Simultaneous Monitoring of Sweat and Interstitial Fluid Using a Single Wearable Biosensor Platform

Fully integrated microneedle biosensor array for wearable multiplexed fitness biomarkers monitoring

Fitness monitoring has become increasingly important in modern lifestyles; the current fitness monitoring always relies on physical sensors, making it challenging to detect pertinent issues at a deeper level when exercising. Here, we report a fully integrated wearable microneedle sensor that simultaneously measures fitness related biomarkers (e.g., glucose, lactate, and alcohol) during physical exercise. Such a sensor integrates a biocompatible 3D-printed microneedle array that can comfortably access skin interstitial fluid and a small circuit for signal processing and calibration, and wireless communication. The microneedle array features good biocompatibility and highly sensitive biochemical sensors that can detect even the slightest variations within the biomarkers of this fluid. On-body experimental results indicate that such a sensor can monitor fitness-related biomarkers across multiple subjects and support multi-day monitoring, with results showing a good correlation with commercial devices. The data was transmitted to a smartphone via Bluetooth and uploaded to cloud platforms for further health assessment. This study has the potential to boost intelligent wearable devices in sports health.

Approaches of wearable and implantable biosensor towards of developing in precision medicine

In the relentless pursuit of precision medicine, the intersection of cutting-edge technology and healthcare has given rise to a transformative era. At the forefront of this revolution stands the burgeoning field of wearable and implantable biosensors, promising a paradigm shift in how we monitor, analyze, and tailor medical interventions. As these miniature marvels seamlessly integrate with the human body, they weave a tapestry of real-time health data, offering unprecedented insights into individual physiological landscapes. This log embarks on a journey into the realm of wearable and implantable biosensors, where the convergence of biology and technology heralds a new dawn in personalized healthcare. Here, we explore the intricate web of innovations, challenges, and the immense potential these bioelectronics sentinels hold in sculpting the future of precision medicine.

Revolutionary Point-of-Care Wearable Diagnostics for Early Disease Detection and Biomarker Discovery through Intelligent Technologies

Early-stage disease detection, particularly in Point-Of-Care (POC) wearable formats, assumes pivotal role in advancing healthcare services and precision-medicine. Public benefits of early detection extend beyond cost-effectively promoting healthcare outcomes, to also include reducing the risk of comorbid diseases. Technological advancements enabling POC biomarker recognition empower discovery of new markers for various health conditions. Integration of POC wearables for biomarker detection with intelligent frameworks represents ground-breaking innovations enabling automation of operations, conducting advanced large-scale data analysis, generating predictive models, and facilitating remote and guided clinical decision-making. These advancements substantially alleviate socioeconomic burdens, creating a paradigm shift in diagnostics, and revolutionizing medical assessments and technology development. This review explores critical topics and recent progress in development of 1) POC systems and wearable solutions for early disease detection and physiological monitoring, as well as 2) discussing current trends in adoption of smart technologies within clinical settings and in developing biological assays, and ultimately 3) exploring utilities of POC systems and smart platforms for biomarker discovery. Additionally, the review explores technology translation from research labs to broader applications. It also addresses associated risks, biases, and challenges of widespread Artificial Intelligence (AI) integration in diagnostics systems, while systematically outlining potential prospects, current challenges, and opportunities.

Microneedle Patches-Integrated Transdermal Bioelectronics for Minimally Invasive Disease Theranostics

Wearable epidermal electronics with non- or minimally-invasive characteristics can collect, transduce, communicate, and interact with accessible physicochemical health indicators on the skin. However, due to the stratum corneum layer, rich information about body health is buried under the skin stratum corneum layer, for example, in the skin interstitial fluid. Microneedle patches are typically designed with arrays of special microsized needles of length within 1000 µm. Such characteristics potentially enable the access and sample of biomolecules under the skin or give therapeutical treatment painlessly and transdermally. Integrating microneedle patches with various electronics allows highly efficient transdermal bioelectronics, showing their great promise for biomedical and healthcare applications. This comprehensive review summarizes and highlights the recent progress on integrated transdermal bioelectronics based on microneedle patches. The design criteria and state-of-the-art fabrication techniques for such devices are initially discussed. Next, devices with different functions, including but not limited to health monitoring, drug delivery, and therapeutical treatment, are highlighted in detail. Finally, key issues associated with current technologies and future opportunities are elaborated to sort out the state of recent research, point out potential bottlenecks, and provide future research directions.

Ultra-Sensitive and Stable Multiplexed Biosensors Array in Fully Printed and Integrated Platforms for Reliable Perspiration Analysis

Electrochemical biosensors have emerged as one of the promising tools for tracking human body physiological dynamics via non-invasive perspiration analysis. However, it remains a key challenge to integrate multiplexed sensors in a highly controllable and reproducible manner to achieve long-term reliable biosensing, especially on flexible platforms. Herein, a fully inkjet printed and integrated multiplexed biosensing patch with remarkably high stability and sensitivity is reported for the first time. These desirable characteristics are enabled by the unique interpenetrating interface design and precise control over active materials mass loading, owing to the optimized ink formulations and droplet-assisted printing processes. The sensors deliver sensitivities of 313.28 µA mm-1 cm-2 for glucose and 0.87 µA mm-1 cm-2 for alcohol sensing with minimal drift over 30 h, which are among the best in the literature. The integrated patch can be used for reliable and wireless diet monitoring or medical intervention via epidermal analysis and would inspire the advances of wearable devices for intelligent healthcare applications.

Wearable Vertical Graphene-Based Microneedle Biosensor for Real-Time Ketogenic Diet Management

Ketogenic diets have attracted substantial interest in the treatment of chronic diseases, but there are health risks with long-term regimes. Despite the advancements in diagnostic and therapeutic methods in modern medicine, there is a huge gap in personalized health management of this dietary strategy. Hence, we present a wearable microneedle biosensor for real-time ketone and glucose monitoring. The microneedle array possesses excellent mechanical properties, allowing for consistent sampling of interstitial biomarkers while reducing the pain associated with skin puncture. Vertical graphene with outstanding electrical conductivity provides the resulting sensor with a high sensitivity of 234.18 μA mM-1 cm-2 and a low limit detection of 1.21 μM. When this fully integrated biosensor was used in human volunteers, it displayed an attractive analytical capability for tracking the dynamic metabolite levels. Moreover, the results of the on-body evaluation established a significant correlation with commercial blood measurements. Overall, this cost-effective and efficient sensing platform can accelerate the application of a ketogenic diet in personal nutrition and wellness management.

