Touch-Based Fingertip Blood-Free Reliable Glucose Monitoring: Personalized Data Processing for Predicting Blood Glucose Concentrations

Multifunctional nanomaterials for smart wearable diabetic healthcare devices

Wearable diabetic healthcare devices have attracted great attention for real-time continuous glucose monitoring (CGM) using biofluids such as tears, sweat, saliva, and interstitial fluid via noninvasive ways. In response to the escalating global demand for CGM, these devices enable proactive management and intervention of diabetic patients with incorporated drug delivery systems (DDSs). In this context, multifunctional nanomaterials can trigger the development of innovative sensing and management platforms to facilitate real-time selective glucose monitoring with remarkable sensitivity, on-demand drug delivery, and wireless power and data transmission. The seamless integration into wearable devices ensures patient's compliance. This comprehensive review evaluates the multifaceted roles of these materials in wearable diabetic healthcare devices, comparing their glucose sensing capabilities with conventionally available glucometers and CGM devices, and finally outlines the merits, limitations, and prospects of these devices. This review would serve as a valuable resource, elucidating the intricate functions of nanomaterials for the successful development of advanced wearable devices in diabetes management.

Synergistic enhancement of wearable biosensor through Pt single-atom catalyst for sweat analysis

Real-time monitoring of biological markers in sweat is a valuable tool for health assessment. In this study, we have developed an innovative wearable biosensor for precise analysis of glucose in sweat during physical activities. The sensor is based on a single-atom catalyst of platinum (Pt) uniformly dispersed on tricobalt tetroxide (Co3O4) nanorods and reduced graphene oxide (rGO), featuring a unique three-dimensional nanostructure and excellent glucose electrocatalytic performance with a wide detection range of 1-800 μM. Additionally, density functional theory calculations have revealed the synergetic role of Pt active sites in the Pt single-atom catalyst (Co3O4/rGO/Pt) in glucose adsorption and electron transfer, thereby enhancing sensor performance. To enable application in wearable devices, we designed an S-shaped microfluidic chip and a point-of-care testing (POCT) device, both of which were validated for effectiveness through actual use by volunteers. This research provides valuable insights and innovative approaches for analyzing sweat glucose using wearable devices, contributing to the advancement of personalized healthcare.

Blood Micro-sampling: An alternative blood collection method for radioiodine therapy dosimetry

PURPOSE

Collecting venous blood samples from patients post administration of high therapeutic activities results in radiation exposure to staff collecting the blood. This study investigated the use of finger-tip capillary-blood collection as an alternative to the venous-blood collection method recommended by the European Association of Nuclear Medicine (EANM) dosimetry protocol for quantifying 131I concentration in the critical organ after therapeutic dose of 131I.

METHODS

The study included differentiated thyroid cancer patients referred to a thyroid cancer centre at St James's Hospital, Ireland, for therapeutic and diagnostic oral administration of 131I. The 15 patients recruited for this study provided 30 venous and capillary paired-blood samples. The activity concentration of the blood samples was compared between the type of blood (venous vs capillary) and the geometry/volume of the blood (1.0 ml versus 0.03 ml). Other variables were also investigated including administered activities, dose to staff performing the sampling, duration of sampling and time since administration.

RESULTS

Blood samples were taken at 2.0-91.9 h post administration using 0.2 ± 0.0 GBq (n = 2) or 4.0 ± 0.1 GBq (n = 28) 131I activities. There was no significant difference found between different blood sampling types (-1.0 ± 4.3 %, p = 0.223), different blood volumes (-3.2 ± 10.0 %, p = 0.070), or between their combination. No significant correlation was found between the percentage differences and investigated parameters.

CONCLUSION

A high degree of accuracy was achieved with blood radioactivity quantified using capillary blood collection using the finger-prick method. Further validation of the method would be required prior to implementation, to investigate patient specific factors which may affect accuracy.

Smartphone based wearable sweat glucose sensing device correlated with machine learning for real-time diabetes screening

BACKGROUND

Diabetes is a significant health threat, with its prevalence and burden increasing worldwide indicating its challenge for global healthcare management. To decrease the disease severity, the diabetic patients are recommended to regularly check their blood glucose levels. The conventional finger-pricking test possesses some drawbacks, including painfulness and infection risk. Nowadays, smartphone has become a part of our lives offering an important benefit in self-health monitoring. Thus, non-invasive wearable sweat glucose sensor connected with a smartphone readout is of interest for real-time glucose detection.

RESULTS

Wearable sweat glucose sensing device is fabricated for self-monitoring of diabetes. This device is designed as a body strap consisting of a sensing strip and a portable potentiostat connected with a smartphone readout via Bluetooth. The sensing strip is modified by carbon nanotubes (CNTs)-cellulose nanofibers (CNFs), followed by electrodeposition of Prussian blue. To preserve the activity of glucose oxidase (GOx) immobilized on the modified sensing strip, chitosan is coated on the top layer of the electrode strip. Herein, machine learning is implemented to correlate between the electrochemical results and the nanomaterial content along with deposition cycle of prussian blue, which provide the highest current response signal. The optimized regression models provide an insight, establishing a robust framework for design of high-performance glucose sensor.

SIGNIFICANCE

This wearable glucose sensing device connected with a smartphone readout offers a user-friendly platform for real-time sweat glucose monitoring. This device provides a linear range of 0.1-1.5 mM with a detection limit of 0.1 mM that is sufficient enough for distinguishing between normal and diabetes patient with a cut-off level of 0.3 mM. This platform might be an alternative tool for improving health management for diabetes patients.

Long-Term Detection of Glycemic Glucose/Hypoglycemia by Microfluidic Sweat Monitoring Patch

A microfluidic sweat monitoring patch that collects human sweat for a long time is designed to achieve the effect of detecting the rise and fall of human sweat glucose over a long period of time by increasing the use time of a single patch. Five collection pools, four serpentine channels, and two different valves are provided. Among them, the three-dimensional valve has a large burst pressure as a balance between the internal and external air pressures of the patch. The bursting pressure of the two-dimensional diverter valve is smaller than that of the three-dimensional gas valve, and its role is to control the flow direction of the liquid. Through plasma hydrophilic treatment of different durations, the optimal hydrophilic duration is obtained. The embedded chromogenic disc detects the sweat glucose value at two adjacent time intervals and compares the information of the human body to increase or reduce glucose. The patch has good flexibility and can fit well with human skin, and because polydimethylsiloxane (PDMS) has good light transmission, it reduces the measurement error caused by the color-taking process and makes the detection results more accurate.

The challenges and promise of sweat sensing

The potential of monitoring biomarkers in sweat for health-related applications has spurred rapid growth in the field of wearable sweat sensors over the past decade. Some of the key challenges have been addressed, including measuring sweat-secretion rate and collecting sufficient sample volumes for real-time, continuous molecular analysis without intense exercise. However, except for assessment of cystic fibrosis and regional nerve function, the ability to accurately measure analytes of interest and their physiological relevance to health metrics remain to be determined. Although sweat is not a crystal ball into every aspect of human health, we expect sweat measurements to continue making inroads into niche applications involving active sweating, such as hydration monitoring for athletes and physical laborers and later for medical and casual health monitoring of relevant drugs and hormones.

