Water Splitting-Assisted Electrocatalytic Oxidation of Glucose with a Metal–Organic Framework for Wearable Nonenzymatic Perspiration Sensing

CTAB-Co-MOFs@AuPt NPs as signal probes for the electrochemical detection of carcinoembryonic antigen 15-3

A sensitive electrochemical strategy for carcinoembryonic antigen 15-3 (CA15-3) detection is reported using CTAB-Co-MOFs@AuPt NPs as signal probes. The electrochemical strategy was designed as follows: First, the graphene aerogel@gold nanoparticles (GA@Au NPs) nanocomposites were employed to modify the sensing surface for promoting electron transfer rate and primary antibody (Ab1) immobilization due to GA possesses a large specific surface area, eminent conductivity, and a 3D network structure. Cobalt metal-organic frameworks (CTAB-Co-MOFs) synthesized were then used as a carrier for AuPt NPs and secondary antibody (Ab2) immobilization (notes: labelled-Ab2). With sandwich immunoreaction, the labelled-Ab2 was captured on the surface of the GA@Au NPs nanocomposites. Finally, differential pulse voltammetry (DPV) was employed to register the electrochemical signal of the immunosensor at the potential of - 0.85 V (vs SCE) in phosphate buffer saline (PBS) containing 2.5 mM H2O2. It was verified that the electrochemical reduction signal from Co3+ to Co2+ was recorded. The AuPt NPs could catalyze the reaction of H2O2 oxidizing Co2+ to Co3+, resulting in the amplification of the electrochemical signal. Under the selected conditions, the immunosensor can detect CA15-3 in the range 10 µU/mL to 250 U/mL with a low detection limit of 1.1 µU/mL. In the designed strategy, the CTAB-Co-MOFs were not only employed as carriers for AuPt NPs, but also acted as signal probes. The CTAB-Co-MOFs were investigated including SEM, TEM, XPS, and XRD. The application ability of the immunosensor was evaluated using serum sample, demonstrating the immunosensor can be applied to clinic serum analysis.

Wearable biosensors for human sweat glucose detection based on carbon black nanoparticles

Wearable glucose biosensors enable noninvasive glucose monitoring, thereby enhancing blood glucose management. In this work, we present a wearable biosensor based on carbon black nanoparticles (CBNPs) for glucose detection in human sweat. The biosensor consists of CBNPs, Prussian blue (PB), glucose oxidase, chitosan, and Nafion. The fabricated biosensor has a linear range of 5 µM to 1250 µM, sensitivity of 14.64 µA mM-1 cm-2, and a low detection potential (-0.05 V, vs. Ag/AgCl). The detection limit for glucose was calculated as 4.83 µM. This reusable biosensor has good selectivity and stability and exhibits a good response to glucose in real sweat. These results demonstrate the potential of our CBNP-based biosensor for monitoring blood glucose in human sweat.

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.

Artificial enzyme innovations in electrochemical devices: advancing wearable and portable sensing technologies

With the rapid evolution of sensing technologies, the integration of nanoscale catalysts, particularly those mimicking enzymatic functions, into electrochemical devices has surfaced as a pivotal advancement. These catalysts, dubbed artificial enzymes, embody a blend of heightened sensitivity, selectivity, and durability, laying the groundwork for innovative applications in real-time health monitoring and environmental detection. This minireview penetrates into the fundamental principles of electrochemical sensing, elucidating the unique attributes that establish artificial enzymes as foundational elements in this field. We spotlight a range of innovations where these catalysts have been proficiently incorporated into wearable and portable platforms. Navigating the pathway of amalgamating these nanoscale wonders into consumer-appealing devices presents a multitude of challenges; nevertheless, the progress made thus far signals a promising trajectory. As the intersection of materials science, biochemistry, and electronics progressively intensifies, a flourishing future seems imminent for artificial enzyme-infused electrochemical devices, with the potential to redefine the landscapes of wearable health diagnostics and portable sensing solutions.

