Wearable Platform for Real-time Monitoring of Sodium in Sweat

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

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

Diagnosing Cystic Fibrosis in the 21st Century-A Complex and Challenging Task

Cystic fibrosis (CF) is a chronic and potentially life-threatening condition, wherein timely diagnosis assumes paramount significance for the prompt initiation of therapeutic interventions, thereby ameliorating pulmonary function, addressing nutritional deficits, averting complications, mitigating morbidity, and ultimately enhancing the quality of life and extending longevity. This review aims to amalgamate existing knowledge to provide a comprehensive appraisal of contemporary diagnostic modalities pertinent to CF in the 21st century. Deliberations encompass discrete delineations of each diagnostic modality and the elucidation of potential diagnostic quandaries encountered in select instances, as well as the delineation of genotype-phenotype correlations germane to genetic counseling endeavors. The synthesis underscores that, notwithstanding the availability and strides in diagnostic methodologies, including genetic assays, the sweat test (ST) retains its position as the preeminent diagnostic standard for CF, serving as a robust surrogate for CFTR functionality. Prospective clinical investigations in the realm of CF should be orchestrated with the objective of discerning novel diagnostic modalities endowed with heightened specificity and sensitivity.

Endoscopic Endonasal Transsphenoidal Surgery for the Resection of Pituitary Adenomas: A Prime Candidate for a Shortened Length of Stay Enhanced Recovery after Surgery Protocol? A Systematic Review

BACKGROUND

Enhanced Recovery After Surgery (ERAS) is a perioperative model of care aimed at optimizing postoperative rehabilitation and reducing hospital length of stay (LOS). Decreasing LOS avoids hospital-acquired complications, reduces cost of care, and improves patient satisfaction. Given the lack of ERAS protocols for endoscopic endonasal transsphenoidal surgery (EETS) resection of pituitary adenomas, a systematic review of EETS was performed to compile patient outcomes and analyze factors that may lead to increased LOS, reoperation, and readmission rates with the intention to contribute to the development of a successful ERAS protocol for EETS.

METHODS

The authors performed a Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines-based systematic review of the literature. Information was extracted regarding patient LOS, surgery complications, and readmission/reoperation rates. Pearson's correlations to LOS and reoperation/readmission rates were performed with variables normalized to the number of participants. Statistical significance was set at P value <0.05.

RESULTS

Fourteen studies were included, consisting of 2083 patients. The most common complications were cerebrospinal fluid leaks (37%) and postoperative diabetes insipidus (DI) (9%). Transient DI was significantly correlated with shorter LOS. Functional pituitary adenomas were significantly correlated with lower readmission rates while nonfunctional pituitary adenomas were correlated with higher readmission rates. No other factor was found to be significantly correlated with a change in LOS or reoperation rate.

CONCLUSIONS

EETS may be an ideal candidate for the development of ERAS cranial protocols. While our data largely supports the safe implementation of shortened LOS protocols in EETS, our findings highlight the importance of transient DI and nonfunctional pituitary adenomas management when formulating ERAS protocols.

Measuring the Salt Content of Sweat inside a Sweat-Absorbing Skin Adhesive

Biofluids contain a wealth of different biomarkers, and their concentrations are indicative of the state of the body. As one of those biofluids, sweat is easily accessible, and its composition can, for example, be related to particular diseases or sports performance. Due to the relatively low sweat flow rates, however, adequate sampling is paramount. Here, we aim to explore the potential use of sweat-absorbing skin adhesives as a sweat sampling system for wearable sensors with a simple construction. Upon absorption of sweat, the electrochemical properties of the skin adhesive are determined by the composition of sweat and the amount of sweat within the skin adhesive (i.e., hydration). Through the incorporation of two polarizable electrodes within the skin adhesive, its electrical properties can be monitored using impedance spectroscopy. Here, the double layer capacitance is used as an indicator of hydration, while the conductance depends on both the ion concentration and hydration (the mobility of ions). By evaluating the conductance as a function of hydration, the ion concentration within an electrolyte solution can be estimated. We demonstrate the concept based on a simple model sensor patch, which is exposed to electrolyte solutions containing various concentrations of NaCl and an artificial sweat solution. Finally, we show that ion concentrations in human sweat can be estimated when the model sensor patch is worn during exercise.

