Human Sweat Samples Research Articles

Biological Ce/Fe-metal organic framework multifunctional nanozyme-based colorimetric sensor array for multi-analyte detection in human sweat

Diabetes, a widespread metabolic disorder, is a major public health concern. To address the ongoing need for effective diagnosis, a novel approach has been developed that allows the rapid, low-cost, and ultra-sensitive detection of disease-specific biomarkers in various body fluids using a single platform. Notably, this method focuses on biomarkers found in human sweat—glucose, L-Tryptophan, uric acid, and acetone—that are indicative of diabetes. The new strategy involves a nanozyme-based colorimetric sensor array made from a Ce/Fe fumarate biological metal–organic framework (Ce/Fe-Fum Bio-MOF) doped with Cu and Ni, and further enhanced with Ag nanoparticles. This nanozyme displays multiple enzyme-like activities, which result in distinct color changes when tested with specific chromogenic substrates. When these color changes are reduced by the introduction of biomarkers, the results can be easily captured using a smartphone. This method offers a wide linear detection range (20–1000 µM) and low detection limits for each biomarker, showing strong selectivity, reproducibility, and practical performance in detecting biomarkers in human sweat samples. The integration of smartphone signaling with this sensor array creates potential for a portable, handheld device for point-of-care applications, and could also be adapted for other sensing and biosensing needs. This colorimetric assay marks a significant advancement in the detection of diabetes biomarkers and the development of point-of-care diagnostic systems.

Quantification of amino acids in small volumes of palm sweat samples

This study investigates the significance of quantifying amino acids in minute sweat volumes using high-performance liquid chromatography with fluorescence detection. Sweat, a valuable biofluid for non-invasive health monitoring, provides real-time insights into physiological changes. Amino acids, which are critical for various physiological processes, are key to protein synthesis and cellular regulation. Therefore, analyzing sweat's amino acid profiles can offer insights into metabolic states, exercise-induced stress, and potential biomarkers for health conditions. For sensitive analysis, amino acids were derivatized with 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F), followed by liquid chromatographic separation on an octadecylsilyl column and fluorescence detection. The developed method was validated and applied to human sweat samples, enabling the quantification of 14 amino acids. The most abundant amino acids in the samples were serine, glycine, and alanine, which aligns with prior studies. This method offers a non-invasive and efficient way to screen for diseases by detecting amino acids in sweat, even with minimal sweat volumes. The approach could also be used to analyze other biomolecules in sweat, expanding its potential applications.

Development of ZnFe(PBA)@Mo3C2Tx Nanohybrid based Non‐Enzymatic Sensor for the Detection of Glucose in Human Sweat

AbstractZnFe (PBA)@Mo3C2Tx is prepared by in‐situ sonication method using ZnFe Prussian blue analogue infused with Mo3C2Tx (MXene) to use as a non‐enzymatic glucose sensor owing to its low cost and biocompatibility. The synthesized ZnFe (PBA)@Mo3C2Tx is characterized for its physical and chemical characterization by XRD, Raman, XPS, EDAX, and FESEM analyses, revealing a functionalized multiple‐layered structure with a cubic nano‐hybrid arrangement. This sensor has undergone electroanalytical investigation, including cyclic voltammetry and chronoamperometry analysis. The electrochemical performance of ZnFe(PBA)@Mo3C2Tx exhibits an excellent analytical performance with a sensitivity of 818.285 μA mM−1 cm−2 and the limit of detection (LOD) of 1.6 μM (S/N=3). The analysis of glucose in human sweat samples, compared with their corresponding blood glucose values, yield a relative standard deviation (RSD) of 2.98 %.

Advancements in Glucose Monitoring: A Thin Film ZnO-Nanoflakes Based Highly Sensitive Wearable Biosensor for Noninvasive Sweat-Based Point-of-Care Monitoring for Diabetes

