Skin-interfaced systems for sweat collection and analytics

Biocompatible Material-Based Flexible Biosensors: From Materials Design to Wearable/Implantable Devices and Integrated Sensing Systems

Human beings have a greater need to pursue life and manage personal or family health in the context of the rapid growth of artificial intelligence, big data, the Internet of Things, and 5G/6G technologies. The application of micro biosensing devices is crucial in connecting technology and personalized medicine. Here, the progress and current status from biocompatible inorganic materials to organic materials and composites are reviewed and the material-to-device processing is described. Next, the operating principles of pressure, chemical, optical, and temperature sensors are dissected and the application of these flexible biosensors in wearable/implantable devices is discussed. Different biosensing systems acting in vivo and in vitro, including signal communication and energy supply are then illustrated. The potential of in-sensor computing for applications in sensing systems is also discussed. Finally, some essential needs for commercial translation are highlighted and future opportunities for flexible biosensors are considered.

Wearable Plasmonic Sweat Biosensor for Acetaminophen Drug Monitoring

Monitoring the acetaminophen dosage is important to prevent the occurrence of adverse reactions such as liver failure and kidney damage. Traditional approaches to monitoring acetaminophen dosage mainly rely on invasive blood collection. Herein, we developed a noninvasive microfluidic-based wearable plasmonic sensor to achieve simultaneous sweat sampling and acetaminophen drug monitoring for vital signs. The fabricated sensor employs an Au nanosphere cone array as the key sensing component, which poses a substrate with surface-enhanced Raman scattering (SERS) activity to noninvasively and sensitively detect the fingerprint of acetaminophen molecules based on its unique SERS spectrum. The developed sensor enabled the sensitive detection and quantification of acetaminophen at concentrations as low as 0.13 μM. We further evaluated the sweat sensor integrated with a Raman spectrometer for monitoring acetaminophen in drug-administered subjects. These results indicated that the sweat sensor could measure acetaminophen levels and reflect drug metabolism. The sweat sensors have revolutionized wearable sensing technology by adopting label-free and sensitive molecular tracking methods for noninvasive and point-of-care drug monitoring and management.

Pt/MXene-Based Flexible Wearable Non-Enzymatic Electrochemical Sensor for Continuous Glucose Detection in Sweat

Wearable non-invasive sensors facilitate the continuous measurement of glucose in sweat for the treatment and management of diabetes. However, the catalysis of glucose and sweat sampling are challenges in the development of efficient wearable glucose sensors. Herein, we report a flexible wearable non-enzymatic electrochemical sensor for continuous glucose detection in sweat. We synthesized a catalyst (Pt/MXene) by the hybridization of Pt nanoparticles onto MXene (Ti₃C₂T_x) nanosheets with a broad linear range of glucose detection (0-8 mmol/L) under neutral conditions. Furthermore, we optimized the structure of the sensor by immobilizing Pt/MXene with a conductive hydrogel to enhance the stability of the sensor. Based on Pt/MXene and the optimized structure, we fabricated a flexible wearable glucose sensor by integrating a microfluidic patch for sweat collection onto a flexible sensor. We evaluated the utility of the sensor for the detection of glucose in sweat, and the sensor could detect the glucose change with the replenishment and consumption of energy by the body, and a similar trend was observed in the blood. An in vivo glucose test in sweat indicated that the fabricated sensor is promising for the continuous measurement of glucose, which is essential for the treatment and management of diabetes.

Paper-based microfluidics in sweat detection: from design to application

Sweat, as a sample that includes a lot of biochemical information, is good for non-invasive monitoring. In recent years, there have been an increasing number of studies on in situ monitoring of sweat. However, there are still some challenges for the continuous analysis of samples. As a hydrophilic, easy-to-process, environmentally friendly, inexpensive and easily accessible material, paper is an ideal substrate material for making in situ sweat analysis microfluidics. This review introduces the development of paper as a sweat analysis microfluidic substrate material, focusing on the advantages of the structural characteristics of paper, trench design and equipment integration applications to expand the design and research ideas for the development of in situ sweat detection technology.

MicroSweat: A Wearable Microfluidic Patch for Noninvasive and Reliable Sweat Collection Enables Human Stress Monitoring

Stress affects cognition, behavior, and physiology, leading to lasting physical and mental illness. The ability to detect and measure stress, however, is poor. Increased circulating cortisol during stress is mirrored by cortisol release from sweat glands, providing an opportunity to use it as an external biomarker for monitoring internal emotional state. Despite the attempts at using wearable sensors for monitoring sweat cortisol, there is a lack of reliable wearable sweat collection devices that preserve the concentration and integrity of sweat biomolecules corresponding to stress levels. Here, a flexible, self-powered, evaporation-free, bubble-free, surfactant-free, and scalable capillary microfluidic device, MicroSweat, is fabricated to reliably collect human sweat from different body locations. Cortisol levels are detected corresponding to severe stress ranging from 25 to 125 ng mL-1 averaged across multiple body regions and 100-1000 ng mL-1 from the axilla. A positive nonlinear correlation exists between cortisol concentration and stress levels quantified using the perceived stress scale (PSS). Moreover, owing to the sweat variation in response to environmental effects and physiological differences, the longitudinal and personalized profile of sweat cortisol is acquired, for the first time, for various body locations. The obtained sweat cortisol data is crucial for analyzing human stress in personalized and clinical healthcare sectors.

Sweat as a diagnostic biofluid

Skin-interfaced microfluidic systems help assess health status and chemical exposure.

Intelligent Soft Sweat Sensors for the Simultaneous Healthcare Monitoring and Safety Warning

Intelligent monitoring human physiological information in real time raises the demand for skin-integrated electronics, as which is a flexible format and can be mounted onto the curved human skin for noninvasive healthcare monitoring. The biofluid such as sweat from skin contains abundant biomarkers reflecting body health conditions. Here, a skin-integrated sweat monitor with six biosensors embedded for the detection of NH₄ ⁺ , Na⁺ , glucose, pH, skin impedance, and surface temperature is described, which could decode the information in the fresh sweat generated during exercising. Furthermore, the system also includes an innovative safety warning mechanism, which is based on a miniaturized actuator to provide mechanical stimuli, and coupled with six changeable colors light emitting diodes corresponding to the six biosensors for providing simultaneous safety alarming to users. The self-developed microfluidics system with a hydrophilic surface allows to enhance the sweat collection rate. Meanwhile, microfluidic filters can reduce the interruption of skin debris during biosignal monitoring. These state-of-art biosensors can real-time monitor health related signals with excellent linearity and specificity. The skin-integrated sweat monitor system exhibits a great potential in human healthcare monitoring and medical treatment.

