A wearable patch for continuous analysis of thermoregulatory sweat at rest

Solid/Liquid/Gas Three-Phase Interface Enzymatic Reaction-Based Lactate Biosensor with Simultaneously High Sensitivity and Wide Linear Range

Electrochemical lactate biosensors with simultaneously high sensitivity and wide linear detection range are desirable for health monitoring. Nevertheless, the low oxygen level in biological fluids compromises oxidase enzymatic kinetics, which consequently results in a narrow linear detection range and/or low sensitivity. In this study, we addressed this issue by fabricating a solid/liquid/gas three-phase enzyme electrode with sufficiently high oxygen levels in the local reaction zone and much enhanced oxidase enzymatic kinetics. The three-phase enzyme electrode was fabricated by successively immobilizing H2O2 electrocatalyst and lactate oxidase (LOx) on a superhydrophobic porous carbon substrate. Owing to the much-enhanced oxidase enzymatic kinetics, the linear detection upper limit of the three-phase lactate biosensor was increased up to 40 mM, about 57-fold higher than that of the conventional two-phase system (0.7 mM), while a sensitivity as high as 22.28 μA mM-1 cm-2 was maintained. Moreover, a sweat lactate sensing device was fabricated based on the three-phase enzyme electrode and utilized for lactate detection in undiluted sweat during exercise. This three-phase enzyme electrode with both high sensitivity and wide linear range provides a new approach for the development of high-performance lactate sensing systems.

Digital Biomarkers for Parkinson Disease: Bibliometric Analysis and a Scoping Review of Deep Learning for Freezing of Gait

BACKGROUND

With the rapid development of digital biomarkers in Parkinson disease (PD) research, it has become increasingly important to explore the current research trends and key areas of focus.

OBJECTIVE

This study aimed to comprehensively evaluate the current status, hot spots, and future trends of global PD biomarker research, and provide a systematic review of deep learning models for freezing of gait (FOG) digital biomarkers.

METHODS

This study used bibliometric analysis based on the Web of Science Core Collection database to conduct a comprehensive analysis of the multidimensional landscape of Parkinson digital biomarkers. After identifying research hot spots, the study also followed the PRISMA-ScR (Preferred Reporting Items for Systematic Reviews and Meta-Analyses Extension for Scoping Reviews) guidelines for a scoping review of deep learning models for FOG from 5 databases: Web of Science, PubMed, IEEE Xplore, Embase, and Google Scholar.

RESULTS

A total of 750 studies were included in the bibliometric analysis, and 40 studies were included in the scoping review. The analysis revealed a growing number of related publications, with 3700 researchers contributing. Neurology had the highest average annual participation rate (12.46/19, 66%). The United States contributed the most research (192/1171, 16.4%), with 210 participating institutions, which was the highest among all countries. In the study of deep learning models for FOG, the average accuracy of the models was 0.92, sensitivity was 0.88, specificity was 0.90, and area under the curve was 0.91. In addition, 31 (78%) studies indicated that the best models were primarily convolutional neural networks or convolutional neural networks-based architectures.

CONCLUSIONS

Research on digital biomarkers for PD is currently at a stable stage of development, with widespread global interest from countries, institutions, and researchers. However, challenges remain, including insufficient interdisciplinary and interinstitutional collaboration, as well as a lack of corporate funding for related projects. Current research trends primarily focus on motor-related studies, particularly FOG monitoring. However, deep learning models for FOG still lack external validation and standardized performance reporting. Future research will likely progress toward deeper applications of artificial intelligence, enhanced interinstitutional collaboration, comprehensive analysis of different data types, and the exploration of digital biomarkers for a broader range of Parkinson symptoms.

TRIAL REGISTRATION

Open Science Foundation (OSF Registries) OSF.IO/RG8Y3; https://doi.org/10.17605/OSF.IO/RG8Y3.

New trends in potentiometric sensors: From design to clinical and biomedical applications

Potentiometry, a well-established electrochemical technique, provides a powerful and versatile method for the sensitive and selective measurement of a variety of analytes by measuring the potential difference between two electrodes, allowing for a direct and rapid readout of ion concentrations. This makes it a valuable tool in a variety of applications including industry, agriculture, forensics, medical, environmental assessment, and pharmaceutical drug analysis, therefore it has received significant attention from the scientific community. Their broad implementation in sensing applications arises through their many benefits, including ease of design, fabrication, and modification; rapid response time; high selectivity; suitability for use with colored and/or turbid solutions; and potential for integration into embedded systems interfaces. Owing to these advantages and diverse applicability, sustained research and development in the field has resulted in the emergence of several notable trends in the field. 3D printing is the most recent technique used in potentiometry which offers many benefits such as improved flexibility and precision in the manufacturing of ion-selective electrodes and rapid prototyping decreases the time needed during optimization of important electrochemical parameters. Additionally, paper-based sensors are cost-effective and versatile platforms for in-field (point-of-care, POC) analysis, permitting rapid determination of a variety of analytes. One of the most interesting applications of potentiometry are wearable sensors which allow for the continuous monitoring of biomarkers, electrolytes and even pharmaceuticals, especially those with a narrow therapeutic index. Herein this review, we discuss several recent trends in potentiometric sensors since 2010, including 3D printing, paper-based devices, and other emerging techniques and the translation of potentiometric systems to wearable devices for the determination of ionic species or pharmaceuticals in biological fluids paving the way to various clinical and biomedical uses.

Wearable MXene-enhanced organic Bio-FET paper patch for glucose detection in sweat with pH and temperature calibration

This paper proposes the design of organic Bio-FET sensors using paper as a substrate. Three different wearable biosensors have been engineered for the non-invasive monitoring of sweat biomarkers. The proposed sensors, which have a field-effect transistor (FET) structure, contribute to an array that is flexible, bendable, affordable, disposable, and biocompatible. The approach of drawing Organic FETs (OFETs) on paper using a paintbrush could successfully make cost-effective sweat biochemical sensors (glucose and pH Sensors) and biophysical sensors (temperature-sensor) which are versatile and sensors for real-time health monitoring. PDMS, PEDOT: PSS, and sensitive materials have been used as the oxide layer, source/drain electrodes, and the FET channel, respectively. The wearable glucose sensor utilizes a composite of copper oxide (CuO), carboxyl-functionalized multiwall carbon nanotubes (MWCNT-COOH), and Ti₃C₂ MXene (Ti₃C₂ MXene/CuO/MWCNT) as the channel material in its FET structure, enhancing its sensitivity and performance. Additionally, Ti3C2 MXene/MWCNT and Ti₃C₂ MXene/rGO/MWCNT composites were employed in the pH and temperature sensors, respectively, to enhance their functionality and performance. The proposed Bio-FETs are fabricated in three different designs: resistive, side-gated and back-gated structures, and their responses are compared and discussed. Continuous health monitoring is achieved through a fully integrated, disposable wireless device that combines glucose, pH, and temperature sensing. The fabricated Bio-FET exhibits high sensitivity and promising reproducibility, stability, and repeatability. To enhance precision, the proposed glucose sensor has been calibrated using real-time temperature and pH measurements.

