conducted for publications from 1995 onwards for 'sensor' OR 'sensing' OR 'biosensor' OR 'biomarker'. Results were combined ('AND') with a search for 'wearable' OR 'actigraphy' OR 'Internet of things' OR 'microneedle' OR 'patch' OR 'e-textile' OR 'smart textile' and atopic dermatitis (MESH terms). Fifty seven abstracts were identified from the database search of which 39 were selected for detailed review. Broadly, wearable sensing systems in atopic dermatitis were split into three categories: wearable biosensor modules (actigraphy and smartwatches), clothing and integrated fabrics placed onto the epidermis and intradermal or subcutaneous sensors. The best evidence for correlation with AD disease severity was with actigraphy measurements of itch. However, newer approaches including sensing skin barrier function, inflammation and small molecule analysis as well as employing artificial intelligence offer more potential for advanced disease monitoring. Skin diseases, specifically AD, stand to benefit greatly from wearable technology, because of the ease of direct contact to the skin, the high prevalence of the disease and the large unmet need for better disease control in this group. However, important emphasis must be placed on validating the correlation of data from such technology with patient-reported outcomes. Wearable biosensors offer a huge potential to deliver better diagnostics, monitoring and treatment outcomes for patients.

Optical blood glucose non-invasive detection and its research progress

Blood glucose concentration is an important index for the diagnosis of diabetes, its self-monitoring technology is the method for scientific diabetes management. Currently, the typical household blood glucose meters have achieved great success in diabetes management, but they are discrete detection methods, and involve invasive blood sampling procedures. Optical detection technologies, which use the physical properties of light to detect the glucose concentration in body fluids non-invasively, have shown great potential in non-invasive blood glucose detection. This article summarized and analyzed the basic principles, research status, existing problems, and application prospects of different optical glucose detection technologies. In addition, this article also discusses the problems of optical detection technology in wearable sensors and perspectives on the future of non-invasive blood glucose detection technology to improve blood glucose monitoring in diabetic patients.

Evaluation of sweat-based biomarkers using wearable biosensors for monitoring stress and fatigue: a systematic review

Objectives. This systematic review aims to report the evaluation of wearable biosensors for the real-time measurement of stress and fatigue using sweat biomarkers. Methods. A thorough search of the literature was carried out in databases such as PubMed, Web of Science and IEEE. A three-step approach for selecting research articles was developed and implemented. Results. Based on a systematic search, a total of 17 articles were included in this review. Lactate, cortisol, glucose and electrolytes were identified as sweat biomarkers. Sweat-based biomarkers are frequently monitored in real time using potentiometric and amperometric biosensors. Wearable biosensors such as an epidermal patch or a sweatband have been widely validated in scientific literature. Conclusions. Sweat is an important biofluid for monitoring general health, including stress and fatigue. It is becoming increasingly common to use biosensors that can measure a wide range of sweat biomarkers to detect fatigue during high-intensity work. Even though wearable biosensors have been validated for monitoring various sweat biomarkers, such biomarkers can only be used to assess stress and fatigue indirectly. In general, this study may serve as a driving force for academics and practitioners to broaden the use of wearable biosensors for the real-time assessment of stress and fatigue.

Sweat gland morphology and physiology in diabetes, neuropathy, and nephropathy: a review

Context: Sweat glands (SGs) play a vital role in thermal regulation. The function and structure are altered during the different pathological conditions.Objective: These alterations are studied through three techniques: biopsy, sweat analytes and electrical activity of SG.Methods: The morphological study of SG through biopsy and various techniques involved in quantifying sweat analytes is focussed on here. Electrical activities of SG in diabetes, neuropathy and nephropathy cases are also discussed, highlighting their limitations and future scope.Results and Conclusion: The result of this review identified three areas of the knowledge gap. The first is wearable sensors to correlate pathological conditions. Secondly, there is no device to look for its structure and quantify its associated function. Finally, therapeutic applications of SG are explored, especially for renal failure. With these aspects, this paper provides information collection and correlates SG with pathologies related to diabetes. Hence this could help researchers develop suitable technologies for the gaps identified.

