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

Development of a wearable microfluidic amperometric sensor based on spatial three-electrode system for sweat glucose analysis

Most amperometric glucose sensors utilize nanomaterials to increase the surface area of the working electrode for sensitivity enhancement. However, this approach not only increases the cost and complicates the fabrication process, but also results in functional surfaces with limited durability. We propose a wearable microfluidic amperometric sensor featuring a spatially arranged three-electrode system (TES) for sweat glucose analysis. We optimize sensing electrodes' shape, size, spacing, and spatial arrangement through simulations and electrochemical measurements by comparing cyclic voltammogram behavior. The spatial TES is then designed based on the geometry of the microfluidic chamber, and the sensor is fabricated using a combination of laser cutting, screen printing, and layer-by-layer assembly techniques. The wearable microfluidic amperometric glucose sensor exhibits excellent linearity and specificity in in-vitro characterization. Additionally, it achieves comparable detection sensitivity (approximately 7.2 μA/mM) relative to sensors utilizing nanomaterials. By continuously analyzing glucose variations in sweat samples from the subject's abdomen, we validate the reliability and practicality of this device for real-time monitoring of sweat glucose.

Wearable epidermal sensor patch with biomimetic microfluidic channels for fast and time-sequence monitoring of sweat glucose and lactate

Wearable sweat sensors enable non-invasive tracking and monitoring of human physiological information, which is expected to attract wide interest and rapid development in dietary health management and disease prevention. Unfortunately, sweat sensors are limited by rapid evaporation and low secretion rates of sweat. Herein, a sweat detection patch is proposed, which integrates bionic microchannels and multiparameter electrochemical sensors. The microfluidic channel (5°), which mimics ginkgo biloba veins, provided a 40 % higher flow rate compared to the normal channel (0°). Combined with burst pressure, the bionic channel enabled unidirectional transport of 6 μL sweat, effectively avoiding the mixing of old and new sweat. The electrochemical sensors possessed excellent specificity recognition, stability and durability, and have been used to detect substances in sweat, in particular to analyze changes in glucose concentration at different dietary intakes and changes in lactate metabolism after exercise. The rapid collection effect of the microchannels on trace sweat and the fast response of sensors have broad application prospects in real-time human health monitoring.

MXenes in healthcare: transformative applications and challenges in medical diagnostics and therapeutics

MXenes, a novel class of two-dimensional transition metal carbides, exhibit exceptional physicochemical properties that make them highly promising for biomedical applications. Their application has been explored in bioinstrumentation, tissue engineering, and infectious disease management. In bioinstrumentation, MXenes enhance the sensitivity and response time of wearable sensors, including piezoresistive, electrochemical, and electrophysiological sensors. They also function effectively as contrast agents in MRI and CT imaging for cancer diagnostics and therapy. In tissue engineering, MXenes contribute to both hard and soft tissue regeneration, playing a key role in neural, cardiac, skin and bone repair. Additionally, they offer innovative solutions in combating infectious and inflammatory diseases by facilitating antimicrobial surfaces and immune modulation. Despite their potential, several challenges hinder the clinical translation of MXene-based technologies. Issues related to synthesis, scalability, biocompatibility, and long-term safety must be addressed to ensure their practical implementation in medical applications. This review provides a comprehensive overview of MXenes in next-generation medical diagnostics, including the role they play in wearable sensors and imaging contrast agents. It further explores their applications in tissue engineering and infectious disease management, highlighting their antimicrobial and immunomodulatory properties. Finally, we discuss the key barriers to clinical translation and propose strategies for overcoming these limitations. This review aims to bridge current advancements with future opportunities for integration of MXenes in healthcare.

A programmable magnetic digital microfluidic platform integrated with electrochemical detection system

Digital microfluidic (DMF) technology is widely used in bioanalysis and chemical reactions due to its accuracy and flexibility in manipulating droplets. However, most DMF systems usually rely on complex electrode fabrication and high driving voltages. Sensor integration in DMF systems is also quite rare. In this study, a programmable magnetic digital microfluidic (PMDMF) platform integrated with electrochemical detection system was proposed. It enables non-contact, flexible droplet manipulation without complex processes and high voltages, meeting the requirements of automated electrochemical detection. The platform includes a magnetic control system, a microfluidic chip, and an electrochemical detection system. The magnetic control system consists of a microcoil array circuit board, a N52 permanent magnet, and an Arduino control module. N52 magnets generate localized magnetic fields to drive droplet movement, while the Arduino module enables programmable control for precise manipulation. The maximum average velocity of the droplet is about 3.9 cm/s. The microfluidic chip was fabricated using 3D printing and the superhydrophobic surface of chip was fabricated by spray coating. The electrochemical detection system consists of the MoS2@CeO2/PVA working electrode, Ag/AgCl reference electrode, and carbon counter electrode. To evaluate the practical value of the integrated platform, glucose in sweat was automatically and accurately detected. The proposed platform has a wide linear detection range (0.01-0.25 mM), a lower LOD (6.5 μM), a superior sensitivity (7833.54 μA·mM-1·cm-2), and excellent recovery rate (88.1-113.5%). It has an extensive potential for future application in the fields of medical diagnostics and point-of-care testing.

