Sweat Ion Research Articles

Multifunctional Siloxene-Decorated Laser-Inscribed Graphene Patch for Sweat Ion Analysis and Electrocardiogram Monitoring.

Potentiometric detection in complex biological fluids enables continuous electrolyte monitoring for personal healthcare; however, the commercialization of ion-selective electrode-based devices has been limited by the rapid loss of potential stability caused by electrode surface inactivation and biofouling. Here, we describe a simple multifunctional hybrid patch incorporating an Au nanoparticle/siloxene-based solid contact (SC) supported by a substrate made of laser-inscribed graphene on poly(dimethylsiloxane) for the noninvasive detection of sweat Na+ and K+. These SC nanocomposites prevent the formation of a water layer during ion-to-electron transfer, preserving 3 and 5 μV/h potential drift for the Na+ and K+ ion-selective electrodes, respectively, after 13 h of exposure. The lamellar structure of the siloxene sheets increases the SC area. In addition, the electroplated Au nanoparticles, which have a large surface area and excellent conductivity, further increased the electric double-layer capacitance at the interface between the ion-selective membranes and solid-state contacts, thus facilitating ion-to-electron transduction and ultimately improving the detection stability of Na+ and K+. Furthermore, the integrated temperature and electrocardiogram sensors in the flexible patch assist in monitoring body temperature and electrocardiogram signals, respectively. Featuring both electrochemical ion-selective and physical sensors, this patch offers immense potential for the self-monitoring of health.

Large-scale fully printed “Lego Bricks” type wearable sweat sensor for physical activity monitoring

Wearable sweat sensors are becoming increasingly popular for their robust capabilities in non-invasive, dynamic, and continuous real-time monitoring of biological information. Real-time monitoring of large-scale samples is crucial for realizing intelligent health. A major bottleneck for enabling large-scale sweat elucidation is the fabrication of wearable sensors equipped with microfluidic devices and flexible electrodes in a cost-effective, homogeneous performance and rapid large-scale way. Herein, a “Screen+Wax”-printing technique was introduced to prepare these components and construct “Lego Bricks” type wearable sweat sensor sensor to monitor sweat Na+ and K+. Flexible electrode arrays and paper-based microfluidic layers (they act as building blocks) were fabricated on polyethylene terephthalate and paper surfaces, respectively, using screen printing and wax printing. Gold nanoparticles and Na+/K+ ion-selective membranes were modified on the electrode surfaces by electrodeposition and drop coating, respectively. In this work, we highlight the excellent performance of the “Lego Bricks” type wearable sweat sensor in testing the Na+ and K+ imbalance of sweat from different body regions during exercise and, more significantly, to track the physical activity during prolonged exercise under different interventions. Furthermore, the prepared “Lego Bricks” wearable sweat ion electrochemical sensor is demonstrated to be capable of large-scale samples elucidation with outstanding performance and cost-effectiveness, which is expected to deeply integrate sweat monitoring into physical activity, providing an important tool for intelligent health.

Wearable Ion Sensors for the Detection of Sweat Ions Fabricated by Heat-Transfer Printing.

Wearable ion sensors for the real-time monitoring of sweat biomarkers have recently attracted increasing research attention. Here, we fabricated a novel chloride ion sensor for real-time sweat monitoring. The printed sensor was heat-transferred onto nonwoven cloth, allowing for easy attachment to various types of clothing, including simple garments. Additionally, the cloth prevents contact between the skin and the sensor and acts as a flow path. The change in the electromotive force of the chloride ion sensor was -59.5 mTV/log CCl-. In addition, the sensor showed a good linear relationship with the concentration range of chloride ions in human sweat. Moreover, the sensor displayed a Nernst response, confirming no changes in the film composition due to heat transfer. Finally, the fabricated ion sensors were applied to the skin of a human volunteer subjected to an exercise test. In addition, a wireless transmitter was combined with the sensor to wirelessly monitor ions in sweat. The sensors showed significant responses to both sweat perspiration and exercise intensity. Thus, our research demonstrates the potential of using wearable ion sensors for the real-time monitoring of sweat biomarkers, which could significantly impact the development of personalized healthcare.

