Battery-free, skin-interfaced microfluidic/electronic systems for simultaneous electrochemical, colorimetric, and volumetric analysis of sweat

Breaking the Specificity Barrier in Microwave Sensing: Highly Specific Lactate Microwave Biosensor for Fitness and Exercise Optimization

Noninvasive biomarker sensing plays a vital role in health monitoring and sports physiology, particularly for tracking sweat lactate in real time to gauge exercise intensity without disrupting activity. This work introduces a high-specificity microwave biosensor for lactate detection, addressing the challenge of specificity seen in current microwave biosensors, which limits their practical applications. Our approach leverages a cost-effective complementary split-ring resonator (CSRR) combined with lactate oxidase (LOx) immobilized on spherical glass beads that act as mini-reactors within a microfluidic reservoir, enabling highly specific lactate sensing. The sensor was tested in phosphate buffer saline (PBS) and artificial sweat, achieving a high linear sensitivity of 10.9 and 11.3 MHz/mM, respectively, across lactate concentrations up to 150 mM and limit-of-detection (LOD) of 8.76 mM, with validation using the gold-standard HPLC method. It demonstrated excellent specificity against common interferences, including glucose, uric acid, and several ions. Testing with a diverse group of adult volunteers confirmed the sensor's capability to detect dynamic lactate changes during exercise and reliably identify the lactate threshold (LT), underscoring its promise for applications in sports physiology. This innovative method not only offers a powerful tool for lactate monitoring but also paves the way for enzyme-specific microwave biosensors adaptable to detect a range of biomarkers by simply exchanging the target enzyme.

Revolutionizing biosensing with wearable microneedle patches: innovations and applications

Wearable microneedle (MN) patches have emerged as a transformative platform for biosensing, offering a minimally invasive and user-friendly approach to real-time health monitoring and disease diagnosis. Primarily designed to access interstitial fluid (ISF) through shallow skin penetration, MNs enable precise and continuous sampling of biomarkers such as glucose, lactate, and electrolytes. Additionally, recent innovations have integrated MN arrays with microfluidic and porous structures to support sweat-based analysis, where MNs act as structural or functional components in hybrid wearable systems. This review explores the design, fabrication, and functional integration of MNs into wearable devices, highlighting advances in multi-analyte detection, wireless data transmission, and self-powered sensing. Challenges related to material biocompatibility, sensor stability, scalability, and user variability are addressed, alongside emerging opportunities in microfluidics, artificial intelligence, and soft materials. Overall, MN-based biosensing platforms are poised to redefine personalized healthcare by enabling dynamic, decentralized, and accessible health monitoring.

From population-based to personalized laboratory medicine: continuous monitoring of individual laboratory data with wearable biosensors

Monitoring individuals' laboratory data is essential for assessing their health status, evaluating the effectiveness of treatments, predicting disease prognosis and detecting subclinical conditions. Currently, monitoring is performed intermittently, measuring serum, plasma, whole blood, urine and occasionally other body fluids at predefined time intervals. The ideal monitoring approach entails continuous measurement of concentration and activity of biomolecules in all body fluids, including solid tissues. This can be achieved through the use of biosensors strategically placed at various locations on the human body where measurements are required for monitoring. High-tech wearable biosensors provide an ideal, noninvasive, and esthetically pleasing solution for monitoring individuals' laboratory data. However, despite significant advances in wearable biosensor technology, the measurement capacities and the number of different analytes that are continuously monitored in patients are not yet at the desired level. In this review, we conducted a literature search and examined: (i) an overview of the background of monitoring for personalized laboratory medicine, (ii) the body fluids and analytes used for monitoring individuals, (iii) the different types of biosensors and methods used for measuring the concentration and activity of biomolecules, and (iv) the statistical algorithms used for personalized data analysis and interpretation in monitoring and evaluation.

Advancements in flexible porous Nanoarchitectonic materials for biosensing applications

The development of nanoporous materials has gained significant attention due to their unique structural properties and multimodalities, which are highly relevant for advanced sensing technologies. The capability to directly grow nanoporous materials on flexible substrates or indirectly integrate them into soft templates through mixing and dispersion opens exciting opportunities for a new class of flexible and stretchable electronics for personalized healthcare applications. This review paper provides a snapshot of recent advancements in flexible nanoporous materials and their applications, emphasizing biological and biomedical sensors. The review highlights the material of choice for flexible and stretchable substrates and effective approaches to synthesize and integrate nanoporous architectures onto soft polymers. Applications from wearable sweat sensors, mechanical sensors for electronic skins, implantable bioelectronics, and gas sensing are also presented. The paper concludes with current challenges and future perspectives within this highly active research paradigm.

Universal Flexible Wearable Biosensors for Noninvasive Health Monitoring

Sweat, with its abundant biomarkers, is a highly appealing biofluid for personalized health monitoring and management. Noninvasive wearable sweat sensors hold great potential in this regard. However, developing an easy-to-prepare, highly sensitive, precise, and versatile wearable biosensor remains challenging. Herein, we report a universal electrochemical wearable biosensor for the accurate and sensitive detection of glucose, uric acid, and lactate in human sweat samples. A Pt nanoparticle-deposited nitrogen-doped mesoporous carbon/reduced graphene oxide composite (PNGO) was synthesized rapidly by using a simple multistage self-assembly strategy. The detection was carried out using electrodes modified with PNGO and enzyme-immobilized membranes, achieving high sensitivities (glucose: 15.33 μA mM-1 cm-2, uric acid: 103.2 μA mM-1 cm-2, lactate: 219.1 μA mM-1 cm-2), along with excellent selectivity, reproducibility, and stability. Based on the excellent performance of the biosensor, we investigated its reliability in detecting sweat targets during physical exercise and assessed its utility for monitoring human health status through glucose and purine dietary challenges, observing trends consistent with blood results. The integrated wearable flexible patch constructed in this work can provide periodic information related to sweat chemistry, and the low-cost electrode suggests the potential for large-scale manufacturing. Thus, it shows extraordinary promise for promotion and application in human health and training management.