A wearable AuNP enhanced metal-organic gel (Au@MOG) sensor for sweat glucose detection with ultrahigh sensitivity

The demand for sensitive and non-invasive sensors for monitoring glucose levels in sweat has grown considerably in recent years. This study presents the development of a wearable sensor for sweat glucose detection with ultrahigh sensitivity. The sensor was fabricated by embedding Au nanoparticles (AuNPs) and metal-organic gels (MOGs) on nickel foam (NF). A non-enzymatic electrocatalytic glucose sensor has been developed to combine the three-dimensional network of MOGs with more active sites favourable for glucose diffusion and the transfer of electrons from glucose to the electrode. These results show that the sensor has an ultrahigh sensitivity of 13.94 mA mM-1 cm-2, a linear detection range between 2 and 600 μM, and a lower detection limit as low as 1 μM (signal/noise = 3) with comparable accuracy and reliability under non-alkaline conditions to those of high-pressure ion chromatography (HPIC). Furthermore, a wearable sweat glucose sensor has been constructed by sputtering an Au conductive layer on a flexible polydimethylsiloxane (PDMS) substrate and coating it with Au@MOGs. Our work demonstrates that the combination of Au NPs and MOGs can enhance the sensitivity and activity of these materials, making them useful for electrocatalytic glucose monitoring with ultrahigh sensitivity.

Mini review about metal organic framework (MOF)-based wearable sensors: Challenges and prospects

Among many types of wearable sensors, MOFs-based wearable sensors have recently been explored in both commercialization and research. There has been much effort in various aspects of the development of MOF-based wearable sensors including but not limited to miniaturization, size control, safety, improvements in conformal and flexible features, improvements in the analytical performance and long-term storage of these devices. Recent progress in the design and deployment of MOFs-based wearable sensors are covered in this paper, as are the remaining obstacles and prospects. This work also highlights the enormous potential for synergistic effects of MOFs used in combination with other nanomaterials for healthcare applications and raise attention toward the economic aspect and market diffusion of MOFs-based wearable sensors.

A flexible and wearable three-electrode electrochemical sensing system consisting of a two-in-one enzyme-mimic working electrode

In this work, a wearable and flexible three-electrode electrochemical sensing system (TESS) by using a two-in-one enzyme-mimic working electrode (TIOWE) is reported. The integrated three-electrode, including working electrodes, reference electrodes, and counter electrodes are formed by transfer printing of Ni2P-based composite electrode ink (Ni2P/G ink), Ag/AgCl ink, and carbon ink onto PDMS substrate, respectively. The Ni2P/G ink-based working electrodes have both good conductivity and enzyme-mimic catalytic activity towards glucose. Under optimized conditions, the TIOWE-TESS has a low detection limit of 0.37 μM and wide linear ranges of 0.001 mM-0.1 mM and 0.1 mM-1.4 mM. Furthermore, the TIOWE-TESS has good applicability in serum samples and reveals remarkable electrochemical performance at fluctuant working temperatures. The proposed TIOWE-TESS can be integrated on a waterproof bandage to fabricate a skin-friendly patch device for sweet glucose monitoring, which highlights its potential applications in flexible and wearable commercial devices for health-monitoring.

Micro-/nanoscale robotics for chemical and biological sensing

The field of micro-/nanorobotics has attracted extensive interest from a variety of research communities and witnessed enormous progress in a broad array of applications ranging from basic research to global healthcare and to environmental remediation and protection. In particular, micro-/nanoscale robots provide an enabling platform for the development of next-generation chemical and biological sensing modalities, owing to their unique advantages as programmable, self-sustainable, and/or autonomous mobile carriers to accommodate and promote physical and chemical processes. In this review, we intend to provide an overview of the state-of-the-art development in this area and share our perspective in the future trend. This review starts with a general introduction of micro-/nanorobotics and the commonly used methods for propulsion of micro-/nanorobots in solution, along with the commonly used methods in their fabrication. Next, we comprehensively summarize the current status of the micro/nanorobotic research in relevance to chemical and biological sensing (e.g., motion-based sensing, optical sensing, and electrochemical sensing). Following that, we provide an overview of the primary challenges currently faced in the micro-/nanorobotic research. Finally, we conclude this review by providing our perspective detailing the future application of soft robotics in chemical and biological sensing.

