A Self-Powered Wearable Noninvasive Electronic-Skin for Perspiration Analysis Based on Piezo-Biosensing Unit Matrix of Enzyme/ZnO Nanoarrays

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.

Cu- or Ag-containing Bi-Sb-Te for in-line roll-to-roll patterned thin-film thermoelectrics

The Selective Metallization Technique shows promise for roll-to-roll in-line patterning of flexible electronics using evaporated metals, but challenges arise when applied to sputtering functional materials. This study overcomes these challenges with simultaneous sputtering of Bi-Sb-Te and evaporation of metal (Ag or Cu) for thermoelectric layers when using Selective Metallization Technique. Large-scale manufacturing is demonstrated through roll-to-roll processing of a 0.8 m wide polymer web at 25 m/min, achieving high-throughput production of functional thin-film patterns with nanometer thickness. The room-temperature-deposited material system exhibits significantly enhanced thermoelectric performance and facilitates an n-type-to-p-type transition in the Cu- or Ag-containing Bi-Sb-Te-based composite film. Here, we show that while applying Selective Metallization Technique, the evaporation of metal modifies the impact of residual oil on Bi-Sb-Te, which can be effectively removed with a few seconds of plasma exposure, and the fabricated thermoelectric devices are validated in wearable applications utilizing a coiled-up wristband design.

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.

From Lab to Life: Self-Powered Sweat Sensors and Their Future in Personal Health Monitoring

The rapid development of wearable sweat sensors has demonstrated their potential for continuous, non-invasive disease diagnosis and health monitoring. Emerging energy harvesters capable of converting various environmental energy sources-biomechanical, thermal, biochemical, and solar-into electrical energy are revolutionizing power solutions for wearable devices. Based on self-powered technology, the integration of the energy harvesters with wearable sweat sensors can drive the device for biosensing, signal processing, and data transmission. As a result, self-powered sweat sensors are able to operate continuously without external power or charging, greatly facilitating the development of wearable electronics and personalized healthcare. This review focuses on the recent advances in self-powered sweat sensors for personalized healthcare, covering sweat sensors, energy harvesters, energy management, and applications. The review begins with the foundations of wearable sweat sensors, providing an overview of their detection methods, materials, and wearable devices. Then, the working mechanism, structure, and a characteristic of different types of energy harvesters are discussed. The features and challenges of different energy harvesters in energy supply and energy management of sweat sensors are emphasized. The review concludes with a look at the future prospects of self-powered sweat sensors, outlining the trajectory of the field and its potential to flourish.

Recent advances in biosensors based on metal-oxide semiconductors system-integrated into bioelectronics

Metal-oxide semiconductors (MOSs) have emerged as pivotal components in technology related to biosensors and bioelectronics. Detecting biomarkers in sweat provides a glimpse into an individual's metabolism without the need for sample preparation or collection steps. The distinctive attributes of this biosensing technology position it as an appealing option for biomedical applications beyond the scope of diagnosis and healthcare monitoring. This review encapsulates ongoing developments of cutting-edge biosensors based on MOSs. Recent advances in MOS-based biosensors for human sweat analyses are reviewed. Also discussed is the progress in sweat-based biosensing technologies to detect and monitor diseases. Next, system integration of biosensors is demonstrated ultimately to ensure the accurate and reliable detection and analysis of target biomarkers beyond individual devices. Finally, the challenges and opportunities related to advanced biosensors and bioelectronics for biomedical applications are discussed.

Electronic Skin Based on Polydopamine-Modified Superelastic Fibers with Superior Conductivity and Durability

Owing to their excellent elasticities and adaptability as sensing materials, ionic hydrogels exhibit significant promise in the field of intelligent wearable devices. Nonetheless, molecular chains within the polymer network of hydrogels are susceptible to damage, leading to crack extension. Hence, we drew inspiration from the composite structure of the human dermis to engineer a composite hydrogel, incorporating dopamine-modified elastic fibers as a reinforcement. This approach mitigates crack expansion and augments sensor sensitivity by fostering intermolecular forces between the dopamine on the fibers, the hydrogel backbone, and water molecules. The design of this composite hydrogel elevates its breaking tensile capacity from 35 KJ to 203 KJ, significantly enhancing the fatigue resistance of the hydrogel. Remarkably, its electrical properties endure stability even after 2000 cycles of testing, and it manifests heightened sensitivity compared to conventional hydrogel configurations. This investigation unveils a novel method for crafting composite-structured hydrogels.

Wearing the Lab: Advances and Challenges in Skin-Interfaced Systems for Continuous Biochemical Sensing

Continuous, on-demand, and, most importantly, contextual data regarding individual biomarker concentrations exemplify the holy grail for personalized health and performance monitoring. This is well-illustrated for continuous glucose monitoring, which has drastically improved outcomes and quality of life for diabetic patients over the past 2 decades. Recent advances in wearable biosensing technologies (biorecognition elements, transduction mechanisms, materials, and integration schemes) have begun to make monitoring of other clinically relevant analytes a reality via minimally invasive skin-interfaced devices. However, several challenges concerning sensitivity, specificity, calibration, sensor longevity, and overall device lifetime must be addressed before these systems can be made commercially viable. In this chapter, a logical framework for developing a wearable skin-interfaced device for a desired application is proposed with careful consideration of the feasibility of monitoring certain analytes in sweat and interstitial fluid and the current development of the tools available to do so. Specifically, we focus on recent advancements in the engineering of biorecognition elements, the development of more robust signal transduction mechanisms, and novel integration schemes that allow for continuous quantitative analysis. Furthermore, we highlight the most compelling and promising prospects in the field of wearable biosensing and the challenges that remain in translating these technologies into useful products for disease management and for optimizing human performance.