Triple-Responsive, Multimodal, Visual Electronic Skin toward All-in-One Health Management for Gestational Diabetes Mellitus

Gestational diabetes mellitus (GDM) is one of the most common metabolic disorders during pregnancy, leading to serious complications for pregnant women and a threat to life safety of infants. Therefore, it is particularly important to establish a multipurpose monitoring pathway to important physiological indicators of pregnant women. In this work, three kinds of double network hydrogels are prepared with poly(vinyl alcohol) (PVA), borax, and cellulose ethers with varying substituents of methyl (methyl cellulose, MC), hydroxypropyl (hydroxypropyl cellulose, HPC), or both (hydroxypropyl methyl cellulose, HPMC), respectively. The corresponding toughness (143.9, 102.3, and 135.9 kJ cm-3) and conductivity (0.69, 0.45, and 0.51 S m-1) of the hydrogels demonstrate that PB-MC was endowed with the prominent performance. Molecular dynamics simulations further revealed the essence that hydrogen bond interactions between PVA and cellulose ethers play a critical role in regulating the structure and properties of hydrogels. Thermochromic capsule powders (TCPs) were subsequently doped in to achieve a composite hydrogel (TCPs@PB-MC) to indicate the change in human body temperature. Furthermore, the process of the TCPs@PB-MC response to glucose, pH, and temperature was tracked in-depth through the electrochemical window. This work provides a novel strategy for all-in-one health management of GDM.

Wireless electrochemiluminescent biosensors: Powering innovation with smartphone technology

Energy supply and sensor response acquisition can be performed wirelessly, enabling biosensors as Internet of Thing (IoT) tools by linking wireless power supply and electrochemical sensors. Here, we used the electromagnetic induction method to clarify the conditions under which electrochemiluminescence is induced by a simple potential modulation circuit without an integrated circuit on the electrode chip that receives the power. Initially, the potential waveform obtained in a circuit with inductance and capacitance components that resonate with the transmission frequency and a diode for rectification was investigated to clarify the conditions inducing an electrochemiluminescence reaction at the printed electrode. A high-sensitivity complementary metal-oxide semiconductor camera built into the smartphone wirelessly detected the luminescence generated on the electrode chip. The images were quantitatively evaluated using open-source image analysis software which determine the sensitivity of detecting hydrogen peroxide. Glucose oxidase (GOD) encapsulated in a matrix of chitosan polymers and photocrosslinkable polymers was immobilized on a mass-producible and inexpensive printed electrode to maintain high activity. The immobilized membrane suppressed luminescence when immobilized on the working electrode; therefore, the enzyme was immobilized on the counter electrode for glucose measurement over a wide concentration. Thus, luminol electrochemiluminescence was induced on the electrode chip by wireless power supply from a smartphone. Human serum and artificial sweat samples were tested and indicated possibility for actual applications. In this way a fully wireless biosensor was developed with potential as an IoT biosensor.

Pursuing precision in medicine and nutrition: the rise of electrochemical biosensing at the molecular level

In the era that we seek personalization in material things, it is becoming increasingly clear that the individualized management of medicine and nutrition plays a key role in life expectancy and quality of life, allowing participation to some extent in our welfare and the use of societal resources in a rationale and equitable way. The implementation of precision medicine and nutrition are highly complex challenges which depend on the development of new technologies able to meet important requirements in terms of cost, simplicity, and versatility, and to determine both individually and simultaneously, almost in real time and with the required sensitivity and reliability, molecular markers of different omics levels in biofluids extracted, secreted (either naturally or stimulated), or circulating in the body. Relying on representative and pioneering examples, this review article critically discusses recent advances driving the position of electrochemical bioplatforms as one of the winning horses for the implementation of suitable tools for advanced diagnostics, therapy, and precision nutrition. In addition to a critical overview of the state of the art, including groundbreaking applications and challenges ahead, the article concludes with a personal vision of the imminent roadmap.

A Review of Recent Advances in Microneedle-Based Sensing within the Dermal ISF That Could Transform Medical Testing

Interstitial fluid (ISF) has attracted extensive attention in an extremely wide range of areas due to its unique advantages, such as portability, high precision, comfortable operation, and superior stability. In recent years, the microneedle (MN) technique has been considered to be an excellent tool for extracting ISF because it is painless and noninvasive. Recent reports have shown that MN has good application prospects in ISF extraction. In this review, we provide comprehensive and in-depth insight into integrated MN devices for ISF detection, covering the basic structure as well as the fabrication of integrated MN devices and various applications in ISF extraction. Challenges and prospects are highlighted, with a discussion on how to transition such MN-integrated devices toward personalized healthcare monitoring systems.

Technological Advances of Wearable Device for Continuous Monitoring of In Vivo Glucose

Managing diabetes is a chronic challenge today, requiring monitoring and timely insulin injections to maintain stable blood glucose levels. Traditional clinical testing relies on fingertip or venous blood collection, which has facilitated the emergence of continuous glucose monitoring (CGM) technology to address data limitations. Continuous glucose monitoring technology is recognized for tracking long-term blood glucose fluctuations, and its development, particularly in wearable devices, has given rise to compact and portable continuous glucose monitoring devices, which facilitates the measurement of blood glucose and adjustment of medication. This review introduces the development of wearable CGM-based technologies, including noninvasive methods using body fluids and invasive methods using implantable electrodes. The advantages and disadvantages of these approaches are discussed as well as the use of microneedle arrays in minimally invasive CGM. Microneedle arrays allow for painless transdermal puncture and are expected to facilitate the development of wearable CGM devices. Finally, we discuss the challenges and opportunities and look forward to the biomedical applications and future directions of wearable CGM-based technologies in biological research.

Liquid Metal-Polymer Conductor-Based Conformal Cyborg Devices

Gallium-based liquid metal (LM) exhibits exceptional properties such as high conductivity and biocompatibility, rendering it highly valuable for the development of conformal bioelectronics. When combined with polymers, liquid metal-polymer conductors (MPC) offer a versatile platform for fabricating conformal cyborg devices, enabling functions such as sensing, restoration, and augmentation within the human body. This review focuses on the synthesis, fabrication, and application of MPC-based cyborg devices. The synthesis of functional materials based on LM and the fabrication techniques for MPC-based devices are elucidated. The review provides a comprehensive overview of MPC-based cyborg devices, encompassing their applications in sensing diverse signals, therapeutic interventions, and augmentation. The objective of this review is to serve as a valuable resource that bridges the gap between the fabrication of MPC-based conformal devices and their potential biomedical applications.