Revolutionizing biosensing with wearable microneedle patches: innovations and applications

Wearable microneedle (MN) patches have emerged as a transformative platform for biosensing, offering a minimally invasive and user-friendly approach to real-time health monitoring and disease diagnosis. Primarily designed to access interstitial fluid (ISF) through shallow skin penetration, MNs enable precise and continuous sampling of biomarkers such as glucose, lactate, and electrolytes. Additionally, recent innovations have integrated MN arrays with microfluidic and porous structures to support sweat-based analysis, where MNs act as structural or functional components in hybrid wearable systems. This review explores the design, fabrication, and functional integration of MNs into wearable devices, highlighting advances in multi-analyte detection, wireless data transmission, and self-powered sensing. Challenges related to material biocompatibility, sensor stability, scalability, and user variability are addressed, alongside emerging opportunities in microfluidics, artificial intelligence, and soft materials. Overall, MN-based biosensing platforms are poised to redefine personalized healthcare by enabling dynamic, decentralized, and accessible health monitoring.

Unperceivable Designs of Wearable Electronics

Wearable smart electronics are taking an increasing part of the consumer electronics market, with applications in advanced healthcare systems, entertainment, and Internet of Things. The advanced development of flexible, stretchable, and breathable electronic materials has paved the way to comfortable and long-term wearables. However, these devices can affect the wearer's appearance and draw attention during use, which may impact the wearer's confidence and social interactions, making them difficult to wear on a daily basis. Apart from comfort, one key condition for user acceptance is that these new technologies seamlessly integrate into our daily lives, remaining unperceivable to others. In this review, strategies to minimize the visual impact of wearable devices and make them more suitable for daily use are discussed. These new devices focus on being unperceivable when worn and comfortable enough that users almost forget their presence, reducing psychological discomfort while maintaining accuracy in signal collection. Materials selection is crucial for developing long-term and unperceivable wearable devices. Recent developments in these unperceivable electronic devices are also covered, including sensors, transistors, and displays, and mechanisms to achieve unperceivability are discussed. Finally, the potential applications are summarized and the remaining challenges and prospects are discussed.

Transforming Healthcare: Intelligent Wearable Sensors Empowered by Smart Materials and Artificial Intelligence

Intelligent wearable sensors, empowered by machine learning and innovative smart materials, enable rapid, accurate disease diagnosis, personalized therapy, and continuous health monitoring without disrupting daily life. This integration facilitates a shift from traditional, hospital-centered healthcare to a more decentralized, patient-centric model, where wearable sensors can collect real-time physiological data, provide deep analysis of these data streams, and generate actionable insights for point-of-care precise diagnostics and personalized therapy. Despite rapid advancements in smart materials, machine learning, and wearable sensing technologies, there is a lack of comprehensive reviews that systematically examine the intersection of these fields. This review addresses this gap, providing a critical analysis of wearable sensing technologies empowered by smart advanced materials and artificial Intelligence. The state-of-the-art smart materials-including self-healing, metamaterials, and responsive materials-that enhance sensor functionality are first examined. Advanced machine learning methodologies integrated into wearable devices are discussed, and their role in biomedical applications is highlighted. The combined impact of wearable sensors, empowered by smart materials and machine learning, and their applications in intelligent diagnostics and therapeutics are also examined. Finally, existing challenges, including technical and compliance issues, information security concerns, and regulatory considerations are addressed, and future directions for advancing intelligent healthcare are proposed.

Emerging Multifunctional Wearable Sensors: Integrating Multimodal Sweat Analysis and Advanced Material Technologies for Next-Generation Health Monitoring

Sweat, a noninvasive and readily accessible biofluid, offers significant potential in health monitoring through its diverse biomarker profile, including electrolytes, metabolites, and hormones, which reflect physiological states in real time. Multimodal wearable sensors, integrating chemical, physical, and thermal sensing capabilities, have emerged as transformative tools for capturing these biomarkers alongside additional physiological signals. By combining advanced materials such as hydrogels, MXenes, and graphene with innovative structural designs, these sensors enable simultaneous monitoring of biomarkers (e.g., glucose, sodium, and cortisol) alongside parameters like movement and temperature. This Review systematically explores the classification and design of multimodal sensors, emphasizing their ability to address health monitoring challenges across applications including metabolic health management, stress detection, and hydration assessment. Key innovations in functional materials, such as conductive hydrogels and biomimetic structures, are discussed alongside challenges in signal integration, data processing, and power management. Additionally, advancements in self-powered systems and energy harvesting technologies have been highlighted as critical enablers for continuous, real-time monitoring. The Review concludes with a perspective on future directions, emphasizing the need for scalable manufacturing techniques, artificial intelligence integration, and standardized frameworks to enhance sensor functionality and adoption. Multimodal wearable sensors, by seamlessly integrating health data into daily life, hold the promise of transforming personalized healthcare, enabling proactive management of health and wellness through noninvasive, comprehensive, and real-time monitoring.

A Touch Enabled Hemodynamic and Metabolic Monitor

Accurate health analysis demands real-time tracking of multiple biomarkers and vital signs under dynamic physiological conditions. Current multimodal hybrid platforms provide biochemical and biophysical data but are limited by active sweat collection for biochemical sensing and bulky designs for biophysical sensing. Here a touch-enabled platform is presented that simultaneously monitors vitals and metabolic markers. With a simple tri-finger touch, the platform measures mean arterial pressure and heart rate using photoplethysmography, and glucose, uric acid, and cortisol at rest by leveraging the natural perspiration at the fingertip. Extended studies involving diverse activities reveal strong dynamic interplay among the metabolic and vital profiles, with mean arterial pressure showing the highest sensitivity to cortisol fluctuations. The platform delivers comprehensive health information linking diet, lifestyle, metabolism, and serves as an early metabolic or hormonal stress indicator. Valuable insights gained through the platform position it as a promising tool for personalized health and wellness management.

Universal Flexible Wearable Biosensors for Noninvasive Health Monitoring

Sweat, with its abundant biomarkers, is a highly appealing biofluid for personalized health monitoring and management. Noninvasive wearable sweat sensors hold great potential in this regard. However, developing an easy-to-prepare, highly sensitive, precise, and versatile wearable biosensor remains challenging. Herein, we report a universal electrochemical wearable biosensor for the accurate and sensitive detection of glucose, uric acid, and lactate in human sweat samples. A Pt nanoparticle-deposited nitrogen-doped mesoporous carbon/reduced graphene oxide composite (PNGO) was synthesized rapidly by using a simple multistage self-assembly strategy. The detection was carried out using electrodes modified with PNGO and enzyme-immobilized membranes, achieving high sensitivities (glucose: 15.33 μA mM-1 cm-2, uric acid: 103.2 μA mM-1 cm-2, lactate: 219.1 μA mM-1 cm-2), along with excellent selectivity, reproducibility, and stability. Based on the excellent performance of the biosensor, we investigated its reliability in detecting sweat targets during physical exercise and assessed its utility for monitoring human health status through glucose and purine dietary challenges, observing trends consistent with blood results. The integrated wearable flexible patch constructed in this work can provide periodic information related to sweat chemistry, and the low-cost electrode suggests the potential for large-scale manufacturing. Thus, it shows extraordinary promise for promotion and application in human health and training management.