Wireless and battery-free wearable biosensing of riboflavin in sweat for precision nutrition

Nutrition assessment is crucial for dietary guidance and prevention of malnutrition. Recent endeavors in wearable biochemical sensors have enabled real-time, in situ analysis of nutrients in sweat. However, the monitoring of riboflavin, an indispensable vitamin B involved in energy metabolism, remains challenging due to its trace level and variations in the sweat matrix. Herein, we report a wireless, battery-free, and flexible wearable biosensing system for the in situ monitoring of sweat riboflavin. Highly sensitive and selective electrochemical voltammetric detection is realized based on the synergistic effect of electrodeposited reduced graphene oxide (rGO) and platinum nanoparticles (PtNPs) with a low detection limit of 1.2 nM. The fully integrated system is capable of sweat sampling with the microfluidic patch, real-time riboflavin analysis and pH calibration with the flexible electrode array, as well as wirelessly simultaneous near field communication (NFC) energy harvesting and data transmission with the flexible circuit and a smartphone. On-body human sweat analysis demonstrates high accuracy cross-validated with gold-standard measurements, and reveals a strong correlation between sweat and urine riboflavin levels. The proposed wearable platform opens up attractive possibilities for noninvasive nutrient tracking, providing strong potential for personalized dietary guidance towards precision nutrition.

Evaluation of a wearable fabric-based sensor for accurate sodium determination in sweat during exercise

INTRODUCTION

Newly developed wearable fabric sensors (WFS) can increase the ease and accuracy of sweat sodium measurements by performing simultaneous sampling and analysis on the body during exercise.

PURPOSE

Determine the accuracy of a WFS for measurement of sodium concentration in sweat.

METHODS

Subjects wore a WFS prototype and sweat collectors on their forearm during cycle ergometry. Subjects exercised at a moderate intensity (~ 65% heart rate reserve) for 30-60 min. Sweat samples were collected and analyzed using a commercial sweat sodium analyzer (SSA) every 10-15 min. WFS were adhered with an armband and connected to custom built electronics. Accuracy was determined by comparing predicted WFS concentration to the actual concentration from the commercial SSA and analyzed statistically using ANOVA and Bland-Altman plots.

RESULTS

A total of 19 subjects completed the study. The average sweat sodium concentration was 59 mM ± 22 mM from a SSA compared with 54 mM ± 22 mM from the WFS. Overall, the average accuracy of the WFS was 88% in comparison to the SSA with p = 0.45. A line of best fit comparing predicted versus actual sweat sodium concentration had a slope of 0.99, intercept of - 4.46, and an r2 of 0.90. Bland-Altman analysis showed the average concentration difference between the WFS and the SSA was 5.35 mM, with 99% of data points between ± 1.96 times the standard deviation.

CONCLUSION

The WFS accurately predicted sweat sodium concentration during moderate intensity cycle ergometry. With the need for precise assessment of sodium loss, especially during long duration exercise, this novel analysis method can benefit athletes and coaches. Further research involving longer duration and more intense exercise is warranted.

Smart Tattoo Sensors 2.0: A Ten-Year Progress Report through a Narrative Review

The increased interest in sensing tattoos reflects a shift in wearable technology, emphasizing their flexible, skin-adherent nature. These devices, driven by advancements in nanotechnology and materials science, offer highly sensitive and customizable sensors. The growing body of research in this area indicates a rising curiosity in their design and applications, with potential uses ranging from vital sign monitoring to biomarker detection. Sensing tattoos present a promising avenue in wearable healthcare technology, attracting attention from researchers, clinicians, and technology enthusiasts. The objective of this study is to analyze the development, application, and integration of the sensing tattoos in the health domain. A review was conducted on PubMed and Scopus, applying a standard checklist and a qualification process. The outcome reported 37 studies. Sensing tattoos hold transformative potential in health monitoring and physiological sensing, driven by their focus on affordability, user-friendly design, and versatile sensorization solutions. Despite their promise, ongoing refinement is essential, addressing limitations in adhesion, signal quality, biocompatibility, and regulatory complexities. Identified opportunities, including non-invasive health monitoring, multiplexed detection, and cost-effective fabrication methods, open avenues for personalized healthcare applications. However, bridging gaps in medical device standards, cybersecurity, and regulatory compliance is imperative for seamless integration. A key theme calls for a holistic, user-centric approach, emphasizing interdisciplinary collaboration. Balancing innovation with practicality, prioritizing ethics, and fostering collaboration are crucial for the evolution of these technologies. The dynamic state of the field is evident, with active exploration of new frontiers. This overview also provides a roadmap, urging scholars, industry players, and regulators to collectively contribute to the responsible integration of sensing tattoos into daily life.

Recent developments and future perspectives of microfluidics and smart technologies in wearable devices

Wearable devices are gaining popularity in the fields of health monitoring, diagnosis, and drug delivery. Recent advances in wearable technology have enabled real-time analysis of biofluids such as sweat, interstitial fluid, tears, saliva, wound fluid, and urine. The integration of microfluidics and emerging smart technologies, such as artificial intelligence (AI), machine learning (ML), and Internet of Things (IoT), into wearable devices offers great potential for accurate and non-invasive monitoring and diagnosis. This paper provides an overview of current trends and developments in microfluidics and smart technologies in wearable devices for analyzing body fluids. The paper discusses common microfluidic technologies in wearable devices and the challenges associated with analyzing each type of biofluid. The paper emphasizes the importance of combining smart technologies with microfluidics in wearable devices, and how they can aid diagnosis and therapy. Finally, the paper covers recent applications, trends, and future developments in the context of intelligent microfluidic wearable devices.