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

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

3D Integrated Physicochemical-Sensing Electronic Skin

The integration of physical and chemical signal sensing is of great significance to bridge the gap between electronic skin (e-skin) and natural skin. However, the existing method of integrating physical and chemical signal sensing units in two dimensions is not conducive to the development of e-skin in multifunctionality and miniaturization. Herein, a new three-dimensional (3D) integrated physicochemical-sensing e-skin (TDPSES) is developed by integrating a piezoresistive sensing unit, a biochemical signal sensing electrode, and a microfluidic system in a 3D superposition mode. For pressure sensing, TDPSES demonstrates an ultra-high sensitivity of 208.6 kPa-1 in 0-15 kPa and excellent stability of 8000 cycles. For glucose sensing in sweat, TDPSES has a sensitivity of 3.925 µA mm-1 and a detection limit of 29.1 µm. Meanwhile, TDPSES can not only continuously detect biological fluids, but also self-monitor its fluid-driving behavior, demonstrating its intelligent fluid-driving characteristics. Furthermore, TDPSES is applied to monitor a variety of physiological signals such as sweat, pulse, and voice, demonstrating its multifunctional sensing capabilities and application potential in health care. In conclusion, the implementation of TDPSES provides a new idea for constructing miniaturized and multifunctional e-skin, which helps to narrow the gap between e-skin and natural skin.

Constructing an electrochemical sensor with screen-printed electrodes incorporating Ti3C2Tx-PDA-AgNPs for lactate detection in sweat

Sweat lactate levels are closely related to an individual's physiological state and serve as critical indicators for assessing exercise intensity, muscle fatigue, and certain pathological conditions. Screen-printed electrodes (SPEs) offer a promising avenue for the development of low-cost, high-performance wearable devices for electrochemical sweat analysis. The material composition of SPEs significantly impacts their detection sensitivity and stability. In this study, we designed a screen-printed carbon electrode (SPCE) modified with Ti3C2Tx Polydopamine (PDA), and silver nanoparticles (AgNPs) (Ti3C2Tx-PDA-AgNPs) for lactate detection in sweat. The accordion-like structure of Ti3C2Tx provides a large specific surface area and exceptional electrical conductivity. PDA, acting as both a reducing agent and binder, supports the in-situ formation of AgNPs on the Ti3C2Tx nanosheets. These AgNPs prevent the restacking of Ti3C2Tx layers, further improving conductivity. The sensor exhibited sensitivities of 0.145 μA mM-1, with limit of detection (LOD) of 0.181 mM (S/N = 3) in phosphate-buffered saline (PBS), meeting the requirements for for sweat lactate detection. The sensor was integrated into a wearable micro-electrochemical platform paired with a custom Android application for real-time sweat analysis. Testing on human sweat demonstrated the platform's potential for practical fitness monitoring and healthcare diagnostics applications.

Superior sensitive graphene fiber sensor enabled by constructing multiple nanoembossments for glucose detection

Metal oxides have been extensively investigated in non-enzymatic biosensors for detecting diabetes owing to their electrochemical catalytic properties and excellent stability. However, lower conductivity and catalytic activity are major obstacles to the commercialization of metal oxide-based non-enzymatic glucose sensors. Herein, we present a novel flexible nonenzymatic glucose sensor utilizing graphene fiber (GF)/Au/Ni(OH)2 composite fiber. The integration of GFs enables a significant uptake of sensing molecules due to its expansive surface area and high electron mobility, ultimately resulting in a decrease in the detection limit. Consequently, the incorporation of Ni(OH)2 provides abundant attachment sites by introducing Au atoms, thereby promoting electron migration and enhancing sensitivity and detection limits. An impressive sensitivity (1095.63 µA mM-1 cm-2) within the detection range (5 µM-2.2 mM) of the integrated GF/Au/Ni(OH)2 fiber is achieved, leading to an incredibly low detection limit (0.294 µM). Additionally, the outstanding repeatability, anti-interference properties, and flexibility of the GF/Au/Ni(OH)2 sensors are obtained as well. Our findings offer a novel method for constructing nano embossments on GFs to achieve superior glucose detection capabilities in the field of wearable electronics in the future.