Skin-Interfaced Bifluidic Paper-Based Device for Quantitative Sweat Analysis

The erratic, intermittent, and unpredictable nature of sweat production, resulting from physiological or psychological fluctuations, poses intricacies to consistently and accurately sample and evaluate sweat biomarkers. Skin-interfaced microfluidic devices that rely on colorimetric mechanisms for semi-quantitative detection are particularly susceptible to these inaccuracies due to variations in sweat secretion rate or instantaneous volume. This work introduces a skin-interfaced colorimetric bifluidic sweat device with two synchronous channels to quantify sweat rate and biomarkers in real-time, even during uncertain sweat activities. In the proposed bifluidic-distance metric approach, with one channel to measure sweat rate and quantify collected sweat volume, the other channel can provide an accurate analysis of the biomarkers based on the collected sweat volume. The closed channel design also reduces evaporation and resists contamination from the external environment. The feasibility of the device is highlighted in a proof-of-the-concept demonstration to analyze sweat chloride for evaluating hydration status and sweat glucose for assessing glucose levels. The low-cost yet highly accurate device provides opportunities for clinical sweat analysis and disease screening in remote and low-resource settings. The developed device platform can be facilely adapted for the other biomarkers when corresponding colorimetric reagents are exploited.

Harvesting and manipulating sweat and interstitial fluid in microfluidic devices

Microfluidic devices began to be used to facilitate sweat and interstitial fluid (ISF) sensing in the mid-2010s. Since then, numerous prototypes involving microfluidics have been developed in different form factors for sensing biomarkers found in these fluids under in vitro, ex vivo, and in vivo (on-body) settings. These devices transport and manipulate biofluids using microfluidic channels composed of silicone, polymer, paper, or fiber. Fluid flow transport and sample management can be achieved by controlling the flow rate, surface morphology of the channel, and rate of fluid evaporation. Although many devices have been developed for estimating sweat rate, electrolyte, and metabolite levels, only a handful have been able to proceed beyond laboratory testing and reach the stage of clinical trials and commercialization. To further this technology, this review reports on the utilization of microfluidics towards sweat and ISF management and transport. The review is distinguished from other recent reviews by focusing on microfluidic principles of sweat and ISF generation, transport, extraction, and management. Challenges and prospects are highlighted, with a discussion on how to transition such prototypes towards personalized healthcare monitoring systems.

Interindividual- and blood-correlated sweat phenylalanine multimodal analytical biochips for tracking exercise metabolism

In situ monitoring of endogenous amino acid loss through sweat can provide physiological insights into health and metabolism. However, existing amino acid biosensors are unable to quantitatively assess metabolic status during exercise and are rarely used to establish blood-sweat correlations because they only detect a single concentration indicator and disregard sweat rate. Here, we present a wearable multimodal biochip integrated with advanced electrochemical electrodes and multipurpose microfluidic channels that enables simultaneous quantification of multiple sweat indicators, including phenylalanine and chloride, as well as sweat rate. This combined measurement approach reveals a negative correlation between sweat phenylalanine levels and sweat rates among individuals, which further enables identification of individuals at high metabolic risk. By tracking phenylalanine fluctuations induced by protein intake during exercise and normalizing the concentration indicator by sweat rates to reduce interindividual variability, we demonstrate a reliable method to correlate and analyze sweat-blood phenylalanine levels for personal health monitoring.

Bioinspired nanoplatforms for human-machine interfaces: Recent progress in materials and device applications

The panoramic characteristics of human-machine interfaces (HMIs) have prompted the needs to update the biotechnology community with the recent trends, developments, and future research direction toward next-generation bioelectronics. Bioinspired materials are promising for integrating various bioelectronic devices to realize HMIs. With the advancement of scientific biotechnology, state-of-the-art bioelectronic applications have been extensively investigated to improve the quality of life by developing and integrating bioinspired nanoplatforms in HMIs. This review highlights recent trends and developments in the field of biotechnology based on bioinspired nanoplatforms by demonstrating recently explored materials and cutting-edge device applications. Section 1 introduces the recent trends and developments of bioinspired nanomaterials for HMIs. Section 2 reviews various flexible, wearable, biocompatible, and biodegradable nanoplatforms for bioinspired applications. Section 3 furnishes recently explored substrates as carriers for advanced nanomaterials in developing HMIs. Section 4 addresses recently invented biomimetic neuroelectronic, nanointerfaces, biointerfaces, and nano/microfluidic wearable bioelectronic devices for various HMI applications, such as healthcare, biopotential monitoring, and body fluid monitoring. Section 5 outlines designing and engineering of bioinspired sensors for HMIs. Finally, the challenges and opportunities for next-generation bioinspired nanoplatforms in extending the potential on HMIs are discussed for a near-future scenario. We believe this review can stimulate the integration of bioinspired nanoplatforms into the HMIs in addition to wearable electronic skin and health-monitoring devices while addressing prevailing and future healthcare and material-related problems in biotechnologies.

Current advancements and prospects of enzymatic and non-enzymatic electrochemical glucose sensors

This review discusses the most current developments and future perspectives in enzymatic and non-enzymatic glucose sensors, which have notably evolved over the preceding quadrennial period. Furthermore, a thorough exploration encompassed the sensor's intricate fabrication processes, the diverse range of materials employed, the underlying principles of detection, and an in-depth assessment of the sensors' efficacy in detecting glucose levels within essential bodily fluids such as human blood serums, urine, saliva, and interstitial fluids. It is worth noting that the accurate quantification of glucose concentrations within human blood has been effectively achieved by utilizing classical enzymatic sensors harmoniously integrated with optical and electrochemical transduction mechanisms. Monitoring glucose levels in various mediums has attracted exceptional attention from industrial to academic researchers for diabetes management, food quality control, clinical medicine, and bioprocess inspection. There has been an enormous demand for the creation of novel glucose sensors over the past ten years. Research has primarily concentrated on succeeding biocompatible and enhanced sensing abilities related to the present technologies, offering innovative avenues for more effective glucose sensors. Recent developments in wearable optical and electrochemical sensors with low cost, high stability, point-of-care testing, and online tracking of glucose concentration levels in biological fluids can aid in managing and controlling diabetes globally. New nanomaterials and biomolecules that can be used in electrochemical sensor systems to identify glucose concentration levels are developed thanks to advances in nanoscience and nanotechnology. Both enzymatic and non-enzymatic glucose electrochemical sensors have garnered much interest recently and have made significant strides in detecting glucose levels. In this review, we summarise several categories of non-enzymatic glucose sensor materials, including composites, non-precious transition metals and their metal oxides, hydroxides, precious metals and their alloys, carbon-based materials, conducting polymers, metal-organic framework (MOF)-based electrocatalysts, and wearable device-based glucose sensors deeply.

Complete Glucose Electrooxidation Enabled by Coordinatively Unsaturated Copper Sites in Metal-Organic Frameworks

The electrocatalytic oxidation of glucose plays a vital role in biomass conversion, renewable energy, and biosensors, but significant challenges remain to achieve high selectivity and high activity simultaneously. In this study, we present a novel approach for achieving complete glucose electrooxidation utilizing Cu-based metal-hydroxide-organic framework (Cu-MHOF) featuring coordinatively unsaturated Cu active sites. In contrast to traditional Cu(OH)2 catalysts, the Cu-MHOF exhibits a remarkable 40-fold increase in electrocatalytic activity for glucose oxidation, enabling exclusive oxidation of glucose into formate and carbonate as the final products. The critical role of open metal sites in enhancing the adsorption affinity of glucose and key intermediates was confirmed by control experiments and density functional theory simulations. Subsequently, a miniaturized nonenzymatic glucose sensor was developed showing superior performance with a high sensitivity of 214.7 μA mM-1  cm-2 , a wide detection range from 0.1 μM to 22 mM, and a low detection limit of 0.086 μM. Our work provides a novel molecule-level strategy for designing catalytically active sites and could inspire the development of novel metal-organic framework for next-generation electrochemical devices.

