Wearable electrochemical device based on butterfly-like paper-based microfluidics for pH and Na+ monitoring in sweat.

A wearable potentiometric device is reported based on an innovative butterfly-like paper-based microfluidic system, allowing for continuous monitoring of pH and Na+ levels in sweat during physical activity. Specifically, the use of the butterfly-like configuration avoids evaporation phenomena and memory effects, enabling precise and timely biomarker determination in sweat. Two ad hoc modified screen-printed electrodes were embedded in the butterfly-like paper-based microfluidics, and the sensing device was further integrated with a portable and miniaturized potentiostat, leveraging Bluetooth technology for efficient data transmission. First, the paper-based microfluidic configuration was tested for optimal fluidic management to obtain optimized performance of the device. Subsequently, the two electrodes were individually tested to detect the two biomarkers, namely pH and Na+. The results demonstrated highly promising near-Nernstian (0.056 ± 0.002 V/dec) and super-Nernstian (- 0.080 ± 0.003 V/pH) responses, for Na+ and pH detection, respectively. Additionally, several important parameters such as storage stability, interferents, and memory effect by hysteresis study were also investigated. Finally, the butterfly-like paper-based microfluidic wearable device was tested for Na+ and pH monitoring during the physical activity of three volunteers engaged in different exercises, obtaining a good correlation between Na+ increase and dehydration phenomena. Furthermore, one volunteer was tested through a cardiopulmonary test, demonstrating a correlation between sodium Na+ increase and the energetic effort by the volunteer. Our wearable device highlights the high potential to enable early evaluation of dehydration and open up new opportunities in sports activity monitoring.

A skin-interfaced microfluidic platform supports dynamic sweat biochemical analysis during human exercise.

Blood lactate concentration is an established circulating biomarker for measuring muscle acidity and can be evaluated for monitoring endurance, training routines, or athletic performance. Sweat is an alternative biofluid that may serve similar purposes and offers the advantage of noninvasive collection and continuous monitoring. The relationship between blood lactate and dynamic sweat biochemistry for wearable engineering applications in physiological fitness remains poorly defined. Here, we developed a microfluidic wearable band with an integrated colorimetric timer and biochemical assays that temporally captures sweat and measures pH and lactate concentration. A colorimetric silver nanoplasmonic assay was used to measure the concentration of lactate, and dye-conjugated SiO2 nanoparticle-agarose composite materials supported dynamic pH analysis. We evaluated these sweat biomarkers in relation to blood lactate in human participant studies during cycling exercise of varying intensity. Iontophoresis-generated sweat pH from regions of actively working muscles decreased with increasing heart rate during exercise and was negatively correlated with blood lactate concentration. In contrast, sweat pH from nonworking muscles did not correlate with blood lactate concentration. Changes in sweat pH and blood lactate were observed in participants who did not regularly exercise but not in individuals who regularly exercised, suggesting a relationship to physical fitness and supporting further development for noninvasive, biochemical fitness evaluations.

Self-powered sensing platform for monitoring uric acid in sweat using cobalt nanocrystal-graphene quantum dot-Ti3C2TX monolithic film electrode with excellent supercapacitor and sensing behavior.

The synthesis of cobalt nanocrystal-graphene quantum dot-Ti3C2TX monolithic film electrode (Co-GQD-Ti3C2TX) is reported via self-assembly of Ti3C2TX nanosheets induced by protonated arginine-functionalized graphene quantum dot and subsequent reduction of cobalt (III). The resulting Co-GQD-Ti3C2TX shows good monolithic architecture, mechanical property, dispersibility and conductivity. The structure achieves excellent supercapacitor and sensing behavior. The self-charging supercapacitor produced by printing viscous Co-GQD-Ti3C2TX hydrogel on the back of flexible solar cell surface provides high specific capacitance (296 F g-1 at 1 A g-1), high-rate capacity (153 F g-1 at 20 A g-1), capacity retention (98.1% over 10,000-cycle) and energy density (29.6 W h kg-1 at 299.9 W kg-1). The electrochemical chip produced by printing Co-GQD-Ti3C2TX hydrogel on paper exhibits sensitive electrochemical response towards uric acid. The increase of uric acid between 0.01 and 800 µM causes a linear increase in differential pulse voltammetry signal with a detection limit of 0.0032 µM. The self-powered sensing platform integrating self-charging supercapacitor, electrochemical chip and micro electrochemical workstation was contentedly applied to monitoring uric acid in sweats and shows one broad application prospect in wearable electronic health monitoring device.