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

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

Clinical evaluation of a polarization-based optical noninvasive glucose sensing system

Diabetes affects millions in the US, causing elevated blood glucose levels that could lead to complications like kidney failure and heart disease. Recent development of continuous glucose monitors has enabled a minimally invasive option, but the discomfort and social factors highlight the need for noninvasive alternatives in diabetes management. We propose a portable noninvasive glucose sensing system based on the glucose's optical activity property which rotates linearly polarized light depending on its concentration level. To enable a portable form factor, a light trap mechanism is used to capture unwanted specular reflection from the palm and the enclosure itself. We fabricate four sensing prototypes and conduct a 363-day multi-session clinical evaluation in real-world settings. 30 participants are provided with a prototype for a 5-day home monitoring study, collecting on average 8 data points per day. We identify the error caused by differences between the sensing boxes and the participants' improper usage. We utilize a machine learning pipeline together with Bayesian Ridge Regressor models and multiple-step data processing techniques to deal with the noisy data. Over 95% of the predictions fall within Zone A (clinically accurate) or B (clinically acceptable) of the Consensus Error Grid with a 0.24 mean absolute relative differences.

Advances in conducting nanocomposite hydrogels for wearable biomonitoring

Recent advancements in wearable biosensors and bioelectronics have led to innovative designs for personalized health management devices, with biocompatible conducting nanocomposite hydrogels emerging as a promising building block for soft electronics engineering. In this review, we provide a comprehensive framework for advancing biosensors using these engineered nanocomposite hydrogels, highlighting their unique properties such as high electrical conductivity, flexibility, self-healing, biocompatibility, biodegradability, and tunable architecture, broadening their biomedical applications. We summarize key properties of nanocomposite hydrogels for thermal, biomechanical, electrophysiological, and biochemical sensing applications on the human body, recent progress in nanocomposite hydrogel design and synthesis, and the latest technologies in developing flexible and wearable devices. This review covers various sensor types, including strain, physiological, and electrochemical sensors, and explores their potential applications in personalized healthcare, from daily activity monitoring to versatile electronic skin applications. Furthermore, we highlight the blueprints of design, working procedures, performance, detection limits, and sensitivity of these soft devices. Finally, we address challenges, prospects, and future outlook for advanced nanocomposite hydrogels in wearable sensors, aiming to provide a comprehensive overview of their current state and future potential in healthcare applications.

A highly sensitive flexible sensor based on the MXene/αFe2O3 composite structure applied for the simultaneous detection of glucose and uric acid

Sensors based on inorganic nanomaterials for the detection of human body fluids show great potential in real-time detection and treatment of human health due to their advantages of small size and easy to wear. Nevertheless, most of the existing sensors have the disadvantage of detecting relatively simple substances and suffer from low sensitivity, which undermines their practical applicability in body fluids detection. In this study, based on the transition metal carbide (Ti3C2Tx, MXene)/αFe2O3 grid composite structure, a highly sensitive flexible sensor is proposed, which can realize accurate and simultaneous detection of glucose and uric acid (UA) concentration. The sensor exhibits outstanding durability, enabling it to withstand prolonged immersion in water and exposure to high flow velocities. More importantly, the sensor has extremely high sensitivity for both glucose (2.14 mA mM-1 cm-2, 5.5 times the mean value) and UA (2.56 μA μM-1 cm-2, 3.5 times the mean value). It also has the advantage of low detection limits (0.27 μM for glucose and 0.31 μM for UA) and a wide linear detection range (1 mM-40 mM for glucose and 10 μM-900 μM for UA) compared to existing sensors for body fluids detection. In addition, the sensor has excellent repeatability, long shelf life (over 40 days) and excellent immunity to interference (accurate detection of glucose and UA in the presence of multiple metal ions as well as organics in human body fluids). This study establishes the groundwork for developing a production-ready and highly sensitive blood detection sensor capable of real-time monitoring.