Advanced Self-Powered Biofuel Cells with Capacitor and Nanogenerator for Biomarker Sensing

Self-powered biofuel cells (BFCs) have evolved for highly sensitive detection of biomarkers such as noncodon micro ribonucleic acids (miRNAs) in the presence of interfering substrates. Self-charging supercapacitive BFCs for in vivo and in vitro cellular microenvironments represent the most prevalent sensing mechanism for diagnosis. Therefore, self-powered biosensing (SPB) with a capacitor and contact separation with a triboelectric nanogenerator (TENG) offers electrochemical and colorimetric dual-mode detection via improved electrical signal intensity. In this review, we discuss three major components: stretchable self-powered BFC design, miRNA sensing, and impedance spectroscopy. A specific focus is given to 1) assembling of sensors for biomarkers, 2) electrical output signal intensification, and 3) role of supercapacitors and nanogenerators in SPBs. We outline the key features of stretchable SPBs and the sequence of miRNA sensing by SPBs. We have emphasized the need of a supercapacitor and nanogenerator for SPBs in the context of advanced assembly of the sensing unit. Finally, we outline the role of impedance spectroscopy in the detection and estimation of biomarkers. We highlight key challenges in SPBs for biomarker sensing, which needs improved sensing accuracy, integration strategies of electrochemical biosensing for in vitro and in vivo microenvironments, and the impact of miRNA sensing on cancer diagnostics. This article attempts a specific focus on the accuracy and limitations of sensing unit for miRNA biomarkers and associated tool for boosting electrical signal intensity for a potential big step further.

Sweat analysis for urea sensing: trends and challenges

With increasing population there is a rise in pathological diseases that the healthcare facilities are grappling with. Sweat-based wearable technologies for continuous monitoring have overcome the demerits associated with sweat sampling and sensing. Hence, sweat as an alternative biofluid holds great promise for the quantification of a host of biomarkers and understanding the functioning of the body, thereby deducing ailments quickly and economically. This comprehensive review accounts for recent advances in sweat-based LOCs (Lab-On-Chips), which are a likely alternative to the existing blood-urea sample testing that is invasive and time-consuming. The present review is focused on the advancements in sweat-based Lab-On-Chips (LOCs) as an alternative to invasive and time-consuming blood-urea sample testing. In addition, different sweat collection methods (direct skin, near skin and microfluidic) and their mechanism for urea sensing are explained in detail. The mechanism of urea in biofluids in protein metabolism, balancing nitrogen levels and a crucial factor of kidney function is described. In the end, research and technological advancements are explained to address current challenges and enable its widespread implementation.

Nanostructured wearable electrochemical and biosensor towards healthcare management: a review

In recent years, there has been a rapid increase in demand for wearable sensors, particularly these tracking the surroundings, fitness, and health of people. Thus, selective detection in human body fluid is a demand for a smart lifestyle by quick monitoring of electrolytes, drugs, toxins, metabolites and biomolecules, proteins, and the immune system. In this review, these parameters along with the main features of the latest and mostly cited research work on nanostructured wearable electrochemical and biosensors are surveyed. This study aims to help researchers and engineers choose the most suitable selective and sensitive sensor. Wearable sensors have broad and effective sensing platforms, such as contact lenses, Google Glass, skin-patch, mouth gourds, smartwatches, underwear, wristbands, and others. For increasing sensor reliability, additional advancements in electrochemical and biosensor precision, stability in uncontrolled environments, and reproducible sample conveyance are necessary. In addition, the optimistic future of wearable electrochemical sensors in fields, such as remote and customized healthcare and well-being is discussed. Overall, wearable electrochemical and biosensing technologies hold great promise for improving personal healthcare and monitoring performance with the potential to have a significant impact on daily lives. These technologies enable real-time body sensing and the communication of comprehensive physiological information.

Wearable non-invasive glucose sensors based on metallic nanomaterials

The development of wearable non-invasive glucose sensors provides a convenient technical means to monitor the glucose concentration of diabetes patients without discomfortability and risk of infection. Apart from enzymes as typical catalytic materials, the active catalytic materials of the glucose sensor are mainly composed of polymers, metals, alloys, metal compounds, and various metals that can undergo catalytic oxidation with glucose. Among them, metallic nanomaterials are the optimal materials applied in the field of wearable non-invasive glucose sensing due to good biocompatibility, large specific surface area, high catalytic activity, and strong adsorption capacity. This review summarizes the metallic nanomaterials used in wearable non-invasive glucose sensors including zero-dimensional (0D), one-dimensional (1D), and two-dimensional (2D) monometallic nanomaterials, bimetallic nanomaterials, metal oxide nanomaterials, etc. Besides, the applications of wearable non-invasive biosensors based on these metallic nanomaterials towards glucose detection are summarized in detail and the development trend of the wearable non-invasive glucose sensors based on metallic nanomaterials is also outlook.

The Evolving Role of Proteins in Wearable Sweat Biosensors

Sweat is an increasingly popular biological medium for fitness monitoring and clinical diagnostics. It contains an abundance of biological information and is available continuously and noninvasively. Sweat-sensing devices often employ proteins in various capacities to create skin-friendly matrices that accurately extract valuable and time-sensitive information from sweat. Proteins were first used in sensors as biorecognition elements in the form of enzymes and antibodies, which are now being tuned to operate at ranges relevant for sweat. In addition, a range of structural proteins, sometimes assembled in conjunction with polymers, can provide flexible and compatible matrices for skin sensors. Other proteins also naturally possess a range of functionalities─as adhesives, charge conductors, fluorescence emitters, and power generators─that can make them useful components in wearable devices. Here, we examine the four main components of wearable sweat sensors─the biorecognition element, the transducer, the scaffold, and the adhesive─and the roles that proteins have played so far, or promise to play in the future, in each component. On a case-by-case basis, we analyze the performance characteristics of existing protein-based devices, their applicable ranges of detection, their transduction mechanism and their mechanical properties. Thereby, we review and compare proteins that can readily be used in sweat sensors and others that will require further efforts to overcome design, stability or scalability challenges. Incorporating proteins in one or multiple components of sweat sensors could lead to the development and deployment of tunable, greener, and safer biosourced devices.

Skin-Interfaced Wearable Sweat Sensors for Precision Medicine

Wearable sensors hold great potential in empowering personalized health monitoring, predictive analytics, and timely intervention toward personalized healthcare. Advances in flexible electronics, materials science, and electrochemistry have spurred the development of wearable sweat sensors that enable the continuous and noninvasive screening of analytes indicative of health status. Existing major challenges in wearable sensors include: improving the sweat extraction and sweat sensing capabilities, improving the form factor of the wearable device for minimal discomfort and reliable measurements when worn, and understanding the clinical value of sweat analytes toward biomarker discovery. This review provides a comprehensive review of wearable sweat sensors and outlines state-of-the-art technologies and research that strive to bridge these gaps. The physiology of sweat, materials, biosensing mechanisms and advances, and approaches for sweat induction and sampling are introduced. Additionally, design considerations for the system-level development of wearable sweat sensing devices, spanning from strategies for prolonged sweat extraction to efficient powering of wearables, are discussed. Furthermore, the applications, data analytics, commercialization efforts, challenges, and prospects of wearable sweat sensors for precision medicine are discussed.