MoS2‐Polyaniline Based Flexible Electrochemical Biosensor: Toward pH Monitoring in Human Sweat

AbstractWearable pH sensors for sweat analysis have garnered significant scientific attention for the detection of early signs of many physiological diseases. In this study, a MoS2‐polyaniline (PANI) modified screen‐printed carbon electrode (SPCE) is fabricated and used as a sweat biosensor. The exfoliated MoS2 nanosheets are drop casted over an SPCE and are functionalized by a conducting polymer, polyaniline (PANI) via the electropolymerization technique. The as‐fabricated biosensor exhibits high super‐Nernstian sensitivity of −70.4 ± 1.7 mV pH−1 in the linear range of pH 4 to 8 of 0.1 m standard phosphate buffer solution (PBS), with outstanding reproducibility. The sensor exhibits excellent selectivity against the common sweat ions including Na+, Cl−, K+, and NH4+ with tremendous long‐term stability over 180 min from pH 4 to 6. The enhanced active surface area and better electrical conductivity as a consequence of the synergistic effect between MoS2 and PANI are correlated with the boosted performance of the as‐produced biosensor. The feasibility of the sensor is further examined using an artificial sweat specimen and the successful detection confirms the potential of the biosensor for a real‐time noninvasive, skin attachable, and flexible wearable pH sensor.

Finite Element Analysis Model of Electronic Skin Based on Surface Acoustic Wave Sensor.

In recent years, with the rapid development of flexible electronic devices, researchers have a great interest in the research of electronic skin (e-skin). Traditional e-skin, which is made of rigid integrated circuit chips, not only limits the overall flexibility, but also consumes a lot of power and poses certain security risks to the human body. In this paper, a wireless passive e-skin is designed based on the surface acoustic wave sensor (SAWS) of lithium niobate piezoelectric film. The e-skin has the advantages of small size, high precision, low power consumption, and good flexibility. With the multi-sensing function of stress, temperature, and sweat ion concentration, etc., the newly designed e-skin is a sensor platform for a wide range of external stimuli, and the measurement results can be directly presented in frequency. In order to explore the characteristic parameters and various application scenarios of the SAWS, finite element analysis is carried out using the simulation software; the relationship between the SAWS and various influencing factors is explored, and the related performance curve is obtained. These simulation results provide important reference and experimental guidance for the design and preparation of SAW e-skin.

Coulometric Response of H+‐Selective Solid‐Contact Ion‐Selective Electrodes and Its Application in Flexible Sensors†

Comprehensive SummaryThe analytical performance of H+‐selective solid‐contact ion‐selective electrodes (SCISEs) based on solid contact polyaniline doped with chloride (PANI(Cl)) and poly(3,4‐ethylenedioxythiophene) doped with poly(styrene sulfonate) (PEDOT(PSS)) was characterized by a developed coulometric signal transduction method. PEDOT(PSS) solid contact is covered by PVC based H+‐selective membrane. The obtained coulometric signal demonstrates that the cumulated charge can be amplified by increasing the capacitance of solid contact. SCISEs covered with spin‐coated membrane behave faster amperometric response than electrodes with drop‐cast membrane. In contrast to earlier works, the amperometric response and impedance spectrum demonstrates H+ transfer through SCISEs is independent from the thickness of membrane. The exceptional behavior of PANI(Cl) H+‐SCISEs shows that the capacitance estimated from impedance spectrum at low frequency 10 mHz and coulometric signal of PANI(Cl) based SCISEs is influenced by the applied potentials, whereas PEDOT(PSS) solid contact is independent from the chosen applied potentials. Furthermore, preliminary investigations of coulometric signal transduction on flexible pH sensor implies its potential applications in wearable sensors for sweat ion concentration detection.

Validation of the Application of Solid Contact Ion-Selective Electrode for Off-Body Sweat Ion Monitoring.