An integrated wearable microfluidic biosensor for simultaneous detection of multiple biomarkers in sweat

Simultaneous detection of biomarkers in sweat is crucial for comprehensive health assessment and personalized monitoring. However, the low sweat secretion rate and low metabolite concentrations present challenges for developing non-invasive wearable sensors. This study aims to develop a flexible wearable biosensor for simultaneous detection of low-concentration biomarkers in sweat, enabling comprehensive health assessment. This study synthesized an innovative bimetallic tungstate Ag@Ag2WO4 and evaluated its performance for detecting uric acid (UA, 10-1000 μM), dopamine (DA, 3-500 μM), and tyrosine (Tyr, 5-1000 μM). The detection limits (LODs) for DA, UA, and Tyr sensors were 3.10 μM, 8.47 μM, and 4.17 μM, respectively, with relative standard deviations (RSDs) of 4.76 %, 2.66 %, and 3.51 %, respectively. Additionally, this study designed a hydrophilic microfluidic collection system inspired by bamboo leaf structures to enhance sweat collection efficiency. Validation studies demonstrated that the wearable biosensor effectively detects UA and TA in the sweat of volunteers. We believe this research could contribute to advancing personalized healthcare by improving the convenience and effectiveness of health monitoring technologies.

Electrophoretic digital colorimetry integrated with electrochemical sweat sensor

Recent advancements in wearable sweat sensors, which use standardized electrochemical and colorimetric mechanisms, offer holistic representation of health status for users. However, the constraints of standardized sweat sensors present ongoing challenges to realization of personalized health management. This study presents an electrocolorimetric (EC) platform that enables the reversible and multiple-time use of colorimetric data visualization using electrophoretic display (EPD). This platform represents the application of low-power EPD in epidermal sweat sensor, evaluated through CIELAB-based methodology which is the first systematic evaluation tool of wearable display performance. Moreover, our platform has been demonstrated in human exercise trials for its ability to detect the lactate threshold (LT). This digital colorimetric system has the potential to play a pivotal role by integrating various health monitoring biomarkers. While providing real-time, continuous, and adjustable range information with high sensitivity, this platform validates its extensive probability as a next-generation wearable epidermal sensor.

A novel type of planar reference electrodes based on ionic liquids

Although electrochemical sensors gained a lot of popularity through recent years, there is very little research on sensors with IL-based reference electrodes. This type of reference electrodes might be the ultimate solution for problem of RE miniaturization. In this paper a novel type of printed reference electrodes based on ionic liquids are presented. The potential stability of electrodes with membranes containing two new ILs with promising properties, namely 1-ethyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate (EMIM+FAP-) and 1-(2-methoxyethyl)-1-methylpyrrolidin-1-ium tris(pentafluoroethyl)trifluorophosphate (PYR(2o1,1)+FAP-), was investigated. Reference membranes were implemented in classic electrodes with internal electrolyte, as well as deposited on planar transducers with electrodes fabricated using screen printing or aerosol jet printing. Membranes were deposited via drop-casting or by using aerosol jet printer, to form fully printed reference electrodes. It was found that while both tested ionic liquids performed similarly, the use of (PYR(2o1,1)+FAP-) resulted in better potential stability. Planar IL-based electrode was finally used as a reference electrode in a simple pH sensor, enabling the detection of pH changes.

Au nanoparticles anchored carbonized ZIF-8 for enabling real-time and noninvasive glucose monitoring in sweat

Wearable sensors can easily enable real-time and noninvasive glucose (Glu) monitoring, providing vital information for effectively preventing various complications caused by high glucose level. Here, a wearable sensor based on nanozyme-catalyzed cascade reactions is designed for Glu monitoring in sweat. Au nanoparticles (AuNPs) are anchored to the carbonated zeolitic imidazolate framework-8 (ZIF-8-C), endowing the sensor with Glu oxidase (GOx)-like and peroxidase (POD)-like activity. A flexible screen-printed carbon electrode (SPCE) is decorated with the resultant AuNPs@ZIF-8-C, which is further modified with biocompatible and swellable calcium alginate (CA) gels for the preparation of the wearable Glu sensor. The linear range for Glu detection is 10∼300 μM with a limit of detection (LOD) of 4.99 μM, which covers the physiological Glu concentration range in human sweat (10-200 μM). The developed wearable Glu sensor can fit well with the skin tissues due to the flexibility of the SPCE, and thus it can be successfully applied in real-time and noninvasive monitoring of Glu in human sweat. Additionally, the wearable Glu sensor exhibits high antibacterial activity resulted from the generated hydroxyl radicals (·OH), enabling long-term Glu monitoring in sweat.

Optimized synergistic effects in sweat glucose detection with a Pt single-atom catalyst on NiO for fingertip wearable biosensors

For the approximately 8.5 % of the global population living with diabetes, puncture-based glucose testing is often an unpleasant experience. Non-invasive sweat glucose testing not only reduces pain and the risk of wound infection but also offers a more suitable method for real-time glucose monitoring. In this study, we developed a fingertip wearable biosensor (FWB) capable of continuously measuring glucose levels in sweat, providing valuable data for assessing glucose concentrations in humans. We successfully synthesized NiO/Pt single-atom catalysts (NiO/Pt SAs) using a UV reduction technique, achieving a detection range of 5 μM to 2 mM that encompasses the full spectrum of physiological glucose levels. Additionally, incorporating 0.075 g of starch enhanced the hydrogel's water absorption and swelling properties, allowing it to absorb over 832 % of its dry weight without breaking, thereby improving sweat absorption efficiency. We also designed an annular microfluidic channel for rapid sweat transport. The circular design fits snugly on the fingertip surface, minimizing footprint and increasing comfort. This makes the device more stable in real-world use and minimizes the effects of external movements or environmental changes. Experimental results confirmed the feasibility of using the FWB to detect glucose in sweat samples from volunteers. We believe our research holds significant promise for advancements in sweat analysis and health monitoring, presenting a novel and efficient approach for continuous glucose monitoring.

Advances in wearable electronics for monitoring human organs: Bridging external and internal health assessments

Devices used for diagnosing disease are often large, expensive, and require operation by trained professionals, which can result in delayed diagnosis and missed opportunities for timely treatment. However, wearable devices are being recognized as a new approach to overcoming these difficulties, as they are small, affordable, and easy to use. Recent advancements in wearable technology have made monitoring information possible from the surface of organs like the skin and eyes, enabling accurate diagnosis of the user's internal status. In this review, we categorize the body's organs into external (e.g., eyes, oral cavity, neck, and skin) and internal (e.g., heart, brain, lung, stomach, and bladder) organ systems and introduce recent developments in the materials and designs of wearable electronics, including electrochemical and electrophysiological sensors applied to each organ system. Further, we explore recent innovations in wearable electronics for monitoring of deep internal organs, such as the heart, brain, and nervous system, using ultrasound, electrical impedance tomography, and temporal interference stimulation. The review also addresses the current challenges in wearable technology and explores future directions to enhance the effectiveness and applicability of these devices in medical diagnostics. This paper establishes a framework for correlating the design and functionality of wearable electronics with the physiological characteristics and requirements of various organ systems.