Stretchable, Rechargeable, Multimodal Hybrid Electronics for Decoupled Sensing toward Emotion Detection

Despite the rapid development of stretchable electronic devices for various applications in biomedicine and healthcare, the coupling between multiple input signals remains an obstacle in multimodal sensing before use in practical environments. This work introduces a fully integrated stretchable, rechargeable, multimodal hybrid device that combines decoupled sensors with a flexible wireless powering and transmitting module for emotion recognition. Through optimized structural design and material selection, the sensors can provide continuous real-time decoupled monitoring of biaxial strain, temperature, humidity, heart rate, and SpO2 levels. With a stacked bilayer for both the sensors and the flexible circuit, the rechargeable system showcases a reduced device footprint and improved comfort. A neural network model is also demonstrated to allow for high-precision facial expression recognition. By transmitting the real-time measured data to mobile devices and the cloud, the system can allow healthcare professionals to evaluate psychological health and provide emotional support through telemedicine when needed.

Liquid Bridge Cutting Valves for Microfluidic Passive Distribution and Sequential Reaction

In bioanalysis, precisely isolating liquid reactions in distinct systems or at different temporal sequences is vital for ensuring accurate results devoid of crosstalk. However, passive liquid isolation is unattainable through existing microfluidic valves. Here, liquid bridge cutting valves (LBCVs) are introduced to automatically segregate liquids by establishing airlocks, offering an innovative microfluidic structure for liquid distribution. The principle of liquid bridge breakup is studied and applied to the design of LBCVs. Additionally, monolithic chips connecting units with LBCVs in different topologies facilitate sequential sampling and reactions, achieving the detection of sweat glucose and lactate in wearable applications, as well as cortisol ELISA on the chips. As a missing puzzle piece of microfluidic elements in liquid separation, LBCVs can be seamlessly integrated with maturing microfluidic structures, creating a lab-on-a-chip device to enable complex fluid manipulation for individual healthcare monitoring and clinical scenarios.

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.

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.

Autonomous, Moisture-Driven Flexible Electrogenerative Dressing for Enhanced Wound Healing

Electrotherapy has shown considerable potential in treating chronic wounds, but conventional approaches relying on bulky external power supplies and mechanical force are limited in their clinical utility. This study introduces an autonomous, moisture-driven flexible electrogenerative dressing (AMFED) that overcomes these limitations. The AMFED integrates a moist-electric generator (MEG), an antibacterial hydrogel dressing, and concentric molybdenum (Mo) electrodes to provide a self-sustaining electrical supply and potent antibacterial activity against Staphylococcus aureus and Escherichia coli. The MEG harnesses chemical energy from moisture to produce a stable direct current of 0.61 V without external input, delivering this therapeutic electrical stimulation to the wound site through the Mo electrodes. The AMFED facilitates macrophage polarization toward reparative M2 phenotype and regulates inflammatory cytokines. Moreover, in vivo studies suggest that the AMFED group significantly enhances chronic wound healing, with an approximate 41% acceleration compared to the control group. Using a diabetic mouse wound model, the AMFED demonstrates its effectiveness in promoting nerve regulation, epithelial migration, and vasculogenesis. These findings present a novel and efficient platform for accelerating chronic wound healing.

A sensor-actuator-coupled gustatory interface chemically connecting virtual and real environments for remote tasting

Recent advancements in virtual reality (VR) and augmented reality (AR) have strengthened the bridge between virtual and real worlds via human-machine interfaces. Despite extensive research into biophysical signals, gustation, a fundamental component of the five senses, has experienced limited progress. This work reports a bio-integrated gustatory interface, "e-Taste," to address the underrepresented chemical dimension in current VR/AR technologies. This system facilitates remote perception and replication of taste sensations through the coupling of physically separated sensors and actuators with wireless communication modules. By using chemicals representing five basic tastes, systematic codesign of key functional components yields reliable performance including tunability, versatility, safety, and mechanical robustness. Field testing involving human subjects focusing on user perception confirms its proficiency in digitally simulating a range of taste intensities and combinations. Overall, this investigation pioneers a chemical dimension in AR/VR technology, paving the way for users to transcend visual and auditory virtual engagements by integrating the taste sensation into virtual environment for enhanced digital experiences.

Nanozyme-based wearable biosensors for application in healthcare

Recent years have witnessed tremendous advances in wearable sensors, which play an essential role in personalized healthcare for their ability for real-time sensing and detection of human health information. Nanozymes, capable of mimicking the functions of natural enzymes and addressing their limitations, possess unique advantages such as structural stability, low cost, and ease of mass production, making them particularly beneficial for constructing recognition units in wearable biosensors. In this review, we aim to delineate the latest advancements in nanozymes for the development of wearable biosensors, focusing on key developments in nanozyme immobilization strategies, detection technologies, and biomedical applications. The review also highlights the current challenges and future perspectives. Ultimately, it aims to provide insights for future research endeavors in this rapidly evolving area.

A wearable platform for biochemical sweat analysis using photonic crystal hydrogel

Wearable systems for health monitoring are highly desired in personal diagnostics and precision medicine while challenges remain in constructing such wearable systems with reliability and high performance. Herein, we report a wearable platform for non-invasive monitoring biomarkers in sweat. The device is composed of a butterfly-shaped like microfluidic platform in which responsive photonic crystal hydrogels are embedded in each butterfly wing as sensors. Sweat lactate concentration and pH can be obtained via the color variation of the sensor with naked eyes. Accurate quantitative analysis of the two target analytes can be obtained via the image analysis on a mobile phone by integrating the linear range response to analytes within the physiological range. Moreover, the sensor exhibits good reproducibility, excellent selectivity and long-term stability. On-body trials have been conducted by attaching the device on volunteers' body, and the obtained results are consistent with those analyzed through standardized methods, demonstrating its potentiality in real-time and continuous monitoring sweat biomarkers. This non-invasive wearable sensor provides a new strategy for personal health monitoring and sports performance assessment.