Point-of-care testing of methamphetamine and cocaine utilizing wearable sensors

The imperative for the point-of-care testing of methamphetamine and cocaine in drug abuse prevention necessitates innovative solutions. To address this need, we have introduced a multi-channel wearable sensor harnessing CRISPR/Cas12a system. A CRISPR/Cas12a based system, integrated with aptamers specific to methamphetamine and cocaine, has been engineered. These aptamers function as signal-mediated intermediaries, converting methamphetamine and cocaine into nucleic acid signals, subsequently generating single-stranded DNA to activate the Cas12 protein. Additionally, we have integrated a microfluidic system and magnetic separation technology into the CRISPR system, enabling rapid and precise detection of cocaine and methamphetamine. The proposed sensing platform demonstrated exceptional sensitivity, achieving a detection limit as low as 0.1 ng/mL. This sensor is expected to be used for on-site drug detection in the future.

Fundamental Study of a Wristwatch Sweat Lactic Acid Monitor

A lactic acid (LA) monitoring system aimed at sweat monitoring was fabricated and tested. The sweat LA monitoring system uses a continuous flow of phosphate buffer saline, instead of chambers or cells, for collecting and storing sweat fluid excreted at the skin surface. To facilitate the use of the sweat LA monitoring system by subjects when exercising, the fluid control system, including the sweat sampling device, was designed to be unaffected by body movements or muscle deformation. An advantage of our system is that the skin surface condition is constantly refreshed by continuous flow. A real sample test was carried out during stationary bike exercise, which showed that LA secretion increased by approximately 10 μg/cm2/min compared to the baseline levels before exercise. The LA levels recovered to baseline levels after exercise due to the effect of continuous flow. This indicates that the wristwatch sweat LA monitor has the potential to enable a detailed understanding of the LA distribution at the skin surface.

Skin-Interfaced Bifluidic Paper-Based Device for Quantitative Sweat Analysis

The erratic, intermittent, and unpredictable nature of sweat production, resulting from physiological or psychological fluctuations, poses intricacies to consistently and accurately sample and evaluate sweat biomarkers. Skin-interfaced microfluidic devices that rely on colorimetric mechanisms for semi-quantitative detection are particularly susceptible to these inaccuracies due to variations in sweat secretion rate or instantaneous volume. This work introduces a skin-interfaced colorimetric bifluidic sweat device with two synchronous channels to quantify sweat rate and biomarkers in real-time, even during uncertain sweat activities. In the proposed bifluidic-distance metric approach, with one channel to measure sweat rate and quantify collected sweat volume, the other channel can provide an accurate analysis of the biomarkers based on the collected sweat volume. The closed channel design also reduces evaporation and resists contamination from the external environment. The feasibility of the device is highlighted in a proof-of-the-concept demonstration to analyze sweat chloride for evaluating hydration status and sweat glucose for assessing glucose levels. The low-cost yet highly accurate device provides opportunities for clinical sweat analysis and disease screening in remote and low-resource settings. The developed device platform can be facilely adapted for the other biomarkers when corresponding colorimetric reagents are exploited.

Harvesting and manipulating sweat and interstitial fluid in microfluidic devices

Microfluidic devices began to be used to facilitate sweat and interstitial fluid (ISF) sensing in the mid-2010s. Since then, numerous prototypes involving microfluidics have been developed in different form factors for sensing biomarkers found in these fluids under in vitro, ex vivo, and in vivo (on-body) settings. These devices transport and manipulate biofluids using microfluidic channels composed of silicone, polymer, paper, or fiber. Fluid flow transport and sample management can be achieved by controlling the flow rate, surface morphology of the channel, and rate of fluid evaporation. Although many devices have been developed for estimating sweat rate, electrolyte, and metabolite levels, only a handful have been able to proceed beyond laboratory testing and reach the stage of clinical trials and commercialization. To further this technology, this review reports on the utilization of microfluidics towards sweat and ISF management and transport. The review is distinguished from other recent reviews by focusing on microfluidic principles of sweat and ISF generation, transport, extraction, and management. Challenges and prospects are highlighted, with a discussion on how to transition such prototypes towards personalized healthcare monitoring systems.

A Miniaturized Wireless Micropump Enabled by Confined Acoustic Streaming

Miniaturization of health care, biomedical, and chemical systems is highly desirable for developing point-of-care testing (POCT) technologies. In system miniaturization, micropumps represent one of the major bottlenecks due to their undesirable pumping performance at such small sizes. Here, we developed a microelectromechanical system fabricated acoustic micropump based on an ultrahigh-frequency bulk acoustic wave resonator. The concept of an inner-boundary-confined acoustic jet was introduced to facilitate unidirectional flow. Benefitting from the high resonant frequency and confined acoustic streaming, the micropump reaches 32.620 kPa/cm3 (pressure/size) and 11.800 ml/min∙cm3 (flow rate/size), showing a 2-order-of-magnitude improvement in the energy transduction efficiency compared with the existing acoustic micropumps. As a proof of concept, the micropump was constructed as a wearable and wirelessly powered integrated drug delivery system with a size of only 9×9×9 mm3 and a weight of 1.16 g. It was demonstrated for ocular disease treatment through animal experimentation and a human pilot test. With superior pumping performance, miniaturized pump size, ultralow power consumption, and complementary metal-oxide-semiconductor compatibility, we expect it to be readily applied to various POCT applications including clinical diagnosis, prognosis, and drug delivery systems.