Vending-Machine-Style Skin Excretion Sensing

Skin metabolites show huge potential for use in clinical diagnostics. However, skin sampling and analysis workflows are tedious and time-consuming. Here, we demonstrate a vending-machine-style skin excretion sensing platform based on hydrogel-assisted sampling of skin metabolites. In this sensing platform, a sampling probe with hydrogel is held by a robotic arm. The robotic arm manoeuvres the probe to press it onto the forearm of a human subject. Due to the highly hydrophilic nature of the hydrogel, water-soluble metabolites─released by skin─are collected into the hydrogel, leaving behind the nonpolar metabolites. The probe is then inserted into a custom-made open port sampling interface coupled to an electrospray ion source of a high-resolution quadrupole-time-of-flight mass spectrometer. Metabolites in the hydrogel are immediately extracted by a solvent liquid junction in the interface and analyzed using the mass spectrometer. The ion current of the target analyte is displayed on a customized graphical user interface, which can also be used to control the key components of the analytical platform. The automated sampling and analysis workflow starts after the user inserts coins or presents an insurance card, presses a button, and extends an arm on the sampling area. The platform relies on low-cost mechanical and electronic modules (a robotic arm, a single-board computer, and two microcontroller boards). The limits of detection for standard analytes─arginine, citrulline, and histidine─embedded in agarose gel beds were 148, 205, and 199 nM, respectively. Various low-molecular-weight metabolites from human skin have been identified with the high-resolution mass spectrometer.

Nanostructured Conductive Polypyrrole for Antibacterial Components in Flexible Wearable Devices

The power generated by flexible wearable devices (FWDs) is normally insufficient to eradicate bacteria, and many conventional antibacterial strategies are also not suitable for flexible and wearable applications because of the strict mechanical and electrical requirements. Here, polypyrrole (PPy), a conductive polymer with a high mass density, is used to form a nanostructured surface on FWDs for antibacterial purposes. The conductive films with PPy nanorods (PNRs) are found to sterilize 98.2 ± 1.6% of Staphylococcus aureus and 99.6 ± 0.2% of Escherichia coli upon mild electrification (1 V). Bacteria killing stems from membrane stress produced by the PNRs and membrane depolarization caused by electrical neutralization. Additionally, the PNR films exhibit excellent biosafety and electrical stability. The results represent pioneering work in fabricating antibacterial components for FWDs by comprehensively taking into consideration the required conductivity, mechanical properties, and biosafety.

Wearable and flexible electrochemical sensors for sweat analysis: a review

Flexible wearable sweat sensors allow continuous, real-time, noninvasive detection of sweat analytes, provide insight into human physiology at the molecular level, and have received significant attention for their promising applications in personalized health monitoring. Electrochemical sensors are the best choice for wearable sweat sensors due to their high performance, low cost, miniaturization, and wide applicability. Recent developments in soft microfluidics, multiplexed biosensing, energy harvesting devices, and materials have advanced the compatibility of wearable electrochemical sweat-sensing platforms. In this review, we summarize the potential of sweat for medical detection and methods for sweat stimulation and collection. This paper provides an overview of the components of wearable sweat sensors and recent developments in materials and power supply technologies and highlights some typical sensing platforms for different types of analytes. Finally, the paper ends with a discussion of the challenges and a view of the prospective development of this exciting field.

Wearable Hydrogel-Based Epidermal Sensor with Thermal Compatibility and Long Term Stability for Smart Colorimetric Multi-Signals Monitoring

Hydrogel-based wearable epidermal sensors (HWESs) have attracted widespread attention in health monitoring, especially considering their colorimetric readout capability. However, it remains challenging for HWESs to work at extreme temperatures with long term stability due to the existence of water. Herein, a wearable transparent epidermal sensor with thermal compatibility and long term stability for smart colorimetric multi-signals monitoring is developed, based on an anti-freezing and anti-drying hydrogel with high transparency (over 90% transmittance), high stretchability (up to 1500%) and desirable adhesiveness to various kinds of substrates. The hydrogel consists of polyacrylic acid, polyacrylamide, and tannic acid-coated cellulose nanocrystals in glycerin/water binary solvents. When glycerin readily forms strong hydrogen bonds with water, the hydrogel exhibits outstanding thermal compatibility. Furthermore, the hydrogel maintains excellent adhesion, stretchability, and transparency after long term storage (45 days) or at subzero temperatures (-20 °C). For smart colorimetric multi-signals monitoring, the freestanding smart colorimetric HWESs are utilized for simultaneously monitoring the pH, T and light, where colorimetric signals can be read and stored by artificial intelligence strategies in a real time manner. In summary, the developed wearable transparent epidermal sensor holds great potential for monitoring multi-signals with visible readouts in long term health monitoring.

Emerging biotransduction strategies on soft interfaces for biosensing

As a lab-on-soft biochip providing accurate and timely biomarker information, wearable biosensors can satisfy the increasing demand for intelligent e-health services, active disease diagnosis/therapy, and huge bioinformation data. As biomolecules generally could not directly produce detectable signals, biotransducers that specifically convert biomolecules to electrical or optical signals are involved, which determines the pivotal sensing performance including 3S (sensitivity, selectivity, and stability), reversibility, etc. The soft interface poses new requirements for biotransducers, especially equipment-free, facile operation, mechanical tolerance, and high sensing performance. In this review, we discussed the emerging electrochemical and optical biotransduction strategies on wearables from the aspects of the transduction mechanism, amplification strategies, biomaterial selection, and device fabrication procedures. Challenges and perspectives regarding future biotransducers for monitoring trace amounts of biomolecules with high fidelity, sensitivity, and multifunctionality are also discussed. It is expected that through fusion with functional electronics, wearable biosensors can provide possibilities to further decentralize the healthcare system and even build biomolecule-based intelligent cyber-physical systems and new modalities of cyborgs.