In the contemporary global landscape, diabetes is a prevalent and concerning presence that contributes to noteworthy mortality rates. The etiology of this condition involves a subtle interaction between insulin deficiency and elevated blood sugar levels which results in a complex metabolic disorder. The harmful consequences of this physiological abnormality become evident through the increased probability of kidney failure, heart attack, chronic liver diseases, and a pernicious ocular affliction leading to blindness. Against this backdrop, the necessity for prompt, accurate, and continuous monitoring of glucose concentrations with any form of flexible sensor becomes notably evident for type I and type II diabetes patients, pregnant women with diabetes, athletes, and high-risk persons. Sweat, an often-overlooked physiological excretion, is a reservoir of vital biological information due to its accessibility and analyzability. It is an advantageous matrix for glucose monitoring, surpassing blood, saliva, and tears. Its non-invasive nature offers a patient-friendly alternative to conventional blood sampling. The continuous, real-time nature of sweat extraction facilitates dynamic monitoring without the discomfort associated with invasive methods. This inherent advantage positions sweat as a promising matrix for glucose sensing, underscoring its potential as a valuable tool in diabetes management. It overcomes the limitations posed by other bodily fluids like saliva and tears in terms of accessibility, patient comfort, and reflective accuracy. The assimilation of nanomaterials into biosensing technologies heralds a paradigm shift, conferring heightened sensitivity upon these mechanisms. Noteworthy among these innovations are flexible wearable biosensors leveraging zinc oxide (ZnO) thin films, offering promising avenues for the discernment of glucose levels within sweat for healthcare monitoring. ZnO nanoflakes (ZnO-NFs) distinguish themselves by endowing flexible biosensors with unparalleled sensitivity, reliability, continuous monitoring capabilities, and non-invasiveness from zinc oxide nanoparticles incorporated graphene-carbon nanotube hybrid (GR-CNT-ZnO) and ergocalciferol-multi walled carbon nanotubes based (ERGOc-MWCNTd/Nf) traditional glucose sensors. The distinctive advantages of ZnO-NFs over bulk materials are multifaceted. Notably, the polarized (0001) plane orientation inherent in ZnO-NFs amplifies enzyme immobilization, thereby augmenting sensing performance. The elevated isoelectric point (9.5) of ZnO-NFs facilitates the immobilization of biomolecules, obviating the need for an ancillary binding layer. A single-step and efficacious sonochemical approach has been used to synthesize a thin layer of ZnO-NFs virtually on any substrate. The electrochemical flexible glucose biosensor was fabricated through the judicious immobilization of glucose oxidase (GOx) on ZnO nanoflakes, possessing a mere 20nm thickness and synthesized adeptly on an Au-coated stretchable polyethylene terephthalate (PET). The sensitivity of the flexible biosensor was determined by 29.97 μA/decade/cm² and the minimum detection limit is 100 μM. The coefficient of determination of the designed flexible electrode is found 97.76%, which is significantly linear. The designed PET/Au/ZnO-NFS/GOx flexible biosensors showed good repeatability for different sample concentrations. The enzymatic flexible sensor also showed good repeatability for three sample concentrations. The reproducibility data for two identical flexible sensors were found within the LoA of the Bland-Altman plot with a statistically significant p-value of 0.08 derived from the student t-test. Moreover, the flexible sensor exhibited notable repeatability, reproducibility, and remarkable stability conducive to the precise quantification of glucose. The application of this flexible wearable sensor has been validated through its utilization in human sweat samples, yielding results that align favorably with conventional methodology.

Copper oxide nanoparticles modified electrodes for high-sensitivity detection of uric acid in athletes

This study introduces an innovative electrochemical sensor leveraging copper oxide nanoparticles for detecting uric acid levels in athletes with enhanced sensitivity and selectivity. Employing a novel synthesis protocol, uniform copper oxide nanoparticles were integrated into a chitosan-glutathione biogel matrix, creating a high-performance sensing electrode. The nanoparticles were extensively characterized using XRD, SEM, FTIR, and XPS techniques, confirming their crystalline structure, morphology, and purity. The average crystallite size was determined to be 18 nm. Electrochemical evaluation of the sensor using cyclic voltammetry and electrochemical impedance spectroscopy revealed significantly improved electron transfer kinetics and catalytic activity towards uric acid oxidation. The sensor exhibited a wide linear detection range from 1 μM to 1.2 mM, encompassing both physiological and pathological uric acid levels. Notably, the limit of detection was found to be 0.27 μM, surpassing the performance of most existing metal oxide based uric acid sensors. The sensor also demonstrated excellent anti-interference capability against commonly coexisting species in biological fluids. Furthermore, the practical applicability of the sensor was validated by successfully determining uric acid concentrations in human serum, plasma, and sweat samples, with impressive recovery rates ranging from 96% to 102%. The stability, reproducibility, and cost-effectiveness of the developed sensor make it a promising tool for routine health monitoring and early intervention in athletes, facilitating personalized training and preventing complications associated with uric acid imbalances. The present work offers a significant advancement in non-invasive, reliable, and efficient assessment of uric acid, with potential for widespread implementation in sports medicine and general healthcare.