Fluorescence-Recovered Wearable Hydrogel Patch for In Vitro Detection of Glucose Based on Rare-Earth Nanoparticles

The physiological state of the human body can be indicated by analyzing the composition of sweat. In this research, a fluorescence-recovered wearable hydrogel patch has been designed and realized which can noninvasively monitor the glucose concentration in human sweat. Rare-earth nanoparticles (RENPs) of NaGdF4 doped with different elements (Yb, Er, and Ce) are synthesized and optimized for better luminescence in the near-infrared second (NIR-II) and visible region. In addition, RENPs are coated with CoOOH of which the absorbance has an extensive peak in the visible and NIR regions. The concentration of H2O2 in the environment can be detected by the fluorescence recovery degree of CoOOH-modified RENPs based on the fluorescence resonance energy transfer effect. For in vivo detection, the physiological state of oxidative stress at tumor sites can be visualized through its fluorescence in NIR-II with low background noise and high penetration depth. For the in vitro detection, CoOOH-modified RENP and glucose oxidase (GOx) were doped into a polyacrylamide hydrogel, and a patch that can emit green upconversion fluorescence under a 980 nm laser was prepared. Compared with the conventional electrochemical detection method, the fluorescence we presented has higher sensitivity and linear detection region to detect the glucose. This improved anti-interference sweat patch that can work in the dark environment was obtained, and the physiological state of the human body is conveniently monitored, which provides a new facile and convenient method to monitor the sweat status.

Skin-interfaced microfluidic sweat collection devices for personalized hydration management through thermal feedback

Non-electronic wearables that utilize skin-interfaced microfluidic technology have revolutionized the collection and analysis of human sweat, providing valuable biochemical information and indicating body hydration status. However, existing microfluidic devices often require constant monitoring of data during sweat assessment, thereby impeding the user experience and potentially missing anomalous physiological events, such as excessive sweating. Moreover, the complex manufacturing process hampers the scalability and large-scale production of such devices. Herein, we present a self-feedback microfluidic device with a unique dehydration reminder through a cost-effective "CAD-to-3D device" approach. It incorporates two independent systems for sweat collection and thermal feedback, including serpentine microchannels, reservoirs, petal-like bursting valves and heating chambers. The device operates by sequentially collecting sweat in the channels and reservoirs, and then activating thermal stimulators in the heating chambers through breaking the valves, initiating a chemical exothermic reaction. Human trials validate that the devices effectively alert users to potential dehydration by inducing skin thermal sensations triggered by sweat sampling. The proposed device offers facile scalability and customizable fabrication, and holds promise for managing hydration strategies in real-world scenarios, benefiting individuals engaged in sporting activities or exposed to high-temperature settings.

Carbon nanomaterials for sweat-based sensors: a review

Sweat is easily accessible from the human skin's surface. It is secreted by the eccrine glands and contains a wealth of physiological information, including metabolites and electrolytes like glucose and Na ions. Sweat is a particularly useful biofluid because of its easy and non-invasive access, unlike other biofluids, like blood. On the other hand, nanomaterials have started to show promise operation as a competitive substitute for biosensors and molecular sensors throughout the last 10 years. Among the most synthetic nanomaterials that are studied, applied, and discussed, carbon nanomaterials are special. They are desirable candidates for sensor applications because of their many intrinsic electrical, magnetic, and optical characteristics; their chemical diversity and simplicity of manipulation; their biocompatibility; and their effectiveness as a chemically resistant platform. Carbon nanofibers (CNFs), carbon dots (CDs), carbon nanotubes (CNTs), and graphene have been intensively investigated as molecular sensors or as components that can be integrated into devices. In this review, we summarize recent advances in the use of carbon nanomaterials as sweat sensors and consider how they can be utilized to detect a diverse range of analytes in sweat, such as glucose, ions, lactate, cortisol, uric acid, and pH.