Improved Performance of g-C3N4 for Optoelectronic Detection of NO2 Gas by Coupling Metal-Organic Framework Nanosheets with Coordinatively Unsaturated Ni(II) Sites

Sensitive and selective optoelectronic detection of NO₂ with g-C₃N₄ (CN) is critical, but it remains challenging to achieve ultralow concentration (ppb-level) detection. Herein, Ni metal-organic frameworks/CN nanosheet heterojunctions were successfully fabricated by the electrostatic induced assembly strategy and then treated by a post-alkali etching process for creating coordinatively unsaturated Ni(II) sites. The optimized heterojunction exhibits a record detection limitation of 1 ppb for NO₂, well below that observed on pristine CN, and an outstanding selectivity over other gases, along with long-time stability (120 days) at room temperature. The resulting superior detection performance benefits from the enhanced charge transfer and separation of the closely contacted heterojunction interface and the favorable adsorption of NO₂ by unsaturated Ni(II) as selective adsorption sites mainly by means of the time-resolved photoluminescence spectra and in situ X-ray photoelectron spectra. Moreover, the in situ Fourier transform infrared spectra and temperature-programmed desorption disclose that the promotion adsorption of NO₂ depends on the strengthened interaction between NO₂ and Ni(II) node sites at the aid of OH groups from unsaturated coordination. This work offers a versatile solution to develop promising CN-based optoelectronic sensors at room temperature.

A Systematic Review on the Advanced Techniques of Wearable Point-of-Care Devices and Their Futuristic Applications

Personalized point-of-care testing (POCT) devices, such as wearable sensors, enable quick access to health monitoring without the use of complex instruments. Wearable sensors are gaining popularity owing to their ability to offer regular and continuous monitoring of physiological data by dynamic, non-invasive assessments of biomarkers in biofluids such as tear, sweat, interstitial fluid and saliva. Current advancements have concentrated on the development of optical and electrochemical wearable sensors as well as advances in non-invasive measurements of biomarkers such as metabolites, hormones and microbes. For enhanced wearability and ease of operation, microfluidic sampling, multiple sensing, and portable systems have been incorporated with materials that are flexible. Although wearable sensors show promise and improved dependability, they still require more knowledge about interaction between the target sample concentrations in blood and non-invasive biofluids. In this review, we have described the importance of wearable sensors for POCT, their design and types of these devices. Following which, we emphasize on the current breakthroughs in the application of wearable sensors in the realm of wearable integrated POCT devices. Lastly, we discuss the present obstacles and forthcoming potentials including the use of Internet of Things (IoT) for offering self-healthcare using wearable POCT.

From Piezoelectric Nanogenerator to Non-Invasive Medical Sensor: A Review

Piezoelectric nanogenerators (PENGs) not only are able to harvest mechanical energy from the ambient environment or body and convert mechanical signals into electricity but can also inform us about pathophysiological changes and communicate this information using electrical signals, thus acting as medical sensors to provide personalized medical solutions to patients. In this review, we aim to present the latest advances in PENG-based non-invasive sensors for clinical diagnosis and medical treatment. While we begin with the basic principles of PENGs and their applications in energy harvesting, this review focuses on the medical sensing applications of PENGs, including detection mechanisms, material selection, and adaptive design, which are oriented toward disease diagnosis. Considering the non-invasive in vitro application scenario, discussions about the individualized designs that are intended to balance a high performance, durability, comfortability, and skin-friendliness are mainly divided into two types: mechanical sensors and biosensors, according to the key role of piezoelectric effects in disease diagnosis. The shortcomings, challenges, and possible corresponding solutions of PENG-based medical sensing devices are also highlighted, promoting the development of robust, reliable, scalable, and cost-effective medical systems that are helpful for the public.

Recent Advances in Wearable Biosensors for Non-Invasive Detection of Human Lactate

Lactate, a crucial product of the anaerobic metabolism of carbohydrates in the human body, is of enormous significance in the diagnosis and treatment of diseases and scientific exercise management. The level of lactate in the bio-fluid is a crucial health indicator because it is related to diseases, such as hypoxia, metabolic disorders, renal failure, heart failure, and respiratory failure. For critically ill patients and those who need to regularly control lactate levels, it is vital to develop a non-invasive wearable sensor to detect lactate levels in matrices other than blood. Due to its high sensitivity, high selectivity, low detection limit, simplicity of use, and ability to identify target molecules in the presence of interfering chemicals, biosensing is a potential analytical approach for lactate detection that has received increasing attention. Various types of wearable lactate biosensors are reviewed in this paper, along with their preparation, key properties, and commonly used flexible substrate materials including polydimethylsiloxane (PDMS), polyethylene terephthalate (PET), paper, and textiles. Key performance indicators, including sensitivity, linear detection range, and detection limit, are also compared. The challenges for future development are also summarized, along with some recommendations for the future development of lactate biosensors.

The development of wearable technologies and their potential for measuring nutrient intake: Towards precision nutrition

Appropriate food intake and nutritional status are crucial for the maintenance of health and disease prevention. Conventional dietary assessment is mainly based on comparisons of nutrient intakes with reference intakes, failing to meet the needs of personalised nutritional guidance based on individual nutritional status. Given their capability of providing insights into health information non-invasively in real time, wearable technologies offer great opportunities for nutrition monitoring. Nutrient metabolic profiles can be monitored immediately and continuously which could potentially offer the possibility for the tracking and guiding of nutrient intake. Here, we review and highlight the recent advances in wearable sensors from the perspective of sensing technologies for nutrient detection in biofluids. The integration of biosensors with wearable devices serves as an ideal platform for the analysis of biofluids including sweat, saliva and tears. The wearable sensing systems applied to the analysis of typical nutrients and important metabolites are demonstrated in terms of carbohydrates, proteins, lipids, vitamins, minerals and others. Taking advantage of their high flexibility and lightweight, wearable sensors have been widely developed for the in situ quantitative detection of metabolic biomarkers. The technical principles, detection methods and applications are summarised. The challenges and future perspectives for wearable nutrition monitoring devices are discussed including the need to better determine relationships among nutrient metabolic profile, nutrient intake and food intake. With the development of materials, sensing techniques and manufacturing processes, wearable technologies are paving the way towards personalised precision nutrition, although there is still a long way to go before they can be utilised for practical clinical applications. Joint research efforts between nutrition scientists, doctors, engineers and sensor researchers are essential to further accelerate the realisation of reliable and practical wearable nutrition monitoring platforms.