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.

Photonic Nanomaterials for Wearable Health Solutions

This review underscores the transformative potential of photonic nanomaterials in wearable health technologies, driven by increasing demands for personalized health monitoring. Their unique optical and physical properties enable rapid, precise, and sensitive real-time monitoring, outperforming conventional electrical-based sensors. Integrated into ultra-thin, flexible, and stretchable formats, these materials enhance compatibility with the human body, enabling prolonged wear, improved efficiency, and reduced power consumption. A comprehensive exploration is provided of the integration of photonic nanomaterials into wearable devices, addressing material selection, light-matter interaction principles, and device assembly strategies. The review highlights critical elements such as device form factors, sensing modalities, and power and data communication, with representative examples in skin patches and contact lenses. These devices enable precise monitoring and management of biomarkers of diseases or biological responses. Furthermore, advancements in materials and integration approaches have paved the way for continuum of care systems combining multifunctional sensors with therapeutic drug delivery mechanisms. To overcome existing barriers, this review outlines strategies of material design, device engineering, system integration, and machine learning to inspire innovation and accelerate the adoption of photonic nanomaterials for next-generation of wearable health, showcasing their versatility and transformative potential for digital health applications.

Wearable microfluidic biosensors with haptic feedback for continuous monitoring of hydration biomarkers in workers

Real-time monitoring of hydration biomarkers in tandem with biophysical markers can offer valuable physiological insights about heat stress and related thermoregulatory response. These metrics have been challenging to achieve with wearable sensors. Here we present a closed-loop electrochemical/biophysical wearable sensing device and algorithms that directly measure whole-body sweat loss, sweating rate, sodium concentration, and sodium loss with electrode arrays embedded in a microfluidic channel. The device contains two temperature sensors for skin temperature and thermal flux recordings, and an accelerometer for real-time monitoring of activity level. An onboard haptic module enables vibratory feedback cues to the wearer once critical sweat loss thresholds are reached. Data is stored onboard in memory and autonomously transmitted via Bluetooth to a smartphone and cloud portal. Field studies conducted in physically demanding activities demonstrate the key capabilities of this platform to inform hydration interventions in highly challenging real-world settings.

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.

Reusable gallium-based electrochemical sensor for efficient glucose detection

Among wearable sensing devices, electrochemical sensors are overwhelming in biochemical detection due to their simple design but high sensitivity. Most electrochemical sensors are disposable, which significantly impairs the service life. Here we present a reusable gallium (Ga)-based multilayer electrochemical glucose biosensor to extend noninvasive monitoring of glucose in the interstitial fluid. This multilayer sensor includes Ga as a conductive interconnector, poly(3,4-ethylenedioxythiophene) as an electrode layer to prevent oxidation and metal leakage, a nano-Pt layer to enhance the electrochemical properties, and a nano-Prussian blue layer for reducing the hydrogen peroxide reduction potential. The biosensor can be renewed without causing damage to its overall structure by automatically eliminating the modified nanocomposites via the electrolysis-induced bubbles. The biosensor showed high sensitivity (24.6 μA mM-1 cm-2), wide linear range (0.01-26 mM), excellent stability (i.e., pH, long-term use) and superior selectivity, that is comparable to those of the current electrochemical tools for glucose detection. More importantly, incorporated with the reverse iontophoresis, the Ga-based hybrid sensor was applied as a skin patch on rat for the in vivo noninvasive and continuous monitoring of interstitial fluid glucose. The results showed a good correlation with that measured by blood glucometer. As a whole, this Ga-based electrochemical biosensor should endow new functions like biochemical analysis in biofluids for Ga-based bioelectronic sensing devices, in which almost are physical sensors. We believe that the reusability of electrochemically controllable processes may further inspire the development of more integrated and long-term stable Ga-based biosensing devices.

Designable Electrochemiluminescence Patterning for Renewable and Enhanced Bioimaging

Electrochemical imaging enables an in-depth analysis of the interface heterogeneity and reaction kinetics of single entities. However, electrode passivation during electrochemical reactions decreases the active sites and harms the long-term stability. Here, we introduce a method using laser-induced photothermal effects to restore the electrochemical activity, which is particularly displayed as enhanced micrometric patterns in electrochemiluminescence (ECL) microscopy. By co-localization characterization and X-ray photoelectron spectroscopy (XPS), the mechanism of active site regeneration is validated as the removal of the oxide film for restoring the local surface ECL reactivity under laser irradiation. The surface-confined and voltage-dependent features of ECL allows for easy pattern erasure and rewriting, and it shows good reversibility and anti-counterfeiting potential. This approach overcomes the passivation processes, evidently improves the image quality of single biological entities including Shewanella bacteria and cells, and makes the subtle contour structures more distinct. The renewable electrode interface also enhances the ECL signal of model bead-based bioassays. This approach not only showcases precise control in fabricating micron patterns but also holds promise for enhancing the sensitivity in electrochemical immunoassays and bioimaging.