Wearable non-invasive glucose sensors based on metallic nanomaterials

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

Application of zeolites and zeolitic imidazolate frameworks in the biosensor development

Biosensors are advanced devices for analysis of composition of blood, urine, environmental samples, and many other media. Their current development is tightly linked with nanomaterials, such as zeolites and zeolitic imidazolate framework (ZIFs). The present review describes electrochemical (amperometric, conductometric, ISFET) and optical (fluorescent and colorimetric) biosensors that incorporate zeolites and ZIFs in their biorecognition elements. The biosensors are based on immobilized enzymes (such as glucose oxidase, urease, and acetylcholinesterase), antibodies, DNA, and aptamers. The review present reasons for application of these nanomaterials, and discusses advantages of zeolite- and ZIF-containing biosensors over other biosensors. In most cases, the biosensors have improved sensitivity, better limit of detection, wider linear range, and other improved characteristics. It is demonstrated that immobilization of biomolecules such as enzymes or antibodies on the surface of zeolites and ZIFs enables creation of unique advanced biosensors that have a potential for further development and practical applications.

Three-Phases Interface Induced Local Alkalinity Generation Enables Electrocatalytic Glucose Oxidation in Neutral Electrolyte

Electrocatalytic glucose oxidation is crucial to the development of non-enzymatic sensors, an attractive alternative for enzymatic biosensors. However, due to OH^- consumption during the catalytic process, non-enzymatic detection generally requires electrolytes having an alkaline pH value, limiting its practical application since biofluids are neutral. Herein, via interfacial microenvironment design, we addressed this limitation by developing a non-enzymatic sensor with an air-solid-liquid triphase interface electrodes that synergistically integrates the functions of local alkalinity generation and electrocatalytic glucose oxidation. A sufficiently high local pH value was achieved via oxygen reduction reaction at the triphase interface, which consequently enabled the electrochemical oxidation (detection) of glucose in neutral solution. Moreover, we found that the linear detection range and sensitivity of triphase non-enzymatic sensor can be tuned by changing the electrocatalysts of the detection electrode. The triphase electrode architecture provides a new platform for further exploration and promotes practical application of non-enzymatic sensors.

Wearable microfluidic-based e-skin sweat sensors

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

Laser-enabled flexible electrochemical sensor on finger for fast food security detection

Today's rampant abuse of antibiotics and lean meat powder disturbs environment and threatens public human health. Therefore, fast in-site detection of antibiotics or lean meat powder residue could avoid potential risks. In this work, flexible graphene electrodes (FGE) were easily and facilely patterned and prepared by CO₂ laser at room environment, which was coupled with a portable electrochemical analyzer for electronic signal transmission. Laser-enabled flexible electrochemical sensor on finger can be used for rapid real-time in-site electrochemical identification of chloramphenicol (CAP), clenbuterol (CLB) and ractopamine (RAC) in meat. The electrochemical response of CAP, CLB and RAC is investigated with the limit of detection of 2.70, 1.29 and 7.81 μM and the linear range of 10-200, 5-80 and 25-250 μM in phosphate buffer saline (PBS) pH 7.0, correspondingly. The minimum detection concentrations of CAP, CLB and RAC were 20, 10 and 30 μM, respectively, in actual samples of pork. And the minimum detection concentrations of CAP, CLB and RAC were 10, 5 and 25 μM in milk, respectively. Such an integrated sensing platform enriches application of sensors on finger in food security and provides information that prevents drug containments from entering food chain.

Applications of Advanced Materials for Non-Enzymatic Glucose Monitoring: From Invasive to the Wearable Device

Diabetes mellitus (DM) is a global health problem leading to many complications and disabilities in life adjusting activities and even dead. Monitoring glucose levels is a key factor in diagnosis and management of DM. Conventional glucose sensors consisted of immobilized enzymes, are so susceptible to environmental conditions. In this way, nonenzymatic biosensors have attracted extensive attentions in many clinical diagnostics applications. To date, the finger pricking test is a common enzyme-based glucometer that is an invasive and inconvenient and may lead to infections in the injection sites. So, working on the possibility of cutaneous or subcutaneous insertion of devices as a noninvasive or minimally-invasive systems for continuous glucose controlling approaches through human biofluids (blood, perspiration, tears, saliva, etc.) have stimulated growing interest. This review summarizes recent nonenzymatic and noninvasive biofluids glucose monitoring systems which are highly resilience and stretchable to continuously adapt to body movements during common physical activity. Sensors are based on their constituent materials including carbon-based, metal nanoparticles, polymer, and hydrogel systems are classified for electrochemical, and optical glucose detection. Finally, we address the drawbacks and challenges of enzyme-free sensors which are aroused sustaining research passion to be used in point-of-care medical diagnostics applications.

