Skin-interfaced systems for sweat collection and analytics

Flexible Biosensors Based on Colorimetry, Fluorescence, and Electrochemistry for Point-of-Care Testing

With the outbreak and pandemic of COVID-19, point-of-care testing (POCT) systems have been attracted much attention due to their significant advantages of small batches of samples, user-friendliness, easy-to-use and simple detection. Among them, flexible biosensors show practical significance as their outstanding properties in terms of flexibility, portability, and high efficiency, which provide great convenience for users. To construct highly functional flexible biosensors, abundant kinds of polymers substrates have been modified with sufficient properties to address certain needs. Paper-based biosensors gain considerable attention as well, owing to their foldability, lightweight and adaptability. The other important flexible biosensor employs textiles as substrate materials, which has a promising prospect in the area of intelligent wearable devices. In this feature article, we performed a comprehensive review about the applications of flexible biosensors based on the classification of substrate materials (polymers, paper and textiles), and illustrated the strategies to design effective and artificial sensing platforms, including colorimetry, fluorescence, and electrochemistry. It is demonstrated that flexible biosensors play a prominent role in medical diagnosis, prognosis, and healthcare.

Biosymbiotic, personalized, and digitally manufactured wireless devices for indefinite collection of high-fidelity biosignals

Digital medicine, the ability to stream continuous information from the body to gain insight into health status, manage disease, and predict onset health problems, is only gradually developing. Key technological hurdles that slow the proliferation of this approach are means by which clinical grade biosignals are continuously obtained without frequent user interaction. To overcome these hurdles, solutions in power supply and interface strategies that maintain high-fidelity readouts chronically are critical. This work introduces a previously unexplored class of devices that overcomes the limitations using digital manufacturing to tailor geometry, mechanics, electromagnetics, electronics, and fluidics to create unique personalized devices optimized to the wearer. These elastomeric, three-dimensional printed, and laser-structured constructs, called biosymbiotic devices, enable adhesive-free interfaces and the inclusion of high-performance, far-field energy harvesting to facilitate continuous wireless and battery-free operation of multimodal and multidevice, high-fidelity biosensing in an at-home setting without user interaction.

Air Bubble Bridge-Based Bioinspired Underwater Adhesion

Wet adhesion is greatly demanded in fields of wearable devices, wound dressings, and smart robotics. However, reusable, noninvasive and convenient adhesive pads in the liquid environment have remained a challenge. Here, a novel concept of underwater adhesion inspired by the diving beetle, which utilizes the air bubbles as an adhesive to realize nondestructive and repeatable adhesion working across a wide range of scales is shown. The mechanism of underwater bubble adhesion is revealed by the capillarity of air-bubble bridge, of which the property depends on the dynamic bubble contact angles and the gap distance. The design principle of the air bubble-based underwater adhesion is proposed and validated to tune the interfacial acting force by theoretical and experimental results. Finally, a strong, reusable surface adhesive based on air bubble bridges is demonstrated from macro- to microscales in applications of particle manipulation and particle self-assembly. This unique view of underwater bubble adhesion provides new ideas for broader applications.

Flexible electrochemical aptasensor for cortisol detection in human sweat

This communication demonstrates an electrochemical DNA aptasensor for the detection of cortisol in human sweat. The aptasensor was fabricated via layer-by-layer assembly on stretchable polydimethylsiloxane (PDMS) coated with conductive nanoporous carbon nanotube-cellulose nanocrystals (CNC/CNT) film using a linker to a cortisol specific DNA aptamer. The flexible cortisol aptasensor had a dynamic range of 2.5-35 ng mL^-1. The aptasensor precision was determined to be 2.7% relative standard deviation (%RSD) across the concentration dynamic range. The aptasensor was determined to have a limit of detection (LOD) of ∼ 1.8 ng mL^-1. The aptasensor was demonstrated to have high selectivity to cortisol and was unresponsive to interfering species including glucose, sodium lactate, and β-estradiol. The aptasensor was successfully evaluated for the detection of cortisol in human sweat indicative of its high specificity.

E-Skin: The Dawn of a New Era of On-Body Monitoring Systems

Real-time "on-body" monitoring of human physiological signals through wearable systems developed on flexible substrates (e-skin) is the next target in human health control and prevention, while an alternative to bulky diagnostic devices routinely used in clinics. The present work summarizes the recent trends in the development of e-skin systems. Firstly, we revised the material development for e-skin systems. Secondly, aspects related to fabrication techniques were presented. Next, the main applications of e-skin systems in monitoring, such as temperature, pulse, and other bio-electric signals related to health status, were analyzed. Finally, aspects regarding the power supply and signal processing were discussed. The special features of e-skin as identified contribute clearly to the developing potential as in situ diagnostic tool for further implementation in clinical practice at patient personal levels.

Trending Technology of Glucose Monitoring during COVID-19 Pandemic: Challenges in Personalized Healthcare

The COVID-19 pandemic has continued to spread rapidly, and patients with diabetes are at risk of experiencing rapid progression and poor prognosis for appropriate treatment. Continuous glucose monitoring (CGM), which includes accurately tracking fluctuations in glucose levels without raising the risk of coronavirus exposure, becomes an important strategy for the self-management of diabetes during this pandemic, efficiently contributing to the diabetes care and the fight against COVID-19. Despite being less accurate than direct blood glucose monitoring, wearable noninvasive systems can encourage patient adherence by guaranteeing reliable results through high correlation between blood glucose levels and glucose concentrations in various other biofluids. This review highlights the trending technologies of glucose sensors during the ongoing COVID-19 pandemic (2019-2020) that have been developed to make a significant contribution to effective management of diabetes and prevention of coronavirus spread, from off-body systems to wearable on-body CGM devices, including nanostructure and sensor performance in various biofluids. The advantages and disadvantages of various human biofluids for use in glucose sensors are also discussed. Furthermore, the challenges faced by wearable CGM sensors with respect to personalized healthcare during and after the pandemic are deliberated to emphasize the potential future directions of CGM devices for diabetes management.