Mill Scale-Derived Magnetite Nanoparticles: A Novel Substrate for Lactate Oxidase-Based Biosensors

Recycling and revalorization of waste are currently essential for sustainable growth. Mill scale, a waste product from steel production industries, which contains high levels of iron and minimal impurities, is proposed in this study as the source to synthesize magnetite nanoparticles (Fe3O4) for an enhancement of a lactate biosensor range. The synthesized Fe3O4 nanoparticles were coated with polydopamine (PDA) to prevent aggregation and degradation, creating a stable platform for immobilizing lactate oxidase enzyme (LOx) on their surfaces. The characterization of the Fe3O4@PDA material was carried out using transmission electron microscopy (TEM), dynamic light scattering (DLS), and measurement of the polydispersity index (PdI). The Fe3O4@PDA-LOx material was then deposited on a screen-printed carbon electrode modified with Prussian blue (SPCE-PB) for lactate detection. The biosensor exhibited a broad, dual linear concentration-response range, one from 0.1 to 4.62 mM with a limit of detection of 0.32 mM and sensitivity of 1.54 μAmM-1cm-2, and another one from 4.62 to 149.21 mM with a limit of detection of 6.31 mM and sensitivity of 0.08 μAmM-1cm-2. The dual-range concentration response of the biosensor makes it an ideal tool for lactate determination in various applications, including sports medicine, clinical diagnosis, and industrial bioprocessing.

Microwave Devices for Wearable Sensors and IoT

The Internet of Things (IoT) paradigm is currently highly demanded in multiple scenarios and in particular plays an important role in solving medical-related challenges. RF and microwave technologies, coupled with wireless energy transfer, are interesting candidates because of their inherent contactless spectrometric capabilities and for the wireless transmission of sensing data. This article reviews some recent achievements in the field of wearable sensors, highlighting the benefits that these solutions introduce in operative contexts, such as indoor localization and microwave sensing. Wireless power transfer is an essential requirement to be fulfilled to allow these sensors to be not only wearable but also compact and lightweight while avoiding bulky batteries. Flexible materials and 3D printing polymers, as well as daily garments, are widely exploited within the presented solutions, allowing comfort and wearability without renouncing the robustness and reliability of the built-in wearable sensor.

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.

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 Review of Recent Advances in Vital Signals Monitoring of Sports and Health via Flexible Wearable Sensors

In recent years, vital signals monitoring in sports and health have been considered the research focus in the field of wearable sensing technologies. Typical signals include bioelectrical signals, biophysical signals, and biochemical signals, which have applications in the fields of athletic training, medical diagnosis and prevention, and rehabilitation. In particular, since the COVID-19 pandemic, there has been a dramatic increase in real-time interest in personal health. This has created an urgent need for flexible, wearable, portable, and real-time monitoring sensors to remotely monitor these signals in response to health management. To this end, the paper reviews recent advances in flexible wearable sensors for monitoring vital signals in sports and health. More precisely, emerging wearable devices and systems for health and exercise-related vital signals (e.g., ECG, EEG, EMG, inertia, body movements, heart rate, blood, sweat, and interstitial fluid) are reviewed first. Then, the paper creatively presents multidimensional and multimodal wearable sensors and systems. The paper also summarizes the current challenges and limitations and future directions of wearable sensors for vital typical signal detection. Through the review, the paper finds that these signals can be effectively monitored and used for health management (e.g., disease prediction) thanks to advanced manufacturing, flexible electronics, IoT, and artificial intelligence algorithms; however, wearable sensors and systems with multidimensional and multimodal are more compliant.

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.

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.