Self-Powered Nitrogen Dioxide Sensor Based on Pd-Decorated ZnO/MoSe2 Nanocomposite Driven by Triboelectric Nanogenerator

This paper introduces a high-performance self-powered nitrogen dioxide gas sensor based on Pd-modified ZnO/MoSe₂ nanocomposites. Poly(vinyl alcohol) (PVA) nanofibers were prepared by high-voltage electrospinning and tribological nanogenerators (TENGs) were designed. The output voltage of TENG and the performance of the generator at different frequencies were measured. The absolute value of the maximum positive and negative voltage exceeds 200 V. Then, the output voltage of a single ZnO thin-film sensor, Pd@ZnO thin-film sensor and Pd@ZnO/MoSe₂ thin-film sensor was tested by using the energy generated by TENG at 5 Hz, when the thin-film sensor was exposed to 1-50 ppm NO₂ gas. The experimental results showed that the sensing response of the Pd@ZnO/MoSe₂ thin-film sensor was higher than that of the single ZnO film sensor and Pd@ZnO thin-film sensor. The TENG-driven response rate of the Pd@ZnO/MoSe₂ sensor on exposure to 50 ppm NO₂ gas was 13.8. At the same time, the sensor had good repeatability and selectivity. The synthetic Pd@ZnO/MoSe₂ ternary nanocomposite was an ideal material for the NO₂ sensor, with excellent structure and performance.

A self-powered wearable brain-machine-interface system for real-time monitoring and regulating body temperature

Heat stroke that may cause acute central nervous system dysfunction, multiple organ dysfunction and even death has become a typical health problem in tropical developing countries. The primary goal of heat stroke treatment is to lower core body temperature, which necessitates physical or medical cooling in time. Here, we design a new self-powered wearable brain-machine-interface system for real-time monitoring and regulating body temperature. This system can monitor body temperature in real time and transmit neural electrical stimulation signals into specific brain regions to lower the body temperature. The whole system can work without an external power supply and be powered by the body itself through the piezoelectric effect. The system comprises a temperature detecting unit, a power supply unit, a data processing module, and a brain stimulator. Demonstration of the system with stimulation electrodes implanted in the median preoptic nucleus brain region in mice reveals an evident decrease in body temperature (1.0 °C within 15 min). This self-powered strategy provides a new concept for future treatment of heat stroke and can extend the application of brain-machine-interface systems in medical care.

Transducer Technologies for Biosensors and Their Wearable Applications

The development of new biosensor technologies and their active use as wearable devices have offered mobility and flexibility to conventional western medicine and personal fitness tracking. In the development of biosensors, transducers stand out as the main elements converting the signals sourced from a biological event into a detectable output. Combined with the suitable bio-receptors and the miniaturization of readout electronics, the functionality and design of the transducers play a key role in the construction of wearable devices for personal health control. Ever-growing research and industrial interest in new transducer technologies for point-of-care (POC) and wearable bio-detection have gained tremendous acceleration by the pandemic-induced digital health transformation. In this article, we provide a comprehensive review of transducers for biosensors and their wearable applications that empower users for the active tracking of biomarkers and personal health parameters.

Piezoelectric nanogenerators for personalized healthcare

The development of flexible piezoelectric nanogenerators has experienced rapid progress in the past decade and is serving as the technological foundation of future state-of-the-art personalized healthcare. Due to their highly efficient mechanical-to-electrical energy conversion, easy implementation, and self-powering nature, these devices permit a plethora of innovative healthcare applications in the space of active sensing, electrical stimulation therapy, as well as passive human biomechanical energy harvesting to third party power on-body devices. This article gives a comprehensive review of the piezoelectric nanogenerators for personalized healthcare. After a brief introduction to the fundamental physical science of the piezoelectric effect, material engineering strategies, device structural designs, and human-body centered energy harvesting, sensing, and therapeutics applications are also systematically discussed. In addition, the challenges and opportunities of utilizing piezoelectric nanogenerators for self-powered bioelectronics and personalized healthcare are outlined in detail.

Wearable plasmonic paper-based microfluidics for continuous sweat analysis

Wearable sweat sensors have the potential to provide clinically meaningful information associated with the health and disease states of individuals. Current sensors mainly rely on enzymes and antibodies as biorecognition elements to achieve specific quantification of metabolite and stress biomarkers in sweat. However, enzymes and antibodies are prone to degrade over time, compromising the sensor performance. Here, we introduce a wearable plasmonic paper-based microfluidic system for continuous and simultaneous quantitative analysis of sweat loss, sweat rate, and metabolites in sweat. Plasmonic sensors based on label-free surface-enhanced Raman spectroscopy (SERS) can provide chemical "fingerprint" information for analyte identification. We demonstrate the sensitive detection and quantification of uric acid in sweat at physiological and pathological concentrations. The well-defined flow characteristics of paper microfluidic devices enable accurate quantification of sweat loss and sweat rate. The wearable plasmonic device is soft, flexible, and stretchable, which can robustly interface with the skin without inducing chemical or physical irritation.

A self-powered wearable brain-machine-interface system for ceasing action

A self-powered wearable brain-machine-interface system with pulse detection and brain stimulation for ceasing action has been realized. The system is composed of (1) a power supply unit that employs a piezoelectric generator and converts the mechanical energy of human daily activities into electricity; (2) a neck pulse biosensor that allows continuous measurements of carotid pulse by using a piezoelectric polyvinylidene fluoride film; (3) a data analysis module that enables a coordinated brain-machine-interface system to output brain stimulation signals; and (4) brain stimulating electrodes linked to the brain that implement behavioral intervention. Demonstration of the system with stimulating electrodes implanted in the periaqueductal gray (PAG) in running mice reveals the great effect of forced ceasing action. The mice stop their running within several seconds when the stimulation signals are sent into the PAG brain region (inducing fear). This self-powered scheme for neural stimulation realizes specific behavioral intervention without any external power supply, thus providing a new concept for future behavior intervention.