A Conformable, Gas-Permeable, and Transparent Skin-Like Micromesh Architecture for Glucose Monitoring

Monitoring the concentration of useful biomarkers via electronic skins (e-skins) is highly important for the development of wearable health management systems. While some biosensor e-skins with high flexibility, sensitivity, and stability have been developed, little attention has been paid to their long-term comfortability and optical transparency. Here, a conformable, gas permeable, and transparent skin-like Cu₂ O@Ni micromesh structural glucose monitoring patch is reported. With its self-supporting micromesh structure, the skin-like glucose monitoring patch exhibits excellent shape conformability, high gas permeability, and high optical transmittance. The skin-like glucose biosensor achieves real-time monitoring of glucose concentrations with high sensitivity (15 420 µA cm^{- 2} mM^{- 1} ), low detection limit (50 nM), fast response time (＜2 s), high selectivity, and long-term stability. These desirable performance properties arise from the synergistic effects of the self-supporting micromesh configuration, high conductivity of the metallic Ni micromesh, and high electrocatalytic activities of the Cu₂ O toward glucose. This work presents a versatile and efficient strategy for constructing conformable, gas permeable, and transparent biosensor e-skins with excellent practicability towards wearable electronics.

Transdermal sensing: in-situ non-invasive techniques for monitoring of human biochemical status

Improving life expectancy necessitates prevention and early diagnosis of any disease state based on active self-monitoring of symptoms and longitudinal biochemical profiling. Non-invasive and continuous measurement of molecular biomarkers that reflect metabolism and health must however be established to realize this plan. Human samples non-invasively obtained via the skin are suitable in this context for in-situ biochemical monitoring. We present a brief classification of transdermal sampling in aqueous and gaseous phases and then introduce a new generation of transdermal monitoring devices for rapid and accurate assessment of important parameters. Finally, we have summarized the diversity of body-wide skin characteristics that have possible effects for transdermal sampling. Because of its passive nature, in-situ biochemical monitoring via transdermal sampling will potentially lead to a greater understanding of important biochemical markers and their temporal variation.

State of Sweat: Emerging Wearable Systems for Real-Time, Noninvasive Sweat Sensing and Analytics

Skin-interfaced wearable systems with integrated colorimetric assays, microfluidic channels, and electrochemical sensors offer powerful capabilities for noninvasive, real-time sweat analysis. This Perspective details recent progress in the development and translation of novel wearable sensors for personalized assessment of sweat dynamics and biomarkers, with precise sampling and real-time analysis. Sensor accuracy, system ruggedness, and large-scale deployment in remote environments represent key opportunity areas, enabling broad deployment in the context of field studies, clinical trials, and recent commercialization. On-body measurements in these contexts show good agreement compared to conventional laboratory-based sweat analysis approaches. These device demonstrations highlight the utility of biochemical sensing platforms for personalized assessment of performance, wellness, and health across a broad range of applications.

Epidermal Sensor for Potentiometric Analysis of Metabolite and Electrolyte

Wearable epidermal sensors that can provide noninvasive and continuous analysis of metabolites and electrolytes in sweat have great significance for healthcare monitoring. This study reports an epidermal sensor that can wirelessly, noninvasively, and potentiometrically analyze metabolites and electrolytes. Potentiometry-based ion-selective electrodes (ISE) are most widely used for detecting electrolytes, such as Na⁺ and K⁺. We develop an enzyme-based glucose ISE for potentiometric analysis of sweat glucose. The glucose ISE sensor is obtained by modifying a glucose oxidase layer (GOD) on an H⁺ ISE sensor. GOD catalyzes glucose to generate H⁺. The generated H⁺ passes through the H⁺ selective membrane to change the potential of the electrode. We have fully examined the limit of detection, detecting range, and stability of our epidermal sensor. Meanwhile, using this epidermal sensor, we can easily analyze the relationship between blood glucose and sweat glucose. The concentration curve of sweat glucose can represent blood glucose concentration, significantly contributing to sports and chronic disease monitoring.

TiO2 Nanotubes Alginate Hydrogel Scaffold for Rapid Sensing of Sweat Biomarkers: Lactate and Glucose

Versatile sensing matrixes are essential for the development of enzyme-immobilized optical biosensors. A novel three-dimensional titanium dioxide nanotubes/alginate hydrogel scaffold is proposed for the detection of sweat biomarkers, lactate, and glucose in artificial sweat. Hydrothermally synthesized titanium dioxide nanotubes were introduced to the alginate polymeric matrix, followed by cross-linking nanocomposite with dicationic calcium ions to fabricate the scaffold platform. Rapid colorimetric detection (blue color optical signal) was carried out for both lactate and glucose biomarkers in artificial sweat at 4 and 6 min, respectively. The superhydrophilicity and the capillarity of the synthesized titanium dioxide nanotubes, when incorporated into the alginate matrix, facilitate the rapid transfer of the artificial sweat components throughout the sensor scaffold, decreasing the detection times. Moreover, the scaffold was integrated on a cellulose paper to demonstrate the adaptability of the material to other matrixes, obtaining fast and homogeneous colorimetric detection of lactate and glucose in the paper substrate when image analysis was performed. The properties of this new composite provide new avenues in the development of paper-based sensor devices. The biocompatibility, the efficient immobilization of biological enzymes/colorimetric assays, and the quick optical signal readout behavior of the titanium dioxide nanotubes/alginate hydrogel scaffolds provide a prospective opportunity for integration into wearable devices.

Luminescent wearable biosensors based on gold nanocluster networks for "turn-on" detection of Uric acid, glucose and alcohol in sweat

From the difficulty of awareness of abnormal concentrations of biochemical indexes in people's daily life come wearable sensing technologies. Recently, luminescent wearable biosensors are emerging with simple fabrication, easy use, cost-effectivity and reliability. But several challenges should be taken up, such as availability of varied analytes, high sensitivity, stability of enzymes, photostability, low signal noises and recyclability of sensors. Here, the Luminescent Wearable Sweat Tape (LWST) biosensor is developed via embedding multi-component nanoprobes onto microwell-patterned paper substrates of hollowed-out double-side tapes. The nanoprobes consist of responsive luminophores, enzyme-loaded gold nanocluster (AuNCs) nano-networks, which are wrapped by the switch, MnO₂ nanosheets. The responsive luminophores are constructed by 3 substitutable components: enzymes (uricase, GOx and alcohol dehydrogenase) for molecular target recognition, glutathione-protected AuNCs (yellow, red and green) for luminescent signal output and polycations PAH for integration. MnO₂ NSs as the switch can quench the emission of the AuNCs but degraded by the reductive product of incorporated enzymes. Thus, targeting analysts (uric acid, glucose and alcohol) can be dose-dependently detected through "turn-on" luminescence approach. After incorporating the nanoprobes into hollow-out tapes, the formed LWST biosensors can detect uric acid, glucose and alcohol in sweat with the help of a smartphone. Subsequently, we primarily apply them into human daily life scenario, sampling from dine parties, and the positive relationships of analyte intakes and the increase of analytes in sweat are significant with individual difference.