Worth your sweat: wearable microfluidic flow rate sensors for meaningful sweat analytics

Wearable microfluidic sweat sensors could play a major role in the future of monitoring health and wellbeing. Sweat contains biomarkers to monitor health and hydration status, and it can provide information on drug intake, making it an interesting non-invasive alternative to blood. However, sweat is not created in excess, and this requires smart sweat collection strategies to handle small volumes. Microfluidic solutions are commonly employed which use capillary action or evaporation to drive flow. In current literature about sweat analytics, the emphasis lies predominantly on developing the sensors for measuring the composition of sweat. Yet, solely measuring sweat composition does not suffice, because the composition varies due to inter- and intra-individual differences in sweat rate. The measurement of sweat rate is thus crucial for enabling a reliable interpretation and standardisation of this data. Recently, more wearable sweat sensors, also integrating a means of measuring flow, have been developed. This manuscript reviews state-of-the-art sweat collection strategies and flow rate measuring techniques. Generally, flow rate measurements are performed by impedimetric or capacitive methods. However, these techniques can be impaired due to limited lifetime and signal interference from changing ionic contents in sweat. Discrete measurement techniques, such as impedance measurements of an advancing fluid front with interdigitated electrodes, calorimetric and colorimetric techniques can be very reliable, because they selectively measure flow. However, one should take the available size, intended application and compatibility with other sensors into account. Overall, accurate flow rate sensors integrated in reliable microfluidic sweat sensor platforms will enable the standardisation of sweat measurements to unlock the potential of sweat analytics in advancing physiological research, personalized diagnostics and treatment of diseases.

Wearable and Flexible Sensor Devices: Recent Advances in Designs, Fabrication Methods, and Applications

The development of wearable sensor devices brings significant benefits to patients by offering real-time healthcare via wireless body area networks (WBANs). These wearable devices have gained significant traction due to advantageous features, including their lightweight nature, comfortable feel, stretchability, flexibility, low power consumption, and cost-effectiveness. Wearable devices play a pivotal role in healthcare, defence, sports, health monitoring, disease detection, and subject tracking. However, the irregular nature of the human body poses a significant challenge in the design of such wearable systems. This manuscript provides a comprehensive review of recent advancements in wearable and flexible smart sensor devices that can support the next generation of such sensor devices. Further, the development of direct ink writing (DIW) and direct writing (DW) methods has revolutionised new high-resolution integrated smart structures, enabling the design of next-generation soft, flexible, and stretchable wearable sensor devices. Recognising the importance of keeping academia and industry informed about cutting-edge technology and time-efficient fabrication tools, this manuscript also provides a thorough overview of the latest progress in various fabrication methods for wearable sensor devices utilised in WBAN and their evaluation using body phantoms. An overview of emerging challenges and future research directions is also discussed in the conclusion.

MWCNTs/PANI silk fibroin film sensor based on microneedle array for sweat pH detection

Incorporating silk fibroin (SF) into the biosensing platform provides a level of flexibility and macro-structure control that holds immense importance for monitoring of sweat pH. It accomplishes non-invasive surveillance of the human physiology while concurrently tackling the issue of electrode-skin friction. The preparation of the multi-walled carbon nanotubes (MWCNTs)/polyaniline (PANI) silk fibroin pH-responsive microneedle array sensor involves the dispersion of PANI powder in silk fibroin and the addition of MWCNTs for the analysis of human sweat. The template method offers an efficient and straightforward means of producing microneedles with a high degree of precision, achieving micrometer resolution. The pH sensor is designed with a two-electrode configuration, comprising an MWCNTs/PANI silk fibroin microneedle array sensing electrode as well as an Ag/AgCl reference electrode. The pH sensor shows a sensitivity of 53.60 mV/pH over the pH range 3 to 9, a response time of 68 s, and a recovery time of 77 s. The pH sensor displays other outstanding sensor performances regarding reversibility, repeatability, selectivity, and stability. The pH sensor is capable of detecting alterations in the pH levels of human sweat.

Sub-femtomolar drug monitoring via co-calibration mechanism with nanoconfined DNA probes

Synthetic drugs fundamentally reshape the illicit drug market due to their low cost, ease of production, and rapid manufacturing processes. However, current drug detection methods, which rely on complex instruments, have limited applicability and often neglect the influence of pH fluctuations, leading to potential bias and unreliable results. Herein, we propose co-calibration DNA probes on a nanoconfined biosensor (NCBS), covering the range of sweat pH 3-8 to achieve significantly enhanced target signal recognition. The NCBS exhibits a linear response range of 103-108 fM with a low limit of detection (LOD) of 3.58 fM in artificial sweat. Compared to the single-aptamer NCBS, the dual-aptamer NCBS offers a broader linear response range, primarily due to the synergistic effects of changes in surface wettability and the capture of hydrion, which together reduce signal interference in proton transport. The linear response range doubles, and its detection sensitivity improves by 4-5 orders of magnitude compared to existing drug detection methods. This sensing strategy expands the application scope of aptamer-based composite probes, offering an approach for ultra-sensitive drug detection and demonstrating significant potential in sweat sensing and drug monitoring fields.

Directional Liquid Transport in Thin Fibrous Matrices: Enhancement of Advanced Applications

Directional liquid transport fibrous matrices (DLTFMs) have the unique ability to direct liquid movement in a single direction through their thickness. Beyond their inherent liquid transport function, DLTFMs can also enhance the effectiveness of additional functionalities. This review focuses on recent advances in DLTFMs, particularly the role of DLTs in enhancing secondary functions. We begin with a brief overview of the historical development and major achievements in DLTFM research, followed by an outline of the classification, fabrication techniques, and basic functions derived from their natural liquid transport properties. The integration of DLT to enhance secondary functionalities such as responsiveness, thermal regulation, and wearable technology for innovative applications in various sectors is then discussed. The review concludes with a discussion of key challenges and prospects in the field, including the durability and reliability of DLT performance, the precise regulation of fluid transport rates, the resilience and longevity of DLTFMs in harsh environments, and the impact of DLT variations on performance enhancement. The goal of this review is to stimulate further innovative studies on DLTFMs and to promote their practical implementation in a variety of industries.