A wearable sensor based on janus fabric upon an electrochemical analysis platform for sweat glucose detection

Wearable sweat sensing devices have drawn much attention due to their noninvasive and portable properties, which is emerging as a promising technology in daily healthiness assessment issues. A sweat sensor based on Janus fabric and electrochemical analysis is proposed in this work. Unidirectional moisture transported behavior of the Janus fabric serves as the quick-drying component directly contacting skin to transfer sweat toward the detection site. The working electrode was treated by repeated activation of Prussian blue followed by chitosan/single-wall carbon nano tubes/glucose oxidase deposition, ensuring the high electrochemical activity and sensitivity to detect the sweat glucose level. A detection system was established based on the electrochemical analysis of this sweat sensor, which can provide accurate glucose level in the testing samples. The limit of detection (LOD) of the sensor for glucose was 15.32 μM (S/N = 3) and the sensitivity was 3.35 μA/mM. One male subject wears this sensor for intermittent intensity training, outputting the real-time changes in sweat glucose levels, which is consistent with the energy consumption and metabolic status during human exercise. And the sweat glucose level for different subjects was tested to be 35-135 μM, which is coincident with the distribution range of normal human sweat glucose levels.

Recent Advances in MXene-Based Electrochemical Sensors

MXene is a new family of two-dimensional nanomaterials with outstanding electrical conductivity, tunable structure, biocompatibility, and a large surface area. Thanks to these unique physicochemical properties, MXene has been used for constructing electrochemical sensors (MECSens) with excellent performance. In particular, the abundant surface termination of MXene can contribute to greatly enhancing the analytical sensitivity and selectivity of MECSens. Recently, MECSens have been widely applied in many fields including clinical diagnosis, infectious disease surveillance, and food security. However, not all MXene materials are suitable for building electrochemical sensors. In this article, we present an overview of different MECSens that have been developed so far. We begin with a short summary of the preparation and characterization of MECSens. Subsequently, the electrochemical performance, detection strategies, and application scenarios of MECSens are classified and briefly discussed. The article ends with a short conclusion and future perspectives. We hope this article will be helpful for designing and constructing MECSens with outstanding activity for electrochemical analysis.

Self-Supported Cu/Fe3O4 Hierarchical Nanosheets on Ni Foam for High-Efficiency Non-Enzymatic Glucose Sensing

Electrochemical glucose sensors are vital for clinical diagnostics and the food industry, where accurate detection is essential. However, the limitations of glucose oxidase (GOx)-based sensors, such as complex preparation, high cost, and environmental sensitivity, highlight the need for non-enzymatic sensors that directly oxidize glucose at the electrode surface. In this study, a self-supporting hierarchical Cu/Fe3O4 nanosheet electrode was successfully fabricated by in situ growth on Ni Foam using a hydrothermal method, followed by annealing treatment. The Cu/Fe3O4 hierarchical nanosheet structure, with its large surface area, provides abundant active sites for electrocatalysis, while the strong interactions between Cu/Fe3O4 and Ni Foam enhance electron transfer efficiency. This novel electrode structure demonstrates exceptional electrochemical performance for non-enzymatic glucose sensing, with an ultrahigh sensitivity of 12.85 μA·μM-1·cm-2, a low detection limit of 0.71 μM, and a linear range extending up to 1 mM. Moreover, the Cu/Fe3O4/NF electrode exhibits excellent stability, a rapid response (~3 s), and good selectivity against interfering substances such as uric acid, ascorbic acid, H2O2, urea, and KCl. It also shows strong reliability in analyzing human serum samples. Therefore, Cu/Fe3O4/NF holds great promise as a non-enzymatic glucose sensor, and this work offers a valuable strategy for the design of advanced electrochemical electrodes.

A novel method for quality evaluation of Radix Angelica sinensis based on molecularly imprinted electrochemical sensor

Rapid and sensitive detection of n-butylidenephthalide (NBP) is crucial for quality control of Radix Angelica Sinensis (RAS) and its related pharmaceuticals due to their shared pharmacological effects, such as immune enhancement and anti-tumor properties. Current detection methods struggle to quantify NBP quickly and accurately. A molecularly imprinted polymer (MIP)-based electrochemical sensor has been developed, forming a film on PCN-222(Fe) via electropolymerization for the rapid and selective detection of NBP. o-Phenylenediamine (o-PD) was polymerized onto PCN-222(Fe), utilizing its high surface area and porous structure to create a high-performance MIP (MIP/PCN-222(Fe)) sensor. This sensor detects NBP binding at the molecularly imprinted sites through a redox probe, with current changes reflecting the NBP content in the sample. This sensor exhibits a strong affinity for NBP, with a linear detection range from 200 nM to 1 mM, a detection limit of 76 nM, and high specificity towards similar phthalide compounds. Experimental results show that the MIP/PCN-222(Fe) sensor can accurately quantify NBP in real samples, offering a simplified method with promising applications for RAS quality evaluation.