A Review on the Role and Performance of Cellulose Nanomaterials in Sensors

Sensors and biosensors play a key role as an analytical tool for the rapid, reliable, and early diagnosis of human diseases. Such devices can also be employed for monitoring environmental pollutants in air and water in an expedited way. More recently, nanomaterials have been proposed as an alternative in sensor fabrication to achieve gains in performance in terms of sensitivity, selectivity, and portability. In this direction, the use of cellulose nanomaterials (CNM), such as cellulose nanofibrils (CNF), cellulose nanocrystals (CNC), and bacterial cellulose (BC), has experienced rapid growth in the fabrication of varied types of sensors. The advantageous properties are related to the supramolecular structures that form the distinct CNM, their biocompatibility, and highly reactive functional groups that enable surface functionalization. The CNM can be applied as hydrogels and xerogels, thin films, nanopapers and other structures interesting for sensor design. Besides, CNM can be combined with other materials (e.g., nanoparticles, enzymes, carbon nanomaterials, etc.) and varied substrates to advanced sensors and biosensors fabrication. This review explores recent advances on CNM and composites applied in the fabrication of optical, electrical, electrochemical, and piezoelectric sensors for detecting analytes ranging from environmental pollutants to human physiological parameters. Emphasis is given to how cellulose nanomaterials can contribute to enhance the performance of varied sensors as well as expand novel sensing applications, which could not be easily achieved using standard materials. Finally, challenges and future trends on the use of cellulose-based materials in sensors and biosensors are also discussed.

Recent advances in liquid-metal-based wearable electronics and materials

Soft wearable electronics are rapidly developing through exploration of new materials, fabrication approaches, and design concepts. Although there have been many efforts for decades, a resurgence of interest in liquid metals (LMs) for sensing and wiring functional properties of materials in soft wearable electronics has brought great advances in wearable electronics and materials. Various forms of LMs enable many routes to fabricate flexible and stretchable sensors, circuits, and functional wearables with many desirable properties. This review article presents a systematic overview of recent progresses in LM-enabled wearable electronics that have been achieved through material innovations and the discovery of new fabrication approaches and design architectures. We also present applications of wearable LM technologies for physiological sensing, activity tracking, and energy harvesting. Finally, we discuss a perspective on future opportunities and challenges for wearable LM electronics as this field continues to grow.

Wearable Biosensors for Non-Invasive Sweat Diagnostics

Recent advances in microfluidics, microelectronics, and electrochemical sensing methods have steered the way for the development of novel and potential wearable biosensors for healthcare monitoring. Wearable bioelectronics has received tremendous attention worldwide due to its great a potential for predictive medical modeling and allowing for personalized point-of-care-testing (POCT). They possess many appealing characteristics, for example, lightweight, flexibility, good stretchability, conformability, and low cost. These characteristics make wearable bioelectronics a promising platform for personalized devices. In this paper, we review recent progress in flexible and wearable sensors for non-invasive biomonitoring using sweat as the bio-fluid. Real-time and molecular-level monitoring of personal health states can be achieved with sweat-based or perspiration-based wearable biosensors. The suitability of sweat and its potential in healthcare monitoring, sweat extraction, and the challenges encountered in sweat-based analysis are summarized. The paper also discusses challenges that still hinder the full-fledged development of sweat-based wearables and presents the areas of future research.

Low dimensional materials for glucose sensing

Biosensors are essential components for effective healthcare management. Since biological processes occur on molecular scales, nanomaterials and nanosensors intrinsically provide the most appropriate landscapes for developing biosensors. Low-dimensional materials have the advantage of offering high surface areas, increased reactivity and unique physicochemical properties for efficient and selective biosensing. So far, nanomaterials and nanodevices have offered significant prospects for glucose sensing. Targeted glucose biosensing using such low-dimensional materials enables much more effective monitoring of blood glucose levels, thus providing significantly better predictive diabetes diagnostics and management. In this review, recent advances in using low dimensional materials for sensing glucose are summarized. Sensing fundamentals are discussed, as well as invasive, minimally-invasive and non-invasive sensing methods. The effects of morphological characteristics and size-dependent properties of low dimensional materials are explored for glucose sensing, and the key performance parameters such as selectivity, stability and sensitivity are also discussed. Finally, the challenges and future opportunities that low dimensional materials can offer for glucose sensing are outlined.

Microneedle-Based Potentiometric Sensing System for Continuous Monitoring of Multiple Electrolytes in Skin Interstitial Fluids

Electrolytes play a pivotal role in regulating cardiovascular functions, hydration, and muscle activation. The current standards for monitoring electrolytes involve periodic sampling of blood and measurements using laboratory techniques, which are often uncomfortable/inconvenient to the subjects and add considerable expense to the management of their underlying disease conditions. The wide range of electrolytes in skin interstitial fluids (ISFs) and their correlations with those in plasma create exciting opportunities for applications such as electrolyte and circadian metabolism monitoring. However, it has been challenging to monitor these electrolytes in the skin ISFs. In this study, we report a minimally invasive microneedle-based potentiometric sensing system for multiplexed and continuous monitoring of Na⁺ and K⁺ in the skin ISFs. The potentiometric sensing system consists of a miniaturized stainless-steel hollow microneedle to prevent sensor delamination and a set of modified microneedle electrodes for multiplex monitoring. We demonstrate the measurement of Na⁺ and K⁺ in artificial ISFs with a fast response time, excellent reversibility and repeatability, adequate selectivity, and negligible potential interferences upon the addition of a physiologically relevant concentration of metabolites, dietary biomarkers, and nutrients. In addition, the sensor maintains the sensitivity after multiple insertions into the chicken skin model. Furthermore, the measurements in artificial ISFs using calibrated sensors confirm the accurate measurements of physiological electrolytes in artificial ISFs. Finally, the skin-mimicking phantom gel and chicken skin model experiments demonstrate the sensor's potential for minimally invasive monitoring of electrolytes in skin ISFs. The developed sensor platform can be adapted for a wide range of other applications, including real-time monitoring of nutrients, metabolites, and proteins.