The solid contact ion-selective electrode (ISE) is a promising skin-interfaced monitoring system for sweat ions. Despite a growing number of on-body usages of ISE with fancy new materials and device fabrications, there are very few reports attempting to validate ISE results with a gold standard technique. For this purpose, this work uses inductively coupled plasma-optical emission spectrometry (ICP-OES) as a reference technique to conduct a direct evaluation of the sweat sodium and potassium ion levels obtained by ISE in an off-body approach. Eight healthy male subjects were recruited to collect exercise-induced sweat. It was found that sweat sodium and potassium ions present a rather wide concentration range. The sweat sodium concentration did not vary greatly in an exercise period of half an hour, while the sweat potassium concentration typically decreased with exercise. Mineral drink intake had no clear impact on the sweat sodium level, but increased the sweat potassium level. A paired t-test and mean absolute relative difference (MARD) analysis, a method typically used for evaluating the performance of glucometers, was employed to compare the results of ISE and ICP-OES. The statistical analysis validated the feasibility of ISE for measuring sweat ions, although better accuracy is required. Our data suggests that overweight subjects are likely to possess a higher sweat sodium level.

Wearable Microfluidic Sensor for the Simultaneous and Continuous Monitoring of Local Sweat Rates and Electrolyte Concentrations.

Temperature elevation due to global warming increases the risks of dehydration, which can induce heat-related illness. Proper rehydration with appropriate amounts of water and electrolytes is essential to aid body fluid homeostasis. Wearable sweat sensors which can monitor both the sweat rate and sweat electrolyte concentration may be an effective tool for determining appropriate rehydration. Here, we developed a novel potentially wearable sensor that can monitor both the local sweat rate and sweat electrolyte concentration continuously. The new device includes a system with a short microfluidic pathway that guides the sweat appearing on the skin to a small space in the device to form a quantifiable droplet. The sweat rate is assessed from the time for the droplet to appear and droplet volume, while an integrated electric sensor detects the sodium chloride concentration in each sweat droplet. We demonstrated that this new device could record both the flow rates of artificial sweat and its sodium chloride concentration in ranges of human sweating with an accuracy within ±10%. This is equivalent to the accuracy of commercially available sweat rate meters and sweat ion sensors. The present study provides a new perspective for the design of wearable sensors that can continuously monitor sweat rates and sweat electrolyte concentrations for potential application to a healthcare device.

Fabrication of laser-induced graphene-based multifunctional sensing platform for sweat ion and human motion monitoring

Human sweat monitoring, which unlike blood monitoring can be easily performed on the skin, can provide valuable personal healthcare data, as well as being suitable for use in diagnosis of disease and other conditions. However, despite the tremendous interest in sweat sensing, the development of low-cost, high-efficiency, multi-biometric sensing-capable platforms is still required for the large-scale utilization of wearable biosensors for extensive monitoring with other physiological signals. Here, we propose a wearable multifunctional LIG-based sensor, complete with Arduino-based readout electronics, which simultaneously monitors concentrations of sodium and potassium ions in human sweat as well as strain generated by vital signals (human motion). Our elastomer substrates were fabricated according to the weight of polydimethylsiloxane (PDMS) and lignin. A wearable multifunctional sensor was developed via the formation of laser-induced graphene (LIG) on PDMS/lignin composite substrates using Laser Direct writing (LDW); PDMS/Lignin transforms into the porous structure after laser irradiation. The fabricated sodium and potassium ion-selective electrodes (ISE), and Ag/AgCl electrode on PDMS/lignin composite were used to measure the potential difference at various different concentrations of both Na+(10−1–10−7) and K+ ions (10−1–10−8), and our sensor showed high sensitivity values of 63.6 mV/dec (Na+, n = 6) and 59.2 mV/dec (K+, n = 7), respectively; these results almost completely follow Nernstian behavior (which predicts values of R2 =0.99988 and 0.99855, respectively) and indicate cyclic stability (5000 cycles, Gauge Factor of ~20). This simple fabrication of a multifunctional and cost-effective sensor platform indicates real-time changes of sodium and potassium ions in sweat and strain generated by human body motion.