Progress of Wearable and Flexible Electrochemical Biosensors With the Aid of Conductive Nanomaterials

Conductive nanomaterials have recently gained a lot of interest due to their excellent physical, chemical, and electrical properties, as well as their numerous nanoscale morphologies, which enable them to be fabricated into a wide range of modern chemical and biological sensors. This study focuses mainly on current applications based on conductive nanostructured materials. They are the key elements in preparing wearable electrochemical Biosensors, including electrochemical immunosensors and DNA biosensors. Conductive nanomaterials such as carbon (Carbon Nanotubes, Graphene), metals and conductive polymers, which provide a large effective surface area, fast electron transfer rate and high electrical conductivity, are summarized in detail. Conductive polymer nanocomposites in combination with carbon and metal nanoparticles have also been addressed to increase sensor performance. In conclusion, a section on current challenges and opportunities in this growing field is forecasted at the end.

Highly Stretchable Wearable Electrochemical Sensor Based on Ni-Co MOF Nanosheet-Decorated Ag/rGO/PU Fiber for Continuous Sweat Glucose Detection

A noninvasive fiber material-based wearable electrochemical sensor to continuously monitor the glucose level in sweat is highly desirable for smart fabrics for personal diabetes management. To achieve it, the key challenge is to construct fibers with high stretchability and excellent electrochemical performance. Herein, a highly stretchable Ni-Co metal-organic framework/Ag/reduced graphene oxide/polyurethane (Ni-Co MOF/Ag/rGO/PU) fiber-based wearable electrochemical sensor is fabricated for monitoring the glucose level in sweat continuously with high sensitivity and accuracy. The rGO/PU fiber was simply produced by an improved wet spinning technology, and the Ni-Co MOF nanosheet was coated on its surface to prepare the Ni-Co MOF/Ag/rGO/PU (NCGP) fiber electrode. The Ni-Co MOF has a large specific surface area and high catalytic activity, which enables the fiber sensors with good electrochemical performance with a high sensitivity of 425.9 μA·mM^-1·cm^-2 and a wide linear range of 10 μM-0.66 mM. More importantly, the NCGP fiber electrode also shows extremely high stretching and bending stability under mechanical deformation. Also, the NCGP fiber electrode has high selectivity and long-time storage stability. Moreover, the NCGP fiber-based three-electrode system was sewn with an absorbent fabric and fixed on a stretchable polydimethylsiloxane film substrate to form a nonenzymatic sweat glucose wearable sensor, which realized real-time monitoring of glucose in human sweat with high accuracy. This indicates that our designed NCGP fiber can be used as a wearable electrochemical sensor for the bio-diagnostics of body sweat.

Laser-induced graphene non-enzymatic glucose sensors for on-body measurements

Non-enzymatic glucose sensors outperform enzymatic ones in terms of cost, sensitivity, stability, and operating duration. Though highly sensitive, it is still desirable to further improve the sensitivity of non-enzymatic glucose sensors to detect a trace amount of glucose in sweat and other biofluids. Among the demonstrated effective approaches using bimetals or 3D porous structures, the porous laser-induced graphene (LIG) on flexible polymers showcases good conductivity and a simple fabrication process for the integration of sensing materials. The uniform electroless plating of the nickel and gold layer on LIG electrodes demonstrates significantly enhanced sensitivity and a large linear range for glucose sensing. The sensor with the porous LIG foam exhibits a high sensitivity of 1080 μA mM-1 cm-2, whereas a further increased sensitivity of 3500 μA mM-1 cm-2 is obtained with LIG fibers (LIGF). Impressively, a large linear range (0-30 mM) can be achieved by changing the bias voltage from 0.5 to 0.1 V due to the Au coating. Because the existing non-enzymatic glucose sensors are limited to use in basic solutions, their application in wearable electronics is elusive. In addition to the reduced requirement for the basic solution, this work integrates a porous encapsulating reaction cavity containing alkali solutions with a soft, skin-interfaced microfluidic component to provide integrated microfluidic non-enzymatic glucose sensors for sweat sampling and glucose sensing. The accurate glucose measurements from the human sweat and cell culture media showcase the practical utility, which opens up opportunities for the non-enzymatic glucose sensors in wearable electronics.

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.