Catalytic effects of magnetic and conductive nanoparticles on immobilized glucose oxidase in skin sensors

Wearable skin sensors is a promising technology for real-time health care monitoring. They are of particular interest for monitoring glucose in diabetic patients. The concentration of glucose in sweat can be more than two orders of magnitude lower than in blood. In consequence, the scientific and technological efforts are focused in developing new concepts to enhance the sensitivity, decrease the limit of detection (LOD) and reduce the response time (RT) of glucose skin sensors. This work explores the effect of adsorbed superparamagnetic magnetite nanoparticles (MNPs) and conductive nanoparticles (CNPs) on carbon nanotube substrates (CNTs) used to immobilize glucose oxidase enzyme in the working electrode of skin sensors. MNPs and CNPs are made of magnetite and gold, respectively. The performance of the sensors was tested in standard buffer solution, artificial sweat, fresh sweat and on the skin of a healthy volunteer during an exercise session. In the case of artificial sweat, the presence of MNPs accelerated the RT from 7 to 5 s at the expense of increasing the LOD from 0.017 to 0.022 mM with slight increase of the sensitivity from 4.90 to 5.09μAm M^-1cm^-2. The presence of CNPs greatly accelerated the RT from 7 to 2 s and lowered the LOD from 0.017 to 0.014 mM at the expense of a great diminution of the sensitivity from 4.90 to 4.09μAm M^-1cm^-2. These effects were explained mechanistically by analyzing the changes in the concentration of free oxygen and electrons promoted by MNPs and CNPs in the CNTs and its consequences on the the glucose oxidation process.

Multifaceted Design and Emerging Applications of Tissue Adhesives

Tissue adhesives can form appreciable adhesion with tissues and have found clinical use in a variety of medical settings such as wound closure, surgical sealants, regenerative medicine, and device attachment. The advantages of tissue adhesives include ease of implementation, rapid application, mitigation of tissue damage, and compatibility with minimally invasive procedures. The field of tissue adhesives is rapidly evolving, leading to tissue adhesives with superior mechanical properties and advanced functionality. Such adhesives enable new applications ranging from mobile health to cancer treatment. To provide guidelines for the rational design of tissue adhesives, here, existing strategies for tissue adhesives are synthesized into a multifaceted design, which comprises three design elements: the tissue, the adhesive surface, and the adhesive matrix. The mechanical, chemical, and biological considerations associated with each design element are reviewed. Throughout the report, the limitations of existing tissue adhesives and immediate opportunities for improvement are discussed. The recent progress of tissue adhesives in topical and implantable applications is highlighted, and then future directions toward next-generation tissue adhesives are outlined. The development of tissue adhesives will fuse disciplines and make broad impacts in engineering and medicine.

Diving beetle-like miniaturized plungers with reversible, rapid biofluid capturing for machine learning-based care of skin disease

Recent advances in bioinspired nano/microstructures have received attention as promising approaches with which to implement smart skin-interfacial devices for personalized health care. In situ skin diagnosis requires adaptable skin adherence and rapid capture of clinical biofluids. Here, we report a simple, all-in-one device consisting of microplungers and hydrogels that can rapidly capture biofluids and conformally attach to skin for stable, real-time monitoring of health. Inspired by the male diving beetle, the microplungers achieve repeatable, enhanced, and multidirectional adhesion to human skin in dry/wet environments, revealing the role of the cavities in these architectures. The hydrogels within the microplungers instantaneously absorb liquids from the epidermis for enhanced adhesiveness and reversibly change color for visual indication of skin pH levels. To realize advanced biomedical technologies for the diagnosis and treatment of skin, our suction-mediated device is integrated with a machine learning framework for accurate and automated colorimetric analysis of pH levels.

Recent progress in silk fibroin-based flexible electronics

With the rapid development of the Internet of Things (IoT) and the emergence of 5G, traditional silicon-based electronics no longer fully meet market demands such as nonplanar application scenarios due to mechanical mismatch. This provides unprecedented opportunities for flexible electronics that bypass the physical rigidity through the introduction of flexible materials. In recent decades, biological materials with outstanding biocompatibility and biodegradability, which are considered some of the most promising candidates for next-generation flexible electronics, have received increasing attention, e.g., silk fibroin, cellulose, pectin, chitosan, and melanin. Among them, silk fibroin presents greater superiorities in biocompatibility and biodegradability, and moreover, it also possesses a variety of attractive properties, such as adjustable water solubility, remarkable optical transmittance, high mechanical robustness, light weight, and ease of processing, which are partially or even completely lacking in other biological materials. Therefore, silk fibroin has been widely used as fundamental components for the construction of biocompatible flexible electronics, particularly for wearable and implantable devices. Furthermore, in recent years, more attention has been paid to the investigation of the functional characteristics of silk fibroin, such as the dielectric properties, piezoelectric properties, strong ability to lose electrons, and sensitivity to environmental variables. Here, this paper not only reviews the preparation technologies for various forms of silk fibroin and the recent progress in the use of silk fibroin as a fundamental material but also focuses on the recent advanced works in which silk fibroin serves as functional components. Additionally, the challenges and future development of silk fibroin-based flexible electronics are summarized. (1) This review focuses on silk fibroin serving as active functional components to construct flexible electronics. (2) Recent representative reports on flexible electronic devices that applied silk fibroin as fundamental supporting components are summarized. (3) This review summarizes the current typical silk fibroin-based materials and the corresponding advanced preparation technologies. (4) The current challenges and future development of silk fibroin-based flexible electronic devices are analyzed.