Microfluidic-Based Non-Invasive Wearable Biosensors for Real-Time Monitoring of Sweat Biomarkers

Wearable biosensors are attracting great interest thanks to their high potential for providing clinical-diagnostic information in real time, exploiting non-invasive sampling of biofluids. In this context, sweat has been demonstrated to contain physiologically relevant biomarkers, even if it has not been exhaustively exploited till now. This biofluid has started to gain attention thanks to the applications offered by wearable biosensors, as it is easily collectable and can be used for continuous monitoring of some parameters. Several studies have reported electrochemical and optical biosensing strategies integrated with flexible, biocompatible, and innovative materials as platforms for biospecific recognition reactions. Furthermore, sampling systems as well as the transport of fluids by microfluidics have been implemented into portable and compact biosensors to improve the wearability of the overall analytical device. In this review, we report and discuss recent pioneering works about the development of sweat sensing technologies, focusing on opportunities and open issues that can be decisive for their applications in routine-personalized healthcare practices.

Advances in Non-Electrochemical Sensing of Human Sweat Biomarkers: From Sweat Sampling to Signal Reading

Sweat, commonly referred to as the ultrafiltrate of blood plasma, is an essential physiological fluid in the human body. It contains a wide range of metabolites, electrolytes, and other biologically significant markers that are closely linked to human health. Compared to other bodily fluids, such as blood, sweat offers distinct advantages in terms of ease of collection and non-invasive detection. In recent years, considerable attention has been focused on wearable sweat sensors due to their potential for continuous monitoring of biomarkers. Electrochemical methods have been extensively used for in situ sweat biomarker analysis, as thoroughly reviewed by various researchers. This comprehensive review aims to provide an overview of recent advances in non-electrochemical methods for analyzing sweat, including colorimetric methods, fluorescence techniques, surface-enhanced Raman spectroscopy, and more. The review covers multiple aspects of non-electrochemical sweat analysis, encompassing sweat sampling methodologies, detection techniques, signal processing, and diverse applications. Furthermore, it highlights the current bottlenecks and challenges faced by non-electrochemical sensors, such as limitations and interference issues. Finally, the review concludes by offering insights into the prospects for non-electrochemical sensing technologies. By providing a valuable reference and inspiring researchers engaged in the field of sweat sensor development, this paper aspires to foster the creation of innovative and practical advancements in this domain.

Access and Management of Sweat for Non-Invasive Biomarker Monitoring: A Comprehensive Review

Sweat is an important biofluid presents in the body since it regulates the internal body temperature, and it is relatively easy to access on the skin unlike other biofluids and contains several biomarkers that are also present in the blood. Although sweat sensing devices have recently displayed tremendous progress, most of the emerging devices primarily focus on the sensor development, integration with electronics, wearability, and data from in vitro studies and short-term on-body trials during exercise. To further the advances in sweat sensing technology, this review aims to present a comprehensive report on the approaches to access and manage sweat from the skin toward improved sweat collection and sensing. It is begun by delineating the sweat secretion mechanism through the skin, and the historical perspective of sweat, followed by a detailed discussion on the mechanisms governing sweat generation and management on the skin. It is concluded by presenting the advanced applications of sweat sensing, supported by a discussion of robust, extended-operation epidermal wearable devices aiming to strengthen personalized healthcare monitoring systems.

Bionanotechnology and bioMEMS (BNM): state-of-the-art applications, opportunities, and challenges

The development of micro- and nanotechnology for biomedical applications has defined the cutting edge of medical technology for over three decades, as advancements in fabrication technology developed originally in the semiconductor industry have been applied to solving ever-more complex problems in medicine and biology. These technologies are ideally suited to interfacing with life sciences, since they are on the scale lengths as cells (microns) and biomacromolecules (nanometers). In this paper, we review the state of the art in bionanotechnology and bioMEMS (collectively BNM), including developments and challenges in the areas of BNM, such as microfluidic organ-on-chip devices, oral drug delivery, emerging technologies for managing infectious diseases, 3D printed microfluidic devices, AC electrokinetics, flexible MEMS devices, implantable microdevices, paper-based microfluidic platforms for cellular analysis, and wearable sensors for point-of-care testing.