Development of a textile based protein sensor for monitoring the healing progress of a wound

This article focuses on the design and fabrication of flexible textile-based protein sensors to be embedded in wound dressings. Chronic wounds require continuous monitoring to prevent further complications and to determine the best course of treatment in the case of infection. As proteins are essential for the progression of wound healing, they can be used as an indicator of wound status. Through measuring protein concentrations, the sensor can assess and monitor the wound condition continuously as a function of time. The protein sensor consists of electrodes that are directly screen printed using both silver and carbon composite inks on polyester nonwoven fabric which was deliberately selected as this is one of the common backing fabric types currently used in wound dressings. These sensors were experimentally evaluated and compared to each other by using albumin protein solution of pH 7. A comprehensive set of cyclic voltammetry measurements was used to determine the optimal sensor design the measurement of protein in solution. As a result, the best sensor design is comprised of silver conductive tracks but a carbon layer as the working and counter electrodes at the interface zone. This design prevents the formation of silver dioxide and protects the sensor from rapid decay, which allows for the recording of consecutive measurements using the same sensor. The chosen printed protein sensor was able to detect bovine serum albumin at concentrations ranging from 30 to 0.3 mg/mL with a sensitivity of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$0.0026 \mu $$\end{document}0.0026μA/M. Further testing was performed to assess the sensor’s ability to identify BSA from other interferential substances usually present in wound fluids and the results show that it can be distinguishable.

Lab on a body for biomedical electrochemical sensing applications: The next generation of microfluidic devices

This chapter highlights applications of microfluidic devices toward on-body biosensors. The emerging application of microfluidics to on-body bioanalysis is a new strategy to establish systems for the continuous, real-time, and on-site determination of informative markers present in biofluids, such as sweat, interstitial fluid, blood, saliva, and tear. Electrochemical sensors are attractive to integrate with such microfluidics due to the possibility to be miniaturized. Moreover, on-body microfluidics coupled with bioelectronics enable smart integration with modern information and communication technology. This chapter discusses requirements and several challenges when developing on-body microfluidics such as difficulties in manipulating small sample volumes while maintaining mechanical flexibility, power-consumption efficiency, and simplicity of total automated systems. We describe key components, e.g., microchannels, microvalves, and electrochemical detectors, used in microfluidics. We also introduce representatives of advanced lab-on-a-body microfluidics combined with electrochemical sensors for biomedical applications. The chapter ends with a discussion of the potential trends of research in this field and opportunities. On-body microfluidics as modern total analysis devices will continue to bring several fascinating opportunities to the field of biomedical and translational research applications.

Wearable Potentiometric Sensor Based on Na0.44MnO2 for Non-invasive Monitoring of Sodium Ions in Sweat

Here, we present a wearable potentiometric ion sensor for real-time monitoring of sodium ions (Na⁺) in human sweat samples using Na_0.44MnO₂ as the sensing material. Na_0.44MnO₂ is an attractive material for developing wearable electrochemical sensors due to its good Na⁺ incorporation ability, electrical conductivity, stability, and low fabrication cost. In the first step, the analytical performance of the electrode prepared using Na_0.44MnO₂ is presented. Then, a miniaturized potentiometric cell integrated into a wearable substrate is developed, which reveals a Nernstian response (58 mV dec^-1). We achieved the detection of Na⁺ in the linear ranges of 0.21-24.54 mmol L^-1, which is well within the physiological range of Na⁺. Finally, for on-body sweat analysis, the potentiometric sensor is fully integrated into a headband textile. This platform can be employed for non-invasive analysis of Na⁺ in human sweat for healthcare and disease diagnosis.

Solid-Contact Potentiometric Cell with Symmetry

By its nature, a traditional potentiometric cell composed of an Ag/AgCl-based reference electrode and a solid-contact indicating electrode is not symmetric. This results in undesirable potential drifts in response to a common perturbation such as a temperature change of the sample. We propose here an approach to restore symmetry by constructing a cell with two identical solid-contact ISEs used as reference and indicating electrodes. In this arrangement, the reference electrode is immersed in a compartment containing a constant background of an ion of interest, while the indicating electrode is directly immersed in the sample solution. This approach was successfully demonstrated for a cell composed of nitrate-selective electrodes with the hydrophobic derivative of poly(3,4-ethylenedioxythiophene) as a transducer layer. In particular, the symmetric setup is shown to lower by 4-5 times the observed potential drift resulting from temperature changes between +25 and +5 °C.