Recent advances in bio-integrated electrochemical sensors for neuroengineering

Detecting and diagnosing neurological diseases in modern healthcare presents substantial challenges that directly impact patient outcomes. The complex nature of these conditions demands precise and quantitative monitoring of disease-associated biomarkers in a continuous, real-time manner. Current chemical sensing strategies exhibit restricted clinical effectiveness due to labor-intensive laboratory analysis prerequisites, dependence on clinician expertise, and prolonged and recurrent interventions. Bio-integrated electronics for chemical sensing is an emerging, multidisciplinary field enabled by rapid advances in electrical engineering, biosensing, materials science, analytical chemistry, and biomedical engineering. This review presents an overview of recent progress in bio-integrated electrochemical sensors, with an emphasis on their relevance to neuroengineering and neuromodulation. It traverses vital neurological biomarkers and explores bio-recognition elements, sensing strategies, transducer designs, and wireless signal transmission methods. The integration of in vivo biochemical sensors is showcased through applications. The review concludes by outlining future trends and advancements in in vivo electrochemical sensing, and highlighting ongoing research and technological innovation, which aims to provide inspiring and practical instructions for future research.

Wearable Electrochemical Biosensors for Advanced Healthcare Monitoring

Recent advancements in wearable electrochemical biosensors have opened new avenues for on-body and continuous detection of biomarkers, enabling personalized, real-time, and preventive healthcare. While glucose monitoring has set a precedent for wearable biosensors, the field is rapidly expanding to include a wider range of analytes crucial for disease diagnosis, treatment, and management. In this review, recent key innovations are examined in the design and manufacturing underpinning these biosensing platforms including biorecognition elements, signal transduction methods, electrode and substrate materials, and fabrication techniques. The applications of these biosensors are then highlighted in detecting a variety of biochemical markers, such as small molecules, hormones, drugs, and macromolecules, in biofluids including interstitial fluid, sweat, wound exudate, saliva, and tears. Additionally, the review also covers recent advances in wearable electrochemical biosensing platforms, such as multi-sensory integration, closed-loop control, and power supply. Furthermore, the challenges associated with critical issues are discussed, such as biocompatibility, biofouling, and sensor degradation, and the opportunities in materials science, nanotechnology, and artificial intelligence to overcome these limitations.

A surface modified laser-induced graphene based flexible biosensor for multiplexed sweat analysis

The growing popularity of electrochemical sensors featuring non-invasive biosensing technologies has generated significant enthusiasm for continuous monitoring of bodily fluid biomarkers, potentially aiding in the early detection of health issues in individuals. However, detection of multiple biomarkers in complex biofluids often necessitates a high-density array which creates a challenge in achieving cost-effective fabrication methods. To overcome this constraint, this work reports the fabrication of an electrochemical sensor utilizing a NiO-Ti3C2Tx MXene-modified flexible laser-induced graphene (LIG) electrode for the separate and concurrent analysis of ascorbic acid (AA), dopamine (DA), and uric acid (UA) in human sweat and also addresses the deficiencies in the existing state of the art by offering a cost-efficient and high-performance sensor that mitigates the degrading constraints of conventional LIG electrodes. Cyclic voltammetry and differential pulse voltammetry measurements reveals that the electrochemical properties of the modified electrode, attain a low detection limit and great sensitivity for the target biomarkers. The NiO-Ti3C2Tx/LIG sensor demonstrated enhanced electrocatalytic activity for the oxidation of ascorbic acid, dopamine, and uric acid, and proved useful for analysing these biomarkers in synthetic sweat samples. Under the optimized conditions, the LOD values were estimated to be 16, 1.97 and 0.78 μM for AA, DA and UA, respectively. The developed high-efficiency sensor holds significant promise for applications in flexible and wearable electronics for health monitoring.

Pumpless microfluidic sweat sensing yarn

Textile sweat sensors possess immense potential for non-invasive health monitoring. Rapid in-situ sweat capture and prevention of its evaporation are crucial for accurate and stable real-time monitoring. Herein, we introduce a unidirectional, pump-free microfluidic sweat management system to tackle this challenge. A nanofiber sheath layer on micrometer-scale sensing filaments enables this pumpless microfluidic design. Utilizing the capillary effect of the nanofibers allows for the swift capture of sweat, while the differential configuration of the hydrophilic and hydrophobic properties of the sheath and core yarns prevents sweat evaporation. The Laplace pressure difference between the cross-scale fibers facilitates the management system to ultimately expulse sweat. This results in microfluidic control of sweat without the need for external forces, resulting in rapid (<5 s), sensitive (19.8 nA μM-1), and stable (with signal noise and drift suppression) sweat detection. This yarn sensor can be easily integrated into various fabrics, enabling the creation of health monitoring smart garments. The garments maintain good monitoring performance even after 20 washes. This work provides a solution for designing smart yarns for high-precision, stable, and non-invasive health monitoring.

Reagent-Free Lactate Detection Using Prussian Blue and Electropolymerized-Molecularly Imprinted Polymers-Based Electrochemical Biosensors

Sweat lactate, a promising biomarker for assessing physical performance and health conditions, calls for noninvasive, convenient, and affordable detection methods. This study leverages molecularly imprinted polymers (MIPs) as a synthetic biorecognition element for lactate detection due to their affordability and high stability. Traditional MIPs-based electrochemical sensors often require external redox probes such as ferricyanide/ferrocyanide in the solution to signal the binding between analytes and MIPs, which restricts their applicability. To address this, our study introduces an innovative approach utilizing a layer of Prussian blue (PB) nanoparticles as the internal redox probe on screen-printed carbon electrodes (SPCE), followed by a layer of electropolymerized MIP (eMIP) for molecular recognition, enabling reagent-free lactate detection. The real-time growth of eMIP and the processes of template elution and lactate rebinding were examined and validated using electrochemical surface plasmon resonance (EC-SPR) spectroscopy. The sensor's performance was thoroughly investigated using Differential Pulsed Voltammetry (DPV) and Electrochemical Impedance Spectroscopy (EIS) with samples spiked in 0.1 M KCl solution and artificial sweat. The developed sensors demonstrated a fast and selective response to lactate, detecting concentrations from 1 to 35 mM with a Limit of Detection (LOD) of 0.20 mM, defined by a signal-to-noise ratio of 3 in the DPV measurements. They also exhibited excellent reproducibility, reusability, and a shelf life of up to 10 months under ambient conditions. These eMIP/PB/SPCE-based lactate sensors show considerable potential as point-of-care (POC) devices for sweat lactate detection, and the technology could be adapted for reagent-free detection of a broad spectrum of molecules.