All-printed wearable biosensor based on MWCNT-iron oxide nanocomposite ink for physiological level detection of glucose in human sweat

Wearable sensors for sweat glucose monitoring are gaining massive interest as a patient-friendly and non-invasive way to manage diabetes. The present work offers an alternative on-body method employing an all-printed flexible electrochemical sensor to quantify the amount of glucose in human sweat. The working electrode of the glucose sensor was printed using a custom-formulated ink containing multi-walled carbon nanotube (MWCNT), poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOPT: PSS), and iron (II, III) oxide (Fe3O4) nanoparticles. This novel ink composition has good conductivity, enhanced catalytic activity, and excellent selectivity. The working electrode was modified using Prussian blue (PB) nanoparticles and glucose oxidase enzyme (GOx). The sensor displayed a linear chronoamperometric response to glucose from 1 μM to 400 μM, with a precise detection limit of ∼0.38 μM and an impressive sensitivity of ∼4.495 μAμM−1cm−2. The sensor stored at 4 °C exhibited excellent stability over 60 days, high selectivity, and greater reproducibility. The glucose detection via the standard addition method in human sweat samples acquired a high recovery rate of 96.0–98.6%. Examining human sweat during physical activity also attested to the biosensor's real-time viability. The results also show an impressive correlation between glucose levels obtained from a commercial blood glucose meter and sweat glucose concentrations. Remarkably, the present results outperform previously published printed glucose sensors in terms of detection range, low cost, ease of manufacturing, stability, selectivity, and wearability.

Sweat lactate biosensor based on lactate oxidase immobilized with flower-like NiCo2O4 and carbon nanotubes

We design a portable and non-invasive lactate biosensor that can conveniently monitor lactate levels in real human sweat. The proposed biosensor is constructed through the immobilization of lactate oxidase (LOx) and horseradish peroxidase (HRP) on flower-like NiCo2O4 microspheres coupled with single-walled carbon nanotubes (SWCNTs). The synergistic effect between NiCo2O4 microspheres and SWCNTs can increase the conductivity and the active surface area of the electrode. Using ferrocene–methanol (FcMeOH) as the electron transfer mediator in buffer, the developed biosensor can detect lactate in a wide linear range of 0.1 mM to 30 mM with a detection limit of 39.9 µM under optimal conditions. Additionally, the biosensor exhibits excellent selectivity and stability. As proof of concept, the biosensor was applied to monitor lactate level in real human sweat samples, and the results were in good agreement with those obtained by high-performance liquid chromatography (HPLC) analysis. The lactate biosensor is cost effective and can be as a non-invasive alternative to blood analysis, which is suitable for rapid analysis of lactate levels in the fields of fitness, health monitoring and clinical diagnosis.

A Portable Electrochemical Dopamine Detector Using a Fish Scale-Derived Graphitized Carbon-Modified Screen-Printed Carbon Electrode.

In this paper, a highly conductive alkali-activated graphitized carbon (a-GC) was prepared using tilapia fish scales as precursors through enzymolysis, activation and pyrolytic carbonization methods. The prepared a-GC was modified on the surface of a screen-printed carbon electrode to construct a flexible portable electrochemical sensing platform, which was applied to the differential pulse voltametric detection of dopamine (DA) using a U-disk electrochemical workstation combined with a smart phone and Bluetooth. The prepared a-GC possesses good electrical conductivity, a large specific surface area and abundant active sites, which are beneficial for the electrooxidation of DA molecules and result in excellent sensitivity and high selectivity for DA analysis. Under the optimal conditions, the oxidation peak current of DA increased gradually, with its concentrations in the range from 1.0 μmol/L to 1000.0 μmol/L, with the detection limit as low as 0.25 μmol/L (3S/N). The proposed sensor was further applied to the determination of DA in human sweat samples, with satisfactory results, which provided an opportunity for developing noninvasive early diagnosis and nursing equipment.

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

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

Capillary electrophoresis with capacitively coupled contactless conductivity detection (C4 D) for rapid and simple determination of lactate in sweat.