Biointerface engineering of flexible and wearable electronics

Biointerface sensing is a cutting-edge interdisciplinary field that merges conceptual and practical aspects. Wearable bioelectronics enable efficient interaction and close contact with biological components such as tissues and organs, paving the way for a wide range of medical applications, including personal health monitoring and medical intervention. To be applicable in real-world settings, the patches must be stable and adhere to the skin without causing discomfort or allergies in both wet and dry conditions, as well as other desirable features such as being ultra-soft, thin, flexible, and stretchable. Biosensors have emerged as promising tools primarily used to directly detect biological and electrophysiological signals, enhancing the efficacy of personalized medical treatments and enabling accurate tracking of human well-being. This review highlights the engineering of skin-tissue surfaces/interfaces and their interactions with wearable patches, aiming for both a broad and in-depth understanding of the mechanical and physicochemical properties required for the advancement of flexible and wearable skin patches. Specifically, the advantages of flexible bioelectronics and sensors with optimized surface geometry for long-term diagnosis are discussed. This insight aims to guide the future development of functional materials that can interact with human tissue in a controlled manner. Finally, we provide perspectives on the challenges and potential applications of biointerface engineering in wearable devices.

A wearable platform for biochemical sweat analysis using photonic crystal hydrogel

Wearable systems for health monitoring are highly desired in personal diagnostics and precision medicine while challenges remain in constructing such wearable systems with reliability and high performance. Herein, we report a wearable platform for non-invasive monitoring biomarkers in sweat. The device is composed of a butterfly-shaped like microfluidic platform in which responsive photonic crystal hydrogels are embedded in each butterfly wing as sensors. Sweat lactate concentration and pH can be obtained via the color variation of the sensor with naked eyes. Accurate quantitative analysis of the two target analytes can be obtained via the image analysis on a mobile phone by integrating the linear range response to analytes within the physiological range. Moreover, the sensor exhibits good reproducibility, excellent selectivity and long-term stability. On-body trials have been conducted by attaching the device on volunteers' body, and the obtained results are consistent with those analyzed through standardized methods, demonstrating its potentiality in real-time and continuous monitoring sweat biomarkers. This non-invasive wearable sensor provides a new strategy for personal health monitoring and sports performance assessment.

Skin-Interfaced Wearable Sensor for Long-Term Reliable Monitoring of Uric Acid and pH in Sweat

Wearable sweat sensors offering real-time monitoring of biomarker levels suffer from stability and accuracy issues, primarily due to low biomarker concentrations, fluctuating sweat pH, and material detachment from sensor deformation. Here, we developed a wearable sensing system integrated with two advanced electrodes and a flexible microchannel for long-term reliable monitoring of sweat pH and uric acid (UA). By printing the ink doped with nanomaterials (Co3O4@CuCo2O4 and polyaniline), we achieved highly stable electrodes for the direct analysis of perspiration, without additional surface modification. Additionally, real-time pH analysis provided a means for sensitivity calibration, reducing the effect of individual metabolism and exercise intensity. As a result, the wearable sensing system for effective gout management was validated by accurately tracking the UA fluctuations in serum and sweat of hyperuricemia patients and healthy individuals. These findings offer a reliable method for tracking biomarkers to assess personal health.

Synergistic color-changing and conductive photonic cellulose nanocrystal patches for sweat sensing with biodegradability and biocompatibility

Given the ongoing requirements for versatility, sustainability, and biocompatibility in wearable applications, cellulose nanocrystal (CNC) photonic materials emerge as excellent candidates for multi-responsive wearable devices due to their tunable structural color, strong electron-donating capacity, and renewable nature. Nonetheless, most CNC-derived materials struggle to incorporate color-changing and electrical sensing into one system since the self-assembly of CNCs is incompatible with conventional conductive mediums. Here we report the design of a conductive photonic patch through constructing a CNC/polyvinyl alcohol hydrogel modulated by phytic acid (PA). The introduction of PA significantly enhances the hydrogen bonding interaction, resulting in the composite film with impressive flexibility (1.4 MJ m-3) and progressive color changes from blue, green, yellow, to ultimately red upon sweat wetting. Interestingly, this system simultaneously demonstrates selective and sensitive electrical sensing functions, as well as satisfactory biocompatibility, biodegradability, and breathability. Importantly, a proof-of-concept demonstration of a skin-adhesive patch is presented, where the optical and electrical dual-signal sweat sensing allows for intuitive visual and multimode electric localization of sweat accumulation during physical exercises. This innovative interactive strategy for monitoring human metabolites could offer a fresh perspective into the design of wearable health-sensing devices, while greatly expanding the applications of CNC-based photonic materials in medicine-related fields.

Trends in ready-to-use portable electrochemical sensing devices for healthcare diagnosis

Compared with previous decades, healthcare has emerged as a key global concern in light of the recurrent outbreak of pandemics. The initial stage in the provision of healthcare involves the process of diagnosis. Countries worldwide advocate for healthcare research due to its efficacy and capacity to assist diverse populations. Enhanced levels of healthcare management can be attained by the implementation of rapid diagnostic procedures and cognitive data analysis. Therefore, there is a constant need for smart therapeutics, analytical tools, and diagnostic systems to improve health and well-being. The past decade witnessed enormous growth in the sensing detection systems integrated into smartphones with printed electrodes and wearable patches for the screening of various healthcare diagnostics biomarkers and therapeutic drugs. This review focuses on the expansion of point-of-care technologies and their incorporation into a broader array of portable devices, a critical aspect in the context of decentralized societies and their healthcare systems. Discussions are broadly focused on the different sensing platforms such as solid electrodes, screen-printed electrodes, and paper-based sensing strategies for the detection of various biomarkers and therapeutic drugs. We also discuss the next-generation healthcare wearable sensing device importance and future research possibilities. Finally, the portable electrochemical sensing devices and their future perspective developments towards healthcare diagnosis are critically summarized.

Influence of next-generation artificial intelligence on headache research, diagnosis and treatment: the junior editorial board members' vision - part 2

Part 2 explores the transformative potential of artificial intelligence (AI) in addressing the complexities of headache disorders through innovative approaches, including digital twin models, wearable healthcare technologies and biosensors, and AI-driven drug discovery. Digital twins, as dynamic digital representations of patients, offer opportunities for personalized headache management by integrating diverse datasets such as neuroimaging, multiomics, and wearable sensor data to advance headache research, optimize treatment, and enable virtual trials. In addition, AI-driven wearable devices equipped with next-generation biosensors combined with multi-agent chatbots could enable real-time physiological and biochemical monitoring, diagnosing, facilitating early headache attack forecasting and prevention, disease tracking, and personalized interventions. Furthermore, AI-driven advances in drug discovery leverage machine learning and generative AI to accelerate the identification of novel therapeutic targets and optimize treatment strategies for migraine and other headache disorders. Despite these advances, challenges such as data standardization, model explainability, and ethical considerations remain pivotal. Collaborative efforts between clinicians, biomedical and biotechnological engineers, AI scientists, legal representatives and bioethics experts are essential to overcoming these barriers and unlocking AI's full potential in transforming headache research and healthcare. This is a call to action in proposing novel frameworks for integrating AI-based technologies into headache care.