Wearable microfluidic-based e-skin sweat sensors

Electronic skins (e-skins) are soft (deformable and stretchable) state-of-the-art wearable devices that emulate the attributes of human skin and act as a Human-Machine Interface (HMI). Recent advances in e-skin for real-time detection of medical signals such as pulse, temperature, electromyogram (EMG), electroencephalogram (EEG), electrooculogram (EOG), electrocardiogram (ECG), and other bioelectric signals laid down an intelligent foundation for early prediction and diagnosis of diseases with a motive of reducing the risk of the ailment reaching to the end stage. In particular, sweat testing has been employed in diverse applications ranging from medical diagnosis of diabetes, cystic fibrosis, tuberculosis, blood pressure, and autonomic neuropathy to evaluating fluid and electrolyte balance in athletes. Typically, sweat testing techniques are done by trained experts and require off-body measurements, which prevent individuals from de-coding health issues quickly and independently. With the onset of soft electronics, wearable sweat sensors overcome this disadvantage via in situ sweat measurements with real-time feedback, timely diagnosis, creating the potential for preventive care and treatment. Over the past few decades, wearable microfluidic-based e-skin sweat sensors have paved a new way, promising sensing interfaces that are highly compatible with arranging medical and electronic applications. The present review highlights the recent research carried out in the microfluidic-based wearable sweat sensors with a critical focus on real-time sensing of lactate, chloride, and glucose concentration; sweat rate, simultaneously with pH, and total sweat loss for preventive care, timely diagnosis, and point-of-care health and fitness monitoring.

Self-Powered Wearable Biosensor in a Baby Diaper for Monitoring Neonatal Jaundice through a Hydrovoltaic-Biosensing Coupling Effect of ZnO Nanoarray

Neonatal jaundice refers to the abnormality of bilirubin metabolism for newborns, and wearable transcutaneous bilirubin meters for real-time measuring the bilirubin concentration is an insistent demand for the babies' parents and doctors. In this paper, a self-powered wearable biosensor in a baby diaper for real-time monitoring neonatal jaundice has been realized by the hydrovoltaic-biosensing coupling effect of ZnO nanoarray. Without external power supply, the system can work independently, and the hydrovoltaic output can be treated as both the power source and biosensing signal. The working mechanism is that the hydrovoltaic output arises from the urine flowing on ZnO nanoarray and the enzymatic reaction on the surface can influence the output. The sensing information can be transmitted through a wireless transmitter, and thus the parents and doctors can treat the neonatal jaundice of babies in time. This work can potentially promote the development of next generation of biosensors and physiological monitoring system, and expand the scope of self-powered technique and smart healthcare area.

Wearable biosensors for real-time sweat analysis and body motion capture based on stretchable fiber-based triboelectric nanogenerators

Carbon neutrality is a global green energy revolution meaning that the carbon dioxide can make ends meet. However, with the mushroom of the fifth generation wireless systems (5G) and the Internet of Things (IoT), it is a great challenge for powering the ubiquitous distributed devices, because the battery production and high overhead maintenance may bring more carbon emissions. Here, we present wearable biosensors for real-time sweat analysis and body motion capture based on stretchable fiber-based triboelectric nanogenerators (F-TENG). The F-TENG is made of stretchable conductive fiber (Ecoflex coating with polyaniline (PANI)) and varnished wires. Based on the coupling effect of triboelectric effect and enzymatic reaction (surface-triboelectric coupling effect), the wearable biosensors can not only precisely sense the motion states, but also detect glucose, creatinine and lactate acid in sweat in real-time. Importantly, the wearable devices can self-drive without any external power source and the response against glucose, creatinine and lactate acid can be up to 103%, 125% and 38%, respectively. On this basis, applications in biosensing and wireless communication have been demonstrated. This work exhibits a prospective potential application of F-TENG in IoT for diverse use.

Recent progress in self-powered multifunctional e-skin for advanced applications

Electronic skin (e-skin), new generation of flexible wearable electronic devices, has characteristics including flexibility, thinness, biocompatibility with broad application prospects, and a crucial place in future wearable electronics. With the increasing demand for wearable sensor systems, the realization of multifunctional e-skin with low power consumption or even autonomous energy is urgently needed. The latest progress of multifunctional self-powered e-skin for applications in physiological health, human-machine interaction (HMI), virtual reality (VR), and artificial intelligence (AI) is presented here. Various energy conversion effects for the driving energy problem of multifunctional e-skin are summarized. An overview of various types of self-powered e-skins, including single-effect e-skins and multifunctional coupling-effects e-skin systems is provided, where the aspects of material preparation, device assembly, and output signal analysis of the self-powered multifunctional e-skin are described. In the end, the existing problems and prospects in this field are also discussed.

Fabrication of nitrogen-enriched carbon dots with green fluorescence for enzyme-free detection of uric acid

Based on the fact that UA directly quenched the green fluorescence of NCDs prepared at RT, a non-invasive sensor was developed.

Wearable Sensors for Remote Health Monitoring: Potential Applications for Early Diagnosis of Covid-19

Wearable sensors are emerging as a new technology to detect physiological and biochemical markers for remote health monitoring. By measuring vital signs such as respiratory rate, body temperature, and blood oxygen level, wearable sensors offer tremendous potential for the noninvasive and early diagnosis of numerous diseases such as Covid-19. Over the past decade, significant progress has been made to develop wearable sensors with high sensitivity, accuracy, flexibility, and stretchability, bringing to reality a new paradigm of remote health monitoring. In this review paper, the latest advances in wearable sensor systems that can measure vital signs at an accuracy level matching those of point-of-care tests are presented. In particular, the focus of this review is placed on wearable sensors for measuring respiratory behavior, body temperature, and blood oxygen level, which are identified as the critical signals for diagnosing and monitoring Covid-19. Various designs based on different materials and working mechanisms are summarized. This review is concluded by identifying the remaining challenges and future opportunities for this emerging field.

Recent Progress in Intelligent Wearable Sensors for Health Monitoring and Wound Healing Based on Biofluids

The intelligent wearable sensors promote the transformation of the health care from a traditional hospital-centered model to a personal portable device-centered model. There is an urgent need of real-time, multi-functional, and personalized monitoring of various biochemical target substances and signals based on the intelligent wearable sensors for health monitoring, especially wound healing. Under this background, this review article first reviews the outstanding progress in the development of intelligent, wearable sensors designed for continuous, real-time analysis, and monitoring of sweat, blood, interstitial fluid, tears, wound fluid, etc. Second, this paper reports the advanced status of intelligent wound monitoring sensors designed for wound diagnosis and treatment. The paper highlights some smart sensors to monitor target analytes in various wounds. Finally, this paper makes conservative recommendations regarding future development of intelligent wearable sensors.