An analytical method based on capillary electrophoresis (CE) using capacitively coupled contactless conductivity detection (C4 D) was developed and validated for fast, straightforward, and reliable determination of lactate in artificial and human sweat samples. The background electrolyte was composed of equimolar concentrations (10mmol/L) of 2-(N-morpholino)ethanesulfonic acid and histidine, with 0.2mmol/L of cetyltrimethylammonium bromide as electroosmotic flow inverter. The limit of detection and quantification were 3.1 and 10.3µmol/L, respectively. Recoveries in the 97 to 118% range were obtained using sweat samples spiked with lactate at three concentration levels, indicating an acceptable accuracy. The intraday and interday precisions were 1.49 and 7.08%, respectively. The proposed CE-C4 D method can be a starting point for monitoring lactate concentrations in sweat samples for diagnostics, physiological studies, and sports performance assessment applications.

Dynamic Behavior of Cortisol and Cortisol Metabolites in Human Eccrine Sweat

The simultaneous measurement of cortisol with its downstream metabolites in human eccrine sweat is a sensitive approach to capture minute-to-minute stress responses. This study investigates exercise stress induced time dependent dynamic changes in cortisol, cortisone and downstream inactive cortisol metabolites in human eccrine sweat using a novel liquid chromatography-tandem mass spectrometry (LC-MS/MS) method. Cortisol and metabolite production (change in concentration over time) was measured in sweat at different time points during an administered exercise stress session with four healthy volunteers. Biomarker production plots were found to be highly individualized and sensitive to stress interventions such as exercise, and corresponded with stress response measures such as increases in heart rate. The LC-MS/MS method yielded baseline resolution between cortisol and cortisol metabolites with lower levels of detection and quantitation for each compound below 1 partper-billion (ppb). Cortisol and cortisol metabolites were found at concentrations ranging from 1 – 25 ppb in human eccrine sweat. They were also found to be stable in sweat with respect to temperature (37 C for up to 5 hours), pH (3-9) and freeze/thaw cycles (up to 4) This indicates that changes in these biomarker concentrations and their rate of production are due to stress-related physiological enzyme activation, rather than passive degradation in sweat. The physiological status of enzyme activation is thus captured and preserved in human eccrine sweat samples. This is advantageous for the development of wearable devices and methodologies which can assess human health, stress, wellbeing and performance.

Effect of glucuronic acid on inducing self-assembly of Au nanoflowers@glucuronic acid on carbon cloth for non-enzymatic glucose sensing

Natural materials' structural variation boosts their performance. Therefore, the precise manipulation of the structure and properties of nanomaterials by self-assembly is a topic of great interest. Here, a self-assembly of glucuronic acid (GlcA)-coated Au nanoflowers (NFs) on flexible carbon cloth (SA-AuNFs@GlcA/CC) for non-enzyme electrochemical glucose detection was fabricated through the sequential deposition of gold and GlcA. The SA-AuNFs@GlcA/CC exhibits more highly exposed nanoedges than the normal AuNFs/CC without GlcA surface deposition, which may change the stereotyped traditional negative hypotheses of GlcA in glucose electrocatalysis. Notably, the unique {110} facets of Au atop the amino group grafted-CC were found in the SA-AuNFs@GlcA/CC, significantly improving the sensor's catalytic performance. The highly exposed nanoedges and unique {110} facets of SA-AuNFs@GlcA were systematically evaluated by scanning electron microscopy, transmission electron microscopy, and other electrochemical characterization tools. The SA-AuNFs@GlcA/CC exhibits excellent performance in glucose detection, including a wide linear range (5 μM-42 mM), a low limit of detection (5 μM, S/N = 3), high detection selectivity, good stability, and reproductivity. The sensor successfully detected glucose in human sweat samples and beverages in real time. Thus, this simple and green manufacturing method could be used as a novel strategy for glucose monitoring in biological and food samples.

Biological studies with comprehensive 2D-GC-HRMS screening: Exploring the human sweat volatilome

A key issue in GCxGC-HRMS data analysis is how to approach large-sample studies in an efficient and comprehensive way. We have developed a semi-automated data-driven workflow from identification to suspect screening, which allows highly selective monitoring of each identified chemical in a large-sample dataset. The example dataset used to illustrate the potential of the approach consisted of human sweat samples from 40 participants, including field blanks (80 samples). These samples have been collected in a Horizon 2020 project to investigate the capacity of body odour to communicate emotion and influence social behaviour. We used dynamic headspace extraction, which allows comprehensive extraction with high preconcentration capability, and has to date only been used for a few biological applications. We were able to detect a set of 326 compounds from a diverse range of chemical classes (278 identified compounds, 39 class unknowns, and 9 true unknowns). Unlike partitioning-based extraction methods, the developed method detects semi-polar (log P < 2) nitrogen and oxygen-containing compounds. However, it is unable to detect certain acids due to the pH conditions of unmodified sweat samples. We believe that our framework will open up the possibility of efficiently using GCxGC-HRMS for large-sample studies in a wide range of applications such as biological and environmental studies.