Enhancing On-Skin Analysis: A Microfluidic Device and Smartphone Imaging Module for Real-Time Quantitative Detection of Multianalytes in Sweat

Wearable sweat sensors present exciting opportunities for advancing personal health monitoring and noninvasive biomarker measurements. However, existing sensors often fall short in accurate detection of low analyte volumes and concentrations and lack multimodal sensing capabilities. Herein, we present a highly portable four-channel microfluidic device capable of conducting simultaneous sweat sampling and fluorometric sensing of potential biomarkers, such as l-Tyr, l-Trp, Crt, and NH4+, specifically designed for kidney disease monitoring. Our microfluidic device seamlessly integrates with smartphones, facilitating easy data retrieval and analysis. The core of the sensing array is a novel fluorometric solid-state mechanism utilizing carbon polymer dots derived from dopamine, catechol, and o-phenylenediamine monomers embedded in gelatin hydrogels. The sensors exhibit exceptional performance, offering linear ranges of 5-275, 6-170, 4-220, and 5-170 μM, with impressively low detection limits of 1.5, 1.2, 1.3, and 1.4 μM for l-Tyr, l-Trp, Crt, and NH4+, respectively. Through meticulous optimization of operational variables, comprising the temperature, sample volume, and assay time, we achieved the best performance of the device. Furthermore, the sensors exhibited remarkable selectivity, effectively distinguishing between biologically similar species and other potential biological compounds found in sweat. Our evaluation also extended to monitoring kidney diseases in patients and healthy individuals, showcasing the device's utility in world scenarios. Promising results showcase the potential of low-cost, multidiagnostic microfluidic sensor arrays, especially with synthetic skin integration, for enhanced disease detection and healthcare outcomes.

3D-printed epidermal sweat microfluidic systems with integrated microcuvettes for precise spectroscopic and fluorometric biochemical assays

Systems for capture, storage and analysis of eccrine sweat can provide insights into physiological health status, quantify losses of water, electrolytes, amino acids and/or other essential species, and identify exposures to adverse environmental species or illicit drugs. Recent advances in materials and device designs serve as the basis for skin-compatible classes of microfluidic platforms and in situ colorimetric assays for precise assessments of sweat rate, sweat loss and concentrations of wide-ranging types of biomarkers in sweat. This paper presents a set of findings that enhances the performance of these systems through the use of microfluidic networks, integrated valves and microscale optical cuvettes formed by three dimensional printing in hard/soft hybrid materials systems, for accurate spectroscopic and fluorometric assays. Field studies demonstrate the capability of these microcuvette systems to evaluate the concentrations of copper, chloride, and glucose in sweat, along with the pH of sweat, with laboratory-grade accuracy and sensitivity.

Recent Advances in Skin-Interfaced Wearable Sweat Sensors: Opportunities for Equitable Personalized Medicine and Global Health Diagnostics

Recent advances in skin-interfaced wearable sweat sensors enable the noninvasive, real-time monitoring of biochemical signals associated with health and wellness. These wearable platforms leverage microfluidic channels, biochemical sensors, and flexible electronics to enable the continuous analysis of sweat-based biomarkers such as electrolytes, metabolites, and hormones. As this field continues to mature, the potential of low-cost, continuous personalized health monitoring enabled by such wearable sensors holds significant promise for addressing some of the formidable obstacles to delivering comprehensive medical care in under-resourced settings. This Perspective highlights the transformative potential of wearable sweat sensing for providing equitable access to cutting-edge healthcare diagnostics, especially in remote or geographically isolated areas. It examines the current understanding of sweat composition as well as recent innovations in microfluidic device architectures and sensing strategies by showcasing emerging applications and opportunities for innovation. It concludes with a discussion on expanding the utility of wearable sweat sensors for clinically relevant health applications and opportunities for enabling equitable access to innovation to address existing health disparities.

Optical Integration in Wearable, Implantable and Swallowable Healthcare Devices

Recent advances in materials and semiconductor technologies have led to extensive research on optical integration in wearable, implantable, and swallowable health devices. These optical systems utilize the properties of light─intensity, wavelength, polarization, and phase─to monitor and potentially intervene in various biological events. The potential of these devices is greatly enhanced through the use of multifunctional optical materials, adaptable integration processes, advanced optical sensing principles, and optimized artificial intelligence algorithms. This synergy creates many possibilities for clinical applications. This Perspective discusses key opportunities, challenges, and future directions, particularly with respect to sensing modalities, multifunctionality, and the integration of miniaturized optoelectronic devices. We present fundamental insights and illustrative examples of such devices in wearable, implantable, and swallowable forms. The constant pursuit of innovation and the dedicated approach to critical challenges are poised to influence diverse fields.