Monitoring of Sweat Ions and Physiological Parameters via a Reconfigurable Modular System

In recent years, wearable sensors have revolutionized health monitoring by enabling continuous, real-time tracking of human health and performance. These noninvasive devices are usually designed to monitor human physical state and biochemical markers. However, enhancing their functionalities often demands intricate customization by designers and additional expenses for users. Here, we present a strategy using assembled modular circuits to customize health monitoring wearables. The modular circuits can be effortlessly reconfigured to meet various specific requirements, facilitating the incorporation of diverse functions at a lower cost. To validate this approach, modular circuits were employed to develop four distinct systems for in vitro evaluations. These systems enabled the detection of sweat biomarkers and physical signals under various scenarios, including sedentary state, exercise, and daily activities with or without incorporating iontophoresis to induce sweat. Four key sweat markers (K+, Ca2+, Na+, and pH) and three essential physical indicators (heart rate, blood oxygen levels, and skin temperature) are selected as the detection targets. Commercial methods were also used to evaluate the potential for effective health monitoring with our technique. This reconfigurable modular wearable (ReModuWear) system promises to provide more easy-to-use and comprehensive health assessments. Additionally, it may contribute to environmental sustainability by reusing modules.

Technological Advances of Wearable Device for Continuous Monitoring of In Vivo Glucose

Managing diabetes is a chronic challenge today, requiring monitoring and timely insulin injections to maintain stable blood glucose levels. Traditional clinical testing relies on fingertip or venous blood collection, which has facilitated the emergence of continuous glucose monitoring (CGM) technology to address data limitations. Continuous glucose monitoring technology is recognized for tracking long-term blood glucose fluctuations, and its development, particularly in wearable devices, has given rise to compact and portable continuous glucose monitoring devices, which facilitates the measurement of blood glucose and adjustment of medication. This review introduces the development of wearable CGM-based technologies, including noninvasive methods using body fluids and invasive methods using implantable electrodes. The advantages and disadvantages of these approaches are discussed as well as the use of microneedle arrays in minimally invasive CGM. Microneedle arrays allow for painless transdermal puncture and are expected to facilitate the development of wearable CGM devices. Finally, we discuss the challenges and opportunities and look forward to the biomedical applications and future directions of wearable CGM-based technologies in biological research.

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.

Advancements in Skin-Mediated Drug Delivery: Mechanisms, Techniques, and Applications

Skin-mediated drug delivery methods currently are receiving significant attention as a promising approach for the enhanced delivery of drugs through the skin. Skin-mediated drug delivery offers the potential to overcome the limitations of traditional drug delivery methods, including oral administration and intravenous injection. The challenges associated with drug permeation through layers of skin, which act as a major barrier, are explored, and strategies to overcome these limitations are discussed in detail. This review categorizes skin-mediated drug delivery methods based on the means of increasing drug permeation, and it provides a comprehensive overview of the mechanisms and techniques associated with these methods. In addition, recent advancements in the application of skin-mediated drug delivery are presented. The review also outlines the limitations of ongoing research and suggests future perspectives of studies regarding the skin-mediated delivery of drugs.

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.

Redox-Concatenated Aptamer Integrated Skin Mimicking Electrochemical Patch for Noninvasive Detection of Cortisol

This research focuses on developing and validating a wearable electrochemical biosensor called the concatenated aptamer integrated skin patch, also known as the Captain Patch. The main objective is to detect cortisol levels in sweat, which can provide valuable insights into an individual's health. The biosensor utilizes a corrugated surface that mimics the skin, allowing for better attachment and an improved electrochemical performance. The study demonstrates the successful application of Captain Patch on the human body by using artificially spiked sweat samples. The results indicate good measurement accuracy and conformity when the patch is worn on the body. However, for long-term usage, the patch needs to be changed every 3-4 h or worn three times a day to enable monitoring of cortisol levels. Despite the need for frequent patch changes, the cost-effectiveness and ease of operation make these skin patches suitable for longitudinal cortisol monitoring and other sweat analytes. By customization of the biorecognition probe, the developed biowearable can be used to monitor a variety of vital biomarkers. Overall, Captain Patch, with its capability of detecting specific health markers such as cortisol, hints at the future potential of wearables to offer valuable data on various other biomarkers. Our approach presents the first step in integrating a cost-effective wearable electrochemical patch integrated with a redox-concatenated aptamer for noninvasive biomarker detection. This personalized approach to monitoring can lead to improved patient outcomes and increased patient engagement in managing their health.

Low-dimensional nanostructures for monolithic 3D-integrated flexible and stretchable electronics

Flexible/stretchable electronics, which are characterized by their ultrathin design, lightweight structure, and excellent mechanical robustness and conformability, have garnered significant attention due to their unprecedented potential in healthcare, advanced robotics, and human-machine interface technologies. An increasing number of low-dimensional nanostructures with exceptional mechanical, electronic, and/or optical properties are being developed for flexible/stretchable electronics to fulfill the functional and application requirements of information sensing, processing, and interactive loops. Compared to the traditional single-layer format, which has a restricted design space, a monolithic three-dimensional (M3D) integrated device architecture offers greater flexibility and stretchability for electronic devices, achieving a high-level of integration to accommodate the state-of-the-art design targets, such as skin-comfort, miniaturization, and multi-functionality. Low-dimensional nanostructures possess small size, unique characteristics, flexible/elastic adaptability, and effective vertical stacking capability, boosting the advancement of M3D-integrated flexible/stretchable systems. In this review, we provide a summary of the typical low-dimensional nanostructures found in semiconductor, interconnect, and substrate materials, and discuss the design rules of flexible/stretchable devices for intelligent sensing and data processing. Furthermore, artificial sensory systems in 3D integration have been reviewed, highlighting the advancements in flexible/stretchable electronics that are deployed with high-density, energy-efficiency, and multi-functionalities. Finally, we discuss the technical challenges and advanced methodologies involved in the design and optimization of low-dimensional nanostructures, to achieve monolithic 3D-integrated flexible/stretchable multi-sensory systems.