Flexible/Regenerative Nanosensor with Automatic Sweat Collection for Cytokine Storm Biomarker Detection.

The real-time monitoring of low-concentration cytokines such as TNF-α in sweat can aid clinical physicians in assessing the severity of inflammation. The challenges associated with the collection and the presence of impurities can significantly impede the detection of proteins in sweat. This issue is addressed by incorporating a nanosphere array designed for automatic sweat transportation, coupled with a reusable sensor that employs a Nafion/aptamer-modified MoS2 field-effect transistor. The nanosphere array with stepwise wettability enables automatic collection of sweat and blocks impurities from contaminating the detection zone. This device enables direct detection of TNF-α proteins in undiluted sweat, within a detection range of 10 fM to 1 nM. The use of an ultrathin, ultraflexible substrate ensures stable electrical performance, even after up to 30 extreme deformations. The findings indicate that in clinical scenarios, this device could potentially provide real-time evaluation and management of patients' immune status via sweat testing.

Sweat lactate sensor for detecting anaerobic threshold in heart failure: a prospective clinical trial (LacS-001).

A simple method for determining the anaerobic threshold in patients with heart failure (HF) is needed. This prospective clinical trial (LacS-001) aimed to investigate the safety of a sweat lactate-monitoring sensor and the correlation between lactate threshold in sweat (sLT) and ventilatory threshold (VT). To this end, we recruited 50 patients with HF and New York Heart Association functional classification I-II (mean age: 63.5 years, interquartile range: 58.0-72.0). Incremental exercise tests were conducted while monitoring sweat lactate levels using our sensor. sLT was defined as the first steep increase in lactate levels from baseline. Primary outcome measures were a correlation coefficient of ≥ 0.6 between sLT and VT, similarities as assessed by the Bland-Altman analysis, and standard deviation of the difference within 15 W. A correlation coefficient of 0.651 (95% confidence interval, 0.391-0.815) was achieved in 32/50 cases. The difference between sLT and VT was -4.9 ± 15.0 W. No comparative error was noted in the Bland-Altman plot. No device-related adverse events were reported among the registered patients. Our sweat lactate sensor is safe and accurate for detecting VT in patients with HF in clinical settings, thereby offering valuable additional information for treatment.

Innovative Wearable Sweat Sensor Array for Real-Time Volatile Organic Compound Detection in Noninvasive Diabetes Monitoring.

Wearable sweat sensors are reshaping healthcare monitoring, providing real-time data on hydration and electrolyte levels with user-friendly, noninvasive devices. This paper introduces a highly portable two-channel microfluidic device for simultaneous sweat sampling and the real-time detection of volatile organic compound (VOC) biomarkers. This innovative wearable microfluidic system is tailored for monitoring diabetes through the continuous and noninvasive tracking of acetone and ammonia VOCs, and it seamlessly integrates with smartphones for easy data management. The core of this system lies in the utilization of carbon polymer dots (CPDs) and carbon dots (CDs) derived from monomers such as catechol, resorcinol, o-phenylenediamine, urea, and citric acid. These dots are seamlessly integrated into hydrogels made from gelatin and poly(vinyl alcohol), resulting in an advanced solid-state fluorometric sensor coating on a cellulose paper substrate. These sensors exhibit exceptional performance, offering linear detection ranges of 0.05-0.15 ppm for acetone and 0.25-0.37 ppm for ammonia, with notably low detection limits of 0.01 and 0.08 ppm, respectively. Rigorous optimization of operational parameters, encompassing the temperature, sample volume, and assay time, has been undertaken to maximize device performance. Furthermore, these sensors demonstrate impressive selectivity, effectively discerning between biologically similar substances and other potential compounds commonly present in sweat. As this field matures, the prospect of cost-effective, continuous, personalized health monitoring through wearable VOC sensors holds significant potential for overcoming barriers to comprehensive medical care in underserved regions. This highlights the transformative capacity of wearable VOC sweat sensing in ensuring equitable access to advanced healthcare diagnostics, particularly in remote or geographically isolated areas.