Wearable Electrochemical Biosensors for Advanced Healthcare Monitoring

Recent advancements in wearable electrochemical biosensors have opened new avenues for on-body and continuous detection of biomarkers, enabling personalized, real-time, and preventive healthcare. While glucose monitoring has set a precedent for wearable biosensors, the field is rapidly expanding to include a wider range of analytes crucial for disease diagnosis, treatment, and management. In this review, recent key innovations are examined in the design and manufacturing underpinning these biosensing platforms including biorecognition elements, signal transduction methods, electrode and substrate materials, and fabrication techniques. The applications of these biosensors are then highlighted in detecting a variety of biochemical markers, such as small molecules, hormones, drugs, and macromolecules, in biofluids including interstitial fluid, sweat, wound exudate, saliva, and tears. Additionally, the review also covers recent advances in wearable electrochemical biosensing platforms, such as multi-sensory integration, closed-loop control, and power supply. Furthermore, the challenges associated with critical issues are discussed, such as biocompatibility, biofouling, and sensor degradation, and the opportunities in materials science, nanotechnology, and artificial intelligence to overcome these limitations.

Optical sensors for transdermal biomarker detection: A review

This review has explored optical sensors and their important role in non-invasive transdermal biomarker detection. While electrochemical sensors have been thoroughly studied for biomarker tracking, optical sensors present a compelling alternative due to their high sensitivity and selectivity, multiplex capabilities, cost-efficiency, and small form factor. This review examines the latest advancements in optical sensing technologies for transdermal biomarker detection, such as colorimetry, fluorescence, surface plasmon resonance (SPR), fiber optics, photonic crystals, and Raman spectroscopy. These technologies have been applied in the analysis of biomarkers present in sweat and skin gases, which are essential for non-invasive health monitoring. Furthermore, the review has discussed the challenges and future perspectives of optical sensors in in transdermal biomarker detection. The analysis of various sensor types and their applications highlights the transformative potential of optical sensors in enhancing disease diagnostics and promoting proactive health management.

Ammonium Sensing Patch with Ultrawide Linear Range and Eliminated Interference for Universal Body Fluids Analysis

Ammonium level in body fluids serves as one of the critical biomarkers for healthcare, especially those relative to liver diseases. The continuous and real-time monitoring in both invasive and non-invasive manners is highly desired, while the ammonium concentrations vary largely in different body fluids. Besides, the sensing reliability based on ion-selective biosensors can be significantly interfered by potassium ions. To tackle these challenges, a flexible and biocompatible sensing patch for wireless ammonium level sensing was reported with an ultrawide linear range for universal body fluids including blood, tears, saliva, sweat and urine. The as-prepared biocompatible sensors deliver a reliable sensitivity of 58.7 mV decade-1 in the range of 1-100 mM and a desirable selectivity coefficient of 0.11 in the interference of potassium ions, attributed to the cross-calibration within the sensors array. The sensor's biocompatibility was validated by the cell growth on the sensor surface (> 80%), hemolysis rates (< 5%), negligible cellular inflammatory responses and weight changes of the mice with implanted sensors. Such biocompatible sensors with ultrawide linear range and desirable selectivity open up new possibility of highly compatible biomarker analysis via different body fluids in versatile approaches.

Pumpless microfluidic sweat sensing yarn

Textile sweat sensors possess immense potential for non-invasive health monitoring. Rapid in-situ sweat capture and prevention of its evaporation are crucial for accurate and stable real-time monitoring. Herein, we introduce a unidirectional, pump-free microfluidic sweat management system to tackle this challenge. A nanofiber sheath layer on micrometer-scale sensing filaments enables this pumpless microfluidic design. Utilizing the capillary effect of the nanofibers allows for the swift capture of sweat, while the differential configuration of the hydrophilic and hydrophobic properties of the sheath and core yarns prevents sweat evaporation. The Laplace pressure difference between the cross-scale fibers facilitates the management system to ultimately expulse sweat. This results in microfluidic control of sweat without the need for external forces, resulting in rapid (<5 s), sensitive (19.8 nA μM-1), and stable (with signal noise and drift suppression) sweat detection. This yarn sensor can be easily integrated into various fabrics, enabling the creation of health monitoring smart garments. The garments maintain good monitoring performance even after 20 washes. This work provides a solution for designing smart yarns for high-precision, stable, and non-invasive health monitoring.

Applied body-fluid analysis by wearable devices

Wearable sensors are a recent paradigm in healthcare, enabling continuous, decentralized, and non- or minimally invasive monitoring of health and disease. Continuous measurements yield information-rich time series of physiological data that are holistic and clinically meaningful. Although most wearable sensors were initially restricted to biophysical measurements, the next generation of wearable devices is now emerging that enable biochemical monitoring of both small and large molecules in a variety of body fluids, such as sweat, breath, saliva, tears and interstitial fluid. Rapidly evolving data analysis and decision-making technologies through artificial intelligence has accelerated the application of wearables around the world. Although recent pilot trials have demonstrated the clinical applicability of these wearable devices, their widespread adoption will require large-scale validation across various conditions, ethical consideration and sociocultural acceptance. Successful translation of wearable devices from laboratory prototypes into clinical tools will further require a comprehensive transitional environment involving all stakeholders. The wearable device platforms must gain acceptance among different user groups, add clinical value for various medical indications, be eligible for reimbursements and contribute to public health initiatives. In this Perspective, we review state-of-the-art wearable devices for body-fluid analysis and their translation into clinical applications, and provide insight into their clinical purpose.

Beyond Flexible: Unveiling the Next Era of Flexible Electronic Systems

Flexible electronics are integral in numerous domains such as wearables, healthcare, physiological monitoring, human-machine interface, and environmental sensing, owing to their inherent flexibility, stretchability, lightweight construction, and low profile. These systems seamlessly conform to curvilinear surfaces, including skin, organs, plants, robots, and marine species, facilitating optimal contact. This capability enables flexible electronic systems to enhance or even supplant the utilization of cumbersome instrumentation across a broad range of monitoring and actuation tasks. Consequently, significant progress has been realized in the development of flexible electronic systems. This study begins by examining the key components of standalone flexible electronic systems-sensors, front-end circuitry, data management, power management and actuators. The next section explores different integration strategies for flexible electronic systems as well as their recent advancements. Flexible hybrid electronics, which is currently the most widely used strategy, is first reviewed to assess their characteristics and applications. Subsequently, transformational electronics, which achieves compact and high-density system integration by leveraging heterogeneous integration of bare-die components, is highlighted as the next era of flexible electronic systems. Finally, the study concludes by suggesting future research directions and outlining critical considerations and challenges for developing and miniaturizing fully integrated standalone flexible electronic systems.