Synergistic Strategies of Biomolecular Transport Technologies in Transdermal Healthcare Systems

Transdermal healthcare systems have gained significant attention for their painless and convenient drug administration, as well as their ability to detect biomarkers promptly. However, the skin barrier limits the candidates of biomolecules that can be transported, and reliance on simple diffusion poses a bottleneck for personalized diagnosis and treatment. Consequently, recent advancements in transdermal transport technologies have evolved toward active methods based on external energy sources. Multiple combinations of these technologies have also shown promise for increasing therapeutic effectiveness and diagnostic accuracy as delivery efficiency is maximized. Furthermore, wearable healthcare platforms are being developed in diverse aspects for patient convenience, safety, and on-demand treatment. Herein, a comprehensive overview of active transdermal delivery technologies is provided, highlighting the combination-based diagnostics, therapeutics, and theragnostics, along with the latest trends in platform advancements. This offers insights into the potential applications of next-generation wearable transdermal medical devices for personalized autonomous healthcare.

Applied body-fluid analysis by wearable devices

Wearable sensors are a recent paradigm in healthcare, enabling continuous, decentralized, and non- or minimally invasive monitoring of health and disease. Continuous measurements yield information-rich time series of physiological data that are holistic and clinically meaningful. Although most wearable sensors were initially restricted to biophysical measurements, the next generation of wearable devices is now emerging that enable biochemical monitoring of both small and large molecules in a variety of body fluids, such as sweat, breath, saliva, tears and interstitial fluid. Rapidly evolving data analysis and decision-making technologies through artificial intelligence has accelerated the application of wearables around the world. Although recent pilot trials have demonstrated the clinical applicability of these wearable devices, their widespread adoption will require large-scale validation across various conditions, ethical consideration and sociocultural acceptance. Successful translation of wearable devices from laboratory prototypes into clinical tools will further require a comprehensive transitional environment involving all stakeholders. The wearable device platforms must gain acceptance among different user groups, add clinical value for various medical indications, be eligible for reimbursements and contribute to public health initiatives. In this Perspective, we review state-of-the-art wearable devices for body-fluid analysis and their translation into clinical applications, and provide insight into their clinical purpose.

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.

Role of wearable electrochemical biosensors in monitoring renal function biomarkers in sweat: a review

Real-time detection of renal biomarkers is crucial for immediate and continuous monitoring of kidney function, facilitating early diagnosis and intervention in kidney-related disorders. This proactive approach enables timely adjustments in treatment plans, particularly in critical situations, and enhances overall patient care. Wearable devices emerge as a promising solution, enabling non-invasive and real-time data collection. This comprehensive review investigates numerous types of wearable sensors designed to detect kidney biomarkers in body fluids such as sweat. It critically evaluates the precision, dependability, and user-friendliness of these devices, contemplating their seamless integration into daily life for continuous health tracking. The review highlights the potential influence of wearable technology on individualized renal healthcare and its role in preventative medicine while also addressing challenges and future directions. The review's goal is to provide guidance to academics, healthcare professionals, and technologists working on wearable solutions for renal biomarker detection by compiling the body of current knowledge and advancements.

Integrating machine learning and biosensors in microfluidic devices: A review

Microfluidic devices are increasingly widespread in the literature, being applied to numerous exciting applications, from chemical research to Point-of-Care devices, passing through drug development and clinical scenarios. Setting up these microenvironments, however, introduces the necessity of locally controlling the variables involved in the phenomena under investigation. For this reason, the literature has deeply explored the possibility of introducing sensing elements to investigate the physical quantities and the biochemical concentration inside microfluidic devices. Biosensors, particularly, are well known for their high accuracy, selectivity, and responsiveness. However, their signals could be challenging to interpret and must be carefully analysed to carry out the correct information. In addition, proper data analysis has been demonstrated even to increase biosensors' mentioned qualities. To this regard, machine learning algorithms are undoubtedly among the most suitable approaches to undertake this job, automatically learning from data and highlighting biosensor signals' characteristics at best. Interestingly, it was also demonstrated to benefit microfluidic devices themselves, in a new paradigm that the literature is starting to name "intelligent microfluidics", ideally closing this benefic interaction among these disciplines. This review aims to demonstrate the advantages of the triad paradigm microfluidics-biosensors-machine learning, which is still little used but has a great perspective. After briefly describing the single entities, the different sections will demonstrate the benefits of the dual interactions, highlighting the applications where the reviewed triad paradigm was employed.

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.

A wireless, battery-free device for electrical neuromodulation of bladder contractions

Lower urinary tract dysfunction (LUTD) is a prevalent condition characterized by symptoms such as urinary frequency, urgency, incontinence, and difficulty in urination, which can significantly impair patient's quality of life and lead to severe physiological complications. Despite the availability of diverse treatment options, including pharmaceutical and behavioral therapies, these approaches are not without challenges. The objective of this study was to enhance treatment options for LUTD by developing a wireless, battery-free device for managing bladder contractions. We designed and validated a compact, fully implantable, battery-free pulse generator using the magnetic induction coupling mechanism of wireless power transmission. Weighing less than 0.2 g and with a volume of less than 0.1 cubic centimeters, this device enables precise stimulation of muscles or neurons at voltages ranging from 0 to 10 V. Wireless technology allows real-time adjustment of key stimulation parameters such as voltage, duration, frequency, pulse width, and pulse interval. Our findings demonstrate that the device effectively controlled bladder contractions in mice when used to stimulate the Major Pelvic Ganglion (MPG). Additionally, the device successfully managed micturition in mice with bilateral transection of the pudendal nerve. In conclusion, the development of this innovative wireless pulse generator provides a safer and more cost-effective alternative to conventional battery-powered neurostimulators for bladder control, addressing the limitations of such devices. We anticipate that this novel technology will play a pivotal role in the future of electrical stimulation therapies for voiding dysfunctions.