Patterned Gold Nanoparticle Superlattice Film for Wearable Sweat Sensors.

Nanoparticle superlattices are beneficial in terms of providing strong and uniform signals in analysis owing to their closely packed uniform structures. However, nanoparticle superlattices are prone to cracking during physical activities because of stress concentrations, which hinders their detection performance and limits their analytical applications. In this work, template printing methods were used in this study to prepare a patterned gold nanoparticle (AuNP) superlattice film. By adjustment of the size of the AuNP superlattice domain below the critical size of fracture, the mechanical stability of the AuNP superlattice domain is improved. Thus, long-term sustainable high-performance signal output is achieved. The patterned AuNP superlattice film was used to construct a wearable sweat sensor based on surface-enhanced Raman scattering (SERS). The designed sensor showed promise for long-term reliable use in actual scenarios in terms of recommending water replenishment, monitoring hydration states, and tracking the intensity of activity.

Silk fibroin-based wearable SERS biosensor for simultaneous sweat monitoring of creatinine and uric acid.

Sweat biomarkers have the potential to offer valuable clinical insights into an individual's health and disease condition. Current sensors predominantly utilize enzymes and antibodies as biometric components to measure biomarkers present in sweat quantitatively. However, enzymes and antibodies are susceptible to interference by environmental factors, which may affect the performance of the sensor. Herein, we present a wearable microfluidic surface-enhanced Raman scattering (SERS) biosensor that enables the non-invasive and label-free detection of biomarkers in sweat. Concretely, we developed a bimetallic self-assembled anti-opal array structure with uniform hot spots, enhanced the Raman scattering effect, and integrated it into a silk fibroin-based sensing patch. Utilizing a silk fibroin substrate in the wearable SERS sensor imparts desirable properties such as softness, breathability, and biocompatibility, which enables the sensor to establish close contact with the skin without causing chemical or physical irritation. In addition, introducing microfluidic channels enables the controlled and high temporal resolution management of sweat, facilitating more efficient sweat collection. The proposed label-free SERS sensor can offer chemical 'fingerprint' information, enabling the identification of sweat analytes. As an illustration of the feasibility, we have effectively monitored the creatinine and uric acid levels in sweat. This study presents a versatile and highly sensitive approach for the simultaneous detection of biomarkers in human sweat, showcasing significant potential for application in point-of-care monitoring.

Integrated mental stress smartwatch based on sweat cortisol and HRV sensors.

Mental stress, a human's common emotion that is difficult to recognize and describe, can give rise to serious psychological disorders. Skin and sweat are easily accessible sources of biomarkers and bio-signals that contain information about mental stress. It is challenging for current wearable devices to monitor psychological stress in real-time with a non-invasive manner. Therefore, we have developed a smartwatch integrated with a sweat cortisol sensor and a heart rate variation (HRV) sensor. This smartwatch can simultaneously record the cortisol levels in sweat and HRV index in real time over a long period. The cortisol sensors based on organic electrochemical transistor (OECT) are fabricated by utilizing the Prussian-blue (PB) doped molecular imprinting polymer (MIP) modified gate electrode. The sensor signal current will decrease following the combination of sweat cortisol, due to the blocking of the PBMIP conductive path, demonstrating good sensitivity, selectivity, and stability. The HRV sensor is manufactured by a photoplethysmography method. We have integrated the two sensors into a wearable smartwatch that can match well with the mobile phone APP and the upper computer software. Through the use of this smartwatch, we have observed a negative correlation between cortisol levels in sweat and the HRV index in short-term stressful environments. Our research presents a great progress in real-time and non-invasive monitoring human's stress levels, which promotes not only the stress management, but also better psychological research.