Advanced thermal sensing techniques for characterizing the physical properties of skin

Measurements of the thermal properties of the skin can serve as the basis for a noninvasive, quantitative characterization of dermatological health and physiological status. Applications range from the detection of subtle spatiotemporal changes in skin temperature associated with thermoregulatory processes, to the evaluation of depth-dependent compositional properties and hydration levels, to the assessment of various features of microvascular/macrovascular blood flow. Examples of recent advances for performing such measurements include thin, skin-interfaced systems that enable continuous, real-time monitoring of the intrinsic thermal properties of the skin beyond its superficial layers, with a path to reliable, inexpensive instruments that offer potential for widespread use as diagnostic tools in clinical settings or in the home. This paper reviews the foundational aspects of the latest thermal sensing techniques with applicability to the skin, summarizes the various devices that exploit these concepts, and provides an overview of specific areas of application in the context of skin health. A concluding section presents an outlook on the challenges and prospects for research in this field.

Patterning Wettability for Open-Surface Fluidic Manipulation: Fundamentals and Applications

Effective manipulation of liquids on open surfaces without external energy input is indispensable for the advancement of point-of-care diagnostic devices. Open-surface microfluidics has the potential to benefit health care, especially in the developing world. This review highlights the prospects for harnessing capillary forces on surface-microfluidic platforms, chiefly by inducing smooth gradients or sharp steps of wettability on substrates, to elicit passive liquid transport and higher-order fluidic manipulations without off-the-chip energy sources. A broad spectrum of the recent progress in the emerging field of passive surface microfluidics is highlighted, and its promise for developing facile, low-cost, easy-to-operate microfluidic devices is discussed in light of recent applications, not only in the domain of biomedical microfluidics but also in the general areas of energy and water conservation.

An epifluidic electronic patch with spiking sweat clearance for event-driven perspiration monitoring

Sensory neurons generate spike patterns upon receiving external stimuli and encode key information to the spike patterns, enabling energy-efficient external information processing. Herein, we report an epifluidic electronic patch with spiking sweat clearance using a sensor containing a vertical sweat-collecting channel for event-driven, energy-efficient, long-term wireless monitoring of epidermal perspiration dynamics. Our sweat sensor contains nanomesh electrodes on its inner wall of the channel and unique sweat-clearing structures. During perspiration, repeated filling and abrupt emptying of the vertical sweat-collecting channel generate electrical spike patterns with the sweat rate and ionic conductivity proportional to the spike frequency and amplitude over a wide dynamic range and long time (> 8 h). With such 'spiking' sweat clearance and corresponding electronic spike patterns, the epifluidic wireless patch successfully decodes epidermal perspiration dynamics in an event-driven manner at different skin locations during exercise, consuming less than 0.6% of the energy required for continuous data transmission. Our patch could integrate various on-skin sensors and emerging edge computing technologies for energy-efficient, intelligent digital healthcare.

Flexible Thin-Film Speaker Integrated with an Array of Quantum-Dot Light-Emitting Diodes for the Interactive Audiovisual Display of Multi-functional Sensor Signals

One of the core technologies for wearable electronics is the use of an interactive display device that is attached to the body or clothes to transmit various bio-signals and environmental stimuli to the user. In this study, we report a flexible audiovisual display device consisting of a polyvinylidene difluoride (PVDF) thin-film speaker stacked on an 8 × 8 array of quantum-dot light-emitting diodes (QD-LEDs) and a multi-functional sensor consisting of temperature and ultraviolet (UV) sensors connected to a pressure sensor, allowing the body temperature and UV exposure to be displayed both visually and acoustically. Polydimethylsiloxane is employed as an insulator between the carbon nanotube (CNT)/polyaniline temperature sensor and the ZnO/CNT UV sensor to form a capacitor-type pressure sensor. With the use of a stretchable polymer substrate, liquid metal Galinstan interconnections, and the flexible Au-grid electrodes, both the PVDF speaker and the QD-LED array are stable under repeated cycles of bending deformation with a bending radius of 7.5 mm. By connecting the audiovisual display device to the skin-attached multi-functional sensor, changes in the body temperature and UV exposure are displayed as LED patterns with accompanying acoustic alarms. This study demonstrates the significant potential of our proposed audiovisual monitoring device and multi-functional sensor for use in health-monitoring applications, especially for the elderly and infants requiring prompt care.

Reversible Wrinkling Surfaces for Enhanced Grip on Wet/Dry Conditions

Friction is important in material design for robotic systems that need to perform tasks regardless of environmental changes. Generally, robotic systems lose their friction in wet environments and fail to accomplish their tasks. Despite the significance of maintaining friction in dry and wet environments, it is still challenging. Here, we report a smart switching surface, which helps to complete missions in both wet and dry environments. Inspired by the reversible wrinkling mechanism of a human finger, the surface reversibly generates and removes wrinkles to adapt to both environments using volume-changing characteristics of the Nafion film. The switchable surfaces with manipulated wrinkle morphologies via patterns of diverse densities, sizes, and shapes induce a relationship between the wrinkle morphologies and friction: wrinkles on denser and smaller hexagonal patterns generate six times more friction than non-switching flat surfaces in wet environments and a similar amount of friction to the flat surfaces in dry environments. In addition, the wrinkle morphologies according to the patterns are predicted through numerical simulation, which is in good agreement with experimental results. This work presents potential applications in robotic systems that are required to perform in and out of water and paves the way for further understanding of wrinkling dynamics, manipulation, and evolutionary function in skin.

Miniaturizing a Chip-Scale Spectrometer Using Local Strain Engineering and Total-Variation Regularized Reconstruction

A wafer-thin chip-scale portable spectrometer suitable for wearable applications based on a reconstructive algorithm was demonstrated. A total of 16 spectral encoders that simultaneously functioned as photodetectors were monolithically integrated on a chip area of 0.16 mm² by applying local strain engineering in compressively strained InGaN/GaN multiple quantum well heterostructures. The built-in GaN pn junction enabled a direct photocurrent measurement. A non-negative least-squares (NNLS) algorithm with total-variation regularization and a choice of a proper kernel function was shown to deliver a decent spectral reconstruction performance in the wavelength range of 400-645 nm. The accuracies of spectral peak positions and intensity ratios between peaks were found to be 0.97% and 10.4%, respectively. No external optics, such as collimation optics and apertures, were used, enabled by angle-insensitive light-harvesting structures, including an array of cone-shaped backreflectors fabricated on the underside of the sapphire substrate.