Multifunctional nanomaterials for smart wearable diabetic healthcare devices

Wearable diabetic healthcare devices have attracted great attention for real-time continuous glucose monitoring (CGM) using biofluids such as tears, sweat, saliva, and interstitial fluid via noninvasive ways. In response to the escalating global demand for CGM, these devices enable proactive management and intervention of diabetic patients with incorporated drug delivery systems (DDSs). In this context, multifunctional nanomaterials can trigger the development of innovative sensing and management platforms to facilitate real-time selective glucose monitoring with remarkable sensitivity, on-demand drug delivery, and wireless power and data transmission. The seamless integration into wearable devices ensures patient's compliance. This comprehensive review evaluates the multifaceted roles of these materials in wearable diabetic healthcare devices, comparing their glucose sensing capabilities with conventionally available glucometers and CGM devices, and finally outlines the merits, limitations, and prospects of these devices. This review would serve as a valuable resource, elucidating the intricate functions of nanomaterials for the successful development of advanced wearable devices in diabetes management.

Microfluidic electrochemical biosensors: tools for advancing the sustainable development goals

New technologies can help to achieve the sustainable development goals (SDGs) of the United Nations. We discuss the contribution of microfluidic electrochemical biosensors to advancing the SDGs. These sensors can be applied in various fields given their low cost, self-powering ability, environmental compatibility, ease of use, and small sample volume requirements.

A comprehensive review on electromagnetic wave based non-invasive glucose monitoring in microwave frequencies

Diabetes is a chronic disease that affects millions of humans worldwide. This review article provides an analysis of the recent advancements in non-invasive blood glucose monitoring, detailing methods and techniques, with a special focus on Electromagnetic wave microwave glucose sensors. While optical, thermal, and electromagnetic techniques have been discussed, the primary emphasis is focussed on microwave frequency sensors due to their distinct advantages. Microwave sensors exhibit rapid response times, require minimal user intervention, and hold potential for continuous monitoring, renders them extremely potential for real-world applications. Additionally, their reduced susceptibility to physiological interferences further enhances their appeal. This review critically assesses the performance of microwave glucose sensors by considering factors such as accuracy, sensitivity, specificity, and user comfort. Moreover, it sheds light on the challenges and upcoming directions in the growth of microwave sensors, including the need for reduction and integration with wearable platforms. By concentrating on microwave sensors within the broader context of non-invasive glucose monitoring, this article aims to offer significant enlightenment that may drive further innovation in diabetes care.

Hybrid Integration of Wearable Devices for Physiological Monitoring

Wearable devices can provide timely, user-friendly, non- or minimally invasive, and continuous monitoring of human health. Recently, multidisciplinary scientific communities have made significant progress regarding fully integrated wearable devices such as sweat wearable sensors, saliva sensors, and wound sensors. However, the translation of these wearables into markets has been slow due to several reasons associated with the poor system-level performance of integrated wearables. The wearability consideration for wearable devices compromises many properties of the wearables. Besides, the limited power capacity of wearables hinders continuous monitoring for extended duration. Furthermore, peak-power operations for intensive computations can quickly create thermal issues in the compact form factor that interfere with wearability and sensor operations. Moreover, wearable devices are constantly subjected to environmental, mechanical, chemical, and electrical interferences and variables that can invalidate the collected data. This generates the need for sophisticated data analytics to contextually identify, include, and exclude data points per multisensor fusion to enable accurate data interpretation. This review synthesizes the challenges surrounding the wearable device integration from three aspects in terms of hardware, energy, and data, focuses on a discussion about hybrid integration of wearable devices, and seeks to provide comprehensive guidance for designing fully functional and stable wearable devices.

Bio-inspired hierarchical wearable patch for fast sweat collection

Sweat contains abundant physiological and metabolic data to evaluate an individual's physical health. Since the non-exercise sweat secretion rate is low, with an average value of 1-10 μl h-1 cm-2, sweat is generally collected during exercise for existing wearable sweat sensors. To expand their applications to include daily scenarios, these sensors developed for sports and fitness are challenged by the difficulty of collecting trace amounts of sweat. This study proposes a wearable patch inspired by the hierarchical structure of Sarracenia trichomes, allowing for the spontaneous and fast collection of a small amount of secreted sweat. The patch contains microfluidic channels featuring a 20 μm-wide rib structure, fully utilizing the capillary force, thereby eliminating the issue of sweat hysteresis. Furthermore, with only 0.5 μl of the sweat secreted at the collection site, it can converge on the detection medium located within the center reservoir. Volunteer verification demonstrated a twofold increase in sweat collection efficiency compared to traditional wearable patches. This patch serves as an efficient sweat-collection configuration, promising potential for diverse in situ sweat colorimetric analyses.

Toward an AI Era: Advances in Electronic Skins

Electronic skins (e-skins) have seen intense research and rapid development in the past two decades. To mimic the capabilities of human skin, a multitude of flexible/stretchable sensors that detect physiological and environmental signals have been designed and integrated into functional systems. Recently, researchers have increasingly deployed machine learning and other artificial intelligence (AI) technologies to mimic the human neural system for the processing and analysis of sensory data collected by e-skins. Integrating AI has the potential to enable advanced applications in robotics, healthcare, and human-machine interfaces but also presents challenges such as data diversity and AI model robustness. In this review, we first summarize the functions and features of e-skins, followed by feature extraction of sensory data and different AI models. Next, we discuss the utilization of AI in the design of e-skin sensors and address the key topic of AI implementation in data processing and analysis of e-skins to accomplish a range of different tasks. Subsequently, we explore hardware-layer in-skin intelligence before concluding with an analysis of the challenges and opportunities in the various aspects of AI-enabled e-skins.