Simultaneous detection of ultraviolet irradiation and vitamin C using an all-carbon-based integrated wearable system powering by a micro-supercapacitor

Ultraviolet (UV) radiation is a harmful exogenous factor for human skin. Wearable UV photodetectors can monitor UV exposure in the surroundings, and wearable vitamin C (VC) sensors tracking the levels in the human body present the potential ability to defend the UV radiation. Herein, we reported on the fabrication of an all-in-one wearable system with a UV photodetector and VC sensor powered by a micro-supercapacitor. Based on direct laser writing carbonization of polyimide sheets, the patterned electrodes and interconnects of the circuit were fabricated by a facile one-step operation, obtaining an all-carbon-based integrated system. Such a system exhibited outstanding energy storage ability (56.2 μWh cm−2 at 4.17 mW cm−2), high areal capacitance (1.06 mF cm−2 at 5 mV s−1), satisfying capacitive stability, and good mechanical flexibility. The UV photodetector and the VC sensor were powered to obtain a linear range of UV intensity from 11 to 44 μW cm−2 (equivalent to Ultraviolet Index 4.4 to 17.6), and VC levels of 1.0–200 μM with a low limit of detection of 0.83 μM. Furthermore, the integrated system was successfully applied to the determination of VC in commercial beverage and human sweat samples. This work provided a simple and promising method to fabricate integrated wearable systems for on-site providing information on the UV intensity of the external environment and the VC level of the human body simultaneously.

Palladium Hydroxide (Pearlman's Catalyst) Doped MXene (Ti3C2Tx) Composite Modified Electrode for Selective Detection of Nicotine in Human Sweat.

High concentrations of nicotine (40 to 60 mg) are more dangerous for adults who weigh about 70 kg. Herein, we developed an electrochemical transducer using an MXene (Ti3C2Tx)/palladium hydroxide-supported carbon (Pearlman's catalyst) composite (MXene/Pd(OH)2/C) for the identification of nicotine levels in human sweat. Firstly, the MXene was doped with Pd(OH)2/C (PHC) by mechanical grinding followed by an ultrasonication process to obtain the MXene/PHC composite. Secondly, XRD, Raman, FE-SEM, EDS and E-mapping analysis were utilized to confirm the successful formation of MXene/PHC composite. Using MXene/PHC composite dispersion, an MXene/PHC composite-modified glassy carbon electrode (MXene/PHC/GCE) was prepared, which showed high sensitivity as well as selectivity towards nicotine (300 µM NIC) oxidation in 0.1 M phosphate buffer (pH = 7.4) by cyclic voltammetry (CV) and amperometry. The MXene/PHC/GCE had reduced the over potential of nicotine oxidation (about 200 mV) and also enhanced the oxidation peak current (8.9 µA) compared to bare/GCE (2.1 µA) and MXene/GCE (5.5 µA). Moreover, the optimized experimental condition was used for the quantification of NIC from 0.25 µM to 37.5 µM. The limit of detection (LOD) and sensitivity were 27 nM and 0.286 µA µM-1 cm2, respectively. The MXene/PHC/GCE was also tested in the presence of Na+, Mg2+, Ca2+, hydrogen peroxide, acetic acid, ascorbic acid, dopamine and glucose. These molecules were not interfered during NIC analysis, which indicated the good selectivity of the MXene/PHC/GCE sensor. In addition, electrochemical determination of NIC was successfully carried out in the human sweat samples collected from a tobacco smoker. The recovery percentage of NIC in the sweat sample was 97%. Finally, we concluded that the MXene/PHC composite-based sensor can be prepared for the accurate determination of NIC with high sensitivity, selectivity and stability in human sweat samples.