Graphene and Its Derivatives: Synthesis and Application in the Electrochemical Detection of Analytes in Sweat

Wearable sensors and invasive devices have been studied extensively in recent years as the demand for real-time human healthcare applications and seamless human-machine interaction has risen exponentially. An explosion in sensor research throughout the globe has been ignited by the unique features such as thermal, electrical, and mechanical properties of graphene. This includes wearable sensors and implants, which can detect a wide range of data, including body temperature, pulse oxygenation, blood pressure, glucose, and the other analytes present in sweat. Graphene-based sensors for real-time human health monitoring are also being developed. This review is a comprehensive discussion about the properties of graphene, routes to its synthesis, derivatives of graphene, etc. Moreover, the basic features of a biosensor along with the chemistry of sweat are also discussed in detail. The review mainly focusses on the graphene and its derivative-based wearable sensors for the detection of analytes in sweat. Graphene-based sensors for health monitoring will be examined and explained in this study as an overview of the most current innovations in sensor designs, sensing processes, technological advancements, sensor system components, and potential hurdles. The future holds great opportunities for the development of efficient and advanced graphene-based sensors for the detection of analytes in sweat.

A Comprehensive Review of the Recent Developments in Wearable Sweat-Sensing Devices

Sweat analysis offers non-invasive real-time on-body measurement for wearable sensors. However, there are still gaps in current developed sweat-sensing devices (SSDs) regarding the concerns of mixing fresh and old sweat and real-time measurement, which are the requirements to ensure accurate the measurement of wearable devices. This review paper discusses these limitations by aiding model designs, features, performance, and the device operation for exploring the SSDs used in different sweat collection tools, focusing on continuous and non-continuous flow sweat analysis. In addition, the paper also comprehensively presents various sweat biomarkers that have been explored by earlier works in order to broaden the use of non-invasive sweat samples in healthcare and related applications. This work also discusses the target analyte's response mechanism for different sweat compositions, categories of sweat collection devices, and recent advances in SSDs regarding optimal design, functionality, and performance.

Ultra-Thin Flexible Encapsulating Materials for Soft Bio-Integrated Electronics

Recently, bioelectronic devices extensively researched and developed through the convergence of flexible biocompatible materials and electronics design that enables  more precise diagnostics and therapeutics in human health care and opens up the potential to expand into various fields, such as clinical medicine and biomedical research. To establish an accurate and stable bidirectional bio-interface, protection against the external environment and high mechanical deformation is essential for wearable bioelectronic devices. In the case of implantable bioelectronics, special encapsulation materials and optimized mechanical designs and configurations that provide electronic stability and functionality are required for accommodating various organ properties, lifespans, and functions in the biofluid environment. Here, this study introduces recent developments of ultra-thin encapsulations with novel materials that can preserve or even improve the electrical performance of wearable and implantable bio-integrated electronics by supporting safety and stability for protection from destruction and contamination as well as optimizing the use of bioelectronic systems in physiological environments. In addition, a summary of the materials, methods, and characteristics of the most widely used encapsulation technologies is introduced, thereby providing a strategic selection of appropriate choices of recently developed flexible bioelectronics.

A Self-Powered Wearable Sensor for Continuous Wireless Sweat Monitoring

Wireless wearable sweat analysis devices can monitor biomarkers at the molecular level continuously and in situ, which is highly desired for personalized health care. The miniaturization, integration, and wireless operation of sweat sensors improve the comfort and convenience while also bringing forward new challenges for power supply technology. Herein, a wireless self-powered wearable sweat analysis system (SWSAS) is designed that effectively converts the mechanical energy of human motion into electricity through hybrid nanogenerator modules (HNGMs). The HNGM shows stable output characteristics at low frequency with a current of 15 mA and a voltage of 60 V. Through real-time on-body sweat analysis powered by HNGM, the SWSAS is demonstrated to selectively monitor biomarkers (Na⁺ and K⁺ ) in sweat and wirelessly transmit the sensing data to the user interface via Bluetooth.

Simplifying the complex: accessible microfluidic solutions for contemporary processes within in vitro diagnostics

In vitro diagnostics (IVDs) form the cornerstone of modern medicine. They are routinely employed throughout the entire treatment pathway, from initial diagnosis through to prognosis, treatment planning, and post-treatment surveillance. Given the proven links between high quality diagnostic testing and overall health, ensuring broad access to IVDs has long been a focus of both researchers and medical professionals. Unfortunately, the current diagnostic paradigm relies heavily on centralized laboratories, complex and expensive equipment, and highly trained personnel. It is commonly assumed that this level of complexity is required to achieve the performance necessary for sensitive and specific disease diagnosis, and that making something affordable and accessible entails significant compromises in test performance. However, recent work in the field of microfluidics is challenging this notion. By exploiting the unique features of microfluidic systems, researchers have been able to create progressively simple devices that can perform increasingly complex diagnostic assays. This review details how microfluidic technologies are disrupting the status quo, and facilitating the development of simple, affordable, and accessible integrated IVDs. Importantly, we discuss the advantages and limitations of various approaches, and highlight the remaining challenges within the field.

Simple, Skin-Attachable, and Multifunctional Colorimetric Sweat Sensor

In situ analysis of sweat provides a simple, convenient, cost-effective, and noninvasive approach for the early diagnosis of physical illness in humans and is particularly useful in family care. In this study, a flexible and skin-attachable colorimetric sweat sensor for multiplexed analysis is developed using a simple, cost-effective, and convenient method. The obtained sweat sensor can be used to simultaneously detect glucose, lactate, urea, and pH value in sweat, as well as sweat loss and skin temperature. Only 2.5 μL of sweat is enough for the whole test, and the sweat loss and chemical-sensing results can be read out conveniently by naked eyes or a smartphone. In addition, body temperature can also be detected with an additional electrical circuit. Our sweat sensor provides a new, cost-effective, and convenient approach for in vitro diagnosis of multiple components in sweat, and the easy fabrication and cost-effectiveness make our sensor commercializable in the near future.

Chip-less wireless electronic skins by remote epitaxial freestanding compound semiconductors

Recent advances in flexible and stretchable electronics have led to a surge of electronic skin (e-skin)-based health monitoring platforms. Conventional wireless e-skins rely on rigid integrated circuit chips that compromise the overall flexibility and consume considerable power. Chip-less wireless e-skins based on inductor-capacitor resonators are limited to mechanical sensors with low sensitivities. We report a chip-less wireless e-skin based on surface acoustic wave sensors made of freestanding ultrathin single-crystalline piezoelectric gallium nitride membranes. Surface acoustic wave-based e-skin offers highly sensitive, low-power, and long-term sensing of strain, ultraviolet light, and ion concentrations in sweat. We demonstrate weeklong monitoring of pulse. These results present routes to inexpensive and versatile low-power, high-sensitivity platforms for wireless health monitoring devices.