Recent advancements in non-invasive wearable electrochemical biosensors for biomarker analysis - A review

A biomarker is a molecular indicator that can be used to identify the presence or severity of a disease. It may be produced due to biochemical or molecular changes in normal biological processes. In some cases, the presence of a biomarker itself is an indication of the disease, while in other cases, the elevated or depleted level of a particular protein or chemical substance aids in identifying a disease. Biomarkers indicate the progression of the disease in response to therapeutic interventions. Identifying these biomarkers can assist in diagnosing the disease early and providing proper therapeutic treatment. In recent years, wearable electrochemical (EC) biosensors have emerged as an important tool for early detection due to their excellent selectivity, low cost, ease of fabrication, and improved sensitivity. There are several challenges in developing a fully integrated wearable sensor, such as device miniaturization, high power consumption, incorporation of a power source, and maintaining the integrity and durability of the biomarker for long-term continuous monitoring. This review covers the recent advancements in the fabrication techniques involved in device development, the types of sensing platforms utilized, different materials used, challenges, and future developments in the field of wearable biosensors.

Multifunctional laser-induced graphene circuits and laser-printed nanomaterials toward non-invasive human kidney function monitoring

Faced with the increasing prevalence of chronic kidney disease (CKD), portable monitoring of CKD-related biomarkers such as potassium ion (K+), creatinine (Cre), and lactic acid (Lac) levels in sweat has shown tremendous potential for early diagnosis. However, a rapidly manufacturable portable device integrating multiple CKD-related biomarker sensors for ease of sweat testing use has yet to be reported. Here, a portable electrochemical sensor integrated with multifunctional laser-induced graphene (LIG) circuits and laser-printed nanomaterials based working electrodes fabricated by fully automatic laser manufacturing is proposed for non-invasive human kidney function monitoring. The sensor comprises a two-electrode LIG circuit for K+ sensing, a three-electrode LIG circuit with a Kelvin compensating connection for Cre and Lac sensing, and a printed circuit board based portable electrochemical workstation. The working electrodes containing Cu and Cu2O nanoparticles fabricated by two-step laser printing show good sensitivity and selectivity toward Cre and Lac sensing. The sensor circuits are fabricated by generating a hydrophilic-hydrophobic interface on a patterned LIG through laser. This sensor recruited rapid laser manufacturing and integrated with multifunctional LIG circuits and laser-printed nanomaterials based working electrodes, which is a potential kidney function monitoring solution for healthy people and kidney disease patients.

Flexible self-powered bioelectronics enables personalized health management from diagnosis to therapy

Flexible self-powered bioelectronics (FSPBs), incorporating flexible electronic features in biomedical applications, have revolutionized the human-machine interface since they hold the potential to offer natural and seamless human interactions while overcoming the limitations of battery-dependent power sources. Furthermore, as biosensors or actuators, FSPBs can dynamically monitor physiological signals to reveal real-time health abnormalities and provide timely and precise treatments. Therefore, FSPBs are increasingly shaping the landscape of health monitoring and disease treatment, weaving a sophisticated and personalized bond between humans and health management. Here, we examine the recent advanced progress of FSPBs in developing working mechanisms, design strategies, and structural configurations toward personalized health management, emphasizing its role in clinical medical scenarios from biophysical/biochemical sensors for sensing diagnosis to robust/biodegradable actuators for intervention therapy. Future perspectives on the challenges and opportunities in emerging multifunctional FSPBs for the next-generation health management systems are also forecasted.

Carbon Micro/Nano Machining toward Miniaturized Device: Structural Engineering, Large-Scale Fabrication, and Performance Optimization

With the rapid development of micro/nano machining, there is an elevated demand for high-performance microdevices with high reliability and low cost. Due to their outstanding electrochemical, optical, electrical, and mechanical performance, carbon materials are extensively utilized in constructing microdevices for energy storage, sensing, and optoelectronics. Carbon micro/nano machining is fundamental in carbon-based intelligent microelectronics, multifunctional integrated microsystems, high-reliability portable/wearable consumer electronics, and portable medical diagnostic systems. Despite numerous reviews on carbon materials, a comprehensive overview is lacking that systematically encapsulates the development of high-performance microdevices based on carbon micro/nano structures, from structural design to manufacturing strategies and specific applications. This review focuses on the latest progress in carbon micro/nano machining toward miniaturized device, including structural engineering, large-scale fabrication, and performance optimization. Especially, the review targets an in-depth evaluation of carbon-based micro energy storage devices, microsensors, microactuators, miniaturized photoresponsive and electromagnetic interference shielding devices. Moreover, it highlights the challenges and opportunities in the large-scale manufacturing of carbon-based microdevices, aiming to spark further exciting research directions and application prospectives.

Wireless Technologies in Flexible and Wearable Sensing: From Materials Design, System Integration to Applications

Wireless and wearable sensors attract considerable interest in personalized healthcare by providing a unique approach for remote, noncontact, and continuous monitoring of various health-related signals without interference with daily life. Recent advances in wireless technologies and wearable sensors have promoted practical applications due to their significantly improved characteristics, such as reduction in size and thickness, enhancement in flexibility and stretchability, and improved conformability to the human body. Currently, most researches focus on active materials and structural designs for wearable sensors, with just a few exceptions reflecting on the technologies for wireless data transmission. This review provides a comprehensive overview of the state-of-the-art wireless technologies and related studies on empowering wearable sensors. The emerging functional nanomaterials utilized for designing unique wireless modules are highlighted, which include metals, carbons, and MXenes. Additionally, the review outlines the system-level integration of wireless modules with flexible sensors, spanning from novel design strategies for enhanced conformability to efficient transmitting data wirelessly. Furthermore, the review introduces representative applications for remote and noninvasive monitoring of physiological signals through on-skin and implantable wireless flexible sensing systems. Finally, the challenges, perspectives, and unprecedented opportunities for wireless and wearable sensors are discussed.