Molecularly Imprinted Wearable Sensor with Paper Microfluidics for Real-Time Sweat Biomarker Analysis.

The urgent need for real-time and noninvasive monitoring of health-associated biochemical parameters has motivated the development of wearable sweat sensors. Existing electrochemical sensors show promise in real-time analysis of various chemical biomarkers. These sensors often rely on labels and redox probes to generate and amplify the signals for the detection and quantification of analytes with limited sensitivity. In this study, we introduce a molecularly imprinted polymer (MIP)-based biochemical sensor to quantify a molecular biomarker in sweat using electrochemical impedance spectroscopy, which eliminates the need for labels or redox probes. The molecularly imprinted biosensor can achieve sensitive and specific detection of cortisol at concentrations as low as 1 pM, 1000-fold lower than previously reported MIP cortisol sensors. We integrated multimodal electrochemical sensors with an iontophoresis sweat extraction module and paper microfluidics for real-time sweat analysis. Several parameters can be simultaneously quantified, including sweat volume, secretion rate, sodium ion, and cortisol concentration. Paper microfluidic modules not only quantify sweat volume and secretion rate but also facilitate continuous sweat analysis without user intervention. While we focus on cortisol sensing as a proof-of-concept, the molecularly imprinted wearable sensors can be extended to real-time detection of other biochemicals, such as protein biomarkers and therapeutic drugs.

Antifouling and antimicrobial wearable electrochemical sweat sensors for accurate dopamine monitoring based on amyloid albumin composite hydrogels.

Wearable electrochemical sweat sensors are potentially promising for health monitoring in a continuous and non-invasive mode with high sensitivity. However, due to the complexity of sweat composition and the growth of skin bacteria, the wearable sweat sensors may gradually lose their sensitivity or even fail over time. To deal with this issue, herein, we proposed a new strategy to construct wearable sweat sensors with antifouling and antimicrobial capabilities. Amyloid albumin hydrogels (ABSAG) were doped with two-dimensional (2D) nanomaterial MXene and CeO2 nanorods to obtain the antifouling and antimicrobial amyloid albumin composite hydrogels (ABSACG, CeO2/MXene/ABSAG), and the wearable sensors were prepared by modifying flexible screen-printed electrodes with the ABSACG. Within this sensing system, the hydrophilic ABSAG possesses strong hydration capability, and it can form a hydration layer on the electrode surface to resist biofouling in sweat. The 2D nanomaterial MXene dispersed in the hydrogel endows the hydrogel with good conductivity and electrocatalytic capability, while the doping of CeO2 nanorods further improves the electrocatalytic performance of the hydrogel and also provides excellent antimicrobial capability. The designed wearable electrochemical sensors based on the ABSACG demonstrated satisfying antifouling and antimicrobial abilities, and they were capable of detecting dopamine accurately in human sweat. It is expected that wearable sensors utilizing the antifouling and antimicrobial ABSACG may find practical applications in human body fluids analysis and health monitoring.

Simultaneous detection of tyrosine and uric acid in sweat using CoWO4@CNT with a hydrogel modified electrochemical biosensor.