Lower Limbs Wearable Sports Garments for Muscle Recovery: An Umbrella Review

This review aims to understand the different technologies incorporated into lower limbs wearable smart garments and their impact on post-exercise recovery. Electronic searches were conducted in the PubMed, Web of Science, and Cochrane electronic databases. Eligibility criteria considered meta-analyses that examined the effects of wearable smart garments on physical fitness in healthy male and female adults. Seven meta-analyses were considered in the current umbrella review, indicating small effects on delayed-onset muscle soreness ([0.40–0.43]), rate of perceived exertion (0.20), proprioception (0.49), anaerobic performance (0.27), and sprints ([0.21–0.37]). The included meta-analyses also indicated wearable smart garments have trivial to large effects on muscle strength and power ([0.14–1.63]), creatine kinase ([0.02–0.44]), lactate dehydrogenase (0.52), muscle swelling (0.73), lactate (0.98) and aerobic pathway (0.24), and endurance (0.37), aerobic performance (0.60), and running performance ([0.06–6.10]). Wearing wearable smart garments did not alter the rate of perceived exertion and had a small effect on delayed-onset muscle soreness. Well-fitting wearable smart garments improve comfort and kinesthesia and proprioception and allow a reduction in strength loss and muscle damage after training and power performance following resistance training or eccentric exercise.

An unconventional vertical fluidic-controlled wearable platform for synchronously detecting sweat rate and electrolyte concentration

Epidermal microfluidic devices with long microchannels have been developed for continuous sweat analysis, which are crucial to assess personal hydration status and underlying health conditions. However, the flow resistance in long channels and the ionic concentration variation significantly affect the accuracy of both the sweat rate and electrolyte concentration measurements. Herein, we present a novel fluidic-controlled wearable platform for synchronously dropwise-detecting the sweat rate and total electrolyte concentration. The unconventional platform consisting of a vertically shortened channel, a pair of embedded electrodes and an absorption layer, is designed to minimize the flow resistance and transform sweat fluidics into uniform micro-droplets for chronological and dropwise detection. Real-time sweat conductance is decoupled from a square-wave-like curve, where the sweat rate and electrolyte concentration can be derived from the interval time and peak value, respectively. Flexible and wearable band devices are demonstrated to show their potential application for hydration status assessment during exercises.

Wearable Sensor for Continuous Sweat Biomarker Monitoring

In recent years, wearable sensors have enabled the unique mode of real-time and noninvasive monitoring to develop rapidly in medical care, sports, and other fields. Sweat contains a wide range of biomarkers such as metabolites, electrolytes, and various hormones. Combined with wearable technology, sweat can reflect human fatigue, disease, mental stress, dehydration, and so on. This paper comprehensively describes the analysis of sweat components such as glucose, lactic acid, electrolytes, pH, cortisol, vitamins, ethanol, and drugs by wearable sensing technology, and the application of sweat wearable devices in glasses, patches, fabrics, tattoos, and paper. The development trend of sweat wearable devices is prospected. It is believed that if the sweat collection, air permeability, biocompatibility, sensing array construction, continuous monitoring, self-healing technology, power consumption, real-time data transmission, specific recognition, and other problems of the wearable sweat sensor are solved, we can provide the wearer with important information about their health level in the true sense.

Materials with Tunable Optical Properties for Wearable Epidermal Sensing in Health Monitoring

Advances in wearable epidermal sensors have revolutionized the way that physiological signals are captured and measured for health monitoring. One major challenge is to convert physiological signals to easily readable signals in a convenient way. One possibility for wearable epidermal sensors is based on visible readouts. There are a range of materials whose optical properties can be tuned by parameters such as temperature, pH, light, and electric fields. Herein, this review covers and highlights a set of materials with tunable optical properties and their integration into wearable epidermal sensors for health monitoring. Specifically, the recent progress, fabrication, and applications of these materials for wearable epidermal sensors are summarized and discussed. Finally, the challenges and perspectives for the next generation wearable devices are proposed.

Artificial neuromorphic cognitive skins based on distributed biaxially stretchable elastomeric synaptic transistors

SignificanceEnabling distributed neurologic and cognitive functions in soft deformable devices, such as robotics, wearables, skin prosthetics, bioelectronics, etc., represents a massive leap in their development. The results presented here reveal the device characteristics of the building block, i.e., a stretchable elastomeric synaptic transistor, its characteristics under various levels of biaxial strain, and performances of various stretchy distributed neuromorphic devices. The stretchable neuromorphic array of synaptic transistors and the neuromorphic imaging sensory skin enable platforms to create a wide range of soft devices and systems with implemented neuromorphic and cognitive functions, including artificial cognitive skins, wearable neuromorphic computing, artificial organs, neurorobotics, and skin prosthetics.

Wearable devices for continuous monitoring of biosignals: Challenges and opportunities

The ability for wearable devices to collect high-fidelity biosignals continuously over weeks and months at a time has become an increasingly sought-after characteristic to provide advanced diagnostic and therapeutic capabilities. Wearable devices for this purpose face a multitude of challenges such as formfactors with long-term user acceptance and power supplies that enable continuous operation without requiring extensive user interaction. This review summarizes design considerations associated with these attributes and summarizes recent advances toward continuous operation with high-fidelity biosignal recording abilities. The review also provides insight into systematic barriers for these device archetypes and outlines most promising technological approaches to expand capabilities. We conclude with a summary of current developments of hardware and approaches for embedded artificial intelligence in this wearable device class, which is pivotal for next generation autonomous diagnostic, therapeutic, and assistive health tools.

Integrated Aptasensor Array for Sweat Drug Analysis

Drug abuse is seriously endangering human health and jeopardizing society. There is an urgent need for rapid, sensitive, portable, and easy-to-operate methods for the daily detection of drugs in biological matrices. However, current drug detection methods based on chromatography, spectroscopy, immunosorbent assays, etc. are limited by the requirements of high logistical instruments and laboratory. Herein, we proposed a wearable electrochemical aptasensor with high sensitivity and specificity for the direct capture and rapid detection of multiple drugs in sweat. The single aptamer and dual aptamers with different base compositions were designed to compose the aptasensor array. Molecular docking simulations demonstrated different binding affinities between bioamines and aptamers. The developed aptasensor array is shown to be sufficient to generate distinct electrochemical fingerprints for different psychoactive drugs and interfering substances by extracting variable features from electrochemical signals. Sixteen analytes in the same concentration or gradient concentrations were identified with 100% accuracy. In addition, the wearable sensor platform was demonstrated to discriminate various drugs with similar chemical structures in artificial sweat and human sweat samples. The sensor array not only provided a new rapid method for the detection of drugs but also served as a reference for developing wearable sensors for onsite and daily testing of human biochemical information.