A Fully Printable and Integrated System with Long-Term Stability for Versatile and Multimodal Perspiration Tracking

Real-time and continuous monitoring of physiological status via noninvasive sweat sensing shows promise for personalized healthcare and fitness management. However, the largely varied perspiration rates in different body statuses introduce challenges for effective sweat collection and accurate sensing. Herein, a fully printable strategy was developed to realize fully integrated patches for wireless sensing of sweat biomarker levels and perspiration rates with desirable stability and versatility. The printable calcium sensors with modified ion-selective membranes displayed an ultrawide linear range of 0.1-100 mM and a long-term stability with minimized drift down to 0.083 mV/h for around 40 h. Moreover, the microfluidic channels in versatile configurations were capable of a minimum sweat rate monitoring of 0.5 μL/min and a large sweat storage volume of up to 200 μL. The as-proposed fully printable sensing platforms provide high compatibility for sensor integration to achieve versatile perspiration tracking and comprehensive health monitoring.

Wearable Patch Biosensor through Electrothermal Film-Stimulated Sweat Secretion for Continuous Sweat Glucose Analysis at Rest

Wearable patch biosensors for noninvasive and continuous diabetes management through sweat glucose analysis present a promising prospect. However, how to obtain sweat samples safely and effectively remains a huge challenge, especially in a resting state. In this work, we propose an innovative wearable patch biosensor through a heat-stimulated approach for sweat collection. A silver nanowire-loaded electrothermal film was designed as the heat source to stimulate sweat glands for sweat secretion. Subsequently, the secreted sweat sample was transported and enriched through microfluidic channels, which was continuously and sensitively analyzed by a Prussian blue and glucose oxidase comodified glucose electrochemical biosensor. Under optimal conditions, its sensitivity could achieve 14 μM sweat glucose within 15 min, which was 17 min shorter than that without heating. The specificity, reproducibility, and accuracy were also adequate. To achieve on-body perspiration monitoring of human subjects, the wearable patch biosensor was integrated with a portable electrochemical workstation, a temperature controller, and a power source. The glucose concentration was presented on a smartphone. Results showed that the glucose concentration in sweat detected by the wearable biosensor presented a highly consistent trend with the blood glucose measured by a blood glucose meter throughout the day with normal meals. Compared with other conventional sweat stimulation strategies, the simple device and safe principle made it more suitable for individuals who were sedentary or at rest. This work provides a new approach to realizing wearable patch biosensors for personalized health monitoring.

Discretised microfluidics for noninvasive health monitoring using sweat sensing

Using sweat instead of blood for monitoring chemical biomarker concentrations of hospitalised patients offers several advantages for both the patients and healthcare workers. Unlike blood, sweat can be noninvasively and continuously sampled without direct involvement of a professional, and sweat contains a rich composition of biomarkers. However, patients in resting state have extremely low sweat rates and they produce correspondingly small sweat volumes, which makes sweat sensing of hospitalised patients highly challenging. We propose a unique solution that enables the use of sweat as a viable biofluid for noninvasive health monitoring, by actively transporting the sweat in a discretised manner. Our device uses electrowetting-on-dielectrics (EWOD) to create and move sweat droplets with a volume of around 1 nanolitre from a sweat gland to sensors integrated in the device. We present the first wearable device with integrated EWOD, and we show that it can collect and transport sweat on-body, while measuring sweat rate, under conditions typical for individuals at rest.

A Passive Perspiration Inspired Wearable Platform for Continuous Glucose Monitoring

The demand for glucose monitoring devices has witnessed continuous growth from the rising diabetic population. The traditional approach of blood glucose (BG) sensor strip testing generates only intermittent glucose readings. Interstitial fluid-based devices measure glucose dynamically, but their sensing approaches remain either minimally invasive or prone to skin irritation. Here, a sweat glucose monitoring system is presented, which completely operates under rest with no sweat stimulation and can generate real-time BG dynamics. Osmotically driven hydrogels, capillary action with paper microfluidics, and self-powered enzymatic biochemical sensor are used for simultaneous sweat extraction, transport, and glucose monitoring, respectively. The osmotic forces facilitate greater flux inflow and minimize sweat rate fluctuations compared to natural perspiration-based sampling. The epidermal platform is tested on fingertip and forearm under varying physiological conditions. Personalized calibration models are developed and validated to obtain real-time BG information from sweat. The estimated BG concentration showed a good correlation with measured BG concentration, with all values lying in the A+B region of consensus error grid (MARD = 10.56% (fingertip) and 13.17% (forearm)). Overall, the successful execution of such osmotically driven continuous BG monitoring system from passive sweat can be a useful addition to the next-generation continuous sweat glucose monitors.

Wearable and Multiplexed Biosensors based on Oxide Field-Effect Transistors

Wearable sensors designed for continuous, non-invasive monitoring of physicochemical signals are important for portable healthcare. Oxide field-effect transistor (FET)-type biosensors provide high sensitivity and scalability. However, they face challenges in mechanical flexibility, multiplexed sensing of different modules, and the absence of integrated on-site signal processing and wireless transmission functionalities for wearable sensing. In this work, a fully integrated wearable oxide FET-based biosensor array is developed to facilitate the multiplexed and simultaneous measurement of ion concentrations (H+, Na+, K+) and temperature. The FET-sensor array is achieved by utilizing a solution-processed ultrathin (≈6 nm thick) In2O3 active channel layer, exhibiting high compatibility with standard semiconductor technology, good mechanical flexibility, high uniformity, and low operational voltage of 0.005 V. This work provides an effective method to enable oxide FET-based biosensors for the fusion of multiplexed physicochemical information and wearable health monitoring applications.

Hybrid Integration of Wearable Devices for Physiological Monitoring

Wearable devices can provide timely, user-friendly, non- or minimally invasive, and continuous monitoring of human health. Recently, multidisciplinary scientific communities have made significant progress regarding fully integrated wearable devices such as sweat wearable sensors, saliva sensors, and wound sensors. However, the translation of these wearables into markets has been slow due to several reasons associated with the poor system-level performance of integrated wearables. The wearability consideration for wearable devices compromises many properties of the wearables. Besides, the limited power capacity of wearables hinders continuous monitoring for extended duration. Furthermore, peak-power operations for intensive computations can quickly create thermal issues in the compact form factor that interfere with wearability and sensor operations. Moreover, wearable devices are constantly subjected to environmental, mechanical, chemical, and electrical interferences and variables that can invalidate the collected data. This generates the need for sophisticated data analytics to contextually identify, include, and exclude data points per multisensor fusion to enable accurate data interpretation. This review synthesizes the challenges surrounding the wearable device integration from three aspects in terms of hardware, energy, and data, focuses on a discussion about hybrid integration of wearable devices, and seeks to provide comprehensive guidance for designing fully functional and stable wearable devices.

Recent advances in nonenzymatic electrochemical biosensors for sports biomarkers: focusing on antibodies, aptamers and molecularly imprinted polymers

Nonenzymatic electrochemical biosensors, renowned for their high sensitivity, multi-target analysis capabilities, and miniaturized integration, align well with the requirements of non-invasive, multi-index integrated, continuous monitoring, and user-friendly wearable biosensors in sports science. In the past three years, novel strategies targeting specific responses to sports biomarkers have opened new avenues for applications in sports science. However, these advancements also pose challenges in achieving adequate sensitivity and specificity for online analysis of complex sweat bio-samples. Our article focuses on three key nonenzymatic electrochemical biosensing strategies: antigen-antibody reactions, nucleic acid aptamer recognition, and molecular imprinting capture. We delve into strategies to enhance specificity and sensitivity in the application of biosensors in sports science, including shortening signal transduction paths through built-in signal probes, increasing reaction sites through increased surface area and the introduction of nanostructures, multi-target analyses, and microfluidic techniques.