Access and Management of Sweat for Non-Invasive Biomarker Monitoring: A Comprehensive Review

Sweat is an important biofluid presents in the body since it regulates the internal body temperature, and it is relatively easy to access on the skin unlike other biofluids and contains several biomarkers that are also present in the blood. Although sweat sensing devices have recently displayed tremendous progress, most of the emerging devices primarily focus on the sensor development, integration with electronics, wearability, and data from in vitro studies and short-term on-body trials during exercise. To further the advances in sweat sensing technology, this review aims to present a comprehensive report on the approaches to access and manage sweat from the skin toward improved sweat collection and sensing. It is begun by delineating the sweat secretion mechanism through the skin, and the historical perspective of sweat, followed by a detailed discussion on the mechanisms governing sweat generation and management on the skin. It is concluded by presenting the advanced applications of sweat sensing, supported by a discussion of robust, extended-operation epidermal wearable devices aiming to strengthen personalized healthcare monitoring systems.

Ultrafast Response in Nonenzymatic Electrochemical Glucose Sensing with Ni(II)-MOFs by Dimensional Manipulation

Metal-organic frameworks (MOFs) are emerging as promising candidates for electrochemical glucose sensing owing to their ordered channels, tunable chemistry, and atom-precision metal sites. Herein, the efficient nonenzymatic electrochemical glucose sensing is achieved by taking advantage of Ni(II)-based metal-organic frameworks (Ni(II)-MOFs) and acquiring the ever-reported fastest response time. Three Ni(II)-MOFs ({[Ni6L2(H2O)26]4H2O}n (CTGU-33), {Ni(bib)1/2(H2L)1/2(H2O)3}n (CTGU-34), {Ni(phen)(H2L)1/2(H2O)2}n (CTGU-35)) have been synthesized for the first time, which use benzene-1,2,3,4,5,6-hexacarboxylic acid (H6L) as an organic ligand and introduce 1,4-bis(1-imidazoly)benzene (bib) or 1,10-phenanthroline (phen) as spatially auxiliary ligands. Bib and phen convert the coordination mode of CTGU-33, affording structural dimensions from 2D of CTGU-33 to 3D of CTGU-34 or 1D of CTGU-35. By tuning the dimension of the skeleton, CTGU-34 with 3D interconnected channels exhibits an ultrafast response of less than 0.4 s, which is superior to the existing nonenzymatic electrochemical sensors. Additionally, a low detection limit of 0.12 μM (S/N = 3) and a high sensitivity of 1705 μA mM-1 cm-2 are simultaneously achieved. CTGU-34 further showcases desirable anti-interference and cycling stability, which demonstrates a promising application prospect in the real-time detection of glucose.

Soft microfiber-based hollow microneedle array for stretchable microfluidic biosensing patch with negative pressure-driven sampling

Wearable point-of-care testing devices are essential for personalized and decentralized healthcare. They can collect biofluid samples from the human body and use an analyzer to detect biomolecules. However, creating an integrated system is challenging due to the difficulty of achieving conformality to the human body, regulating the collection and transport of biofluids, developing a biosensor patch capable of precise biomolecule detection, and establishing a simple operation protocol that requires minimal wearer attention. In this study, we propose using a hollow microneedle (HMN) based on soft hollow microfibers and a microneedle-integrated microfluidic biosensor patch (MIMBP) capable of integrated blood sampling and electrochemical biosensing of biomolecules. The soft MIMBP includes a stretchable microfluidic device, a flexible electrochemical biosensor, and a HMN array made from flexible hollow microfibers. The HMNs are fabricated by electroplating flexible and mechanically durable hollow microfibers made from a nanocomposite matrix of polyimide, a poly (vinylidene fluoride-co-trifluoroethylene) copolymer, and single-walled carbon nanotubes. The MIMBP uses the negative pressure generated by a single button push to collect blood and deliver it to a flexible electrochemical biosensor modified with a gold nanostructure and Pt nanoparticles. We have demonstrated that glucose can be accurately measured up to the molar range in whole human blood collected through the microneedle. The MIMBP platform with HMNs has great potential as a foundation for the future development of simple, wearable, self-testing systems for minimally invasive biomolecule detection. This platform capable of sequential blood collection and high sensitivity glucose detection, which are ideal for personalized and decentralized healthcare.

Advanced Textile-Based Wearable Biosensors for Healthcare Monitoring

With the innovation of wearable technology and the rapid development of biosensors, wearable biosensors based on flexible textile materials have become a hot topic. Such textile-based wearable biosensors promote the development of health monitoring, motion detection and medical management, and they have become an important support tool for human healthcare monitoring. Textile-based wearable biosensors not only non-invasively monitor various physiological indicators of the human body in real time, but they also provide accurate feedback of individual health information. This review examines the recent research progress of fabric-based wearable biosensors. Moreover, materials, detection principles and fabrication methods for textile-based wearable biosensors are introduced. In addition, the applications of biosensors in monitoring vital signs and detecting body fluids are also presented. Finally, we also discuss several challenges faced by textile-based wearable biosensors and the direction of future development.

Wearable sensor platforms for real-time monitoring and early warning of metabolic disorders in humans

Nowadays, the prevalence of metabolic syndromes (MSs) has attracted increasing concerns as it is closely related to overweight and obesity, physical inactivity and overconsumption of energy, making the diagnosis and real-time monitoring of the physiological range essential and necessary for avoiding illness due to defects in the human body such as higher risk of cardiovascular disease, diabetes, stroke and diseases related to artery walls. However, the current sensing techniques are inconvenient and do not continuously monitor the health status of humans. Alternatively, the use of recent wearable device technology is a preferable method for the prevention of these diseases. This can enable the monitoring of the health status of humans in different health domains, including environment and structure. The use wearable devices with the purpose of facilitating rapid treatment and real-time monitoring can decrease the prevalence of MS and long-time monitor the health status of patients. This review highlights the recent advances in wearable sensors toward continuous monitoring of blood pressure and blood glucose, and further details the monitoring of abnormal obesity, triglycerides and HDL. We also discuss the challenges and future prospective of monitoring MS in humans.

Screen-Printed Textile-Based Electrochemical Biosensor for Noninvasive Monitoring of Glucose in Sweat

Wearable sweat biosensors for noninvasive monitoring of health parameters have attracted significant attention. Having these biosensors embedded in textile substrates can provide a convenient experience due to their soft and flexible nature that conforms to the skin, creating good contact for long-term use. These biosensors can be easily integrated with everyday clothing by using textile fabrication processes to enhance affordable and scalable manufacturing. Herein, a flexible electrochemical glucose sensor that can be screen-printed onto a textile substrate has been demonstrated. The screen-printed textile-based glucose biosensor achieved a linear response in the range of 20-1000 µM of glucose concentration and high sensitivity (18.41 µA mM^-1 cm^-2, R² = 0.996). In addition, the biosensors show high selectivity toward glucose among other interfering analytes and excellent stability over 30 days of storage. The developed textile-based biosensor can serve as a platform for monitoring bio analytes in sweat, and it is expected to impact the next generation of wearable devices.