Recent Progress in Microneedles-Mediated Diagnosis, Therapy, and Theranostic Systems

Theranostic system combined diagnostic and therapeutic modalities is critical for the real-time monitoring of disease-related biomarkers and personalized therapy. Microneedles, as a multifunctional platform, are promising for transdermal diagnostics and drug delivery. They have shown attractive properties including painless skin penetration, easy self-administration, prominent therapeutic effects, and good biosafety. Herein, an overview of the microneedles-based diagnosis, therapies, and theranostic systems is given. Four microneedles-based detection methods are concluded based on the sensing mechanism: i) electrochemistry, ii) fluorometric, iii) colorimetric, and iv) Raman methods. Additionally, robust microneedles are suitable for implantable drug delivery. Microneedles-assisted transdermal drug delivery can be primarily classified as passive, active, and responsive drug release, based on the release mechanisms. Microneedles-assisted oral and implantable drug delivery mechanisms are also presented in this review. Furthermore, the key frontier developments in microneedles-mediated theranostic systems as the major selling points are emphasized in this review. These systems are classified into open-loop and closed-loop theranostic systems based on the indirectness and directness of feedback between the transdermal diagnosis and therapy, respectively. Finally, conclusions and future perspectives for next-generation microneedles-mediated theranostic systems are also discussed. Taken together, microneedle-based systems are promising as the new avenue for diagnosis, therapy, and disease-specific closed-loop theranostic applications.

Sweating Rate and Sweat Chloride Concentration of Elite Male Basketball Players Measured With a Wearable Microfluidic Device Versus the Standard Absorbent Patch Method

The purpose of this study was to compare a wearable microfluidic device and standard absorbent patch in measuring local sweating rate (LSR) and sweat chloride concentration ([Cl-]) in elite basketball players. Participants were 53 male basketball players (25 ± 3 years, 92.2 ± 10.4 kg) in the National Basketball Association's development league. Players were tested during a moderate-intensity, coach-led practice (98 ± 30 min, 21.0 ± 1.2 °C). From the right ventral forearm, sweat was collected using an absorbent patch (3M Tegaderm™ + Pad). Subsequently, LSR and local sweat [Cl-] were determined via gravimetry and ion chromatography. From the left ventral forearm, LSR and local sweat [Cl-] were measured using a wearable microfluidic device and associated smartphone application-based algorithms. Whole-body sweating rate (WBSR) was determined from pre- to postexercise change in body mass corrected for fluid/food intake (ad libitum), urine loss, and estimated respiratory water and metabolic mass loss. The WBSR values predicted by the algorithms in the smartphone application were also recorded. There were no differences between the absorbent patch and microfluidic patch for LSR (1.25 ± 0.91 mg·cm-2·min-1 vs. 1.14 ±0.78 mg·cm-2·min-1, p = .34) or local sweat [Cl-] (30.6 ± 17.3 mmol/L vs. 29.6 ± 19.4 mmol/L, p = .55). There was no difference between measured and predicted WBSR (0.97 ± 0.41 L/hr vs. 0.89 ± 0.35 L/hr, p = .22; 95% limits of agreement = 0.61 L/hr). The wearable microfluidic device provides similar LSR, local sweat [Cl-], and WBSR results compared with standard field-based methods in elite male basketball players during moderate-intensity practices.

Skin bioelectronics towards long-term, continuous health monitoring

Skin bioelectronics are considered as an ideal platform for personalised healthcare because of their unique characteristics, such as thinness, light weight, good biocompatibility, excellent mechanical robustness, and great skin conformability. Recent advances in skin-interfaced bioelectronics have promoted various applications in healthcare and precision medicine. Particularly, skin bioelectronics for long-term, continuous health monitoring offer powerful analysis of a broad spectrum of health statuses, providing a route to early disease diagnosis and treatment. In this review, we discuss (1) representative healthcare sensing devices, (2) material and structure selection, device properties, and wireless technologies of skin bioelectronics towards long-term, continuous health monitoring, (3) healthcare applications: acquisition and analysis of electrophysiological, biophysical, and biochemical signals, and comprehensive monitoring, and (4) rational guidelines for the design of future skin bioelectronics for long-term, continuous health monitoring. Long-term, continuous health monitoring of advanced skin bioelectronics will open unprecedented opportunities for timely disease prevention, screening, diagnosis, and treatment, demonstrating great promise to revolutionise traditional medical practices.

Fabrication of a Flexible, Wireless Micro-Heater on Elastomer for Wearable Gas Sensor Applications

Thin-film microdevices can be applied to various wearable devices due to their high flexibility compared to conventional bulk-type electronic devices. Among the various microdevice types, many IoT-based sensor devices have been developed recently. In the case of such sensor elements, it is important to control the surrounding environment to optimize the sensing characteristics. Among these environmental factors, temperature often has a great influence. There are cases where temperature significantly affects the sensor characteristics, as is the case for gas sensors. For this purpose, the development of thin-film-type micro-heaters is important. For this study, a wirelessly driven thin-film micro-heater was fabricated on the flexible and stretchable elastomer, a polydimethylsiloxane (PDMS); the antenna was optimized; and the heater was driven at the temperature up to 102 degrees Celsius. The effect of its use on gas-sensing characteristics was compared through the application of the proposed micro-heater to a gas sensor. The heated SnO₂ nanowire gas sensor improved the performance of detecting carbon monoxide (CO) by more than 20%, and the recovery time was reduced to less than half. It is expected that thin-film-type micro-heaters that can be operated wirelessly are suitable for application in various wearable devices, including those for smart sensors and health monitoring.