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.

The Future of Nanotechnology-Driven Electrochemical and Electrical Point-of-Care Devices and Diagnostic Tests

Point-of-care (POC) devices have become rising stars in the biosensing field, aiming at prognosis and diagnosis of diseases with a positive impact on the patient but also on healthcare and social care systems. Putting the patient at the center of interest requires the implementation of noninvasive technologies for collecting biofluids and the development of wearable platforms with integrated artificial intelligence-based tools for improved analytical accuracy and wireless readout technologies. Many electrical and electrochemical transducer technologies have been proposed for POC-based sensing, but several necessitate further development before being widely deployable. This review focuses on recent innovations in electrochemical and electrical biosensors and their growth opportunities for nanotechnology-driven multidisciplinary approaches. With a focus on analytical aspects to pave the way for future electrical/electrochemical diagnostics tests, current limitations and drawbacks as well as directions for future developments are highlighted.

3D-Printed Flexible Microfluidic Health Monitor for In Situ Sweat Analysis and Biomarker Detection

Wearable sweat biosensors have shown great progress in noninvasive, in situ, and continuous health monitoring to demonstrate individuals' physiological states. Advances in novel nanomaterials and fabrication methods promise to usher in a new era of wearable biosensors. Here, we introduce a three-dimensional (3D)-printed flexible wearable health monitor fabricated through a unique one-step continuous manufacturing process with self-supporting microfluidic channels and novel single-atom catalyst-based bioassays for measuring the sweat rate and concentration of three biomarkers. Direct ink writing is adapted to print the microfluidic device with self-supporting structures to harvest human sweat, which eliminates the need for removing sacrificial supporting materials and addresses the contamination and sweat evaporation issues associated with traditional sampling methods. Additionally, the pick-and-place strategy is employed during the printing process to accurately integrate the bioassays, improving manufacturing efficiency. A single-atom catalyst is developed and utilized in colorimetric bioassays to improve sensitivity and accuracy. A feasibility study on human skin successfully demonstrates the functionality and reliability of our health monitor, generating reliable and quantitative in situ results of sweat rate, glucose, lactate, and uric acid concentrations during physical exercise.

The challenges and promise of sweat sensing

The potential of monitoring biomarkers in sweat for health-related applications has spurred rapid growth in the field of wearable sweat sensors over the past decade. Some of the key challenges have been addressed, including measuring sweat-secretion rate and collecting sufficient sample volumes for real-time, continuous molecular analysis without intense exercise. However, except for assessment of cystic fibrosis and regional nerve function, the ability to accurately measure analytes of interest and their physiological relevance to health metrics remain to be determined. Although sweat is not a crystal ball into every aspect of human health, we expect sweat measurements to continue making inroads into niche applications involving active sweating, such as hydration monitoring for athletes and physical laborers and later for medical and casual health monitoring of relevant drugs and hormones.

Materials and Structural Designs toward Motion Artifact-Free Bioelectronics

Bioelectronics encompassing electronic components and circuits for accessing human information play a vital role in real-time and continuous monitoring of biophysiological signals of electrophysiology, mechanical physiology, and electrochemical physiology. However, mechanical noise, particularly motion artifacts, poses a significant challenge in accurately detecting and analyzing target signals. While software-based "postprocessing" methods and signal filtering techniques have been widely employed, challenges such as signal distortion, major requirement of accurate models for classification, power consumption, and data delay inevitably persist. This review presents an overview of noise reduction strategies in bioelectronics, focusing on reducing motion artifacts and improving the signal-to-noise ratio through hardware-based approaches such as "preprocessing". One of the main stress-avoiding strategies is reducing elastic mechanical energies applied to bioelectronics to prevent stress-induced motion artifacts. Various approaches including strain-compliance, strain-resistance, and stress-damping techniques using unique materials and structures have been explored. Future research should optimize materials and structure designs, establish stable processes and measurement methods, and develop techniques for selectively separating and processing overlapping noises. Ultimately, these advancements will contribute to the development of more reliable and effective bioelectronics for healthcare monitoring and diagnostics.

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.

Mechanical Robustness Enhanced Flexible Antennas Using Ti3C2 MXene and Nanocellulose Composites for Noninvasive Glucose Sensing

Electromagnetic sensors with flexible antennas as sensing elements have attracted increasing attention in noninvasive continuous glucose monitoring for diabetic patients. The significant radiation performance loss of flexible antennas during mechanical deformation impairs the reliability of glucose monitoring. Here, we present flexible ultrawideband monopole antennas composed of Ti3C2 MXene and cellulose nanofibril (CNF) composite films for continuous glucose monitoring. The flexible MXene/CNF antenna with 20% CNF content can obtain a gain of up to 3.33 dBi and a radiation efficiency of up to 65.40% at a frequency range from 2.3 to 6.0 GHz. Compared with the pure MXene antenna, this antenna offers a comparable radiation performance and a lower performance loss in mechanical bending deformation. Moreover, the MXene/CNF antenna shows a stable response to fetal bovine serum/glucose, with a correlation of >0.9 at the reference glucose levels, and responds sensitively to the variations in blood glucose levels during human trials. The proposed strategy enhancing the mechanical robustness of MXene-based flexible antennas makes metallic two-dimensional nanomaterials more promising in wearable electromagnetic sensors.

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.