A critical review on the use of potentiometric based biosensors for biomarkers detection

Potentiometric-based biosensors have the potential to advance the detection of several biological compounds and help in early diagnosis of various diseases. They belong to the portable analytical class of biosensors for monitoring biomarkers in the human body. They contain ion-sensitive membranes sensors can be used to determine potassium, sodium, and chloride ions activity while being used as a biomarker to gauge human health. The potentiometric based ion-sensitive membrane systems can be coupled with various techniques to create a sensitive tool for the fast and early detection of cancer biomarkers and other critical biological compounds. This paper discusses the application of potentiometric-based biosensors and classifies them into four major categories: photoelectrochemical potentiometric biomarkers, potentiometric biosensors amplified with molecular imprinted polymer systems, wearable potentiometric biomarkers and light-addressable potentiometric biosensors. This review demonstrated the development of several innovative biosensor-based techniques that could potentially provide reliable tools to test biomarkers. Some challenges however remain, but these can be removed by coupling techniques to maximize the testing sensitivity.

Soft, skin-interfaced sweat stickers for cystic fibrosis diagnosis and management

The concentration of chloride in sweat remains the most robust biomarker for confirmatory diagnosis of cystic fibrosis (CF), a common life-shortening genetic disorder. Early diagnosis via quantitative assessment of sweat chloride allows prompt initiation of care and is critically important to extend life expectancy and improve quality of life. The collection and analysis of sweat using conventional wrist-strapped devices and iontophoresis can be cumbersome, particularly for infants with fragile skin, who often have insufficient sweat production. Here, we introduce a soft, epidermal microfluidic device ("sweat sticker") designed for the simple and rapid collection and analysis of sweat. Intimate, conformal coupling with the skin supports nearly perfect efficiency in sweat collection without leakage. Real-time image analysis of chloride reagents allows for quantitative assessment of chloride concentrations using a smartphone camera, without requiring extraction of sweat or external analysis. Clinical validation studies involving patients with CF and healthy subjects, across a spectrum of age groups, support clinical equivalence compared to existing device platforms in terms of accuracy and demonstrate meaningful reductions in rates of leakage. The wearable microfluidic technologies and smartphone-based analytics reported here establish the foundation for diagnosis of CF outside of clinical settings.

Highly Concentrated, Conductive, Defect-free Graphene Ink for Screen-Printed Sensor Application

Ultrathin and defect-free graphene ink is prepared through a high-throughput fluid dynamics process, resulting in a high exfoliation yield (53.5%) and a high concentration (47.5 mg mL^-1). A screen-printed graphene conductor exhibits a high electrical conductivity of 1.49 × 10⁴ S m^-1 and good mechanical flexibility. An electrochemical sodium ion sensor based on graphene ink exhibits an excellent potentiometric sensing performance in a mechanically bent state. Real-time monitoring of sodium ion concentration in sweat is demonstrated. Conductive inks based on graphene materials have received significant attention for the fabrication of a wide range of printed and flexible devices. However, the application of graphene fillers is limited by their restricted mass production and the low concentration of their suspensions. In this study, a highly concentrated and conductive ink based on defect-free graphene was developed by a scalable fluid dynamics process. A high shear exfoliation and mixing process enabled the production of graphene at a high concentration of 47.5 mg mL^-1 for graphene ink. The screen-printed graphene conductor exhibits a high electrical conductivity of 1.49 × 10⁴ S m^-1 and maintains high conductivity under mechanical bending, compressing, and fatigue tests. Based on the as-prepared graphene ink, a printed electrochemical sodium ion (Na⁺) sensor that shows high potentiometric sensing performance was fabricated. Further, by integrating a wireless electronic module, a prototype Na⁺-sensing watch is demonstrated for the real-time monitoring of the sodium ion concentration in human sweat during the indoor exercise of a volunteer. The scalable and efficient procedure for the preparation of graphene ink presented in this work is very promising for the low-cost, reproducible, and large-scale printing of flexible and wearable electronic devices.