The levels of uric acid (UA) and tyrosine (Tyr) in sweat reflect a person's overall health. However, simultaneously identifying several components in sweat remains challenging. Here, we achieve simultaneous detection of UA and Tyr by synthesizing CoWO4@CNT in a single step using a hydrothermal method. CoWO4's high catalytic efficacy and large CNT reaction area allow the detection of 1-1000 µM UA (LOD = 0.14 µM) and 5-1000 µM Tyr (LOD = 4.2 µM). To increase sweat collection, we developed a polydopamine-polyacrylamide (PDA-PAM) hydrogel with a sweat absorption rate of up to 226%. Finally, by monitoring sweat at various times of day, our sensors can discriminate between UA and Tyr in real sweat, and the results are consistent with the individuals' activity levels. Overall, the effective electrocatalytically active materials and PDA-PAM hydrogel improve the detection of UA and Tyr. The remarkable performance of CoWO4@CNT in real samples shows that it has the potential to improve health detection and real-time sweat analysis.

Machine learning-powered wearable interface for distinguishable and predictable sweat sensing.

The constrained resources on wearable devices pose a challenge in meeting the demands for comprehensive sensing information, and current wearable non-enzymatic sensors face difficulties in achieving specific detection in biofluids. To address this issue, we have developed a highly selective non-enzymatic sweat sensor that seamlessly integrates with machine learning, ensuring reliable sensing and physiological monitoring of sweat biomarkers during exercise. The sensor consists of two electrodes supported by a microsystem that incorporates signal processing and wireless communication. The device generates four explainable features that can be used to accurately predict tyrosine and tryptophan concentrations, as well as sweat pH. The reliability of this device has been validated through rigorous statistical analysis, and its performance has been tested in subjects with and without supplemental amino acid intake during cycling trials. Notably, a robust linear relationship has been identified between tryptophan and tyrosine concentrations in the collected samples, irrespective of the pH dimension. This innovative sensing platform is highly portable and has significant potential to advance the biomedical applications of non-enzymatic sensors. It can markedly improve accuracy while decreasing costs.

Sweat-based stress screening with gas chromatography-ion mobility spectrometry and electronic nose.

BACKGROUND: Diagnosis of stress generally involves uses of questionnaires which can provide biased results. The more reliable approach relies on observation of individual symptoms by psychiatrists which is time consuming and could not be applicable for massive scale screening tests. This research established alternative approaches with gas chromatography-ion mobility spectrometry (GC-IMS) and electronic nose (e-nose) to perform fast stress screening based on fingerprinting of highly volatile compounds in headspaces of sweat. The investigated samples were obtained from 154 female nurse volunteers who also provided the data of questionnaire-based mental health scores with the high stress cases confirmed by psychiatrists. RESULTS: The interviews by psychiatrists revealed 14 volunteers with high stress. Their axillary sweat samples and that from 32 nurses with low/moderate stress (controls) were collected onto cotton rods and analysed with GC-IMS. The possible marker peaks were selected based on the accuracy data. They were tentatively identified as ammonia, diethyl ether, methanol, octane, pentane, acetone and dimethylamine which could involve different endogenous mechanisms or the relationships with the local microbiomes. The data were further analysed using partial least squares discriminant analysis with the receiver operating characteristic curves showing the optimum accuracy, sensitivity and selectivity of 87%, 86% and 88%, respectively. Providing that the samples were obtained from the nurses without deodorant uses, the high stress cases could be screened using e-nose sensors with the accuracy of 89%. The sensor responses could be correlated with the marker peak area data in GC-IMS with the coefficients ranging from -0.70 to 0.80. SIGNIFICANCE: This represents the first investigation of highly volatile compound markers in sweat for high stress screening. The established methods were simple, reliable, rapid and non-invasive, which could be further adapted into the portable platform of e-nose sensors with the practical application to perform the screening tests for nurses in Phra Nakorn Si Ayutthaya hospital, Thailand.

Skin-attachable Tb-MOF ratio fluorescent sensor for real-time detection of human sweat pH.