An integrated wearable sticker based on extended-gate AlGaN/GaN high electron mobility transistors for real-time cortisol detection in human sweat

Cortisol hormone imbalances can be detected through non-invasive sweat monitoring using field-effect transistor (FET) biosensors, which provide rapid and sensitive detection. However, challenges like skin compatibility and integration with sweat collection have hindered FET biosensors as wearable sensing platforms. In this study, we present an integrated wearable sticker for real-time cortisol detection based on an extended-gate AlGaN/GaN high electron mobility transistor (HEMT) combined with a soft bottom substrate and flexible channel for sweat collection. The developed devices exhibit excellent linearity (R2 = 0.990) and a high sensitivity of 1.245 μA dec-1 for cortisol sensing from 1 nM to 100 μM in high-ionic-strength solution, with successful cortisol detection demonstrated using authentic human sweat samples. Additionally, the chip's microminiature design effectively reduces bending impact during the wearable process of traditional soft binding sweat sensors. The extendedgate structure design of the HEMT chip enhances both width-to-length ratio and active sensing area, resulting in an exceptionally low detection limit of 100 fM. Futhermore, due to GaN material's inherent stability, this device exhibits long-term stability with sustained performance within a certain attenuation range even after 60 days. These stickers possess small, lightweight, and portable features that enable real-time cortisol detection within 5 minutes through direct sweat collection. The application of this technology holds great potential in the field of personal health management, facilitating users to conveniently monitor their mental and physical conditions.

Advances and Opportunities of Mobile Health in the Postpandemic Era: Smartphonization of Wearable Devices and Wearable Deviceization of Smartphones

Mobile health (mHealth) with continuous real-time monitoring is leading the era of digital medical convergence. Wearable devices and smartphones optimized as personalized health management platforms enable disease prediction, prevention, diagnosis, and even treatment. Ubiquitous and accessible medical services offered through mHealth strengthen universal health coverage to facilitate service use without discrimination. This viewpoint investigates the latest trends in mHealth technology, which are comprehensive in terms of form factors and detection targets according to body attachment location and type. Insights and breakthroughs from the perspective of mHealth sensing through a new form factor and sensor-integrated display overcome the problems of existing mHealth by proposing a solution of smartphonization of wearable devices and the wearable deviceization of smartphones. This approach maximizes the infinite potential of stagnant mHealth technology and will present a new milestone leading to the popularization of mHealth. In the postpandemic era, innovative mHealth solutions through the smartphonization of wearable devices and the wearable deviceization of smartphones could become the standard for a new paradigm in the field of digital medicine.

Reverse iontophoresis generated by porous microneedles produces an electroosmotic flow for glucose determination

Blood glucose level is a key indicator of a patient's health, notably the symptoms associated with diabetes. Painless and continuously monitored interstitial glucose is highly preferable for diabetes management. Microneedle arrays can be used as an effective but minimally invasive technique to break the skin barrier. Simultaneous reverse iontophoresis enables non-invasive interstitial fluid extraction from the intercellular matrix ≤25 mm under the skin's surface. Here, we describe an ion-conductive porous microneedle (PMN)-based glucose sensing device combined with reverse ion electroosmosis, in which glucose extraction can be significantly enhanced. Four novel benefits of ionophoresis are concurrently brought about by the charged PMN: (1) decreased transdermal resistance with the low invasive penetration of highly resistant stratum corneum; (2) a reduction of transdermal resistance through interconnectivity; (3) the movement of larger molecules through linked micropores; and (4) the production of an electroosmotic flow (EOF). The EOF generated by PMN is effectively extracted from the skin interstitial fluid for glucose concentration measurement. And this will likely contribute to the long-term home management of chronic diseases.

Conductive and Eco-friendly Biomaterials-based Hydrogels for Noninvasive Epidermal Sensors: A Review

As noninvasive wearable electronic devices, epidermal sensors enable continuous, real-time, and remote monitoring of various human physiological parameters. Conductive biomaterials-based hydrogels as sensor matrix materials have good biocompatibility, biodegradability, and efficient stimulus response capabilities and are widely applied in motion monitoring, healthcare, and human-machine interaction. However, biomass hydrogel-based epidermal sensing devices still need excellent mechanical properties, prolonged stability, multifunctionality, and extensive practicality. Therefore, this paper reviews the common biomass hydrogel materials for epidermal sensing (proteins, polysaccharides, polyphenols, etc.) and the various types of noninvasive sensing devices (strain/pressure sensors, temperature sensors, glucose sensors, electrocardiograms, etc.). Moreover, this review focuses on the strategies of scholars to enhance sensor properties, such as strength, conductivity, stability, adhesion, and self-healing ability. This work will guide the preparation and optimization of high-performance biomaterials-based hydrogel epidermal sensors.

Wearable biosensors for human health: A bibliometric analysis from 2007 to 2022

Objective

This study aimed to determine the status of scientific production on biosensor usage for human health monitoring.

Methods

We used bibliometrics based on the data and metadata retrieved from the Web of Science between 2007 and 2022. Articles unrelated to health and medicine were excluded. The databases were processed using the VOSviewer software and auxiliary spreadsheets. Data extraction yielded 275 articles published in 161 journals, mainly concentrated on 13 journals and 881 keywords plus.

Results

The keywords plus of high occurrences were estimated at 27, with seven to 30 occurrences. From the 1595 identified authors, 125 were consistently connected in the coauthorship network in the total set and were grouped into nine clusters. Using Lotka's law, we identified 24 prolific authors, and Hirsch index analysis revealed that 45 articles were cited more than 45 times. Crosses were identified between 17 articles in the Hirsch index and 17 prolific authors, highlighting the presence of a large set of prolific authors from various interconnected clusters, a triad, and a solitary prolific author.

Conclusion

An exponential trend was observed in biosensor research for health monitoring, identifying areas of innovation, collaboration, and technological challenges that can guide future research on this topic.