Evolution of nanostructured skin patches towards multifunctional wearable platforms for biomedical applications

Recent advances in the field of skin patches have promoted the development of wearable and implantable bioelectronics for long-term, continuous healthcare management and targeted therapy. However, the design of electronic skin (e-skin) patches with stretchable components is still challenging and requires an in-depth understanding of the skin-attachable substrate layer, functional biomaterials and advanced self-powered electronics. In this comprehensive review, we present the evolution of skin patches from functional nanostructured materials to multi-functional and stimuli-responsive patches towards flexible substrates and emerging biomaterials for e-skin patches, including the material selection, structure design and promising applications. Stretchable sensors and self-powered e-skin patches are also discussed, ranging from electrical stimulation for clinical procedures to continuous health monitoring and integrated systems for comprehensive healthcare management. Moreover, an integrated energy harvester with bioelectronics enables the fabrication of self-powered electronic skin patches, which can effectively solve the energy supply and overcome the drawbacks induced by bulky battery-driven devices. However, to realize the full potential offered by these advancements, several challenges must be addressed for next-generation e-skin patches. Finally, future opportunities and positive outlooks are presented on the future directions of bioelectronics. It is believed that innovative material design, structure engineering, and in-depth study of fundamental principles can foster the rapid evolution of electronic skin patches, and eventually enable self-powered close-looped bioelectronic systems to benefit mankind.

Graphene-interfaced flexible and stretchable micro-nano electrodes: from fabrication to sweat glucose detection

Flexible and stretchable wearable electronic devices have received tremendous attention for their non-invasive and personal health monitoring applications. These devices have been fabricated by integrating flexible substrates and graphene nanostructures for non-invasive detection of physiological risk biomarkers from human bodily fluids, such as sweat, and monitoring of human physical motion tracking parameters. The extraordinary properties of graphene nanostructures in fully integrated wearable devices have enabled improved sensitivity, electronic readouts, signal conditioning and communication, energy harvesting from power sources through electrode design and patterning, and graphene surface modification or treatment. This review explores advances made toward the fabrication of graphene-interfaced wearable sensors, flexible and stretchable conductive graphene electrodes, as well as their potential applications in electrochemical sensors and field-effect-transistors (FETs) with special emphasis on monitoring sweat biomarkers, mainly in glucose-sensing applications. The review emphasizes flexible wearable sweat sensors and provides various approaches thus far employed for the fabrication of graphene-enabled conductive and stretchable micro-nano electrodes, such as photolithography, electron-beam evaporation, laser-induced graphene designing, ink printing, chemical-synthesis and graphene surface modification. It further explores existing graphene-interfaced flexible wearable electronic devices utilized for sweat glucose sensing, and their technological potential for non-invasive health monitoring applications.

Skin-Interfaced Wearable Sweat Sensors for Precision Medicine

Wearable sensors hold great potential in empowering personalized health monitoring, predictive analytics, and timely intervention toward personalized healthcare. Advances in flexible electronics, materials science, and electrochemistry have spurred the development of wearable sweat sensors that enable the continuous and noninvasive screening of analytes indicative of health status. Existing major challenges in wearable sensors include: improving the sweat extraction and sweat sensing capabilities, improving the form factor of the wearable device for minimal discomfort and reliable measurements when worn, and understanding the clinical value of sweat analytes toward biomarker discovery. This review provides a comprehensive review of wearable sweat sensors and outlines state-of-the-art technologies and research that strive to bridge these gaps. The physiology of sweat, materials, biosensing mechanisms and advances, and approaches for sweat induction and sampling are introduced. Additionally, design considerations for the system-level development of wearable sweat sensing devices, spanning from strategies for prolonged sweat extraction to efficient powering of wearables, are discussed. Furthermore, the applications, data analytics, commercialization efforts, challenges, and prospects of wearable sweat sensors for precision medicine are discussed.

Reshaping healthcare with wearable biosensors

Wearable health sensors could monitor the wearer's health and surrounding environment in real-time. With the development of sensor and operating system hardware technology, the functions of wearable devices have been gradually enriched with more diversified forms and more accurate physiological indicators. These sensors are moving towards high precision, continuity, and comfort, making great contributions to improving personalized health care. At the same time, in the context of the rapid development of the Internet of Things, the ubiquitous regulatory capabilities have been released. Some sensor chips are equipped with data readout and signal conditioning circuits, and a wireless communication module for transmitting data to computer equipment. At the same time, for data analysis of wearable health sensors, most companies use artificial neural networks (ANN). In addition, artificial neural networks could help users effectively get relevant health feedback. Through the physiological response of the human body, various sensors worn could effectively transmit data to the control unit, which analyzes the data and provides feedback of the health value to the user through the computer. This is the working principle of wearable sensors for health. This article focuses on wearable biosensors used for healthcare monitoring in different situations, as well as the development, technology, business, ethics, and future of wearable sensors for health monitoring.