Highly Stretchable Fiber-Based Potentiometric Ion Sensors for Multichannel Real-Time Analysis of Human Sweat

Wearable potentiometric ion sensors are attracting attention for real-time ion monitoring in biological fluids. One of the key challenges lies in keeping the analytical performances under a stretchable state. Herein, we report a highly stretchable fiber-based ion-selective electrode (ISE) prepared by coating an ion-selective membrane (ISM) on a stretchable gold fiber electrode. The fiber ISE ensures high stretchability up to 200% strain with only 2.1% increase in resistance of the fiber electrode. Owing to a strong attachment between the ISM and gold fiber electrode substrate, the ISE discloses favorable stability and potential repeatability. The Nernst slope of the ion response fluctuates from 59.2 to 57.4 mV/dec between 0 and 200% strain. Minor fluctuation of the intercept (E⁰) (±4.97 mV) also results. The ISE can endure 1000 cycles at the maximum stretch. Sodium, chloride, and pH fiber sensors were fabricated and integrated into a hairband for real-time analysis of human sweat. The result displays a high accuracy compared with ex situ analysis. The integrated sensors were calibrated before and just after on-body measurements, and they offer reliable results for sweat analysis.

Microfluidics by Additive Manufacturing for Wearable Biosensors: A Review

Wearable devices are nowadays at the edge-front in both academic research as well as in industry, and several wearable devices have been already introduced in the market. One of the most recent advancements in wearable technologies for biosensing is in the area of the remote monitoring of human health by detection on-the-skin. However, almost all the wearable devices present in the market nowadays are still providing information not related to human ‘metabolites and/or disease’ biomarkers, excluding the well-known case of the continuous monitoring of glucose in diabetic patients. Moreover, even in this last case, the glycaemic level is acquired under-the-skin and not on-the-skin. On the other hand, it has been proven that human sweat is very rich in molecules and other biomarkers (e.g., ions), which makes sweat a quite interesting human liquid with regards to gathering medical information at the molecular level in a totally non-invasive manner. Of course, a proper collection of sweat as it is emerging on top of the skin is required to correctly convey such liquid to the molecular biosensors on board of the wearable system. Microfluidic systems have efficiently come to the aid of wearable sensors, in this case. These devices were originally built using methods such as photolithographic and chemical etching techniques with rigid materials. Nowadays, fabrication methods of microfluidic systems are moving towards three-dimensional (3D) printing methods. These methods overcome some of the limitations of the previous method, including expensiveness and non-flexibility. The 3D printing methods have a high speed and according to the application, can control the textures and mechanical properties of an object by using multiple materials in a cheaper way. Therefore, the aim of this paper is to review all the most recent advancements in the methods for 3D printing to fabricate wearable fluidics and provide a critical frame for the future developments of a wearable device for the remote monitoring of the human metabolism directly on-the-skin.

A wearable sensor for the detection of sodium and potassium in human sweat during exercise