Metal-organic frameworks for chemical sensing devices

Metal-organic frameworks (MOFs) are exceptionally large surface area materials with organized porous cages that have been investigated for nearly three decades. Due to the flexibility in their design and predisposition toward functionalization, they have shown promise in many areas of application, including chemical sensing. Consequently, they are identified as advanced materials with potential for deployment in analytical devices for chemical and biochemical sensing applications, where high sensitivity is desirable, for example, in environmental monitoring and to advance personal diagnostics. To keep abreast of new research, which signposts the future directions in the development of MOF-based chemical sensors, this review examines studies since 2015 that focus on the applications of MOF films and devices in chemical sensing. Various examples that use MOF films in solid-state sensing applications were drawn from recent studies based on electronic, electrochemical, electromechanical and optical sensing methods. These examples underscore the readiness of MOFs to be integrated in optical and electronic analytical devices. Also, preliminary demonstrations of future sensors are indicated in the performances of MOF-based wearables and smartphone sensors. This review will inspire collaborative efforts between scientists and engineers working within the field of MOFs, leading to greater innovations and accelerating the development of MOF-based analytical devices for chemical and biochemical sensing applications.

Highly sensitive non-enzymatic electrochemical glucose sensor surpassing water oxidation interference

An electrochemical non-enzymatic sensor based on a NiVP/Pi material was developed for the selective and sensitive determination of glucose. The novel sensor showed a high sensitivity of 6.04 mA μM-1 cm-2 with a lowest detection limit of 3.7 nM in a wide detection range of 100 nM-10 mM. The proposed sensor exhibited a superior selectivity without any interference from the oxygen evolution reaction during glucose sensing. We also found that this glucose sensor showed negligible interference from various interferents, such as ascorbic acid, uric acid, dopamine and sodium chloride. Additionally, a novel flexible sensor was developed by coating the NiVP/Pi over Whatman filter paper, which exhibited two linear ranges of 100 nM to 1 μM and 100 μM to 10 mM with an ultra-sensitivity of 1.130 mA μM-1 cm-2 and 0.746 mA μM-1 cm-2, respectively, in 0.1 M NaOH. The proposed sensor was tested with human blood serum samples demonstrating its practical application. Our findings provide a new route by fine tuning the composition of nickel and vanadium that sheds new light on better understanding the processes. This NiVP/Pi-based sensor offers a new approach towards the electrochemical detection of glucose, enabling glucose monitoring in a convenient way.

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.

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

Diabetes prevalence has been rising exponentially, increasing the need for reliable noninvasive approaches for glucose monitoring. Different biofluids have been explored recently for replacing current blood finger-stick glucose strips with noninvasive painless sensing devices. While sweat has received considerable attention, there are mixed reports on correlating the sweat results with blood glucose levels. Here, we demonstrate a new rapid and reliable approach that combines a simple touch-based fingertip sweat electrochemical sensor with a new algorithm that addresses for personal variations toward the accurate estimate of blood glucose concentrations. The new painless and simple glucose self-testing protocol leverages the fast sweat rate on the fingertip for rapid assays of natural perspiration, without any sweat stimulation, along with the personalized sweat-response-to-blood concentration translation. A reliable estimate of the blood glucose sensing concentrations can thus be realized through a simple one-time personal precalibration. Such system training leads to a substantially improved accuracy with a Pearson correlation coefficient higher than 0.95, along with an overall mean absolute relative difference of 7.79%, with 100% paired points residing in the A + B region of the Clarke error grid. The speed and simplicity of the touch-based blood-free fingertip sweat assay, and the elimination of periodic blood calibrations, should lead to frequent self-testing of glucose and enhanced patient compliance toward the improved management of diabetes.

Intelligent Patches for Wound Management: In Situ Sensing and Treatment

Intelligent wound patches have the potential properties of ultra-adhesion, self-healing ability, biosensing, antibacterial, anti-inflammatory, etc. In situ sensing (biosensing and monitoring) and intelligent drug delivery deserve more exploration, and new strategies of these two factors are of great importance. In this Feature, a comprehensive set of the progress in the area of intelligent wound patches, especially those based on multiple biosensing and electronics, and their potentials in drug release is deliberated. In addition, the major challenges in this field and opinions on its future developments are portrayed.