Soft Electronics for Health Monitoring Assisted by Machine Learning

Due to the development of the novel materials, the past two decades have witnessed the rapid advances of soft electronics. The soft electronics have huge potential in the physical sign monitoring and health care. One of the important advantages of soft electronics is forming good interface with skin, which can increase the user scale and improve the signal quality. Therefore, it is easy to build the specific dataset, which is important to improve the performance of machine learning algorithm. At the same time, with the assistance of machine learning algorithm, the soft electronics have become more and more intelligent to realize real-time analysis and diagnosis. The soft electronics and machining learning algorithms complement each other very well. It is indubitable that the soft electronics will bring us to a healthier and more intelligent world in the near future. Therefore, in this review, we will give a careful introduction about the new soft material, physiological signal detected by soft devices, and the soft devices assisted by machine learning algorithm. Some soft materials will be discussed such as two-dimensional material, carbon nanotube, nanowire, nanomesh, and hydrogel. Then, soft sensors will be discussed according to the physiological signal types (pulse, respiration, human motion, intraocular pressure, phonation, etc.). After that, the soft electronics assisted by various algorithms will be reviewed, including some classical algorithms and powerful neural network algorithms. Especially, the soft device assisted by neural network will be introduced carefully. Finally, the outlook, challenge, and conclusion of soft system powered by machine learning algorithm will be discussed.

Laser-Cutted Epidermal Microfluidic Patch with Capillary Bursting Valves for Chronological Capture, Storage, and Colorimetric Sensing of Sweat

Flexible wearable microfluidic devices show great feasibility and potential development in the collection and analysis of sweat due to their convenience and non-invasive characteristics in health-level feedback and disease prediction. However, the traditional production process of microfluidic patches relies on resource-intensive laboratory and high-cost facilities. In this paper, a low-cost laser-cutting technology is proposed to fabricate epidermal microfluidic patches for the collection, storage and colorimetric analysis of sweat. Two different types of capillary bursting valves are designed and integrated into microchannel layers to produce two-stage bursting pressure for the reliable routing of sweat into microreservoirs in sequential fashion, avoiding the mixing of old and new sweat. Additionally, an enzyme-based reagent is embedded into the microreservoirs to quantify the glucose level in sweat by using colorimetric methods, demonstrating a high detection sensitivity at the glucose concentration from 0.1 mM to 1 mM in sweat and an excellent anti-interference performance that prevents interference from substances probably existent in sweat. In vitro and on-body experiments demonstrate the validity of the low-cost, laser-cut epidermal microfluidic patch for the chronological analysis of sweat glucose concentration and its potential application in the monitoring of human physiological information.

Smartphone-based platforms implementing microfluidic detection with image-based artificial intelligence

The frequent outbreak of global infectious diseases has prompted the development of rapid and effective diagnostic tools for the early screening of potential patients in point-of-care testing scenarios. With advances in mobile computing power and microfluidic technology, the smartphone-based mobile health platform has drawn significant attention from researchers developing point-of-care testing devices that integrate microfluidic optical detection with artificial intelligence analysis. In this article, we summarize recent progress in these mobile health platforms, including the aspects of microfluidic chips, imaging modalities, supporting components, and the development of software algorithms. We document the application of mobile health platforms in terms of the detection objects, including molecules, viruses, cells, and parasites. Finally, we discuss the prospects for future development of mobile health platforms.

Moving toward smart biomedical sensing

The development of novel biomedical sensors as highly promising devices/tools in early diagnosis and therapy monitoring of many diseases and disorders has recently witnessed unprecedented growth; more and faster than ever. Nonetheless, on the eve of Industry 5.0 and by learning from defects of current sensors in smart diagnostics of pandemics, there is still a long way to go to achieve the ideal biomedical sensors capable of meeting the growing needs and expectations for smart biomedical/diagnostic sensing through eHealth systems. Herein, an overview is provided to highlight the importance and necessity of an inevitable transition in the era of digital health/Healthcare 4.0 towards smart biomedical/diagnostic sensing and how to approach it via new digital technologies including Internet of Things (IoT), artificial intelligence, IoT gateways (smartphones, readers), etc. This review will bring together the different types of smartphone/reader-based biomedical sensors, which have been employing for a wide variety of optical/electrical/electrochemical biosensing applications and paving the way for future eHealth diagnostic devices by moving towards smart biomedical sensing. Here, alongside highlighting the characteristics/criteria that should be met by the developed sensors towards smart biomedical sensing, the challenging issues ahead are delineated along with a comprehensive outlook on this extremely necessary field.