Pre-loading large volume oral electrolytes: tracing fluid and ion fluxes in horses during rest, exercise and recovery.

Exercise results in rapid and large extracellular to intracellular fluid shifts, as well as significant sweating losses of water and ions. It is unknown whether ions within oral electrolyte supplements are taken up by muscle (and other soft tissues) and whether oral supplementation can effectively offset sweating losses. Pre-loading with 8L of a balanced hypotonic electrolyte supplement attenuated extracellular fluid losses, increased exercise duration and increased sweating fluid and ion losses during submaximal exercise. Supplemented electrolytes appear in skeletal muscle within 1h after administration. Electrolyte supplementation increased exercise performance, improved maintenance of extracellular fluid volumes, and attenuated body fluid losses while maintaining sweating rates. This study used radioactive sodium (24 Na) and potassium (42 K) in a balanced, hypotonic electrolyte supplement to trace their appearance in skeletal muscle, and also quantified extracellular and whole-body fluid and ion changes during electrolyte supplementation, exercise and recovery. In a randomized crossover design, 1h after administration of 1 to 3L of water or electrolyte supplement with 24 Na, horses were exercised at 35% VO2max to voluntary fatigue or, after administration of 8L of water or electrolyte supplement with 42 K were exercised at 50% peak VO2 for 45 min (n = 4 in each trial). Pre-exercise electrolyte supplementation was associated with decreased loss of fluid and electrolytes from the extracellular fluid compartments during exercise and recovery compared with water alone. The improved fluid and ion balance during prolonged exercise was associated with increased exercise duration, despite continuing sweating losses of fluid and ions. Nasogastric administration of radiotracer 24 Na+ and 42 K+ showed rapid absorption into the blood with plasma levels peaking 45min after administration, followed by distribution into the extracellular space and intracellular fluid of muscle within 1h. Following exercise, virtually all Na+ remained within the extracellular compartment, while the majority of K+ underwent intracellular uptake by 2h of recovery. It is concluded that pre-loading with a large volume, balanced electrolyte supplement helps maintain whole-body fluid and ion balance and support muscle function during periods of prolonged sweat ion losses.

Role of sweat ion ratios in diagnosing cystic fibrosis.

Sweat chloride (Cl- ) concentration is the gold standard for diagnosing cystic fibrosis (CF). This is, however, challenging among patients with borderline values. Previous studies have reported that the sweat Cl- /Na+ ratio may be useful for diagnosing CF; however, little is known about Cl- /K+ and (Cl- + Na+ )/K+ ratios. This study aimed to retrospectively define the most appropriate outcome of the sweat test. Samples of sweat were collected using the Gibson and Cooke method. Cl- , Na+ , and K+ were further quantified in 2084 participants-1283 CF and 801 non-CF-based on clinical diagnosis. Among those with borderline sweat Cl- values (n = 502), 34.8% had CF. In the receiver operating characteristic curve analysis, the area under the curve was calculated to evaluate the diagnostic value of the ion ratios. In the overall population, all the ratios significantly discriminated CF from non-CF, whereas in the borderline group, only Cl- /Na+ significantly discriminated CF and non-CF subjects, regardless of age.

Rate normalization for sweat metabolomics biomarker discovery

As the demand for real-time exercise performance feedback increases, excreted sweat has become a biosource of interest for continuous human performance assessment. For sweat to truly fulfill this requirement, analyte concentrations must be normalized to adequately assess day-to-day differences within and among individuals. In this manuscript, data are presented highlighting the use of accurate localized sweat rate as a means for ion and global metabolomic data normalization. The results illustrate large sweat rate variability among individuals over the course of two distinct exercises protocols. Furthermore, the data show sweat rate is not symmetrical at similar locations among right and left forearms of individuals (p = 0.0007). Sweat ion conductivity analysis suggest overall sweat rate normalization reduces variability collectively among ion values and participants with principal component analysis showing 77.8% of variation in the data set attributable to sweat rate normalization. Global metabolomic analysis of sweat illustrated overall rate normalization increases the variability among test subjects with 72.7% of the variation explained by sweat rate normalization. Finally, overall rate normalized metabolomic features of sweat significantly correlated (ρ ≥ 0.7, ρ ≤ −0.7) with measured performance metrics of the individual, establishing the potential for sweat to be used as a biosource for performance monitoring. Collectively, these data illustrate the importance of accurate localized sweat rate determination, for analyte data normalization, in support for the use of sweat in biomarker discovery efforts to predict human performance.