Wearable biochemical sensors for human health monitoring: sensing materials and manufacturing technologies

Wearable biochemical sensors are of great interest nowadays due to their powerful potential in personalized medicine and continuous monitoring of human health. Thus, a great deal of effort has been put into the development of such sensors to enable real-time and non-invasive quantification of various chemical constituents in the human body such as sweat, saliva, and tears. Owing to the advances in materials science and mechanical engineering, wearable biochemical sensors have been developed to probe various biomarkers and have been subsequently considered as wearable electronic devices for practical applications. In this review, we present a broad overview on the recent advances in electrochemical wearable sensors towards various organic components and ions closely linked to human health. With an emphasis on materials and manufacturing technologies of the sensing electrodes, the research status is summarized, and the challenges and opportunities in this growing field are prospected.

2D metal azolate framework as nanozyme for amperometric detection of glucose at physiological pH and alkaline medium

The synthesis of Co-based two-dimensional (2D) metal azolate framework nanosheets (MAF-5-Co^II NS) is described using a simple hydrothermal method. The product was isostructural to MAF-5 (Zn). The as-prepared MAF-5-Co^II NS exhibited high surface area (1155 m²/g), purity, and crystallinity. The MAF-5-Co^II NS-modified screen-printed electrode (MAF-5-Co^II NS/SPE) was used for nonenzymatic detection of glucose in diluted human blood plasma (BP) samples with phosphate buffer saline (PBS, pH 7.4) and NaOH (0.1 M, pH 13.0) solutions. The MAF-5-Co^II NS nanozyme displayed good redox activity in both neutral and alkaline media with the formation of Co^II/Co^III redox pair, which induced the catalytic oxidation of glucose. Under the optimized detection potential, the sensor presented a chronoamperometric current response for the oxidation of glucose with two wide concentration ranges in PBS-diluted (62.80 to 180 μM and 305 to 8055 μM) and NaOH-diluted (58.90 to 117.6 μM and 180 to 10,055 μM) BP samples, which were within the limit of blood glucose levels of diabetic patients before (4.4-7.2 mM) and after (10 mM) meals (recommended by the American Diabetes Association). The sensor has a limit of detection of ca. 0.25 and 0.05 μM, respectively, and maximum sensitivity of ca. 36.55 and 1361.65 mA/cm²/mM, respectively, in PBS- and NaOH-diluted BP samples. The sensor also displayed excellent stability in the neutral and alkaline media due to the existence of hydrophobic linkers (2-ethyl imidazole) in the MAF-5-Co^II NS, good repeatability and reproducibility, and interference-free signals. Thus, MAF-5-Co^II NS is a promising nanozyme for the development of the disposable type of sensor for glucose detection in human body fluids. Graphical abstract.

Introducing reticular chemistry into agrochemistry

For survival and quality of life, human society has sought more productive, precise, and sustainable agriculture. Agrochemistry, which solves farming issues in a chemical manner, is the core engine that drives the evolution of modern agriculture. To date, agrochemistry has utilized chemical technologies in the form of pesticides, fertilizers, veterinary drugs and various functional materials to meet fundamental demands from human society, while increasing the socio-ecological consequences due to inefficient use. Thus, more useful, precise, and designable scaffolding materials are required to support sustainable agrochemistry. Reticular chemistry, which weaves molecular units into frameworks, has been applied in many fields based on two cutting-edge porous framework materials, namely metal-organic frameworks (MOFs) and covalent-organic frameworks (COFs). With flexibility in composition, structure, and pore chemistry, MOFs and COFs have shown increasing functionalities associated with agrochemistry in the last decade, potentially introducing reticular chemistry as a highly accessible chemical toolbox into agrochemical technologies. In this critical review, we will demonstrate how reticular chemistry shapes the future of agrochemistry in the fields of farm sensing, agro-ecological preservation and reutilization, agrochemical formulations, smart indoor farming, agrobiotechnology, and beyond.

Recent advances of electrochemical and optical enzyme-free glucose sensors operating at physiological conditions

Diabetes is a pathological condition that requires the continuous monitoring of glucose level in the blood. Its control has been tremendously improved by the application of point-of-care devices. Conventional enzyme-based sensors with electrochemical and optical transduction systems can successfully measure the glucose concentration in human blood, but they suffer from the low stability of the enzyme. Non-enzymatic wearable electrochemical and optical sensors, with low-cost, high stability, point-of-care testing and online monitoring of glucose levels in biological fluids, have recently been developed and can help to manage and control diabetes worldwide. Advances in nanoscience and nanotechnology have enabled the development of novel nanomaterials that can be implemented for the use in enzyme-free systems to detect glucose. This review summarizes recent developments of enzyme-free electrochemical and optical glucose sensors, as well as their respective wearable and commercially available devices, capable of detecting glucose at physiological pH conditions without the need to pretreat the biological fluids. Additionally, the evolution of electrochemical glucose sensor technology and a couple of widely used optical detection systems along with the glucose detection mechanism is also discussed. Finally, this review addresses limitations and challenges of current non-enzymatic electrochemical, optical, and wearable glucose sensor technologies and highlights opportunities for future research directions.