A Systematic Review on the Advanced Techniques of Wearable Point-of-Care Devices and Their Futuristic Applications

Personalized point-of-care testing (POCT) devices, such as wearable sensors, enable quick access to health monitoring without the use of complex instruments. Wearable sensors are gaining popularity owing to their ability to offer regular and continuous monitoring of physiological data by dynamic, non-invasive assessments of biomarkers in biofluids such as tear, sweat, interstitial fluid and saliva. Current advancements have concentrated on the development of optical and electrochemical wearable sensors as well as advances in non-invasive measurements of biomarkers such as metabolites, hormones and microbes. For enhanced wearability and ease of operation, microfluidic sampling, multiple sensing, and portable systems have been incorporated with materials that are flexible. Although wearable sensors show promise and improved dependability, they still require more knowledge about interaction between the target sample concentrations in blood and non-invasive biofluids. In this review, we have described the importance of wearable sensors for POCT, their design and types of these devices. Following which, we emphasize on the current breakthroughs in the application of wearable sensors in the realm of wearable integrated POCT devices. Lastly, we discuss the present obstacles and forthcoming potentials including the use of Internet of Things (IoT) for offering self-healthcare using wearable POCT.

Flexible Sweat Sensors: From Films to Textiles

Flexible sweat sensors have found widespread potential applications for long-term wear and tracking and real-time monitoring of human health. However, the main substrate currently used in common flexible sweat sensors is thin film, which has disadvantages such as poor air permeability and the need for additional wearables. In this Review, the recent progress of sweat sensors has been systematically summarized by the types of monitoring methods of sweat sensors. In addition, this Review introduces and compares the performance of sweat sensors based on thin film and textile substrates such as fiber/yarn. Finally, opportunities and suggestions for the development of flexible sweat sensors are presented by summarizing the integration methods of sensors and human body monitoring sites.

Novel Wearable Optical Sensors for Vital Health Monitoring Systems-A Review

Wearable sensors are pioneering devices to monitor health issues that allow the constant monitoring of physical and biological parameters. The immunity towards electromagnetic interference, miniaturization, detection of nano-volumes, integration with fiber, high sensitivity, low cost, usable in harsh environments and corrosion-resistant have made optical wearable sensor an emerging sensing technology in the recent year. This review presents the progress made in the development of novel wearable optical sensors for vital health monitoring systems. The details of different substrates, sensing platforms, and biofluids used for the detection of target molecules are discussed in detail. Wearable technologies could increase the quality of health monitoring systems at a nominal cost and enable continuous and early disease diagnosis. Various optical sensing principles, including surface-enhanced Raman scattering, colorimetric, fluorescence, plasmonic, photoplethysmography, and interferometric-based sensors, are discussed in detail for health monitoring applications. The performance of optical wearable sensors utilizing two-dimensional materials is also discussed. Future challenges associated with the development of optical wearable sensors for point-of-care applications and clinical diagnosis have been thoroughly discussed.

Wearable biosensors for human fatigue diagnosis: A review

Fatigue causes deleterious effects to physical and mental health of human being and may cause loss of lives. Therefore, the adverse effects of fatigue on individuals and the society are massive. With the ever-increasing frequency of overtraining among modern military and sports personnel, timely, portable and accurate fatigue diagnosis is essential to avoid fatigue-induced accidents. However, traditional detection methods require complex sample preparation and blood sampling processes, which cannot meet the timeliness and portability of fatigue diagnosis. With the development of flexible materials and biosensing technology, wearable biosensors have attracted increased attention to the researchers. Wearable biosensors collect biomarkers from noninvasive biofluids, such as sweat, saliva, and tears, followed by biosensing with the help of biosensing modules continuously and quantitatively. The detection signal can then be transmitted through wireless communication modules that constitute a method for real-time understanding of abnormality. Recent developments of wearable biosensors are focused on miniaturized wearable electrochemistry and optical biosensors for metabolites detection, of which, few have exhibited satisfactory results in medical diagnosis. However, detection performance limits the wide-range applicability of wearable fatigue diagnosis. In this article, the application of wearable biosensors in fatigue diagnosis has been discussed. In fact, exploration of the composition of different biofluids and their potential toward fatigue diagnosis have been discussed here for the very first time. Moreover, discussions regarding the current bottlenecks in wearable fatigue biosensors and the latest advancements in biochemical reaction and data communication modules have been incorporated herein. Finally, the main challenges and opportunities were discussed for wearable fatigue diagnosis in the future.