Wearing the Lab: Advances and Challenges in Skin-Interfaced Systems for Continuous Biochemical Sensing

Continuous, on-demand, and, most importantly, contextual data regarding individual biomarker concentrations exemplify the holy grail for personalized health and performance monitoring. This is well-illustrated for continuous glucose monitoring, which has drastically improved outcomes and quality of life for diabetic patients over the past 2 decades. Recent advances in wearable biosensing technologies (biorecognition elements, transduction mechanisms, materials, and integration schemes) have begun to make monitoring of other clinically relevant analytes a reality via minimally invasive skin-interfaced devices. However, several challenges concerning sensitivity, specificity, calibration, sensor longevity, and overall device lifetime must be addressed before these systems can be made commercially viable. In this chapter, a logical framework for developing a wearable skin-interfaced device for a desired application is proposed with careful consideration of the feasibility of monitoring certain analytes in sweat and interstitial fluid and the current development of the tools available to do so. Specifically, we focus on recent advancements in the engineering of biorecognition elements, the development of more robust signal transduction mechanisms, and novel integration schemes that allow for continuous quantitative analysis. Furthermore, we highlight the most compelling and promising prospects in the field of wearable biosensing and the challenges that remain in translating these technologies into useful products for disease management and for optimizing human performance.

Bioadhesive Technology Platforms

Bioadhesives have emerged as transformative and versatile tools in healthcare, offering the ability to attach tissues with ease and minimal damage. These materials present numerous opportunities for tissue repair and biomedical device integration, creating a broad landscape of applications that have captivated clinical and scientific interest alike. However, fully unlocking their potential requires multifaceted design strategies involving optimal adhesion, suitable biological interactions, and efficient signal communication. In this Review, we delve into these pivotal aspects of bioadhesive design, highlight the latest advances in their biomedical applications, and identify potential opportunities that lie ahead for bioadhesives as multifunctional technology platforms.

Soft and Conductive Polyethylene Glycol Hydrogel Electrodes for Electrocardiogram Monitoring

The measurement of biosignals in the clinical and healthcare fields is fundamental; however, conventional electrodes pose challenges such as incomplete skin contact and skin-related issues, hindering accurate biosignal measurement. To address these challenges, conductive hydrogels, which are valuable owing to their biocompatibility and flexibility, have been widely developed and explored for electrode applications. In this study, we fabricated a conductive hydrogel by mixing polyethylene glycol diacrylate (PEGDA) with poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) polymers dissolved in deionized water, followed by light-triggered crosslinking. Notably, this study pioneered the use of a PEGDA-PEDOT:PSS hydrogel for electrocardiogram (ECG) monitoring- a type of biosignal. The resulting PEGDA-PEDOT:PSS hydrogel demonstrated remarkable conductivity while closely approximating the modulus of skin elasticity. Additionally, it demonstrated biocompatibility and a high signal-to-noise ratio in the waveforms. This study confirmed the exceptional suitability of the PEGDA-PEDOT:PSS hydrogel for accurate biosignal measurements with potential applications in various wearable devices designed for biosignal monitoring.

Wearable Sensor Patch with Hydrogel Microneedles for In Situ Analysis of Interstitial Fluid

Continuous real-time monitoring of biomarkers in interstitial fluid is essential for tracking metabolic changes and facilitating the early detection and management of chronic diseases such as diabetes. However, developing minimally invasive sensors for the in situ analysis of interstitial fluid and addressing signal delays remain a challenge. Here, we introduce a wearable sensor patch incorporating hydrogel microneedles for rapid, minimally invasive collection of interstitial fluid from the skin while simultaneously measuring biomarker levels in situ. The sensor patch is stretchable to accommodate the swelling of the hydrogel microneedles upon extracting interstitial fluid and adapts to skin deformation during measurements, ensuring consistent sensing performance in detecting model biomarker concentrations, such as glucose and lactate, in a mouse model. The sensor patch exhibits in vitro sensitivities of 0.024 ± 0.002 μA mM-1 for glucose and 0.0030 ± 0.0004 μA mM-1 for lactate, with corresponding linear ranges of 0.1-3 and 0.1-12 mM, respectively. For in vivo glucose sensing, the sensor patch demonstrates a sensitivity of 0.020 ± 0.001 μA mM-1 and a detection range of 1-8 mM. By integrating a predictive model, the sensor patch can analyze and compensate for signal delays, improving calibration reliability and providing guidance for potential optimization in sensing performance. The sensor patch is expected to serve as a minimally invasive platform for the in situ analysis of multiple biomarkers in interstitial fluid, offering a promising solution for continuous health monitoring and disease management.

Wearable Clinic: From Microneedle-Based Sensors to Next-Generation Healthcare Platforms

The rapid development of wearable biosensing calls for next-generation devices that allow continuous, real-time, and painless monitoring of health status along with responsive medical treatment. Microneedles have exhibited great potential for the direct access of dermal interstitial fluid (ISF) in a minimally invasive manner. Recent studies of microneedle-based devices have evolved from conventional off-line detection to multiplexed, wireless, and integrated sensing. In this review, the classification and fabrication techniques of microneedles are first introduced, and then the representative examples of microneedles for transdermal monitoring with different sensing modalities are summarized. State-of-the-art advances in therapeutic and closed-loop systems are presented to formulate guidelines for the development of next-generation microneedle-based healthcare platforms. The potential challenges and prospects are discussed to pave a new avenue toward pragmatic applications in the real world.

Ultrasound-activatable and skin-associated minimally invasive microdevices for smart drug delivery and diagnosis

Ultrasound-activatable and skin-associated minimally invasive microdevices (USMIMs) have garnered significant attention in the domains of smart drug delivery and biomedical diagnosis for on-demand healthcare, owing to their outstanding wearability, flexibility, and comfort. In this review, we present a comprehensive overview of the noteworthy advancements in USMIMs, with a specific focus on device design, potential applications, challenges, and future prospects. The classification of such microdevices primarily encompasses biointerfacing microsystems, including skin-perforable US-assisted microneedles (MNs), skin-attachable sonophoresis and their combination with microbubbles, as well as non-biointerfacing microsystems for drug delivery. Additionally, US-mediated and skin-attached microtransducers utilized in biomedical diagnosis are classified into imaging-related microtransducers, diagramming detection devices, and their combinative systems with applications on diverse signal detection. Besides, the review also highlights the challenges associated with USMIMs, focusing on aspects such as safety, environmental tolerance, wearability/comfortability, and personalization. Furthermore, it offers insights into future perspectives that address these challenges and discuss potential advancements in the field. It is firmly believed that the proposed USMIMs possess immense potential to significantly improve human lives in the near future.