3D-printed electrochemical glucose device with integrated Fe(II)-MOF nanozyme

Estimation of glucose (GLU) levels in the human organism is very important in the diagnosis and monitoring of diabetes. Scientific advances in nanomaterials have led to the construction of new generations of enzymatic-free GLU sensors. In this work, an innovative 3D-printed device modified with a water-stable and non-toxic metal-organic framework of iron (Fe(II)-MOF), which serves as a nanozyme, has been developed for the voltammetric determination of GLU in artificial sweat. In contrast to existing MOF-based GLU sensors which exhibit electrocatalytic activity for the oxidation of GLU in alkaline media, the nanozyme Fe(II)-MOF/3D-printed device can operate in the acidic epidermal sweat environment. The enzymatic-free GLU sensor is composed of a 3-electrode 3D-printed device with the MOF nanozyme immobilized on the surface of the working electrode. GLU sensing is conducted by differential pulse voltammetry without interference from other co-existing metabolites in artificial sweat. The response is based on the oxidation of glucose to gluconolactone, induced by the redox activity of the Fe-centers of the MOF. GLU gives rise to an easily detectable and well-defined voltammetric peak at about - 1.2 V and the limit of detection is 17.6 μmol L-1. The synergy of a nanozyme with 3D printing technology results in an advanced, sensitive, and low-cost sensor, paving the way for on-skin applications.

Versatile sweat bioanalysis on demand with hydrogel-programmed wearables

Wearable sweat bioanalysis is promising for non-invasive diagnostics of diseases. However, collection of representative sweat samples without disturbing daily life and wearable bioanalysis of targets that are clinically significant are still challenging. In this work, we report on a versatile method for the sweat bioanalysis. The method is based on a thermoresponsive hydrogel which can imperceptibly absorb slowly secreted sweat without stimulation such as heat or sport exercise. The wearable bioanalysis is accomplished by programmed electric heating of hydrogel modules to 42°C to release absorbed sweat or preloaded reagents into a microfluidic detection channel. Using our method, not only one-step detection of glucose but also multi-step immunoassay of cortisol is accomplished within 1 h, even at a very low sweat rate. Our test results are also compared with those obtained with conventional blood samples and stimulated sweat samples to evaluate the applicability of our method to non-invasive clinical practice.

Evolution of nanostructured skin patches towards multifunctional wearable platforms for biomedical applications

Recent advances in the field of skin patches have promoted the development of wearable and implantable bioelectronics for long-term, continuous healthcare management and targeted therapy. However, the design of electronic skin (e-skin) patches with stretchable components is still challenging and requires an in-depth understanding of the skin-attachable substrate layer, functional biomaterials and advanced self-powered electronics. In this comprehensive review, we present the evolution of skin patches from functional nanostructured materials to multi-functional and stimuli-responsive patches towards flexible substrates and emerging biomaterials for e-skin patches, including the material selection, structure design and promising applications. Stretchable sensors and self-powered e-skin patches are also discussed, ranging from electrical stimulation for clinical procedures to continuous health monitoring and integrated systems for comprehensive healthcare management. Moreover, an integrated energy harvester with bioelectronics enables the fabrication of self-powered electronic skin patches, which can effectively solve the energy supply and overcome the drawbacks induced by bulky battery-driven devices. However, to realize the full potential offered by these advancements, several challenges must be addressed for next-generation e-skin patches. Finally, future opportunities and positive outlooks are presented on the future directions of bioelectronics. It is believed that innovative material design, structure engineering, and in-depth study of fundamental principles can foster the rapid evolution of electronic skin patches, and eventually enable self-powered close-looped bioelectronic systems to benefit mankind.

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.

Non-invasive in-vivo glucose-based stress monitoring in plants

Plant stress responses involve a suite of genetically encoded mechanisms triggered by real-time interactions with their surrounding environment. Although sophisticated regulatory networks maintain proper homeostasis to prevent damage, the tolerance thresholds to these stresses vary significantly among organisms. Current plant phenotyping techniques and observables must be better suited to characterize the real-time metabolic response to stresses. This impedes practical agronomic intervention to avoid irreversible damage and limits our ability to breed improved plant organisms. Here, we introduce a sensitive, wearable electrochemical glucose-selective sensing platform that addresses these problems. Glucose is a primary plant metabolite, a source of energy produced during photosynthesis, and a critical molecular modulator of various cellular processes ranging from germination to senescence. The wearable-like technology integrates a reverse iontophoresis glucose extraction capability with an enzymatic glucose biosensor that offers a sensitivity of 22.7 nA/(μM·cm²), a limit of detection (LOD) of 9.4 μM, and a limit of quantification (LOQ) of 28.5 μM. The system's performance was validated by subjecting three different plant models (sweet pepper, gerbera, and romaine lettuce) to low-light and low-high temperature stresses and demonstrating critical differential physiological responses associated with their glucose metabolism. This technology enables non-invasive, non-destructive, real-time, in-situ, and in-vivo identification of early stress response in plants and provides a unique tool for timely agronomic management of crops and improving breeding strategies based on the dynamics of genome-metabolome-phenome relationships.

Pt/MXene-Based Flexible Wearable Non-Enzymatic Electrochemical Sensor for Continuous Glucose Detection in Sweat

Wearable non-invasive sensors facilitate the continuous measurement of glucose in sweat for the treatment and management of diabetes. However, the catalysis of glucose and sweat sampling are challenges in the development of efficient wearable glucose sensors. Herein, we report a flexible wearable non-enzymatic electrochemical sensor for continuous glucose detection in sweat. We synthesized a catalyst (Pt/MXene) by the hybridization of Pt nanoparticles onto MXene (Ti₃C₂T_x) nanosheets with a broad linear range of glucose detection (0-8 mmol/L) under neutral conditions. Furthermore, we optimized the structure of the sensor by immobilizing Pt/MXene with a conductive hydrogel to enhance the stability of the sensor. Based on Pt/MXene and the optimized structure, we fabricated a flexible wearable glucose sensor by integrating a microfluidic patch for sweat collection onto a flexible sensor. We evaluated the utility of the sensor for the detection of glucose in sweat, and the sensor could detect the glucose change with the replenishment and consumption of energy by the body, and a similar trend was observed in the blood. An in vivo glucose test in sweat indicated that the fabricated sensor is promising for the continuous measurement of glucose, which is essential for the treatment and management of diabetes.