Wearable plasmonic paper-based microfluidics for continuous sweat analysis

Wearable sweat sensors have the potential to provide clinically meaningful information associated with the health and disease states of individuals. Current sensors mainly rely on enzymes and antibodies as biorecognition elements to achieve specific quantification of metabolite and stress biomarkers in sweat. However, enzymes and antibodies are prone to degrade over time, compromising the sensor performance. Here, we introduce a wearable plasmonic paper-based microfluidic system for continuous and simultaneous quantitative analysis of sweat loss, sweat rate, and metabolites in sweat. Plasmonic sensors based on label-free surface-enhanced Raman spectroscopy (SERS) can provide chemical "fingerprint" information for analyte identification. We demonstrate the sensitive detection and quantification of uric acid in sweat at physiological and pathological concentrations. The well-defined flow characteristics of paper microfluidic devices enable accurate quantification of sweat loss and sweat rate. The wearable plasmonic device is soft, flexible, and stretchable, which can robustly interface with the skin without inducing chemical or physical irritation.

Wearable microfluidic-based e-skin sweat sensors

Electronic skins (e-skins) are soft (deformable and stretchable) state-of-the-art wearable devices that emulate the attributes of human skin and act as a Human-Machine Interface (HMI). Recent advances in e-skin for real-time detection of medical signals such as pulse, temperature, electromyogram (EMG), electroencephalogram (EEG), electrooculogram (EOG), electrocardiogram (ECG), and other bioelectric signals laid down an intelligent foundation for early prediction and diagnosis of diseases with a motive of reducing the risk of the ailment reaching to the end stage. In particular, sweat testing has been employed in diverse applications ranging from medical diagnosis of diabetes, cystic fibrosis, tuberculosis, blood pressure, and autonomic neuropathy to evaluating fluid and electrolyte balance in athletes. Typically, sweat testing techniques are done by trained experts and require off-body measurements, which prevent individuals from de-coding health issues quickly and independently. With the onset of soft electronics, wearable sweat sensors overcome this disadvantage via in situ sweat measurements with real-time feedback, timely diagnosis, creating the potential for preventive care and treatment. Over the past few decades, wearable microfluidic-based e-skin sweat sensors have paved a new way, promising sensing interfaces that are highly compatible with arranging medical and electronic applications. The present review highlights the recent research carried out in the microfluidic-based wearable sweat sensors with a critical focus on real-time sensing of lactate, chloride, and glucose concentration; sweat rate, simultaneously with pH, and total sweat loss for preventive care, timely diagnosis, and point-of-care health and fitness monitoring.

Biomarkers and Detection Platforms for Human Health and Performance Monitoring: A Review

Human health and performance monitoring (HHPM) is imperative to provide information necessary for protecting, sustaining, evaluating, and improving personnel in various occupational sectors, such as industry, academy, sports, recreation, and military. While various commercially wearable sensors are on the market with their capability of "quantitative assessments" on human health, physical, and psychological states, their sensing is mostly based on physical traits, and thus lacks precision in HHPM. Minimally or noninvasive biomarkers detectable from the human body, such as body fluid (e.g., sweat, tear, urine, and interstitial fluid), exhaled breath, and skin surface, can provide abundant additional information to the HHPM. Detecting these biomarkers with novel or existing sensor technologies is emerging as critical human monitoring research. This review provides a broad perspective on the state of the art biosensor technologies for HHPM, including the list of biomarkers and their physiochemical/physical characteristics, fundamental sensing principles, and high-performance sensing transducers. Further, this paper expands to the additional scope on the key technical challenges in applying the current HHPM system to the real field.

Wearable Microbial Fuel Cells for Sustainable Self-Powered Electronic Skins

Autonomous energy systems are key to sustainably powering electronic skins. Potential autonomous energy resources include sunlight, human motion, sweat, and body heat, among which the biofuel in human sweat is a most natural and available candidate. In this perspective, we discuss the promise of wearable microbial fuel cells as autonomous power suppliers for electronic skins by using the biofuels in human sweat. In comparison to wearable enzymatic biofuel cells, wearable microbial fuel cells offer easy access, low cost and superior sustainability. We summarize the present achievements and provide our vision toward future research to make wearable microbial fuel cells reliable on-skin power suppliers.

Wearable biosensors for real-time sweat analysis and body motion capture based on stretchable fiber-based triboelectric nanogenerators

Carbon neutrality is a global green energy revolution meaning that the carbon dioxide can make ends meet. However, with the mushroom of the fifth generation wireless systems (5G) and the Internet of Things (IoT), it is a great challenge for powering the ubiquitous distributed devices, because the battery production and high overhead maintenance may bring more carbon emissions. Here, we present wearable biosensors for real-time sweat analysis and body motion capture based on stretchable fiber-based triboelectric nanogenerators (F-TENG). The F-TENG is made of stretchable conductive fiber (Ecoflex coating with polyaniline (PANI)) and varnished wires. Based on the coupling effect of triboelectric effect and enzymatic reaction (surface-triboelectric coupling effect), the wearable biosensors can not only precisely sense the motion states, but also detect glucose, creatinine and lactate acid in sweat in real-time. Importantly, the wearable devices can self-drive without any external power source and the response against glucose, creatinine and lactate acid can be up to 103%, 125% and 38%, respectively. On this basis, applications in biosensing and wireless communication have been demonstrated. This work exhibits a prospective potential application of F-TENG in IoT for diverse use.

Recent Advances in Wearable Optical Sensor Automation Powered by Battery versus Skin-like Battery-Free Devices for Personal Healthcare-A Review

Currently, old-style personal Medicare techniques rely mostly on traditional methods, such as cumbersome tools and complicated processes, which can be time consuming and inconvenient in some circumstances. Furthermore, such old methods need the use of heavy equipment, blood draws, and traditional bench-top testing procedures. Invasive ways of acquiring test samples can potentially cause patient discomfort and anguish. Wearable sensors, on the other hand, may be attached to numerous body areas to capture diverse biochemical and physiological characteristics as a developing analytical tool. Physical, chemical, and biological data transferred via the skin are used to monitor health in various circumstances. Wearable sensors can assess the aberrant conditions of the physical or chemical components of the human body in real time, exposing the body state in time, thanks to unintrusive sampling and high accuracy. Most commercially available wearable gadgets are mechanically hard components attached to bands and worn on the wrist, with form factors ultimately constrained by the size and weight of the batteries required for the power supply. Basic physiological signals comprise a lot of health-related data. The estimation of critical physiological characteristics, such as pulse inconstancy or variability using photoplethysmography (PPG) and oxygen saturation in arterial blood using pulse oximetry, is possible by utilizing an analysis of the pulsatile component of the bloodstream. Wearable gadgets with “skin-like” qualities are a new type of automation that is only starting to make its way out of research labs and into pre-commercial prototypes. Flexible skin-like sensing devices have accomplished several functionalities previously inaccessible for typical sensing devices due to their deformability, lightness, portability, and flexibility. In this paper, we studied the recent advancement in battery-powered wearable sensors established on optical phenomena and skin-like battery-free sensors, which brings a breakthrough in wearable sensing automation.