Applications of Functional Metal-Organic Frameworks in Biosensors

In recent decades, fast advancements in the fields of metal-organic frameworks (MOFs) are providing unprecedented opportunities for the development of novel functional MOFs for various biosensing applications. Exciting progress is achieved due to the combination of MOFs with various functional components, which introduces novel structures and new features to the MOFs-based biosensing applications, such as higher stability, higher sensitivity, higher flexibility, and higher specificity. This review aims to be a comprehensive summary of the most recent advances in the development of functional MOFs for various biosensing applications, placing special attention on important contributions in recent 3 years. In this review, the most recent developments in design and synthesis of functional MOFs for biosensing applications are summarized. MOFs-based biosensing applications are outlined according to the central roles of MOFs in biosensors, which include carriers of sensitive elements, enzyme-mimic elements, electrochemical signaling, optical signaling, and gas sensing. Finally, the current challenges and future development trends of functional MOFs for biosensing applications are proposed and discussed.

Zeolitic imidazolate frameworks for use in electrochemical and optical chemical sensing and biosensing: a review

This review (with 145 refs.) summarizes the progress that has been made in the use of zeolitic imidazolate frameworks in chemical sensing and biosensing. Zeolitic imidazolate frameworks (ZIFs) are a type of porous material with zeolite topological structure that combine the advantages of zeolite and traditional metal-organic frameworks. Owing to the structural flexibility of ZIFs, their pore sizes and surface functionalization can be reasonably designed. Following an introduction into the field of metal-organic frameworks and the zeolitic imidazolate framework (ZIF) subclass, a first large section covers the various kinds and properties of ZIFs. The next large section covers electrochemical sensors and assays (with subsections on methods for gases, electrochemiluminescence, electrochemical biomolecules). This is followed by main sections on ZIF-based colorimetric and luminescent sensors, with subsections on sensors for metal ions and anions, for gases, and for organic biomolecules. The last section covers SERS-based assays. Several tables are presented that give an overview on the wealth of methods and materials. A concluding section summarizes the current status, addresses current challenges, and gives an outlook on potential future trends. Graphical abstract In recent years, ZIFs and their composites have been widely used as probes in chemical sensing, and these probes have shown great advantages over other materials. This review describes the current progress on ZIFs toward electrochemical, luminescence, colorimetric, and SERS-based sensing applications, highlighting the different strategies for designing ZIFs and their composites and potential challenges in this field.

The review of Lab-on-PCB for biomedical application

Prevention of infectious diseases, diagnosis of diseases, and determination of treatment options all rely on biosensors to detect and analyze biomarkers, which are usually divided into four parts: cell analysis, biochemical analysis, immunoassay, and molecular diagnosis. However, traditional biosensing devices are expensive, bulky, and require a lot of time to detect, which also limited its application in resource-limited areas. In recent years, Lab-on-PCB, which combines biosensing technology and PCB technology, has been widely used in biomedical applications due to its high integration, personalized design, and easy mass production. Among these Lab-on-PCB sensing devices, the PCB circuit plays an important role. It can be directly used as a resistance sensor to count cells, and also used as a control device to automatically control the detection device. Flexible PCBs can be used to make wearable medical biosensors. In addition, due to the high degree of integration of the PCB circuit, Lab-on-PCB can perform multiple inspections on the same platform, which reduces the inspection time equivalently. Therefore, in this review paper, we discuss the application of Lab-on-PCB in four analysis methods of cell analysis, biochemical analysis, immunoassay, and molecular diagnosis, and give some suggestions for improvement and future development trends at the end.

Engineering the valence state of ZIF-67 by Cu2O for efficient nonenzymatic glucose detection

The valence state regulation of Co-based electrocatalysts is extremely important and greatly challenging to enhance the electrochemical performance toward glucose oxidation.