Portable Prussian Blue-Based Sensor for Bacterial Detection in Urine

Bacterial infections can affect the skin, lungs, blood, and brain, and are among the leading causes of mortality globally. Early infection detection is critical in diagnosis and treatment but is a time- and work-consuming process taking several days, creating a hitherto unmet need to develop simple, rapid, and accurate methods for bacterial detection at the point of care. The most frequent type of bacterial infection is infection of the urinary tract. Here, we present a wireless-enabled, portable, potentiometric sensor for E. coli. E. coli was chosen as a model bacterium since it is the most common cause of urinary tract infections. The sensing principle is based on reduction of Prussian blue by the metabolic activity of the bacteria, detected by monitoring the potential of the sensor, transferring the sensor signal via Bluetooth, and recording the output on a laptop or a mobile phone. In sensing of bacteria in an artificial urine medium, E. coli was detected in ~4 h (237 ± 19 min; n = 4) and in less than 0.5 h (21 ± 7 min, n = 3) using initial E. coli concentrations of ~10³ and 10⁵ cells mL^-1, respectively, which is under or on the limit for classification of a urinary tract infection. Detection of E. coli was also demonstrated in authentic urine samples with bacteria concentration as low as 10⁴ cells mL^-1, with a similar response recorded between urine samples collected from different volunteers as well as from morning and afternoon urine samples.

A Step Forward for Smart Clothes─Fabric-Based Microfluidic Sensors for Wearable Health Monitoring

We report the first demonstration of fabric-based microfluidics for wearable sensing. A new technology to develop microfluidics on fabrics, as a part of an undergarment, is described here. Compared to conventional microfluidics from polydimethylsiloxane, fabric-based microfluidics are simple to make, robust, and suitable for efficient sweat delivery. Specifically, acrylonitrile butadiene styrene (ABS) films with precut microfluidic patterns were infused through fabrics to form hydrophobic areas in a specially controlled sandwich structure. Experimental tests and simulations confirmed the sweat delivery efficiency of the microfluidics. Electrodes were screen-printed onto the fabric-based microfluidic. A novel wearable potentiometer based on Arduino was also developed as the transducer and signal readouts, which was low-cost, standardized, open-source, and capable of wireless data transfer. We applied the sensor system as a standalone or as a module of a T-shirt to quantify [Ca²⁺] in a wearer's sweat, with physiological and accurate results generated. Overall, this work represents a critical step in turning regular undergarments into biochemically smart platforms for health monitoring, which will broadly benefit human healthcare.

Self-Testing of Ketone Bodies, along with Glucose, Using Touch-Based Sweat Analysis

β-Hydroxybutyrate (HB) is one of the main physiological ketone bodies that play key roles in human health and wellness. Besides their important role in diabetes ketoacidosis, ketone bodies are currently receiving tremendous attention for personal nutrition in connection to the growing popularity of oral ketone supplements. Accordingly, there are urgent needs for developing a rapid, simple, and low-cost device for frequent onsite measurements of β-hydroxybutyrate (HB), one of the main physiological ketone bodies. However, real-time profiling of dynamically changing HB concentrations is challenging and still limited to laboratory settings or to painful and invasive measurements (e.g., a commercial blood ketone meter). Herein, we address the critical need for pain-free frequent HB measurements in decentralized settings and report on a reliable noninvasive, simple, and rapid touch-based sweat HB testing and on its ability to track dynamic HB changes in secreted fingertip sweat, following the intake of commercial ketone supplements. The new touch-based HB detection method relies on an instantaneous collection of the fingertip sweat at rest on a porous poly(vinyl alcohol) (PVA) hydrogel that transports the sweat to a biocatalytic layer, composed of the β-hydroxybutyrate dehydrogenase (HBD) enzyme and its nicotinamide adenine dinucleotide (NAD⁺) cofactor, covering the modified screen-printed carbon working electrode. As a result, the sweat HB can be measured rapidly by the mediated oxidation reaction of the nicotinamide adenine dinucleotide (NADH) product. A personalized HB dose-response relationship is demonstrated within a group of healthy human subjects taking commercial ketone supplements, along with a correlation between the sweat and capillary blood HB levels. Furthermore, a dual disposable biosensing device, consisting of neighboring ketone and glucose enzyme electrodes on a single-strip substrate, has been developed toward the simultaneous touch-based detection of dynamically changing sweat HB and glucose levels, following the intake of ketone and glucose drinks.

Machine-Learning Assisted Handwriting Recognition Using Graphene Oxide-Based Hydrogel

Machine-learning assisted handwriting recognition is crucial for development of next-generation biometric technologies. However, most of the currently reported handwriting recognition systems are lacking in flexible sensing and machine learning capabilities, both of which are essential for implementation of intelligent systems. Herein, assisted by machine learning, we develop a new handwriting recognition system, which can be applied as both a recognizer for written texts and an encryptor for confidential information. This flexible and intelligent handwriting recognition system combines a printed circuit board with graphene oxide-based hydrogel sensors. It offers fast response and good sensitivity and allows high-precision recognition of handwritten content from a single letter to words and signatures. By analyzing 690 acquired handwritten signatures obtained from seven participants, we successfully demonstrate a fast recognition time (less than 1 s) and a high recognition rate (∼91.30%). Our developed handwriting recognition system has great potential in advanced human-machine interactions, wearable communication devices, soft robotics manipulators, and augmented virtual reality.

Wearable Healthcare Monitoring Based on a Microfluidic Electrochemical Integrated Device for Sensing Glucose in Natural Sweat

Wearable sweat sensors offer the possibility of continuous real-time health monitoring of an individual at a low cost without invasion. A variety of sweat glucose sensors have been developed thus far to help diabetes patients frequently monitor blood glucose levels through sweat glucose as a surrogate marker. The present study demonstrates the development and characterization of a three-dimensional paper-based microfluidic electrochemical integrated device (3D PMED) for measuring glucose concentration in sweat in real-time via simple, non-invasive, capillary-action-based sample collection. The device was selective for glucose, and it detected glucose accurately in the clinically relevant range (0~2 mM) in an off-body setup. To the best of our knowledge, this is the first time NEXAR™ has been used for biosensing applications. Further, the developed glucose sensor has acceptable sensitivity of 16.8 µA/mM/cm². Importantly, in an on-body setup, the device achieved a significant amperometric response to sweat glucose in a very short amount of time (a few seconds). With detailed investigations, this proof-of-concept study could help further the development of sensitive and selective sweat-based glucose sensing devices for real-time glucose monitoring in diabetes patients.

A Soft Wearable Microfluidic Patch with Finger-Actuated Pumps and Valves for On-Demand, Longitudinal, and Multianalyte Sweat Sensing

Easy sample collection, physiological relevance, and ability to noninvasively and longitudinally monitor the human body are some of the key attributes of wearable sweat sensors. Examples typically include reversible sensors or an array of single-use sensors embedded in specialized microfluidics for temporal analysis of sweat. However, evolving this field to a level that truly represents "lab-on-skin" technology will require the incorporation of advanced functionalities that give the user the freedom to (1) choose the precise time for performing sample analysis and (2) select sensors from an array embedded within the device for performing condition-specific sample analysis. Here, we introduce new concepts in wearable microfluidic platforms that offer such capabilities. The described technology involves a series of finger-actuated pumps, valves, and sensors incorporated within soft, wearable microfluidics. The incoming sweat collects in the inlet chamber and can be analyzed by the user at the time of their choosing. On-demand sweat analyte assessment is achieved by pulling a thin tab to activate a pump which opens a valve and allows the pooled sweat to enter a chamber embedded with sensors for the desired analytes. The article describes a thorough characterization of the platform that demonstrates the robustness of the pumping, valving, and sensing aspects of the device under conditions mimicking real-life scenarios. A two-day-long human pilot study validates the system and illustrates the device's ability to offer on-demand, longitudinal, and multianalyte sensing. Our work represents the first example of a wearable system with such on-demand sensing capabilities and opens exciting avenues in sweat sensing for acquiring new insights into human physiology.