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.

In-human testing of a non-invasive continuous low-energy microwave glucose sensor with advanced machine learning capabilities

Continuous glucose monitoring schemes that avoid finger pricking are of utmost importance to enhance the comfort and lifestyle of diabetic patients. To this aim, we propose a microwave planar sensing platform as a potent sensing technology that extends its applications to biomedical analytes. In this paper, a compact planar resonator-based sensor is introduced for noncontact sensing of glucose. Furthermore, in vivo and in-vitro tests using a microfluidic channel system and in clinical trial settings demonstrate its reliable operation. The proposed sensor offers real-time response and a high linear correlation (R2 ∼ 0.913) between the measured sensor response and the blood glucose level (GL). The sensor is also enhanced with machine learning to predict the variation of body glucose levels for non-diabetic and diabetic patients. This addition is instrumental in triggering preemptive measures in cases of unusual glucose level trends. In addition, it allows for the detection of common artifacts of the sensor as anomalies so that they can be removed from the measured data. The proposed system is designed to noninvasively monitor interstitial glucose levels in humans, introducing the opportunity to create a customized wearable apparatus with the ability to learn.

Mini review about metal organic framework (MOF)-based wearable sensors: Challenges and prospects

Among many types of wearable sensors, MOFs-based wearable sensors have recently been explored in both commercialization and research. There has been much effort in various aspects of the development of MOF-based wearable sensors including but not limited to miniaturization, size control, safety, improvements in conformal and flexible features, improvements in the analytical performance and long-term storage of these devices. Recent progress in the design and deployment of MOFs-based wearable sensors are covered in this paper, as are the remaining obstacles and prospects. This work also highlights the enormous potential for synergistic effects of MOFs used in combination with other nanomaterials for healthcare applications and raise attention toward the economic aspect and market diffusion of MOFs-based wearable sensors.

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.

Review of Noninvasive Continuous Glucose Monitoring in Diabetics

For diabetics, taking regular blood glucose measurements is crucial. However, traditional blood glucose monitoring methods are invasive and unfriendly to diabetics. Recent studies have proposed a biofluid-based glucose sensing technique that creatively combines wearable devices with noninvasive glucose monitoring technology to enhance diabetes management. This is a revolutionary advance in the diagnosis and management of diabetes, reflects the thoughtful modernization of medicine, and promotes the development of digital medicine. This paper reviews the research progress of noninvasive continuous blood glucose monitoring (CGM), with a focus on the biological liquids that replace blood in monitoring systems, the technical principles of continuous noninvasive glucose detection, and the output and calibration of sensor signals. In addition, the existing limits of noninvasive CGM systems and prospects for the future are discussed. This work serves as a resource for further promoting the development of noninvasive CGM systems.

Highly sensitive flexible heat flux sensor based on a microhole array for ultralow to high temperatures

With the growing demand for thermal management of electronic devices, cooling of high-precision instruments, and biological cryopreservation, heat flux measurement of complex surfaces and at ultralow temperatures has become highly imperative. However, current heat flux sensors (HFSs) are commonly used in high-temperature scenarios and have problems when applied in low-temperature conditions, such as low sensitivity and embrittlement. In this study, we developed a flexible and highly sensitive HFS that can operate at ultralow to high temperatures, ranging from -196 °C to 273 °C. The sensitivities of HFSs with thicknesses of 0.2 mm and 0.3 mm, which are efficiently manufactured by the screen-printing method, reach 11.21 μV/(W/m2) and 13.43 μV/(W/m2), respectively. The experimental results show that there is a less than 3% resistance change from bending to stretching. Additionally, the HFS can measure heat flux in both exothermic and absorptive cases and can measure heat flux up to 25 kW/m2. Additionally, we demonstrate the application of the HFS to the measurement of minuscule heat flux, such as heat dissipation of human skin and cold water. This technology is expected to be used in heat flux measurements at ultralow temperatures or on complex surfaces, which has great importance in the superconductor and cryobiology field.

Advanced Self-Powered Biofuel Cells with Capacitor and Nanogenerator for Biomarker Sensing

Self-powered biofuel cells (BFCs) have evolved for highly sensitive detection of biomarkers such as noncodon micro ribonucleic acids (miRNAs) in the presence of interfering substrates. Self-charging supercapacitive BFCs for in vivo and in vitro cellular microenvironments represent the most prevalent sensing mechanism for diagnosis. Therefore, self-powered biosensing (SPB) with a capacitor and contact separation with a triboelectric nanogenerator (TENG) offers electrochemical and colorimetric dual-mode detection via improved electrical signal intensity. In this review, we discuss three major components: stretchable self-powered BFC design, miRNA sensing, and impedance spectroscopy. A specific focus is given to 1) assembling of sensors for biomarkers, 2) electrical output signal intensification, and 3) role of supercapacitors and nanogenerators in SPBs. We outline the key features of stretchable SPBs and the sequence of miRNA sensing by SPBs. We have emphasized the need of a supercapacitor and nanogenerator for SPBs in the context of advanced assembly of the sensing unit. Finally, we outline the role of impedance spectroscopy in the detection and estimation of biomarkers. We highlight key challenges in SPBs for biomarker sensing, which needs improved sensing accuracy, integration strategies of electrochemical biosensing for in vitro and in vivo microenvironments, and the impact of miRNA sensing on cancer diagnostics. This article attempts a specific focus on the accuracy and limitations of sensing unit for miRNA biomarkers and associated tool for boosting electrical signal intensity for a potential big step further.