The sweat glands' maximum ion reabsorption rates following heat acclimation in healthy older adults.

What is the central question to this study? Do the sweat glands' maximum ion reabsorption rates increase following heat acclimation in healthy older individuals and is this associated with elevated aldosterone concentrations? What is the main finding and its importance? Sweat gland maximum ion reabsorption rates improved heterogeneously across body sites, which occurred without any changes in aldosterone concentration following a controlled hyperthermic heat acclimation protocol in healthy older individuals. We examined whether the eccrine sweat glands' ion reabsorption rates improved following heat acclimation (HA) in older individuals. Ten healthy older adults (>65years) completed a controlled hyperthermic (+0.9°C rectal temperature, Tre ) HA protocol for nine non-consecutive days. Participants completed a passive heat stress test (lower leg 42°C water submersion) pre-HA and post-HA to assess physiological regulation of sweat gland ion reabsorption at the chest, forearm and thigh. The maximum ion reabsorption rate was defined as the inflection point in the slope of the relation between galvanic skin conductance and sweat rate (SR). We explored the responses again after a 7-day decay. During passive heating, the Tb thresholds for sweat onset on the chest and forearm were lowered after HA (P<0.05). However, sweat sensitivity (i.e. the slope), the SR at a given Tre and gross sweat loss did not improve after HA (P>0.05). Any changes observed were lost during the decay. Pilocarpine-induced sudomotor responses to iontophoresis did not change after HA (P≥0.801). Maximum ion reabsorption rate was only enhanced at the chest (P=0.001) despite unaltered aldosterone concentration after HA. The data suggest that this adaptation is lost after 7days' decay. The HA protocol employed in the present study induced partial adaptive sudomotor responses. Eccrine sweat gland ion reabsorption rates improved heterogeneously across the skin sites. It is likely that aldosterone secretion did not alter the chest sweat ion reabsorption rates observed in the older adults.

Medium-distance affordable, flexible and wireless epidermal sensor for pH monitoring in sweat

In the last decade, wearable sensors have gained a key role on biomedical research field for reliable health state monitoring. A wide plethora of physics marker sensors is already commercially available, including activity tracker, heart rate devices, and fitness smartwatch. On the contrary, wearable and epidermal sensors for chemical biomarker monitoring in several biofluids are not ready yet. Herein, we report a wireless and flexible epidermal device for pH monitoring in sweat, fabricated by encompassing a screen-printed potentiometric sensor, an integrated circuit, and antenna embedded onto the same Kapton substrate. An iridium oxide film was electrodeposited onto the graphite working electrode providing the pH sensitive layer, while the integrated circuit board allows for data acquisition and storing. Furthermore, a radio frequency identification antenna surrounding the entire system enables data transmission to an external reader up to nearly 2 m in the most favourable case. The potentiometric sensor was firstly characterised by cyclic voltammetry experiments, then the iridium oxide electrodeposition procedure was optimised. Next, the sensor was tested toward pH detection in buffer solutions with a near-Nernstian response equal to −0.079 ± 0.002 V for unit of pH. Interference studies of common sweat ions, including Na+, K+ and Cl−, showed any influence on the pH sensor response. Finally, the integrated epidermal device was tested for real-time on-body pH sweat monitoring during a running activity. Data recorded for a running subject were wireless transmitted to an external receiver, showing a pH value close to 5.5, in agreement with value obtained by pH-meter reference measurement.

Counterpoint: Investigators should not control for menstrual cycle phase when performing studies of vascular control that include women.