The pH of human sweat is highly related with a variety of diseases, whereas the monitoring of sweat pH still remains challenging for ordinary families. In this study, we developed a novel dual-emission Tb-MOF using DPA as the ligand and further designed and constructed a skin-attachable Tb-MOF ratio fluorescent sensor for real-time detection of human sweat pH. With the increased concentration of H+, the interaction of H+ with carbonyl organic ligand leads to the collapse of the Tb-MOF crystal structure, resulting in the interruption of antenna effect, and correspondingly increasing the emission of the ligand at 380 nm and decreasing the emission of the central ion Tb3+ at 544 nm. This Tb-MOF nanoprobe has a good linear response in the pH range of 4.12-7.05 (R2 = 0.9914) with excellent anti-interference ability. Based on the merits of fast pH response and high sensitivity, the nanoprobe was further used to prepare flexible wearable sensor. The wearable sensor can detect pH in the linear range of 3.50-6.70, which covers the pH range of normal human sweat (4.50-6.50). Subsequently, the storage stability and detection accuracy of the sensors were evaluated. Finally, the sensor has been successfully applied for the detection of pH in actual sweat samples from 21 volunteer and the real-time monitoring of pH variation during movement processing. This skin-attachable Tb-MOF sensor, with the advantages of low cost, visible color change and long shelf-life, is appealing for sweat pH monitoring especially for ordinary families.

A sensor platform based on SERS detection/janus textile for sweat glucose and lactate analysis toward portable monitoring of wellness status.

Herein we report a wearable sweat sensor of a Janus fabric based on surface enhanced Raman scattering (SERS) technology, mainly detecting the two important metabolites glucose and lactate. Janus fabric is composed of electrospinning PU on a piece of medical gauze (cotton), working as the unidirectional moisture transport component (R = 1305%) to collect and transfer sweat efficiently. SERS tags with different structures act as the probe to recognize and detect the glucose and lactate in high sensitivity. Core-shell structured gold nanorods with DTNB inside (AuNRs@DTNB@Au) are used to detect lactate, while gold nanorods with MPBA (AuNRs@MPBA) are used to detect glucose. Through the characteristic SERS information, two calibration functions were established for the concentration determination of glucose and lactate. The concentrations of glucose and lactate in sweat of a 23 years volunteer during three-stage interval running are tested to be 95.5, 53.2, 30.5 µM and 4.9, 13.9, 10.8 mM, indicating the glucose (energy) consumption during exercise and the rapid accumulation of lactate at the early stage accompanied by the subsequent relief. As expected, this sensing system is able to provide a novel strategy for effective acquisition and rapid detection of essential biomarkers in sweat.

A wearable nanozyme-enzyme electrochemical biosensor for sweat lactate monitoring.

In this study, we developed a wearable nanozyme-enzyme electrochemical biosensor that enablies sweat lactate monitoring. The biosensor comprises a flexible electrode system prepared on a polyimide (PI) film and the Janus textile for unidirectional sweat transport. We obtained favorable electrochemical activities for hydrogen peroxide reduction by modifying the laser-scribed graphene (LSG) electrode with cerium dioxide (CeO2)-molybdenum disulphide (MoS2) nanozyme and gold nanoparticles (AuNPs). By further immobilisation of lactate oxidase (LOx), the proposed biosensor achieves chronoamperometric lactate detection in artificial sweat within a range of 0.1-50.0 mM, a high sensitivity of 25.58 µA mM-1cm-2 and a limit of detection (LoD) down to 0.135 mM, which fully meets the requirements of clinical diagnostics. We demonstrated accurate lactate measurements in spiked artificial sweat, which is consistent with standard ELISA results. To monitor the sweat produced by volunteers while exercising, we conducted on-body tests, showcasing the wearable biosensor's ability to provide clinical sweat lactate diagnosis for medical treatment and sports management.

A large scale study of portable sweat test sensor for accurate, non-invasive and rapid COVID-19 screening based on volatile compound marker detection.