The SwEatch platform, a wearable sensor for sampling and measuring the concentration of electrolytes in human sweat in real time, has been improved in order to allow the sensing of two analytes. The solid contact ion-sensitive electrodes (ISEs) for the detection of Na⁺ and K⁺ have been developed in two alternative formulations, containing either poly(3,4-ethylenedioxythiophene) (PEDOT) or poly(3-octylthiophene-2,5-diyl) (POT) as a conductive polymer transducing component. The solution-processable POT formulation simplifies the fabrication process, and sensor to sensor reproducibility has been improved via partial automation using an Opentron® automated pipetting robot. The resulting electrodes showed good sensitivity (52.4 ± 6.3 mV/decade (PEDOT) and 56.4 ± 2.2 mV/decade (POT) for Na⁺ ISEs, and 45.7 ± 7.4 mV/decade (PEDOT) and 54.3 ± 1.5 mV/decade (POT) for K⁺) and excellent selectivity towards potential interferents present in human sweat (H⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺). The 3D printed SwEatch platform has been redesigned to incorporate a double, mirrored fluidic unit which is capable of drawing sweat from the skin through passive capillary action and bring it in contact with two independent electrodes. The potentiometric signal generated by the electrodes is measured by an integrated electronics board, digitised and transmitted via Bluetooth to a laptop. The results obtained from on-body trials on athletes during cycling show a relatively small increase in sodium (1.89 mM-2.97 mM) and potassium (3.31 mM-7.25 mM) concentrations during the exercise period of up to 90 min.

Advanced Wearable Microfluidic Sensors for Healthcare Monitoring

Wearable flexible sensors based on integrated microfluidic networks with multiplex analysis capability are emerging as a new paradigm to assess human health status and show great potential in application fields such as clinical medicine and athletic monitoring. Well-designed microfluidic sensors can be attached to the skin surface to acquire various pieces of physiological information with high precision, such as sweat loss, information regarding metabolites, and electrolyte balance. Herein, the recent progress of wearable microfluidic sensors for applications in healthcare monitoring is summarized, including analysis principles and microfabrication methods. Finally, the challenges and opportunities for wearable microfluidic sensors in practical applications are discussed.

Introducing "Insertive Stripping Voltammetry": Electrochemical Determination of Sodium Ions Using an Iron(III) Phosphate-Modified Electrode

A new type of stripping voltammetry is introduced, in which the preconcentration step includes ion insertion into a solid phase followed by a quantification step in which the ion is expelled via linear sweep voltammetry. Specifically, sodium-ion concentrations in both aqueous solution and synthetic sweat are electrochemically determined using iron(III) phosphate-modified glassy carbon electrodes. The electrochemical method consists of a potentiostatic step, holding the potential of -0.5 V vs saturated calomel electrode (SCE) for 100 s, followed by linear sweep voltammetry. It is shown that a thermal and mechanical pretreatment at 800 °C and with a ball mill, respectively, improve the electrochemical response of the iron(III) phosphate toward Na⁺. The involved structural and morphological changes were assessed by thermogravimetric analysis, scanning electron microscopy, and powder X-ray diffraction. The sensor exhibits a good selectivity toward Li⁺ and K⁺ and shows a linear response between 0.025 and 0.2 M Na⁺. As a proof-of-principle, the sensor was used to determine the sodium level in synthetic sweat.

Recent advances in solid-contact ion-selective electrodes: functional materials, transduction mechanisms, and development trends

This article presents a comprehensive overview of recent progress in the design and applications of solid-contact ion-selective electrodes (SC-ISEs).

Integrated textile sensor patch for real-time and multiplex sweat analysis

Wearable sweat analysis devices for monitoring of multiple health-related biomarkers with high sensitivity are highly desired for noninvasive and real-time monitoring of human health. Here, we report a flexible sweat analysis patch based on a silk fabric-derived carbon textile for simultaneous detection of six health-related biomarkers. The intrinsically N-doped graphitic structure and the hierarchical woven, porous structure provided the carbon textile good electrical conductivity, rich active sites, and good water wettability for efficient electron transmission and abundant access to reactants, enabling it to serve as an excellent working electrode in electrochemical sensors. On the basis of the above, we fabricated a multiplex sweat analysis patch that is capable of simultaneous detection of glucose, lactate, ascorbic acid, uric acid, Na⁺, and K⁺. The integration of selective detectors with signal collection and transmission components in this device has enabled us to realize real-time analysis of sweat.