Lightening Effect of Skin Lightening Cream Containing Piper betle L. Extract in Human Volunteers

Hyperpigmentation affects people globally with negative psychological impacts. Piper betle L. leaf (PBL) extract has many benefits including skin lightening which may reduce hyperpigmentation. The objective of this study was to develop an effective skin-lightening cream containing PBL with ideal characteristics. A formulation of base cream and PBL cream was prepared and characterized by centrifugation, particle size and zeta potential analysis, rheological profile studies and physical properties’ observation. In vivo studies on 30 human subjects tested the effects of base and PBL cream on skin-lightening, hydration, trans-epidermal water loss (TEWL) and elasticity through weekly tests 4 weeks in duration. Base and PBL creams had a non-Newtonian property with acceptable color, odor, texture, zeta potential, particle size and showed no phase separation. The in vivo study indicated a significant reduction in melanin content and an improvement in skin tone for PBL cream but not in base cream. TEWL and elasticity also showed significant reduction for both formulations, indicating a healthier skin barrier and supple skin with consistent use, although hydration fluctuated with no significant changes. The developed PBL cream showed significant results in the reduction in melanin content and improving skin tone, which shows the formulation can confer skin-lightening effect.

A critical review on the use of potentiometric based biosensors for biomarkers detection

Potentiometric-based biosensors have the potential to advance the detection of several biological compounds and help in early diagnosis of various diseases. They belong to the portable analytical class of biosensors for monitoring biomarkers in the human body. They contain ion-sensitive membranes sensors can be used to determine potassium, sodium, and chloride ions activity while being used as a biomarker to gauge human health. The potentiometric based ion-sensitive membrane systems can be coupled with various techniques to create a sensitive tool for the fast and early detection of cancer biomarkers and other critical biological compounds. This paper discusses the application of potentiometric-based biosensors and classifies them into four major categories: photoelectrochemical potentiometric biomarkers, potentiometric biosensors amplified with molecular imprinted polymer systems, wearable potentiometric biomarkers and light-addressable potentiometric biosensors. This review demonstrated the development of several innovative biosensor-based techniques that could potentially provide reliable tools to test biomarkers. Some challenges however remain, but these can be removed by coupling techniques to maximize the testing sensitivity.

Wireless and battery-free platforms for collection of biosignals

Recent progress in biosensors have quantitively expanded current capabilities in exploratory research tools, diagnostics and therapeutics. This rapid pace in sensor development has been accentuated by vast improvements in data analysis methods in the form of machine learning and artificial intelligence that, together, promise fantastic opportunities in chronic sensing of biosignals to enable preventative screening, automated diagnosis, and tools for personalized treatment strategies. At the same time, the importance of widely accessible personal monitoring has become evident by recent events such as the COVID-19 pandemic. Progress in fully integrated and chronic sensing solutions is therefore increasingly important. Chronic operation, however, is not truly possible with tethered approaches or bulky, battery-powered systems that require frequent user interaction. A solution for this integration challenge is offered by wireless and battery-free platforms that enable continuous collection of biosignals. This review summarizes current approaches to realize such device architectures and discusses their building blocks. Specifically, power supplies, wireless communication methods and compatible sensing modalities in the context of most prevalent implementations in target organ systems. Additionally, we highlight examples of current embodiments that quantitively expand sensing capabilities because of their use of wireless and battery-free architectures.

Recent progress, challenges, and opportunities for wearable biochemical sensors for sweat analysis

Sweat is a promising, yet relatively unexplored biofluid containing biochemical information that offers broad insights into the underlying dynamic metabolic activity of the human body. The rich composition of electrolytes, metabolites, hormones, proteins, nucleic acids, micronutrients, and exogenous agents found in sweat dynamically vary in response to the state of health, stress, and diet. Emerging classes of skin-interfaced wearable sensors offer powerful capabilities for the real-time, continuous analysis of sweat produced by the eccrine glands in a manner suitable for use in athletics, consumer wellness, military, and healthcare industries. This perspective examines the rapid and continuous progress of wearable sweat sensors through the most advanced embodiments that address the fundamental challenges currently restricting widespread deployment. It concludes with a discussion of efforts to expand the overall utility of wearable sweat sensors and opportunities for commercialization, in which advances in biochemical sensor technologies will be critically important.

Soft, skin-interfaced sweat stickers for cystic fibrosis diagnosis and management

The concentration of chloride in sweat remains the most robust biomarker for confirmatory diagnosis of cystic fibrosis (CF), a common life-shortening genetic disorder. Early diagnosis via quantitative assessment of sweat chloride allows prompt initiation of care and is critically important to extend life expectancy and improve quality of life. The collection and analysis of sweat using conventional wrist-strapped devices and iontophoresis can be cumbersome, particularly for infants with fragile skin, who often have insufficient sweat production. Here, we introduce a soft, epidermal microfluidic device ("sweat sticker") designed for the simple and rapid collection and analysis of sweat. Intimate, conformal coupling with the skin supports nearly perfect efficiency in sweat collection without leakage. Real-time image analysis of chloride reagents allows for quantitative assessment of chloride concentrations using a smartphone camera, without requiring extraction of sweat or external analysis. Clinical validation studies involving patients with CF and healthy subjects, across a spectrum of age groups, support clinical equivalence compared to existing device platforms in terms of accuracy and demonstrate meaningful reductions in rates of leakage. The wearable microfluidic technologies and smartphone-based analytics reported here establish the foundation for diagnosis of CF outside of clinical settings.

Sweating Out the Circadian Rhythm: A Technical Review

Circadian dysfunction or dysregulation is associated with many chronic morbidities. Current state-of-art technologies do not provide an accurate estimation of the extent of disease affliction. Recent advances call for using wearables for improving management and diagnosis of circadian related disorders. Sweat contains an abundance of relevant biomarkers like cortisol, DHEA, and so forth, which could be leveraged toward tracking the user's chronobiology. In this article, we provide a review of the key developments in the field of wearable sensors for circadian technologies. We highlight the value of using sweat along with portable electronics toward developing state-of-the-art platforms for efficient diagnosis and management of chronic conditions. Finally, we discuss challenges and opportunities for using wearable sweat sensors for circadian diagnosis and disease management.