Silicon Micropillar Array-Based Wearable Sweat Glucose Sensor

Wearable technologies have great potential in health monitoring and disease diagnostics. As a consequence, interest in the study of wearable sensors has dramatically increased over recent years. Successful translation of this technology from research prototypes to commercial products requires addressing some of the major challenges faced by wearable sensors such as loss of, and damage in, the biological recognition layer of the skin-interfaced sensors. In this work, we propose a solution to this challenge by integrating micropillar array (MPA) surfaces as part of the sensing layer with the aim to protect and prevent the loss of the enzyme layer from mechanical stress while the sensor is worn. The proposed wearable sensing patch is composed of reference, counter, and working electrodes, all made of MPAs and is designed for measuring glucose in sweat. MPA sensing patch has a wide linear range of 50 μM to 1.4 mM, a sensitivity of 4.7 ± 0.8 μA mM^-1, and a limit of detection of 26 ± 5 μM. The glucose sensing patch was tested using human sweat where glucose-level changes were successfully measured before and after meal consumption. The developed patch provides an alternative solution to the problem of the damage to the sensor microenvironment upon wear. But in addition, it also offers a user-friendly, cost-effective, and reliable sweat analysis platform with significant potential in health monitoring applications.

Wearable Sweat Loss Measuring Devices: From the Role of Sweat Loss to Advanced Mechanisms and Designs

Wearable sweat sensors have received significant research interest and have become popular as sweat contains considerable health information about physiological and psychological states. However, measured biomarker concentrations vary with sweat rates, which has a significant effect on the accuracy and reliability of sweat biosensors. Wearable sweat loss measuring devices (SLMDs) have recently been proposed to overcome the limitations of biomarker tracking and reduce inter- and intraindividual variability. In addition, they offer substantial potential for monitoring human body homeostasis, because sweat loss plays an indispensable role in thermoregulation and skin hydration. Previous studies have not carried out a comprehensive and systematic review of the principles, importance, and development of wearable SLMDs. This paper reviews wearable SLMDs with a new health perspective from the role of sweat loss to advanced mechanisms and designs. Two types of sweat and their measurement significance for practical applications are highlighted. Then, a comprehensive review of advances in different wearable SLMDs based on hygrometers, absorbent materials, and microfluidics is presented by describing their respective device architectures, present situations, and future directions. Finally, concluding remarks on opportunities for future application fields and challenges for future sweat sensing are presented.

Smartphone-based photoelectrochemical biosensing system with graphitic carbon nitride/gold nanoparticles modified electrodes for matrix metalloproteinase-2 detection

Photoelectrochemical analysis has been widely used in the field of biosensing due to its high sensitivity and strong anti-interference ability. Herein, a portable and versatile smartphone-based photoelectrochemical biosensing platform was developed for the rapid and on-site biomedical analysis. In the system, light excitation and photocurrent measurements were accomplished by a miniaturized and integrated circuit board. Smartphone with a specifically designed application was utilized to wirelessly control the system via Bluetooth. For photoelectrochemical sensor, graphitic carbon nitride (g-C₃N₄) and gold nanoparticles loaded on indium tin oxide electrodes were utilized as photoactive materials and signal amplification elements, respectively. The gold nanoparticles were also used to immobilized matrix metalloproteinase-2 (MMP-2) specific cleavage peptide that modified with bovine serum albumin (BSA) on the terminal. In the presence of MMP-2, the peptide was specifically hydrolyzed and cleaved. Thus, parts of the peptide chain and BSA were detached from the electrode resulting in the decrease of steric hindrance and the increase of photoelectrochemical currents. The photocurrents changed linearly with the logarithm of MMP-2 concentrations ranging from 1 pg/mL to 100 ng/mL in both buffer and artificial serum with correlation coefficient of 0.9943 and 0.9698. The limit of detections were as low as 0.48 pg/mL in buffer and 0.55 pg/mL in artifical serum. It indicated that the biosensor has good linearity and high sensitivity, which also verified the effectiveness of the portable instrument. This system provides a pioneering solution for the development of miniaturized and portable photoelectrochemical analysis instruments used for the field monitoring of different analytes.

Ultra-Thin Chips With ISFET Array for Continuous Monitoring of Body Fluids Ph

This paper presents ISFET array based pH-sensing system-on-ultra-thin-chip (SoUTC) designed and fabricated in 350 nm CMOS technology. The SoUTC with the proposed current-mode active-pixel ISFET circuit array is desined to operate at 2 V and consumes 6.28 μW per-pixel. The presented SoUTC exhibits low sensitivity to process, voltage, temperature and strain-induced (PVTS) variations. The silicon area occupancy of each active-pixel is 44.9 × 33.5 µm² with an ion-sensing area of 576 µm². The design of presented ISFET device is analysed with finite element modeling in COMSOL Multiphysics using compact model parameters of MOSFET in 350 nm CMOS technology. Owing to thin (∼30 µm) Si-substrate the presented SoUTC can conform to curvilinear surfaces, allowing intimate contact necessary for reliable data for monitoring of analytes in body fluids such as sweat. Further, it can operate either in a rolling shutter fashion or in a pseudo-random pixel selection mode allowing the simultaneous detection of pH from different skin regions. Finally, the circuits have been tested in aqueous Dulbecco's Modified Eagle Medium (DMEM) culture media with 5-9 pH values, which mimics cellular environments, to demonstrate their potential use for continuous monitoring of body-fluids pH.

Wearable Electronic Tongue for Non-Invasive Assessment of Human Sweat

Sweat is a promising biofluid in allowing for non-invasive sampling. Here, we investigate the use of a voltammetric electronic tongue, combining different metal electrodes, for the purpose of non-invasive sample assessment, specifically focusing on sweat. A wearable electronic tongue is presented by incorporating metal electrodes on a flexible circuit board and used to non-invasively monitor sweat on the body. The data obtained from the measurements were treated by multivariate data processing. Using principal component analysis to analyze the data collected by the wearable electronic tongue enabled differentiation of sweat samples of different chemical composition, and when combined with ¹H-NMR sample differentiation could be attributed to changing analyte concentrations.