Preliminary Evaluation of a Solar-Powered Wristband for Continuous Multi-Modal Electrochemical Monitoring

Continuous, non-invasive wearable measurement of metabolic biomarkers could provide vital insight into patient condition for personalized health and wellness monitoring. We present our efforts towards developing a wearable solar-powered electrochemical platform for multimodal sweat based metabolic monitoring. This wrist-worn wearable system consists of a flexible photovoltaic cell connected to a circuit board containing ultra low power circuitry for sensor data collection, energy harvesting, and wireless data transmission, all integrated into an elastic fabric wristband. The system continuously samples amperometric, potentiometric, temperature, and motion data and wirelessly transmits these to a data aggregator. The full wearable system is 7.5 cm long and 5 cm in diameter, weighs 22 grams, and can run directly from harvested light energy. Relatively low levels of light such as residential lighting (∼200 lux) are sufficient for continuous operation of the system. Excess harvested energy is stored in a small 37 mWh lithium polymer battery. The battery can be charged in ∼14 minutes under full sunlight and can power the system for ∼8 days when fully charged. The system has an average power consumption of 176 µW. The solar-harvesting performance of the system was characterized in a variety of lighting conditions, and the amperometric and potentiometric electrochemical capabilities of the system were validated in vitro.Clinical relevance-The presented solar-powered wearable system enables continuous wireless multi-modal electrochemical monitoring for uninterrupted sensing of metabolic biomarkers in sweat while harvesting energy from indoor lighting or sunlight.

Skin-Inspired Hair-Epidermis-Dermis Hierarchical Structures for Electronic Skin Sensors with High Sensitivity over a Wide Linear Range

The quest for both high sensitivity and a wide linear range in electronic skin design is perpetual; unfortunately, these two key parameters are generally mutually exclusive. Although limited success in attaining both high sensitivity and a wide linear range has been achieved via material-specific or complicated structure design, addressing the conflict between these parameters remains a critical challenge. Here, inspired by the human somatosensory system, we propose hair-epidermis-dermis hierarchical structures based on a reduced graphene oxide/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) aerogel to reconcile this contradiction between high sensitivity and a wide linear range. This hierarchical structure enables an electronic skin (e-skin) sensor linear sensing range up to 30 kPa without sacrificing the high sensitivity (137.7 kPa^-1), revealing an effective strategy to overcome the above-mentioned conflict. In addition, the e-skin sensor also exhibits a low detection limit (1.1 Pa), fast responsiveness (∼80 ms), and excellent stability and reproducibility (over 10 000 cycles); as a result, the e-skin platform is capable of detecting small air flow and monitoring human pulse and even sound-induced vibrations. This structure may boost the ongoing research on the structural design and performance regulation of emerging flexible electronics.

Self-Powered Biosensor for Specifically Detecting Creatinine in Real Time Based on the Piezo-Enzymatic-Reaction Effect of Enzyme-Modified ZnO Nanowires

Creatinine has become an important indicator for the early detection of uremia. However, due to the disadvantages of external power supply and large volume, some commercial devices for detecting creatinine concentration have lost a lot of popularity in everyday life. This paper describes the development of a self-powered biosensor for detecting creatinine in sweat. The biosensor can detect human creatinine levels in real time without the need for an external power source, providing information about the body's overall health. The piezoelectric output voltage of creatininase/creatinase/sarcosine oxidase-modified ZnO nanowires (NWs) is significantly dependent on the creatinine concentration due to the coupling effect of the piezoelectric effect and enzymatic reaction (piezo-enzymatic-reaction effect), which can be regarded as both electrical energy and biosensing signal. Our results can be used for the detection of creatinine levels in the human body and have great potential in the prediction of related diseases.

Energy Autonomous Sweat-Based Wearable Systems

The continuous operation of wearable electronics demands reliable sources of energy, currently met through Li-ion batteries and various energy harvesters. These solutions are being used out of necessity despite potential safety issues and unsustainable environmental impact. Safe and sustainable energy sources can boost the use of wearables systems in diverse applications such as health monitoring, prosthetics, and sports. In this regard, sweat- and sweat-equivalent-based studies have attracted tremendous attention through the demonstration of energy-generating biofuel cells, promising power densities as high as 3.5 mW cm-2 , storage using sweat-electrolyte-based supercapacitors with energy and power densities of 1.36 Wh kg-1 and 329.70 W kg-1 , respectively, and sweat-activated batteries with an impressive energy density of 67 Ah kg-1 . A combination of these energy generating, and storage devices can lead to fully energy-autonomous wearables capable of providing sustainable power in the µW to mW range, which is sufficient to operate both sensing and communication devices. Here, a comprehensive review covering these advances, addressing future challenges and potential solutions related to fully energy-autonomous wearables is presented, with emphasis on sweat-based energy storage and energy generation elements along with sweat-based sensors as applications.

Progress in micro/nano sensors and nanoenergy for future AIoT-based smart home applications

Self-sustainable sensing systems composed of micro/nano sensors and nano-energy harvesters contribute significantly to developing the internet of things (IoT) systems. As one of the most promising IoT applications, smart home relies on implementing wireless sensor networks with miniaturized and multi-functional sensors, and distributed, reliable, and sustainable power sources, namely energy harvesters with a variety of conversion mechanisms. To extend the capabilities of IoT in the smart home, a technology fusion of IoT and artificial intelligence (AI), called the artificial intelligence of things (AIoT), enables the detection, analysis, and decision-making functions with the aids of machine learning assisted algorithms to form a smart home based intelligent system. In this review, we introduce the conventional rigid microelectromechanical system (MEMS) based micro/nano sensors and energy harvesters, followed by presenting the advances in the wearable counterparts for better human interactions. We then discuss the viable integration approaches for micro/nano sensors and energy harvesters to form self-sustainable IoT systems. Whereafter, we emphasize the recent development of AIoT based systems and the corresponding applications enabled by the machine learning algorithms. Smart home based healthcare technology enabled by the integrated multi-functional sensing platform and bioelectronic medicine is also presented as an important future direction, as well as wearable photonics sensing system as a complement to the wearable electronics sensing system.