Is Raman the best strategy towards the development of non-invasive continuous glucose monitoring devices for diabetes management?

Diabetes has no well-established cure; thus, its management is critical for avoiding severe health complications involving multiple organs. This requires frequent glycaemia monitoring, and the gold standards for this are fingerstick tests. During the last decades, several blood-withdrawal-free platforms have been being studied to replace this test and to improve significantly the quality of life of people with diabetes (PWD). Devices estimating glycaemia level targeting blood or biofluids such as tears, saliva, breath and sweat, are gaining attention; however, most are not reliable, user-friendly and/or cheap. Given the complexity of the topic and the rise of diabetes, a careful analysis is essential to track scientific and industrial progresses in developing diabetes management systems. Here, we summarize the emerging blood glucose level (BGL) measurement methods and report some examples of devices which have been under development in the last decades, discussing the reasons for them not reaching the market or not being really non-invasive and continuous. After discussing more in depth the history of Raman spectroscopy-based researches and devices for BGL measurements, we will examine if this technique could have the potential for the development of a user-friendly, miniaturized, non-invasive and continuous blood glucose-monitoring device, which can operate reliably, without inter-patient variability, over sustained periods.

Sweat gland morphology and physiology in diabetes, neuropathy, and nephropathy: a review

Context: Sweat glands (SGs) play a vital role in thermal regulation. The function and structure are altered during the different pathological conditions.Objective: These alterations are studied through three techniques: biopsy, sweat analytes and electrical activity of SG.Methods: The morphological study of SG through biopsy and various techniques involved in quantifying sweat analytes is focussed on here. Electrical activities of SG in diabetes, neuropathy and nephropathy cases are also discussed, highlighting their limitations and future scope.Results and Conclusion: The result of this review identified three areas of the knowledge gap. The first is wearable sensors to correlate pathological conditions. Secondly, there is no device to look for its structure and quantify its associated function. Finally, therapeutic applications of SG are explored, especially for renal failure. With these aspects, this paper provides information collection and correlates SG with pathologies related to diabetes. Hence this could help researchers develop suitable technologies for the gaps identified.

Hydrogel-extraction technique for non-invasive detection of blue fluorescent substances in plant leaves

This paper reports a new hydrogel extraction technique for detecting blue fluorescent substances in plant leaves. These blue fluorescent substances were extracted by placing a hydrogel film on the leaf of a cherry tomato plant infected with Ralstonia solanacearum; herein, chlorogenic acid was confirmed to be a blue fluorescent substance. The wavelength at the maximum fluorescence intensity of the film after the hydrogel extraction was similar to that of the methanolic extract obtained from the infected cherry tomato leaves. Chlorophyll was not extracted from the hydrogel film because no fluorescence peak was observed at 680 nm. Accordingly, the blue fluorescence of the substances extracted from the hydrogel film was not quenched by the strong absorption of chlorophyll in the blue light region. This hydrogel extraction technique can potentially detect small amounts of blue fluorescent substances and the changes in its amount within the leaves of infected plants. These changes in the amount of blue fluorescent substances in the early stages of infection can be used to detect presymptomatic infections. Therefore, hydrogel extraction is a promising technique for the noninvasive detection of infections before onset.

Smartphone-Based Electrochemical Systems for Glucose Monitoring in Biofluids: A Review

As a vital biomarker, glucose plays an important role in multiple physiological and pathological processes. Thus, glucose detection has become an important direction in the electrochemical analysis field. In order to realize more convenient, real-time, comfortable and accurate monitoring, smartphone-based portable, wearable and implantable electrochemical glucose monitoring is progressing rapidly. In this review, we firstly introduce technologies integrated in smartphones and the advantages of these technologies in electrochemical glucose detection. Subsequently, this overview illustrates the advances of smartphone-based portable, wearable and implantable electrochemical glucose monitoring systems in diverse biofluids over the last ten years (2012-2022). Specifically, some interesting and innovative technologies are highlighted. In the last section, after discussing the challenges in this field, we offer some future directions, such as application of advanced nanomaterials, novel power sources, simultaneous detection of multiple markers and a closed-loop system.

Surface Engineering of Laser-Induced Graphene Enables Long-Term Monitoring of On-Body Uric Acid and pH Simultaneously

Laser-induced graphene (LIG) suffers from serious decay in long-term biosensing, which greatly restricts its practical applications. Herein, we report a new strategy to engineer the LIG surface with Au clusters and chitosan sequentially to form a C-Au-LIG electrode with a superhydrophilic and highly conductive 3D graphene surface, which demonstrates superior performance and negligible decay in both long-term storage and practical usage in vitro and in vivo environments. Moreover, the C-Au-LIG electrode can be used for detecting uric acid (UA) and pH simultaneously from a single differential pulse voltammetry curve with low-detection limitation, high accuracy, and negligible interference with other sweat biomarkers. The integrated C-Au-LIG wearable biosensor was employed to continuously monitor the UA content in human sweat, which can well reflect the daily intake of purines for at least 10 days. Therefore, the C-Au-LIG electrode demonstrates significant application potential and provides inspiration for surface engineering of other biosensor materials and electrodes.

Towards Multiplexed and Multimodal Biosensor Platforms in Real-Time Monitoring of Metabolic Disorders

Metabolic syndrome (MS) is a cluster of conditions that increases the probability of heart disease, stroke, and diabetes, and is very common worldwide. While the exact cause of MS has yet to be understood, there is evidence indicating the relationship between MS and the dysregulation of the immune system. The resultant biomarkers that are expressed in the process are gaining relevance in the early detection of related MS. However, sensing only a single analyte has its limitations because one analyte can be involved with various conditions. Thus, for MS, which generally results from the co-existence of multiple complications, a multi-analyte sensing platform is necessary for precise diagnosis. In this review, we summarize various types of biomarkers related to MS and the non-invasively accessible biofluids that are available for sensing. Then two types of widely used sensing platform, the electrochemical and optical, are discussed in terms of multimodal biosensing, figure-of-merit (FOM), sensitivity, and specificity for early diagnosis of MS. This provides a thorough insight into the current status of the available platforms and how the electrochemical and optical modalities can complement each other for a more reliable sensing platform for MS.