A Fully Integrated and Self-Powered Smartwatch for Continuous Sweat Glucose Monitoring

Wearable devices for health monitoring and fitness management have foreseen a rapidly expanding market, especially those for noninvasive and continuous measurements with real-time display that provide practical convenience and eliminated safety/infection risks. Herein, a self-powered and fully integrated smartwatch that consists of flexible photovoltaic cells and rechargeable batteries in the forms of a "watch strap", electrochemical glucose sensors, customized circuits, and display units integrated into a "dial" platform is successfully fabricated for real-time and continuous monitoring of sweat glucose levels. The functionality of the smartwatch, including sweat glucose sensing, signal processing, and display, can be supported with the harvested/converted solar energy without external charging devices. The Zn-MnO₂ batteries serve as intermediate energy storage units and the utilization of aqueous electrolytes eliminated safety concerns for batteries, which is critical for wearable devices. Such a wearable system in a smartwatch fashion realizes integration of energy modules with self-powered capability, electrochemical sensors for noninvasive glucose monitoring, and in situ and real-time signal processing/display in a single platform for the first time. The as-fabricated fully integrated and self-powered smartwatch also provides a promising protocol for statistical study and clinical investigation to reveal correlations between sweat compositions and human body dynamics.

Skin-Mountable Biosensors and Therapeutics: A Review

Miniaturization of electronic components and advances in flexible and stretchable materials have stimulated the development of wearable health care systems that can reflect and monitor personal health status by health care professionals. New skin-mountable devices that offer seamless contact onto the human skin, even under large deformations by natural motions of the wearer, provide a route for both high-fidelity monitoring and patient-controlled therapy. This article provides an overview of several important aspects of skin-mountable devices and their applications in many medical settings and clinical practices. We comprehensively describe various transdermal sensors and therapeutic systems that are capable of detecting physical, electrophysiological, and electrochemical responses and/or providing electrical and thermal therapies and drug delivery services, and we discuss the current challenges, opportunities, and future perspectives in the field. Finally, we present ways to protect the embedded electronic components of skin-mountable devices from the environment by use of mechanically soft packaging materials.

Exercise intensity effects on total sweat electrolyte losses and regional vs. whole-body sweat [Na+], [Cl-], and [K+]

Purpose

To quantify total sweat electrolyte losses at two relative exercise intensities and determine the effect of workload on the relation between regional (REG) and whole body (WB) sweat electrolyte concentrations.

Methods

Eleven recreational athletes (7 men, 4 women; 71.5 ± 8.4 kg) completed two randomized trials cycling (30 °C, 44% rh) for 90 min at 45% (LOW) and 65% (MOD) of VO_2max in a plastic isolation chamber to determine WB sweat [Na⁺] and [Cl⁻] using the washdown technique. REG sweat [Na⁺] and [Cl⁻] were measured at 11 REG sites using absorbent patches. Total sweat electrolyte losses were the product of WB sweat loss (WBSL) and WB sweat electrolyte concentrations.

Results

WBSL (0.86 ± 0.15 vs. 1.27 ± 0.24 L), WB sweat [Na⁺] (32.6 ± 14.3 vs. 52.7 ± 14.6 mmol/L), WB sweat [Cl⁻] (29.8 ± 13.6 vs. 52.5 ± 15.6 mmol/L), total sweat Na⁺ loss (659 ± 340 vs. 1565 ± 590 mg), and total sweat Cl⁻ loss (931 ± 494 vs. 2378 ± 853 mg) increased significantly (p < 0.05) from LOW to MOD. REG sweat [Na⁺] and [Cl⁻] increased from LOW to MOD at all sites except thigh and calf. Intensity had a significant effect on the regression model predicting WB from REG at the ventral wrist, lower back, thigh, and calf for sweat [Na⁺] and [Cl⁻].

Conclusion

Total sweat Na⁺ and Cl⁻ losses increased by ~ 150% with increased exercise intensity. Regression equations can be used to predict WB sweat [Na⁺] and [Cl⁻] from some REG sites (e.g., dorsal forearm) irrespective of intensity (between 45 and 65% VO_2max), but other sites (especially ventral wrist, lower back, thigh, and calf) require separate prediction equations accounting for workload.