A highly electrocatalytic, stretchable, and breathable enzyme-free electrochemical patch based on electrospun fibers decorated with platinum nano pine needles for continuous glucose sensing in neutral conditions

Given the worldwide increase in diabetes, there is an urgent need for glucose sensors that can achieve the on-body detection of glucose concentration. With the development of nanomaterials and flexible electronics, wearable electrochemical enzyme-free glucose biosensors that can conveniently, continuously and stably monitor the glucose concentrations of diabetes patients without invasion and risk of infection are coming into focus. However, despite the enormous efforts toward wearable electrochemical enzyme-free glucose sensors, there have been limited achievements in developing a stretchable and breathable glucose sensor with high sensitivity, low detection limit, and excellent catalytic activity towards glucose oxidation in neutral media, to meet the need for continuous wearable glucose monitoring in scenarios such as the on-body detection of glucose in human sweat. Herein, we demonstrate a novel electrochemical enzyme-free glucose-sensing patch on the foundation of electrospun polyurethane (PU) fibrous mats to address some of the aforementioned challenges. The sensing patch was fabricated through a facile technology of electrospinning, followed by magnetron sputtering of gold (Au) to enable high conductivity. After that, ultrasonic-assisted electrodeposition was utilized to in situ introduce well-dispersed platinum nano pine needles along each fiber. Due to the good stretchability of PU materials, porous structure, and large specific surface area of electrochemical sites, the glucose-sensing patch promises merits such as good stretchability (performs well under 10% strain), high sensitivity (203.13 μA mM-1 cm-1), prominently low detection limit (14.77 μM), excellent selectivity, and efficient vapor permeability. Notably, the advanced hierarchical nanostructures with excellent catalytic activity towards glucose oxidation could be capable of detecting glucose in neutral conditions (pH = 7.4) without the assistance of enzymes. Given the facile fabrication methods and the integrated superior performances, this enzyme-free glucose-sensing patch could play a vital role in wearable glucose sensors.

Microneedle-based glucose monitoring: a review from sampling methods to wearable biosensors

Blood glucose (BG) monitoring is critical for diabetes management. In recent years, microneedle (MN)-based technology has attracted emerging attention in glucose sensing and detection. In this review, we summarized MN-based sampling for glucose collection and glucose analysis in detail. First, different principles of MN-based biofluid extraction were elaborated, including external negative pressure, capillary force, swelling force and iontophoresis, which would guide the shape design and material optimization of MNs. Second, MNs coupled with different analysis approaches, including Raman methods, colorimetry, fluorescence, and electrochemical sensing, were emphasized to exhibit the trend towards highly integrated wearable sensors. Finally, the future development prospects of MN-based devices were discussed.

Nanostructured wearable electrochemical and biosensor towards healthcare management: a review

In recent years, there has been a rapid increase in demand for wearable sensors, particularly these tracking the surroundings, fitness, and health of people. Thus, selective detection in human body fluid is a demand for a smart lifestyle by quick monitoring of electrolytes, drugs, toxins, metabolites and biomolecules, proteins, and the immune system. In this review, these parameters along with the main features of the latest and mostly cited research work on nanostructured wearable electrochemical and biosensors are surveyed. This study aims to help researchers and engineers choose the most suitable selective and sensitive sensor. Wearable sensors have broad and effective sensing platforms, such as contact lenses, Google Glass, skin-patch, mouth gourds, smartwatches, underwear, wristbands, and others. For increasing sensor reliability, additional advancements in electrochemical and biosensor precision, stability in uncontrolled environments, and reproducible sample conveyance are necessary. In addition, the optimistic future of wearable electrochemical sensors in fields, such as remote and customized healthcare and well-being is discussed. Overall, wearable electrochemical and biosensing technologies hold great promise for improving personal healthcare and monitoring performance with the potential to have a significant impact on daily lives. These technologies enable real-time body sensing and the communication of comprehensive physiological information.

Flexible, stretchable, and single-molecule-sensitive SERS-active sensor for wearable biosensing applications

The development of wearable sensors for remote patient monitoring and personalized medicine has led to a revolution in biomedical technology. Plasmonic metasurfaces that enhance Raman scattering signals have recently gained attention as wearable sensors. However, finding a flexible, sensitive, and easy-to-fabricate metasurface has been a challenge for decades. In this paper, a novel wearable device, the flexible, stretchable, and single-molecule-sensetive SERS-active sensor, is proposed. This device offers an unprecedented SERS enhancement factor in the order of 1011, along with other long-desired characteristics for SERS applications such as a high scattering to absorption ratio (∼2.5) and a large hotspot volume (40 nm × 40 nm × 5 nm). To achieve flexibility, we use polydimethylsiloxane (PDMS) as the substrate, which is stable, transparent, and biologically compatible. Our numerical calculations show that the proposed sensor offers reliable SERS performance even under bending (up to 100° angles) or stretching (up to 50% stretch). The easy-to-fabricate and flexible nature of our sensor offers a promising avenue for developing highly sensitive wearable sensors for a range of applications, particularly in the field of personalized medicine and remote patient monitoring.

Biomimetic Flexible Sensors and Their Applications in Human Health Detection

Bionic flexible sensors are a new type of biosensor with high sensitivity, selectivity, stability, and reliability to achieve detection in complex natural and physiological environments. They provide efficient, energy-saving and convenient applications in medical monitoring and diagnosis, environmental monitoring, and detection and identification. Combining sensor devices with flexible substrates to imitate flexible structures in living organisms, thus enabling the detection of various physiological signals, has become a hot topic of interest. In the field of human health detection, the application of bionic flexible sensors is flourishing and will evolve into patient-centric diagnosis and treatment in the future of healthcare. In this review, we provide an up-to-date overview of bionic flexible devices for human health detection applications and a comprehensive summary of the research progress and potential of flexible sensors. First, we evaluate the working mechanisms of different classes of bionic flexible sensors, describing the selection and fabrication of bionic flexible materials and their excellent electrochemical properties; then, we introduce some interesting applications for monitoring physical, electrophysiological, chemical, and biological signals according to more segmented health fields (e.g., medical diagnosis, rehabilitation assistance, and sports monitoring). We conclude with a summary of the advantages of current results and the challenges and possible future developments.