Integrated non-invasive biochemical and biophysical sensing systems for health and performance monitoring: A systems perspective

Advances in materials, bio-recognition elements, transducers, and microfabrication techniques, as well as progress in electronics, signal processing, and wireless communication have generated a new class of skin-interfaced wearable health monitoring systems for applications in personalized medicine and digital health. In comparison to conventional medical devices, these wearable systems are at the cusp of initiating a new era of longitudinal and noninvasive sensing for the prevention, detection, diagnosis, and treatment of diseases at the molecular level. Herein, we provide a review of recent developments in wearable biochemical and biophysical systems. We survey the sweat sampling and collection methods for biochemical systems, followed by an assessment of biochemical and biophysical sensors deployed in current wearable systems with an emphasis on their hardware specifications. Specifically, we address how sweat collection and sample handling platforms may be a rate limiting technology to realizing the clinical translation of wearable health monitoring systems; moreover, we highlight the importance of achieving both longitudinal sensing and assessment of intrapersonal variation in sweat-blood correlations to have the greatest clinical impact. Lastly, we assess a snapshot of integrated wireless wearable systems with multimodal sensing capabilities, and we conclude with our perspective on the state-of-the-art and the required developments to achieve the next-generation of integrated wearable health and performance monitoring systems.

Understanding the plasmon-enhanced photothermal effect of a polarized laser on metal nanowires

Improving photothermal efficiency can reduce the melting threshold of metal nanowires. The photothermal efficiency of a polarized laser to Cu nanowires was investigated by numerical simulation and experiment. Our simulation results reveal that the photothermal efficiency of a polarized laser depends on the intensity and distribution area of surface plasmons excited by the laser. As the angle between the polarization direction of the incident laser and the long axis of the Cu nanowire increases, the laser-excited surface plasmons shift from both ends to the sidewall of the Cu nanowire. Such a distribution of surface plasmons was confirmed by the melting behavior of Cu nanowires irradiated by a 450 nm polarized laser. Increasing the laser wavelength will enhance the intensity of the surface plasmons but reduce the distribution area of the surface plasmons. As a result, a higher photothermal efficiency was achieved using a laser with a polarization direction perpendicular to the long axis of the Cu nanowire and a wavelength less than 550 nm. Due to the higher photothermal efficiency, the melting threshold of Cu nanowire irradiated by a laser with polarization perpendicular to the long axis of the Cu nanowire is 32 mW, which is around 20% lower that of Cu nanowire irradiated by a laser with polarization parallel to the long axis of the Cu nanowire.

A thread/fabric-based band as a flexible and wearable microfluidic device for sweat sensing and monitoring

Flexible biosensors for monitoring systems have emerged as a promising portable diagnostics platform due to their potential for in situ point-of-care (POC) analytic devices. Assessment of biological analytes in sweat can provide essential information for human physiology. Conventional measurements rely on laboratory equipment. This work exploits an alternative approach for epidermal sweat sensing and detection through a wearable microfluidic thread/fabric-based analytical device (μTFAD). This μTFAD is a flexible and skin-mounted band that integrates hydrophilic dot-patterns with a hydrophobic surface via embroidering thread into fabric. After chromogenic reaction treatment, the thread-embroidered patterns serve as the detection zones for sweat transferred by the hydrophilic threads, enabling precise analysis of local sweat loss, pH and concentrations of chloride and glucose in sweat. Colorimetric reference markers embroidered surrounding the working dots provide accurate data readout either by apparent color comparison or by digital acquirement through smartphone-assisted calibration plots. On-body tests were conducted on five healthy volunteers. Detection results of pH, chloride and glucose in sweat from the volunteers were 5.0-6.0, 25-80 mM and 50-200 μM by apparent color comparison with reference markers through direct visual observation. Similar results of 5.47-6.30, 50-77 mM and 47-66 μM for pH, chloride and glucose were obtained through calibration plots based on the RGB values from the smartphone app Lanse®. The limit of detection (LOD) is 10 mM for chloride concentration, 4.0-9.0 for pH and 10 μM for glucose concentration, respectively. For local sweat loss, it is found that the forehead is the region of heavy sweat loss. Sweat secretion is a cumulating process with a lower sweat rate at the beginning which increases as body movement continues along with increased heat production. These results demonstrate the capability and availability of our sensing device for quantitative detection of multiple biomarkers in sweat, suggesting the great potential for development of feasible non-invasive biosensors, with a similar performance to conventional measurements.

Evaluating the Possibility of Translating Technological Advances in Non-Invasive Continuous Lactate Monitoring into Critical Care

Lactate is widely measured in critically ill patients as a robust indicator of patient deterioration and response to treatment. Plasma concentrations represent a balance between lactate production and clearance. Analysis has typically been performed with the aim of detecting tissue hypoxia. However, there is a diverse range of processes unrelated to increased anaerobic metabolism that result in the accumulation of lactate, complicating clinical interpretation. Further, lactate levels can change rapidly over short spaces of time, and even subtle changes can reflect a profound change in the patient's condition. Hence, there is a significant need for frequent lactate monitoring in critical care. Lactate monitoring is commonplace in sports performance monitoring, given the elevation of lactate during anaerobic exercise. The desire to continuously monitor lactate in athletes has led to the development of various technological approaches for non-invasive, continuous lactate measurements. This review aims firstly to reflect on the potential benefits of non-invasive continuous monitoring technology within the critical care setting. Secondly, we review the current devices used to measure lactate non-invasively outside of this setting and consider the challenges that must be overcome to allow for the translation of this technology into intensive care medicine. This review will be of interest to those developing continuous monitoring sensors, opening up a new field of research.

Self-powered wearable electronics

Wearable electronics are an essential direction for the future development of smart wearables. Among them, the battery life of wearable electronics is a key technology that limits their development. The proposal of self-powered wearable electronics (SWE) provides a promising solution to the problem of long-term stable working of wearable electronics. This review has made a comprehensive summary and analysis of recent advances on SWE from the perspectives of energy, materials, and ergonomics methods. At the same time, some representative research work was introduced in detail. SWE can be divided into energy type SWE and sensor type SWE according to their working types. Both types of SWE are broadly applied in human-machine interaction, motion information monitoring, diagnostics, and therapy systems. Finally, this article summarizes the existing bottlenecks of SWE, and predicts the future development direction of SWE.