ANTIGONE: A Programmable Energy-Efficient Current Digitizer for an ISFET Wearable Sweat Sensing System

This article describes the design and the characterization of the ANTIGONE (ANalog To dIGital cONvErter) ASIC (Application Specific Integrated Circuit) built in AMS 0.35 m technology for low dc-current sensing. This energy-efficient ASIC was specifically designed to interface with multiple Ion-Sensitive Field-Effect Transistors (ISFETs) and detect biomarkers like pH, Na+, K+ and Ca2+ in human sweat. The ISFET-ASIC system can allow real-time noninvasive and continuous health monitoring. The ANTIGONE ASIC architecture is based on the current-to-frequency converter through the charge balancing principle. The same front-end can digitize multiple currents produced by four sweat ISFET sensors in time multiplexing. The front-end demonstrates good linearity over a dynamic range that spans from 1 pA up to 500 nA. The consumed energy per conversion is less than 1 J. The chip is programmable and works in eight different modes of operation. The system uses a standard Serial Peripheral Interface (SPI) to configure, control and read the digitally converted sensor data. The chip is controlled by a portable device over Bluetooth Low Energy (BLE) through a Microcontroller Unit (MCU). The sweat sensing system is part of a bigger wearable platform that exploits the convergence of multiparameter biosensors and environmental sensors for personalized and preventive healthcare.

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.

Skin-Interfaced Microfluidic Systems that Combine Hard and Soft Materials for Demanding Applications in Sweat Capture and Analysis

Eccrine sweat contains a rich blend of electrolytes, metabolites, proteins, metal ions, and other biomarkers. Changes in the concentrations of these chemical species can indicate alterations in hydration status and they can also reflect health conditions such as cystic fibrosis, schizophrenia, and depression. Recent advances in soft, skin-interfaced microfluidic systems enable real-time measurement of local sweat loss and sweat biomarker concentrations, with a wide range of applications in healthcare. Uses in certain contexts involve, however, physical impacts on the body that can dynamically deform these platforms, with adverse effects on measurement reliability. The work presented here overcomes this limitation through the use of microfluidic structures constructed in relatively high modulus polymers, and designed in geometries that offer soft, system level mechanics when embedded low modulus elastomers. Analytical models and finite element analysis quantitatively define the relevant mechanics of these systems, and serve as the basis for layouts optimized to allow robust operation in demanding, rugged scenarios such as those encountered in football, while preserving mechanical stretchability for comfortable, water-tight bonding to the skin. Benchtop testing and on-body field studies of measurements of sweat loss and chloride concentration under imposed mechanical stresses and impacts demonstrate the key features of these platforms.

Wearable Analytical Platform with Enzyme-Modulated Dynamic Range for the Simultaneous Colorimetric Detection of Sweat Volume and Sweat Biomarkers

In this manuscript, we introduce a wearable analytical platform that simultaneously measures the concentration of sweat lactate and sample volume. It contains two sensors entirely made of filter paper that can be easily affixed on the skin with medical-grade tape. The lactate biosensor features a unique signal modulation mechanism that enables fine-tuning the dynamic range. It consists of adding a competitive enzyme inhibitor in different reservoirs. Thanks to this, it is possible to choose between a very low limit of detection (0.06 mM) and a linear response in the physiological concentration range (10-30 mM). The sweat volume sensor was obtained by adding a reservoir containing gold nanoparticles. As the wearer sweats, the nanoparticles are carried through a paper channel. This is used to gauge the volume of sample by measuring the distance traveled by the nanoprobes. Using fine-tuned lactate biosensors and combining them with the volume sensors allowed us to quantify variations in the levels of sweat lactate independently of the wearer's sweat rate during an exercise routine. The platform design can be customized to meet the end user's needs, which makes it ideal for developing a wide array of disposable wearable biosensors.

Colorimetric sensing of chloride in sweat based on fluorescence wavelength shift via halide exchange of CsPbBr3 perovskite nanocrystals

Considering the high importance of the rapid detection of chloride ion (Cl^-) in sweat for the diagnosis of fibrotic cysts, we have investigated the heterogeneous halide exchange between CsPbBr₃ perovskite nanocrystals (PNCs) in n-hexane and Cl^- in aqueous solution. The results show that CsPbBr₃ PNCs could achieve fast halide exchange with Cl^- in the aqueous phase under magnetic stirring at pH = 1, accompanied by a significant wavelength blue shift and vivid fluorescence color changes from green to blue. Therefore, a fluorescence wavelength shift-based colorimetric sensing of Cl^- based on the halide exchange of CsPbBr₃ PNCs has been developed to realize the rapid detection of Cl^- in sweat. Compared with the conventional fluorescence intensity-based method, this method is of high convenience since the whole procedure could be achieved within 5 min without any sample pretreatment (even no dilution), demonstrating promising application prospects. Graphical Abstract Fluorescence wavelength-shift based colorimetric sensing of chloride in sweat via halide exchange of CsPbBr₃ perovskite nanocrystals.

Wearable strain sensor for real-time sweat volume monitoring

Reliably monitoring sweat volume has attracted much attention due to its important role in the assessment of physiological health conditions and the prevention of dehydration. Here, we present the first example of wearable strain sensor for real-time sweat volume monitoring. Such sweat volume monitoring sensor is simply fabricated via embedding strain sensing fabric in super-absorbent hydrogels, the hydrogels can wick sweat up off the skin surface to swell and then trigger the strain sensing fabrics response. This sensor can realize real-time detection of sweat volume (0.15-700 μL), shows excellent repeatability and stability against movement or light interference, reliability in the non-pathological range (pH: 4-9 and salinity: 0-100 mM NaCl) in addition. Such sensor combing swellable hydrogels with strain sensing fabrics provides a novel measurement method of wearable devices for sweat volume monitoring.

Construction of highly accessible single Co site catalyst for glucose detection

The development of high-performance glucose sensors is an urgent need, especially for diabetes mellitus diagnosis. However, the glucose monitoring is conventionally operated in an invasive finger-prick manner and their noninvasive alternatives largely suffered from the relatively poor sensitivity, selectivity, and stability, resulted from the lack of robust and efficient catalysts. In this paper, we design a concave shaped nitrogen-doped carbon framework embellished with single Co site catalyst (Co SSC) by selectively controlling the etching rate on different facet of carbon substrate, which is beneficial to the diffusion and contact of analyte. The Co SSC prompts a significant improvement in the sensitivity of the solution-gated graphene transistor (SGGT) devices, with three orders of magnitude better than those of SGGT devices without catalysts. Our findings expand the field of single site catalyst in the application of biosensors, diabetes diagnostics and personalized health-care monitoring.