This study established a novel infield sensing approach based on detection of the volatile compound markers in skin secretions. This was based on analysis of volatile compounds in axillary sweat samples collected from RT-PCR-proven Coronavirus disease 2019 (COVID-19) positive and negative populations using gas chromatography-mass spectrometry (GC-MS). The analysis proposed the possible markers of the monoaromatic compounds and ethyl hexyl acrylate. A portable photo ionization detector (PID) incorporated with the selective material towards the marker compounds was then developed with the pressurized injection approach. This provided the accuracy of 100% in the research phase (n = 125). The developed approach was then applied for screening of 2207 COVID-19 related cases covering the periods of the Alpha, Beta, Delta and Omicron variants of SARS-CoV-2 infection in Bangkok, Thailand. This offered the sensitivity, specificity and accuracy ranges of 92-99, 93-98 and 95-97%, respectively.

Highly Sensitive Biosensors Based on All-PEDOT:PSS Organic Electrochemical Transistors with Laser-Induced Micropatterning.

Recent advances in numerous biological applications have increased the accuracy of monitoring the level of biologically significant analytes in the human body to manage personal nutrition and physiological conditions. However, despite promising reports about costly wearable devices with high sensing performance, there has been a growing demand for inexpensive sensors that can quickly detect biological molecules. Herein, we present highly sensitive biosensors based on organic electrochemical transistors (OECTs), which are types of organic semiconductor-based sensors that operate consistently at low operating voltages in aqueous solutions. Instead of the gold or platinum electrode used in current electrochemical devices, poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) was used as both the channel and gate electrodes in the OECT. Additionally, to overcome the patterning resolution limitations of conventional solution processing, we confirmed that the irradiation of a high-power IR laser (λ = 1064 nm) onto the coated PEDOT:PSS film was able to produce spatially resolvable micropatterns in a digital-printing manner. The proposed patterning technique exhibits high suitability for the fabrication of all-PEDOT:PSS OECT devices. The device geometry was optimized by fine-tuning the gate area and the channel-to-gate distance. Consequently, the sensor for detecting ascorbic acid (vitamin C) concentrations in an electrolyte exhibited the best sensitivity of 125 µA dec-1 with a limit of detection of 1.3 µM, which is nearly 2 orders of magnitude higher than previous findings. Subsequently, an all-plastic flexible epidermal biosensor was established by transferring the patterned all-PEDOT:PSS OECT from a glass substrate to a PET substrate, taking full advantage of the flexibility of PEDOT:PSS. The prepared all-plastic sensor device is highly cost-effective and suitable for single-use applications because of its acceptable sensing performance and reliable signal for detecting vitamin C. Additionally, the epidermal sensor successfully obtained the temporal profile of vitamin C in the sweat of a human volunteer after the consumption of vitamin C drinks. We believe that the highly sensitive all-PEDOT:PSS OECT device fabricated using the accurate patterning process exhibits versatile potential as a low-cost and single-use biosensor for emerging bioelectronic applications.

Lactate threshold evaluation in swimming using a sweat lactate sensor: A prospective study.

Since assessing aerobic capacity is key to enhancing swimming performance, a simple and widely applicable technology should be developed. Therefore, we aimed to noninvasively visualize real-time changes in sweat lactate (sLA) levels during swimming and investigate the relationship between lactate thresholds in sweat (sLT) and blood (bLT). This prospective study included 24 university swimmers (age: 20.7 s ± 1.8 years, 58% male) who underwent exercise tests at incremental speeds with or without breaks in a swimming flume to measure heart rate (HR), bLT, and sLT based on sLA levels using a waterproof wearable lactate sensor attached to the dorsal upper arm on two different days. The correlation coefficient and Bland-Altman methods were used to verify the similarities of the sLT with bLT and personal performance. In all tests, dynamic changes in sLA levels were continuously measured and projected onto the wearable device without delay, artifacts, or contamination. Following an initial minimal current response, with increasing speed the sLA levels increased substantially, coinciding with a continuous rise in HR. The speed at sLT strongly correlated with that at bLT (p < 0.01 and r = 0.824). The Bland-Altman plot showed a strong agreement (mean difference: 0.08 ± 0.1 m/s). This prospective study achieved real-time sLA monitoring during swimming, even with vigorous movement. The sLT closely approximated bLT; both were subsequently validated for their relevance to performance.