3D Layer-By-Layer Pd-Containing Nanocomposite Platforms for Enhancing the Performance of Hydrogen Sensors

Herein, a nanowelding technique is adopted to fabricate three-dimensional layer-by-layer Pd-containing nanocomposite structures with special properties. Nanowires fabricated from noble metals (Pd, Pt, Au, and Ag) were used to prepare Pd-Pd nanostructures and Pd-Au, Pd-Pt, Pd-Ag, and Pd-Pt-Au nanocomposite structures by controlling the welding temperature. The recrystallization behavior of the welded composite materials was observed and analyzed. In addition, their excellent mechanical and electrical properties were confirmed by performing 10,000 bending test cycles and measuring the resistances. Finally, flexible and wearable nanoheaters and gas sensors were fabricated using our proposed method. In comparison with conventional techniques, our proposed method can not only easily achieve sensors with a large surface area and flexibility but also improve their performance through the addition of catalyst metals. A gas sensor fabricated using the Pd-Au nanocomposites demonstrated 3.9-fold and 1.1-fold faster H₂ recovery and response, respectively, than a pure Pd-Pd gas sensor device. Moreover, the Pd-Ag nanocomposite exhibited a high sensitivity of 5.5% (better than that of other fabricated gas sensors) for 1.6% H₂ concentration. Therefore, we believe that the fabricated nanocomposites appear promising for wide applications in wearable gas sensors, flexible optical devices, and flexible catalytic devices.

Multisensor Systems and Arrays for Medical Applications Employing Naturally-Occurring Compounds and Materials

The significant improvement of quality of life achieved over the last decades has stimulated the development of new approaches in medicine to take into account the personal needs of each patient. Precision medicine, providing healthcare customization, opens new horizons in the diagnosis, treatment and prevention of numerous diseases. As a consequence, there is a growing demand for novel analytical devices and methods capable of addressing the challenges of precision medicine. For example, various types of sensors or their arrays are highly suitable for simultaneous monitoring of multiple analytes in complex biological media in order to obtain more information about the health status of a patient or to follow the treatment process. Besides, the development of sustainable sensors based on natural chemicals allows reducing their environmental impact. This review is concerned with the application of such analytical platforms in various areas of medicine: analysis of body fluids, wearable sensors, drug manufacturing and screening. The importance and role of naturally-occurring compounds in the development of electrochemical multisensor systems and arrays are discussed.

Piezoelectric Nanocellulose Thin Film with Large-Scale Vertical Crystal Alignment

Cellulosic materials are attractive candidates for nature piezoelectrics. Vertically aligned cellulose nanocrystal (CNC) films are expected to show strong piezoelectricity as the largest dipole moment in CNCs exists along the cellulose chain. In this work, we adapted the confinement cell technology that was used to fabricate colloidal opal structures to align CNC rods vertically on a large scale. The high interfacial energy between the CNC-poly(tetrafluoroethylene) (PTFE) surface and torque induced by the shear force led to a large degree to the vertical alignment of CNC rods. An external DC electric field was added to further align the dipole moment of each CNC to the same direction. The as-obtained CNC film displayed excellent piezoelectric performance, and the piezoelectric coefficient was found to be 19.3 ± 2.9 pm/V, comparable to the piezoelectric coefficient d₃₃ of poly(vinylidene difluoride) (PVDF) (20-30 pm/V). This work presents a new class of high-performance piezoelectric polymeric materials from renewable and biocompatible natural resources.

Wearable Battery-Free Perspiration Analyzing Sites Based on Sweat Flowing on ZnO Nanoarrays

We fabricated wearable perspiration analyzing sites for actively monitoring physiological status during exercises without any batteries or other power supply. The device mainly consists of ZnO nanowire (NW) arrays and flexible polydimethylsiloxane substrate. Sweat on the skin can flow into the flow channels of the device through capillary action and flow along the channels to ZnO NWs. The sweat flowing on the NWs (with lactate oxidase modification) can output a DC electrical signal, and the outputting voltage is dependent on the lactate concentration in the sweat as the biosensing signal. ZnO NWs generate electric double layer (EDL) in sweat, which causes a potential difference between the upper and lower ends (hydrovoltaic effect). The product of the enzymatic reaction can adjust the EDL and influence the output. This device can be integrated with wireless transmitter and may have potential application in constructing sports big data. This work promotes the development of next generation of biosensors and expands the scope of self-powered physiological monitoring system.

Nanomaterial-Enabled Flexible and Stretchable Sensing Systems: Processing, Integration, and Applications

Nanomaterial-enabled flexible and stretchable electronics have seen tremendous progress in recent years, evolving from single sensors to integrated sensing systems. Compared with nanomaterial-enabled sensors with a single function, integration of multiple sensors is conducive to comprehensive monitoring of personal health and environment, intelligent human-machine interfaces, and realistic imitation of human skin in robotics and prosthetics. Integration of sensors with other functional components promotes real-world applications of the sensing systems. Here, an overview of the design and integration strategies and manufacturing techniques for such sensing systems is given. Then, representative nanomaterial-enabled flexible and stretchable sensing systems are presented. Following that, representative applications in personal health, fitness tracking, electronic skins, artificial nervous systems, and human-machine interactions are provided. To conclude, perspectives on the challenges and opportunities in this burgeoning field are considered.

Recent progress, challenges, and prospects of fully integrated mobile and wearable point-of-care testing systems for self-testing

The rapid growth of research in the areas of chemical and biochemical sensors, lab-on-a-chip, mobile technology, and wearable electronics offers an unprecedented opportunity in the development of mobile and wearable point-of-care testing (POCT) systems for self-testing. Successful implementation of such POCT technologies leads to minimal user intervention during operation to reduce user errors; user-friendly, easy-to-use and simple detection platforms; high diagnostic sensitivity and specificity; immediate clinical assessment; and low manufacturing and consumables costs. In this review, we discuss recent developments in the field of highly integrated mobile and wearable POCT systems. In particular, aspects of sample handling platforms, recognition elements and sensing methods, and new materials for signal transducers and powering devices for integration into mobile or wearable POCT systems will be highlighted. We also summarize current challenges and future prospects for providing personal healthcare with sample-in result-out mobile and wearable POCT.