Screen-Printed Textile-Based Electrochemical Biosensor for Noninvasive Monitoring of Glucose in Sweat

Wearable sweat biosensors for noninvasive monitoring of health parameters have attracted significant attention. Having these biosensors embedded in textile substrates can provide a convenient experience due to their soft and flexible nature that conforms to the skin, creating good contact for long-term use. These biosensors can be easily integrated with everyday clothing by using textile fabrication processes to enhance affordable and scalable manufacturing. Herein, a flexible electrochemical glucose sensor that can be screen-printed onto a textile substrate has been demonstrated. The screen-printed textile-based glucose biosensor achieved a linear response in the range of 20-1000 µM of glucose concentration and high sensitivity (18.41 µA mM^-1 cm^-2, R² = 0.996). In addition, the biosensors show high selectivity toward glucose among other interfering analytes and excellent stability over 30 days of storage. The developed textile-based biosensor can serve as a platform for monitoring bio analytes in sweat, and it is expected to impact the next generation of wearable devices.

Wearable Microfluidics for Continuous Assay

The development of wearable devices provides approaches for the realization of self-health care. Easily carried wearable devices allow individual health monitoring at any place whenever necessary. There are various interesting monitoring targets, including body motion, organ pressure, and biomarkers. An efficient use of space in one small device is a promising resolution to increase the functions of wearable devices. Through integration of a microfluidic system into wearable devices, embedding complicated structures in one design becomes possible and can enable multifunction analyses within a limited device volume. This article reviews the reported microfluidic wearable devices, introduces applications to different biofluids, discusses characteristics of the design strategies and sensing principles, and highlights the attractive configurations of each device. This review seeks to provide a detailed summary of recent advanced microfluidic wearable devices. The overview of advanced key components is the basis for the development of future microfluidic wearable devices.

Fluid-based wearable sensors: a turning point in personalized healthcare

Nowadays, it has become very popular to develop wearable devices that can monitor biomarkers to analyze the health status of the human body more comprehensively and accurately. Wearable sensors, specially designed for home care services, show great promise with their ease of use, especially during pandemic periods. Scientists have conducted many innovative studies on new wearable sensors that can noninvasively and simultaneously monitor biochemical indicators in body fluids for disease prediction, diagnosis, and management. Using noninvasive electrochemical sensors, biomarkers can be detected in tears, saliva, perspiration, and skin interstitial fluid (ISF). In this review, biofluids used for noninvasive wearable sensor detection under four main headings, saliva, sweat, tears, and ISF-based wearable sensors, were examined in detail. This report analyzes nearly 50 recent articles from 2017 to 2023. Based on current research, this review also discusses the evolution of wearable sensors, potential implementation challenges, and future prospects.

Effect of interstitial fluid pH on transdermal glucose extraction by reverse iontophoresis

Reverse iontophoresis (RI) is a promising technology in the field of continuous glucose monitoring (CGM), offering significant advantages such as finger-stick-free operation, wearability, and non-invasiveness. In the glucose extraction process based on RI, the pH of the interstitial fluid (ISF) is a critical factor that needs further investigation, as it directly influences the accuracy of transdermal glucose monitoring. In this study, a theoretical analysis was conducted to investigate the mechanism by which pH affects the glucose extraction flux. Modeling and numerical simulations performed at different pH conditions indicated that the zeta potential was significantly impacted by the pH, thereby altering the direction and flux of the glucose iontophoretic extraction. A screen-printed glucose biosensor integrated with RI extraction electrodes was developed for ISF extraction and glucose monitoring. The accuracy and stability of the ISF extraction and glucose detection device were demonstrated with extraction experiments using different subdermal glucose concentrations ranging from 0 to 20 mM. The extraction results for different ISF pH values exhibited that at 5 mM and 10 mM subcutaneous glucose, the extracted glucose concentration was increased by 0.08212 mM and 0.14639 mM for every 1 pH unit increase, respectively. Furthermore, the normalized results for 5 mM and 10 mM glucose demonstrated a linear correlation, indicating considerable potential for incorporating a pH correction factor in the blood glucose prediction model used to calibrate glucose monitoring.

Recent Advancements in Physiological, Biochemical, and Multimodal Sensors Based on Flexible Substrates: Strategies, Technologies, and Integrations

Flexible wearable devices have been widely used in biomedical applications, the Internet of Things, and other fields, attracting the attention of many researchers. The physiological and biochemical information on the human body reflects various health states, providing essential data for human health examination and personalized medical treatment. Meanwhile, physiological and biochemical information reveals the moving state and position of the human body, and it is the data basis for realizing human-computer interactions. Flexible wearable physiological and biochemical sensors provide real-time, human-friendly monitoring because of their light weight, wearability, and high flexibility. This paper reviews the latest advancements, strategies, and technologies of flexibly wearable physiological and biochemical sensors (pressure, strain, humidity, saliva, sweat, and tears). Next, we systematically summarize the integration principles of flexible physiological and biochemical sensors with the current research progress. Finally, important directions and challenges of physiological, biochemical, and multimodal sensors are proposed to realize their potential applications for human movement, health monitoring, and personalized medicine.

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.

Technology Roadmap for Flexible Sensors

Humans rely increasingly on sensors to address grand challenges and to improve quality of life in the era of digitalization and big data. For ubiquitous sensing, flexible sensors are developed to overcome the limitations of conventional rigid counterparts. Despite rapid advancement in bench-side research over the last decade, the market adoption of flexible sensors remains limited. To ease and to expedite their deployment, here, we identify bottlenecks hindering the maturation of flexible sensors and propose promising solutions. We first analyze challenges in achieving satisfactory sensing performance for real-world applications and then summarize issues in compatible sensor-biology interfaces, followed by brief discussions on powering and connecting sensor networks. Issues en route to commercialization and for sustainable growth of the sector are also analyzed, highlighting environmental concerns and emphasizing nontechnical issues such as business, regulatory, and ethical considerations. Additionally, we look at future intelligent flexible sensors. In proposing a comprehensive roadmap, we hope to steer research efforts towards common goals and to guide coordinated development strategies from disparate communities. Through such collaborative efforts, scientific breakthroughs can be made sooner and capitalized for the betterment of humanity.

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.

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.