Effect of Electrode Modification with Chitosan and Nafion® on the Efficiency of Real-Time Enzyme Glucose Biosensors Based on ZnO Tetrapods

Noninvasive, continuous glucose detection can provide some insights into daily fluctuations in blood glucose levels, which can help us balance diet, exercise, and medication. Since current commercially available glucose sensors can barely provide real-time glucose monitoring and usually imply different invasive sampling, there is an extraordinary need to develop new harmless methods for detecting glucose in non-invasive body fluids. Therefore, it is crucial to design (bio)sensors that can detect very low levels of glucose (down to tens of µM) normally found in sweat or tears. Apart from the selection of materials with high catalytic activity for glucose oxidation, it is also important to pay considerable attention to the electrode functionalization process, as it significantly contributes to the overall detection efficiency. In this study, the (ZnO tetrapods) ZnO TPs-based electrodes were functionalized with Nafion and chitosan polymers to compare their glucose detection efficiency. Cyclic voltammetry (CV) measurements have shown that chitosan-modified ZnO TPs require a lower applied potential for glucose oxidation, which may be due to the larger size of chitosan micelles (compared to Nafion micelles), and thus easier penetration of glucose through the chitosan membrane. However, despite this, both ZnO TPs modified with chitosan and Nafion membranes, provided quite similar glucose detection parameters (sensitivities, 7.5 µA mM⁻¹ cm⁻¹ and 19.2 µA mM⁻¹ cm⁻¹, and limits of detection, 24.4 µM and 22.2 µM, respectively). Our results show that both electrodes have a high potential for accurate real-time sweat/tears glucose detection.

Sense and Learn: Recent Advances in Wearable Sensing and Machine Learning for Blood Glucose Monitoring and Trend-Detection

Diabetes mellitus is characterized by elevated blood glucose levels, however patients with diabetes may also develop hypoglycemia due to treatment. There is an increasing demand for non-invasive blood glucose monitoring and trends detection amongst people with diabetes and healthy individuals, especially athletes. Wearable devices and non-invasive sensors for blood glucose monitoring have witnessed considerable advances. This review is an update on recent contributions utilizing novel sensing technologies over the past five years which include electrocardiogram, electromagnetic, bioimpedance, photoplethysmography, and acceleration measures as well as bodily fluid glucose sensors to monitor glucose and trend detection. We also review methods that use machine learning algorithms to predict blood glucose trends, especially for high risk events such as hypoglycemia. Convolutional and recurrent neural networks, support vector machines, and decision trees are examples of such machine learning algorithms. Finally, we address the key limitations and challenges of these studies and provide recommendations for future work.

An epidermal wearable microfluidic patch for simultaneous sampling, storage, and analysis of biofluids with counterion monitoring

Simultaneous access to different biofluids enables an accurate analysis of multiple analytes, leading to a precision diagnosis and appropriate medication. Additionally, establishing a relationship between various markers in different biofluids and their correlation to biomarkers in blood allows the development of an algorithmic approach, which aids non-invasive diagnosis through single parameter monitoring. However, the main bottleneck that exists in multiple biofluid analyses for its clinical implementation is the requirement of an advanced microfluidic coupled device design, which empowers simultaneous collection and monitoring. To tackle this challenge, an epidermal wearable bio-fluidic patch that facilitates simultaneous on-demand extraction, sampling, and storage of sweat and interstitial fluid (ISF) together with monitoring of their corresponding counterions is presented. The clean room free development of a biofluidic patch is realized through 3D integration of laser patterned optimized microfluidic structures, a low-cost screen-printed stimulation module, and a potentiometric chloride (Cl^-) and calcium (Ca²⁺) ion sensing module for adequate dual biofluid sampling and analysis. The developed Cl^- and Ca²⁺ ion-selective sensors exhibit good repeatability, selectivity, acceptable stability, and sensitivity. The proof-of-concept demonstration of the fabricated patch for simultaneous dual-sampling, storage, and monitoring of the sweat Cl^- and ISF Ca²⁺ on a healthy volunteer during different periods of the day leverages its potential in real-time personalized healthcare clinical usages. Furthermore, the patch's electronic interface and use of wireless transmission facilitates a point-of-care non-invasive lab-on-skin application for monitoring the health status of individuals.

A Laser-Induced Photoelectrochemical Sensor for Natural Sweat Cu2+ Detection

Tracking fluctuations in the Cu2+ level in sweat is meaningful for non-invasive and real-time assessment of Cu2+-abnormality-related diseases and provides important diagnostic information. However, the user-unfriendly ways to obtain sweat and sweat biofouling have limited the development of this field. Herein, we exploit a highly sensitive photoelectrochemical (PEC) sensor as a detection method, a powerful laser engraving technique for the large-scale fabrication of laser-induced graphene and In-doped CdS (LIG-In-CdS) photoelectrodes, and a hydrophilic porous polyvinyl alcohol (PVA) hydrogel for natural sweat collection for fingertip touch sweat Cu2+ monitoring. The proposed sensor has several very attractive features: (i) the LIG-In-CdS photoelectrode with high photoelectric conversion efficiency can be produced by a cheap 450 nm semiconductor laser system; (ii) the sensor performs Cu2+ detection with a wide linear range of 1.28 ng/mL~5.12 μg/mL and good selectivity; (iii) the PVA hydrogel possesses an excellent antifouling effect ability and a rapid natural sweat collection ability; and (iv) the sensor exhibits feasibility and good reliability for PEC sensing of sweat Cu2+. Thus, these advantages endow the proposed method with a great deal of potential for smart monitoring of heavy metals in sweat in the future.

A touch-based multimodal and cryptographic bio-human-machine interface

The awareness of the individuals’ biological status is critical for creating interactive environments. Accordingly, we devised a multimodal cryptographic bio-human–machine interface (CB-HMI), which seamlessly translates touch-based entries into encrypted biochemical, biophysical, and biometric indices (i.e., circulating biomarkers levels, heart rate, oxygen saturation level, and fingerprint pattern). As its central component, the CB-HMI features thin hydrogel-coated chemical sensors and a signal interpretation framework to access/interpret biochemical indices, bypassing the challenge of circulating analyte accessibility and the confounding effect of pressing force variability. Upgrading the surrounding objects with CB-HMI, we demonstrated new interactive solutions for driving safety and medication use, where the integrated CB-HMI uniquely enabled one-touch bioauthentication (based on the user’s biological state/identity), prior to rendering the intended services.

The awareness of individuals’ biological status is critical for creating interactive and adaptive environments that can actively assist the users to achieve optimal outcomes. Accordingly, specialized human–machine interfaces—equipped with bioperception and interpretation capabilities—are required. To this end, we devised a multimodal cryptographic bio-human–machine interface (CB-HMI), which seamlessly translates the user’s touch-based entries into encrypted biochemical, biophysical, and biometric indices. As its central component, the CB-HMI features thin hydrogel-coated chemical sensors and inference algorithms to noninvasively and inconspicuously acquire biochemical indices such as circulating molecules that partition onto the skin (here, ethanol and acetaminophen). Additionally, the CB-HMI hosts physical sensors and associated algorithms to simultaneously acquire the user’s heart rate, blood oxygen level, and fingerprint minutiae pattern. Supported by human subject studies, we demonstrated the CB-HMI’s capability in terms of acquiring physiologically relevant readouts of target bioindices, as well as user-identifying and biometrically encrypting/decrypting these indices in situ (leveraging the fingerprint feature). By upgrading the common surrounding objects with the CB-HMI, we created interactive solutions for driving safety and medication use. Specifically, we demonstrated a vehicle-activation system and a medication-dispensing system, where the integrated CB-HMI uniquely enabled user bioauthentication (on the basis of the user’s biological state and identity) prior to rendering the intended services. Harnessing the levels of bioperception achieved by the CB-HMI and other intelligent HMIs, we can equip our surroundings with a comprehensive and deep awareness of individuals’ psychophysiological state and needs.