A wearable fluidic collection patch and ion chromatography method for sweat electrolyte monitoring during exercise

This paper presents a method to continuously collect and reliably measure sweat analyte concentrations during exercise. The method can be used to validate newly developed sweat sensors and to obtain insight into intraindividual variations of sweat analytes in athletes. First, a novel design of a sweat collection system is created. The sweat collection patch, that is made from hydrophilized foil and a double-sided acrylate adhesive, consists of a reservoir array that collects samples consecutively in time. During a physiological experiment, sweat can be collected from the back of a participant and the filling speed of the collector is monitored by using a camera. After the experiment, Na+, Cl- and K+ levels are measured with ion chromatography. Sweat analyte variations are measured during exercise for an hour at three different locations on the back. The Na+ and Cl- variations show a similar trend and the absolute concentrations vary with the patch location. Na+ and Cl- concentrations increase and K+ concentrations seem to decrease during this exercise. With this new sweat collection system, sweat Na+, Cl- and K+ concentrations can be collected over time during exercise at medium to high intensity, to analyse the trend in electrolyte variations per individual.

Emerging Telemedicine Tools for Remote COVID-19 Diagnosis, Monitoring, and Management

The management of the COVID-19 pandemic has relied on cautious contact tracing, quarantine, and sterilization protocols while we await a vaccine to be made widely available. Telemedicine or mobile health (mHealth) is well-positioned during this time to reduce potential disease spread and prevent overloading of the healthcare system through at-home COVID-19 screening, diagnosis, and monitoring. With the rise of mass-fabricated electronics for wearable and portable sensors, emerging telemedicine tools have been developed to address shortcomings in COVID-19 diagnostics, monitoring, and management. In this Perspective, we summarize current implementations of mHealth sensors for COVID-19, highlight recent technological advances, and provide an overview on how these tools may be utilized to better control the COVID-19 pandemic.

Recent Progress in Wearable Biosensors: From Healthcare Monitoring to Sports Analytics

Recent advances in lab-on-a-chip technology establish solid foundations for wearable biosensors. These newly emerging wearable biosensors are capable of non-invasive, continuous monitoring by miniaturization of electronics and integration with microfluidics. The advent of flexible electronics, biochemical sensors, soft microfluidics, and pain-free microneedles have created new generations of wearable biosensors that explore brand-new avenues to interface with the human epidermis for monitoring physiological status. However, these devices are relatively underexplored for sports monitoring and analytics, which may be largely facilitated by the recent emergence of wearable biosensors characterized by real-time, non-invasive, and non-irritating sensing capacities. Here, we present a systematic review of wearable biosensing technologies with a focus on materials and fabrication strategies, sampling modalities, sensing modalities, as well as key analytes and wearable biosensing platforms for healthcare and sports monitoring with an emphasis on sweat and interstitial fluid biosensing. This review concludes with a summary of unresolved challenges and opportunities for future researchers interested in these technologies. With an in-depth understanding of the state-of-the-art wearable biosensing technologies, wearable biosensors for sports analytics would have a significant impact on the rapidly growing field-microfluidics for biosensing.

Shape-adaptable biodevices for wearable and implantable applications

Emerging wearable and implantable biodevices have been significantly revolutionizing the diagnosis and treatment of disease. However, the geometrical mismatch between tissues and biodevices remains a great challenge for achieving optimal performances and functionalities for biodevices. Shape-adaptable biodevices enabling active compliance with human body tissues offer promising opportunities for addressing the challenge through programming their geometries on demand. This article reviews the design principles and control strategies for shape-adaptable biodevices with programmable shapes and actively compliant capabilities, which have offered innovative diagnostic/therapeutic tools and facilitated a variety of wearable and implantable applications. The state-of-the-art progress in applications of shape-adaptable biodevices in the fields of smart textiles, wound care, healthcare monitoring, drug and cell delivery, tissue repair and regeneration, nerve stimulation and recording, and biopsy and surgery, is highlighted. Despite the remarkable advances already made, shape-adaptable biodevices still confront many challenges on the road toward the clinic, such as enhanced intelligence for actively sensing and operating in response to physiological environments. Next-generation paradigms will shed light on future directions for extending the breadth and performance of shape-adaptable biodevices for wearable and implantable applications.

Skin-interfaced soft microfluidic systems with modular and reusable electronics for in situ capacitive sensing of sweat loss, rate and conductivity

Important insights into human health can be obtained through the non-invasive collection and detailed analysis of sweat, a biofluid that contains a wide range of essential biomarkers. Skin-interfaced microfluidic platforms, characterized by soft materials and thin geometries, offer a collection of capabilities for in situ capture, storage, and analysis of sweat and its constituents. In ambulatory uses cases, the ability to provide real-time feedback on sweat loss, rate and content, without visual inspection of the device, can be important. This paper introduces a low-profile skin-interfaced system that couples disposable microfluidic sampling devices with reusable 'stick-on' electrodes and wireless readout electronics that remain isolated from the sweat. An ultra-thin capping layer on the microfluidic platform permits high-sensitivity, contactless capacitive measurements of both sweat loss and sweat conductivity. This architecture avoids the potential for corrosion of the sensing components and eliminates the need for cleaning/sterilizing the electronics, thereby resulting in a cost-effective platform that is simple to use. Optimized electrode designs follow from a combination of extensive benchtop testing, analytical calculations and FEA simulations for two sensing configurations: (1) sweat rate and loss, and (2) sweat conductivity, which contains information about electrolyte content. Both configurations couple to a flexible, wireless electronics platform that digitizes and transmits information to Bluetooth-enabled devices. On-body field testing during physical exercise validates the performance of the system in scenarios of practical relevance to human health and performance.