Bio-inspired hierarchical wearable patch for fast sweat collection

Sweat contains abundant physiological and metabolic data to evaluate an individual's physical health. Since the non-exercise sweat secretion rate is low, with an average value of 1-10 μl h-1 cm-2, sweat is generally collected during exercise for existing wearable sweat sensors. To expand their applications to include daily scenarios, these sensors developed for sports and fitness are challenged by the difficulty of collecting trace amounts of sweat. This study proposes a wearable patch inspired by the hierarchical structure of Sarracenia trichomes, allowing for the spontaneous and fast collection of a small amount of secreted sweat. The patch contains microfluidic channels featuring a 20 μm-wide rib structure, fully utilizing the capillary force, thereby eliminating the issue of sweat hysteresis. Furthermore, with only 0.5 μl of the sweat secreted at the collection site, it can converge on the detection medium located within the center reservoir. Volunteer verification demonstrated a twofold increase in sweat collection efficiency compared to traditional wearable patches. This patch serves as an efficient sweat-collection configuration, promising potential for diverse in situ sweat colorimetric analyses.

Diving into Sweat: Advances, Challenges, and Future Directions in Wearable Sweat Sensing

Sweat analysis has advanced from diagnosing cystic fibrosis and testing for illicit drugs to noninvasive monitoring of health biomarkers. This article introduces the rapid development of wearable and flexible sweat sensors, highlighting key milestones and various sensing strategies for real-time monitoring of analytes. We discuss challenges such as developing high-performance nanomaterial-based biosensors, ensuring continuous sweat production and sampling, achieving high sweat/blood correlation, and biocompatibility. The potential of machine learning to enhance these sensors for personalized healthcare is presented, enabling real-time tracking and prediction of physiological changes and disease onset. Leveraging advancements in flexible electronics, nanomaterials, biosensing, and data analytics, wearable sweat biosensors promise to revolutionize disease management, prevention, and prediction, promoting healthier lifestyles and transforming medical practices globally.

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.

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.

Micropatterned Polymer Nanoarrays with Distinct Superwettability for a Highly Efficient Sweat Collection and Sensing Patch

Wearable sweat sensor offers a promising means for noninvasive real-time health monitoring, but the efficient collection and accurate analysis of sweat remains challenging. One of the obstacles is to precisely modulate the surface wettability of the microfluidics to achieve efficient sweat collection. Here a facile initiated chemical vapor deposition (iCVD) method is presented to grow and pattern polymer nanocone arrays with distinct superwettability on polydimethylsiloxane microfluidics, which facilitate highly efficient sweat transportation and collection. The nanoarray is synthesized by manipulating monomer supersaturation during iCVD to induce controlled nucleation and preferential vertical growth of fluorinated polymer. Subsequent selective vapor deposition of a conformal hydrogel nanolayer results in superhydrophilic nanoarray floor and walls within the microchannel that provide a large capillary force and a superhydrophobic ceiling that drastically reduces flow friction, enabling rapid sweat transport along varied flow directions. A carbon/hydrogel/enzyme nanocomposite electrode is then fabricated by sequential deposition of highly porous carbon nanoparticles and hydrogel nanocoating to achieve sensitive and stable sweat detection. Further encapsulation of the assembled sweatsensing patch with superhydrophobic nanoarray imparts self-cleaning and water-proof capability. Finally, the sweat sensing patch demonstrates selective and sensitive glucose and lactate detection during the on-body test.

Wetting Behavior-Induced Interfacial transmission of Energy and Signal: Materials, Mechanisms, and Applications

Wetting behaviors can significantly affect the transport of energy and signal (E&S) through vapor, solid, and liquid interfaces, which has prompted increased interest in interfacial science and technology. E&S transmission can be achieved using electricity, light, and heat, which often accompany and interact with each other. Over the past decade, their distinctive transport phenomena during wetting processes have made significant contributions to various domains. However, few studies have analyzed the intricate relationship between wetting behavior and E&S transport. This review summarizes and discusses the mechanisms of electrical, light, and heat transmission at wetting interfaces to elucidate their respective scientific issues, technical characteristics, challenges, commonalities, and potential for technological convergence. The materials, structures, and devices involved in E&S transportation are also analyzed. Particularly, harnessing synergistic advantages in practical applications and constructing advanced, multifunctional, and highly efficient smart systems based on wetted interfaces is the aim to provide strategies.

Magnetic Porous Hydrogel-Enhanced Wearable Patch Sensor for Sweat Zinc Ion Monitoring

Wearable sensors for sweat trace metal monitoring have the challenges of effective sweat collection and the real-time recording of detection signals. The existing detection technologies are implemented by generating enough sweat through exercise, which makes detecting trace metals in sweat cumbersome. Generally, it takes around 20 min to obtain enough sweat, resulting in dallied and prolonged detection signals that cannot reflect the endogenous fluctuations of the body. To solve these problems, we prepared a multifunctional hydrogel as an electrolyte and combined it with a flexible patch electrode to realize real-time monitoring of sweat Zn2+. Such hydrogel has magnetic and porous properties, and the porous structure of hydrogel enables a fast absorption of sweat, and the magnetic property of the addition of fabricated Fe3O4 NPs not only improves the conductivity but also ensures the adjustable internal structures of the hydrogel. Such a sensing platform for sweat Zn2+ monitoring shows a satisfied linear relationship in the concentration range of 0.16-16 µg/mL via differential pulsed anodic striping voltammetry (DPASV) and successfully detects the sweat Zn2+ of four volunteers during exercise and resting, displaying a promising path for commercial application.

Sensing patches for biomarker identification in skin-derived biofluids

In conventional clinical disease diagnosis and screening based on biomarker detection, most analysis samples are collected from serum, blood. However, these invasive collection methods require specific instruments, professionals, and may lead to infection risks. Additionally, the diagnosis process suffers from untimely results. The identification of skin-related biomarkers plays an unprecedented role in early disease diagnosis. More importantly, these skin-mediated approaches for collecting biomarker-containing biofluid samples are noninvasive or minimally invasive, which is more preferable for point-of-care testing (POCT). Therefore, skin-based biomarker detection patches have been promoted, owing to their unique advantages, such as simple fabrication, desirable transdermal properties and no requirements for professional medical staff. Currently, the skin biomarkers extracted from sweat, interstitial fluid (ISF) and wound exudate, are achieved with wearable sweat patches, transdermal MN patches, and wound patches, respectively. In this review, we detail these three types of skin patches in biofluids collection and diseases-related biomarkers identification. Patch classification and the corresponding manufacturing as well as detection strategies are also summarized. The remaining challenges in clinical applications and current issues in accurate detection are discussed for further advancement of this technology (Scheme 1).

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.