Observed sex differences in the epidemiology of cardiovascular disease incidence and the efficacy of clinical intervention strategies, coupled with recent mandates from the National Institutes of Health (NIH), and its international counterparts to consider sex as a biological variable in all preclinical and clinical work (15), have led to increased enrollment of women in human physiology studies of vascular function with the goal of improving external validity and clinical applicability of the findings. However, standard practice in these studies is to test women during the early follicular phase (~days 1-5) of the menstrual cycle, during which estrogen and progesterone concentrations are lowest, and either exclude or limit testing of women who use hormonal contraceptives to the placebo phase. This approach seeks to control for, or limit, differences in circulating hormone concentrations between men and women and is based on the dogmatic theory that cyclic changes in estrogen and progesterone concentrations lead to greater variability in study outcomes and uninterpretable datasets. Contrary to this common approach, we propose that limiting testing of women to this single phase 1) decreases external validity of the findings, 2) obfuscates potential physiological differences contributable to differences in sex hormone concentrations between men and women, and 3) is, in many instances, contradicted by literature that demonstrates limited or no variability in vascular measurements across the menstrual cycle.

P030 Skin-wipe sweat ion ratios - sensitivity and specificity in time

P030 Skin-wipe sweat ion ratios - sensitivity and specificity in time

P031 What is the role of sweat ions ratio in the diagnosis of cystic fibrosis?

P031 What is the role of sweat ions ratio in the diagnosis of cystic fibrosis?

Printed Wearable Sensor Patch for Multi-Analytes Detection in the Sweat Range

Printed Wearable Sensor Patch for Multi-Analytes Detection in the Sweat Range

A multichannel electrochemical all-solid-state wearable potentiometric sensor for real-time sweat ion monitoring

There is considerable interest in wearable potentiometric ion sensors that can provide information about the quality of a person's health by monitoring ion concentration levels in biofluids. Significant progress has been achieved, particularly in device integration. However, the crucial interfacial water layer and the use of transducer materials remain challenging. Herein we report a paper-based, flexible, all-solid-state, ion-selective electrode (ISE) for the real-time analysis of sweat. The super-hydrophobic paper matrix was modified with a fluorinated alkyl silane to reduce the water-layer effect. We used a high-quality graphene suspension with high conductivity and capacitance as an ion-to-electron transducer, which further stabilized the potential. The integrated solid ISE has four channels that can detect K+, Na+, Cl− and pH simultaneously. This wearable potentiometric sensor has reliable accuracy, good potential stability and low detection limits, and could be used in healthcare and clinical analysis.

The influence of local skin temperature on the sweat glands maximum ion reabsorption rate

Changes in mean skin temperature (Tsk) have been shown to modify the maximum rate of sweat ion reabsorption. This study aims to extend this knowledge by investigating if modifications could also be caused by local Tsk. The influence of local Tsk on the sweat gland maximum ion reabsorption rates was investigated in ten healthy volunteers (three female and seven male; 20.8 ± 1.2years, 60.4 ± 7.7kg, 169.4 ± 10.4cm) during passive heating (water-perfused suit and lower leg water immersion). In two separate trials, in a randomized order, one forearm was always manipulated to 33°C (Neutral), whilst the other was manipulated to either 30°C (Cool) or 36°C (Warm) using water-perfused patches. Oesophageal temperature (Tes), forearm Tsk, sweat rate (SR), galvanic skin conductance (GSC) and salivary aldosterone concentrations were measured. The sweat gland maximum ion reabsorption rates were identified using the ∆SR threshold for an increasing ∆GSC. Thermal [Tes and body temperature (Tb)] and non-thermal responses (aldosterone) were similar across all conditions (p > 0.05). A temperature-dependent response for the sweat gland maximum ion reabsorption rates was evident between 30°C (0.18 ± 0.10mg/cm2/min) and 36°C (0.28 ± 0.14mg/cm2/min, d = 0.88, p < 0.05), but not for 33°C (0.22 ± 0.12mg/cm2/min), d = 0.44 and d = 0.36, p > 0.05. The data indicate that small variations in local Tsk may not affect the sweat gland maximum ion reabsorption rates but when the local Tsk increases by > 6°C, ion reabsorption rates also increase.