A Noninvasive Wearable Device for Real-Time Monitoring of Secretion Sweat Pressure by Digital Display

Sweat-based wearable devices have attracted increasing attention by providing abundant physiological information and continuous measurement through noninvasive healthcare monitoring. Sweat pressure generated via sweat glands to the skin surface associated with osmotic effects may help to elucidate such parameters as physiological conditions and psychological factors. This study introduces a wearable device for measuring secretion sweat pressure through noninvasive, continuous monitoring. Secretion pressure is detected by a microfluidic chip that shows the resistance variance from a paired electrode pattern and transfers digital signals to a smartphone for real-time display. A human study demonstrates this measurement with different exercise activities, showing the pressure ranges from 1.3 to 2.5 kPa. This device is user-friendly and applicable to exercise training and personal health care. The convenience and easy-to-wear characteristics of this device may establish a foundation for future research investigating sweat physiology and personal health care.

Effects of smart garments on the well-being of athletes: a scoping review protocol

INTRODUCTION

With the advancements in wearable electronics, electronically integrated smart garments started to transpire in our daily lives. Smart garment technologies are incorporated into sportswear applications to enhance the well-being and performance of athletes. Smart garments applications in the sports sector are increasing, and the variety of smart garment applications available in the literature is overwhelming. Therefore, it is essential to compare the vast array of technologies incorporated in smart garments for athletes to understand the knowledge gaps for future studies. The protocol paper aims to examine the smart garments used in the sports domain to enhance the health and well-being of athletes.

METHODS AND ANALYSIS

Relevant studies will be retrieved using predefined search terms from Scopus, Web of Science, Science Direct, PubMed and IEEE Xplore. The retrieved articles will be eliminated in two phases: title and abstract screening and full-text screening. The included articles will be primary studies published in the English language within the last 10 years. Subsequently, the included articles will be further studied to extract data using a data extraction form. The extracted data will undergo a thematic analysis. Also, quantitative analysis will be carried out using descriptive statistics.

ETHICS AND DISSEMINATION

The results of this review will provide a comprehensive understanding of smart garment concepts used in the sports domain. The findings of this scoping review will be shared through a journal publication and a conference presentation. Ethical approval is not needed for this scoping review.

PROTOCOL REGISTRATION NUMBER

DOI 10.17605/OSF.IO/34MF2 (https://osf.io/34mf2).

Battery-free, wireless, and flexible electrochemical patch for in situ analysis of sweat cortisol via near field communication

Wearable and flexible biosensing devices have been widely developed for in situ detections. Cortisol is a vital biomarker which plays crucial regulatory role in numerous physiological processes of the human body. Here, a wireless, battery-free, and flexible integrated patch is developed for real-time on-body sweat cortisol detection. The patch integrated with all-printed flexible electrochemical immunosensor, which was used to detect cortisol through differential pulse voltammetry (DPV). The near field communication (NFC) module on the patch enables wireless power harvesting and data interaction with an NFC-enabled smartphone, which makes the patch get rid of rigid batteries and realize epidermal on-body testing. Multiple in situ detections on volunteers' sweat on the surface of skin showed that the flexible integrated patch could reflect the circadian rhythm of the body's sweat cortisol level changes in relaxed mood or under stress, which could be confirmed with the enzyme linked immunosorbent assay (ELISA) kit. In this way, the patch provides a rapid-detecting, convenient, and non-invasive sensing solution for in situ analysis of sweat cortisol, which can be applied for the personalized mental health management.

Plasmene nanosheets as optical skin strain sensors

Skin-like optoelectronic sensors can have a wide range of technical applications ranging from wearable/implantable biodiagnostics, human-machine interfaces, and soft robotics to artificial intelligence. The previous focus has been on electrical signal transduction, whether resistive, capacitive, or piezoelectric. Here, we report on "optical skin" strain sensors based on elastomer-supported, highly ordered, and closely packed plasmonic nanocrystal arrays (plasmene). Using gold nanocubes (AuNCs) as a model system, we find that the types of polymeric ligands, interparticle spacing, and AuNC sizes play vital roles in strain-induced plasmonic responses. In particular, brush-forming polystyrene (PS) is a "good" ligand for forming elastic plasmenes which display strain-induced blue shift of high-energy plasmonic peaks with high reversibility upon strain release. Further experimental and simulation studies reveal the transition from isotropic uniform plasmon coupling at a non-strained state to anisotropic plasmon coupling at strained states, due to the AuNC alignment perpendicular to the straining direction. The two-term plasmonic ruler model may predict the primary high-energy peak location. Using the relative shift of the averaged high-energy peak to the coupling peak before straining, a plasmene nanosheet may be used as a strain sensor with the sensitivity depending on its internal structures, such as the constituent AuNC size or inter-particle spacing.

Electrochemical glucose sensors in diabetes management: an updated review (2010-2020)

While over half a century has passed since the introduction of enzyme glucose biosensors by Clark and Lyons, this important field has continued to be the focus of immense research activity. Extensive efforts during the past decade have led to major scientific and technological innovations towards tight monitoring of diabetes. Such continued progress toward advanced continuous glucose monitoring platforms, either minimal- or non-invasive, holds considerable promise for addressing the limitations of finger-prick blood testing toward tracking glucose trends over time, optimal therapeutic interventions, and improving the life of diabetes patients. However, despite these major developments, the field of glucose biosensors is still facing major challenges. The scope of this review is to present the key scientific and technological advances in electrochemical glucose biosensing over the past decade (2010-present), along with current obstacles and prospects towards the ultimate goal of highly stable and reliable real-time minimally-invasive or non-invasive glucose monitoring. After an introduction to electrochemical glucose biosensors, we highlight recent progress based on using advanced nanomaterials at the electrode-enzyme interface of three generations of glucose sensors. Subsequently, we cover recent activity and challenges towards next-generation wearable non-invasive glucose monitoring devices based on innovative sensing principles, alternative body fluids, advanced flexible materials, and novel platforms. This is followed by highlighting the latest progress in the field of minimally-invasive continuous glucose monitoring (CGM) which offers real-time information about interstitial glucose levels, by focusing on the challenges toward developing biocompatible membrane coatings to protect electrochemical glucose sensors against surface biofouling. Subsequent sections cover new analytical concepts of self-powered glucose sensors, paper-based glucose sensing and multiplexed detection of diabetes-related biomarkers. Finally, we will cover the latest advances in commercially available devices along with the upcoming future technologies.