Sweat cortisol determination utilizing MXene and multi-walled carbon nanotube nanocomposite functionalized immunosensor

In this work, a highly selective and sensitive cortisol immunosensor based on MXene and multi-walled carbon nanotubes (MXene-MWCNTs) hybrid composite was proposed. The immunosensor was developed by screen printing technique on a flexible polyethyleneterephthalate (PET) substrate followed by modification of MXene-MWCNTs and anti-cortisol antibodies with EDC/NHS coupling agent. Owing to the large surface area and excellent conductivity of MXene-MWCNTs, the immunosensor exhibited a low detection limit and a wide linear range toward cortisol from 0.1 fg/mL to 1 µg/mL, which covered the normal range of free cortisol in sweat. Additionally, the immunosensor was applied to evaluate the cortisol level in human sweat samples, and the results were validated by a commercial chemiluminescence immunoassay (CLIA) assay. The present platform provides an effective method for non-invasive monitoring of human sweat cortisol levels, which may be well-suited for hormone screenings in healthy monitoring and medical diagnosis.

Aggregation Kinetics of TiO2 Nanoparticles in Human and Artificial Sweat Solutions: Effects of Particle Properties and Sweat Constituents.

Dermal penetration potentials of titanium dioxide nanoparticles (TiO2 NPs) may be affected by aggregation upon contact with sweat. This study investigated the aggregation kinetics of three TiO2 NPs in thirty human sweat samples and four artificial sweat standards. Effects of particle concentration, sweat type, and inorganic (sodium chloride, disodium hydrogen phosphate, and sodium dihydrogen phosphate) and organic (l-histidine, lactic acid, and urea) constituents were examined. Three TiO2 NPs remained colloidally stable in >20/30 human sweat samples and showed significant negative correlations (P < 0.01) between aggregation rates and |zeta potentials|. They aggregated rapidly over 20 min to >750 nm in three artificial sweat standards, while remained more stable in the International-Standard-Organization-pH-5.5 standard. Aggregation behaviors of three TiO2 NPs mostly followed the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, allowing for determining their critical coagulation concentrations in inorganic constituents (15-491 mM) and Hamaker constants (3.3-7.9 × 10-21 J). Higher concentrations of particles, inorganic constituents, and l-histidine destabilized three TiO2 NPs, whereas urea inhibited aggregation. Three TiO2 NPs adsorbed organic sweat constituents via complexation with amino or carboxyl groups, with isotherms following the Langmuir model. Correlation analyses further suggested that the adsorbed organic constituents may stabilize three TiO2 NPs against aggregation in sweat by steric hindrance.

A smartphone-assisted hybrid sensor for simultaneous potentiometric and distance-based detection of electrolytes

At home electrolyte analysis is of growing interest due to the importance for early diagnosis for various diseases. This work presents the first device that integrates a potentiometric ion-selective electrode (ISE) with distance-based colorimetric detection for the simultaneous analysis of K+ and Cl− ions at the point of care (POC). This hybrid sensing device was designed in a two-dimensional configuration using a plastic transparency sheet containing a stencil printed K+-ISE and a paper substrate for distance-based colorimetric detection of Cl−. K+ quantification was performed using a low-cost (<$25) lab-made Wi-Fi supported potentiometer with a custom smartphone application while Cl− ions were quantified with an instrument-free distance-based paper analytical device (dPAD). The total analysis time is 5 min once the sample is added. The K+-ISE showed a sensitivity of 55.89 ± 2.52 mV/decade from 0.1 to 100 mM with a limit of detection (LOD) of 0.01 mM. The linear working range for Cl− detection was 0.5–50 mM whereas the LOD was 0.16 ± 0.05 mM. The proof-of-concept application of the sensing hybrid device was demonstrated in human urine and artificial sweat samples containing K+ and Cl− ions at physiologically relevant ranges. The recoveries were found to be 88–108% for K+ and 90–104% for Cl−, showing the potential use of the proposed device for low-cost routine analysis of biological samples at POC.

Label-free photoelectric sensor for lactic acid determination in human sweat

A label-free lactic acid sensor has been successfully developed by using a Dysprosium single crystal-based photoelectric potential technique via Dy-SCN/FTO electrode. Interestingly, the proposed sensor demonstrated excellent performance for l-lactic acid analysis with a wide linear range of 0.0196∼16.31 mmol/L, the detection limit of as low as 3.20 µmol/L as well as an advisable stability. The feasibility of this strategy was also verified by practical application towards human sweat samples. The mechanism studies indicated that lactic acid molecules specifically bind to the surface of semiconductor materials, which alters the charge distribution of the electrode surface and subsequently results in band bending/photoelectric potential changes. The theoretical formula for this photoelectric chemistry (PEC) strategy was then derived according to charge balance theory. We believe that the proposed Dy-SCN/FTO sensor would open a new way for rapid, non-invasive l-lactic acid level evaluation during human physical condition monitoring.

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.