An Optoelectronic Sensing Real-Time Glucose Detection Film Using Photonic Crystal Enhanced Rare Earth Fluorescence and Additive Manufacturing

In this research, a novel detection method employing rare-earth upconversion nanoparticle (UCNP) as the core, coated with MnO2 nanosheets is designed, which formed a color and fluorescence dual-responsive UCNP composite material, MnO2-modified NaYF4:Yb,Tm@NaYF4. By enabling both colorimetric and fluorescence methods simultaneously, this composite material allows for the detection of glucose concentration under different conditions, while exhibiting strong resistance to environmental interference, chemical stability, and accuracy. To further enhance the sensitivity of the detection method, a photonic crystals (PCs)-PDMS array where polymethyl methacrylate PCs are deposited onto a substrate composed of PDMS-glass slice with hydrophobic surfaces is developed. This array can serve as a substrate that specifically reflected blue light while allowing other colors of light to pass through, which effectively reduced background signal interference and improved detection sensitivity (1.2 µm) with a wider linear range (20-800 µm). Finally, a portable fluorescence intensity detection device is designed to enhance the portability of the platform. Numerous experimental results demonstrated that this research significantly improved the sensitivity of glucose detection, providing new research directions for the field of fluid biomarker detectio.

Recent progress on nanomaterial-based electrochemical sensors for glucose detection in human body fluids

In the modern age, half of the population is facing various chronic illnesses due to glucose maintenance in the body, major causes of fatality and inefficiency. The early identification of glucose plays a crucial role in medical treatment and the food industry, particularly in diabetes diagnosis. In the past few years, non-enzymatic electrochemical glucose sensors have received a lot of interest for their ability to identify glucose levels accurately. Electrochemical biosensors are developing as a propitious solution for personalized health monitoring due to their accuracy, specificity, and affordability. This review article provides an observation of a variety of non-enzymatic glucose sensor resources, such as carbon nanomaterials, noble metals gold and silver, transition metal and their oxides, and porous material composites. Moreover, basic knowledge of the reaction mechanism of enzymatic and nonenzymatic glucose sensors are outlined and recent advancements in glucose sensors applications to various human body biofluids such as sweat, tears, urine, saliva, and blood are presented. Finally, this review summarizes electrochemical sensors for glucose detection in human body fluids, the challenges they faced, and their solutions.

Electrochemical biosensor based on copper sulfide/reduced graphene oxide/glucose oxidase construct for glucose detection

Due to the current increase in the number of people suffering from diabetes worldwide, how to monitor the blood glucose level in the human body has become an urgent problem to be solved nowadays. The electrochemical sensor method can be used for real-time glucose monitoring due to its advantages of real-time monitoring capability and high sensitivity. Reduced graphene oxide (rGO) has great potential for application in the field of sensors due to its advantages of large specific surface area, high stability, and good electrical and thermal conductivity. Meanwhile, the synergistic effect between two-dimensional transition metal sulfides and graphene can improve the electrochemical performance of materials due to their similar mechanical flexibility and strength. This article uses flake graphite, copper sulfate, and glucose oxidase (GOx) as raw materials to prepare CuS/rGO/GOx/GCE electrodes, and explores the performance of electrode electrocatalysis for glucose. The results showed that the prepared sensor was characterized by a low detection limit (1.75 nM) and a wide linear range (0.1-100 mM) for glucose detection, displaying a good overall detection performance, and its sensing mechanism and dynamic process were also investigated. In addition, the sensor has outstanding selectivity, anti-interference, repeatability, reproducibility and practicality.

Advancements in electrochemical glucose sensors

The development of electrochemical glucose sensors with high sensitivity, specificity, and stability, enabling real-time continuous monitoring, has posed a significant challenge. However, an opportunity exists to fabricate electrochemical glucose biosensors with optimal performance through innovative device structures and surface modification materials. This paper provides a comprehensive review of recent advances in electrochemical glucose sensors. Novel classes of nanomaterials-including metal nanoparticles, carbon-based nanomaterials, and metal-organic frameworks-with excellent electronic conductivity and high specific surface areas, have increased the availability of reactive sites to improved contact with glucose molecules. Furthermore, in line with the trend in electrochemical glucose sensor development, research progress concerning their utilisation with sweat, tears, saliva, and interstitial fluid is described. To facilitate the commercialisation of these sensors, further enhancements in biocompatibility and stability are required. Finally, the characteristics of the ideal electrochemical glucose sensor are described and the developmental trends in this field are outlines.

MXene Hydrogels for Soft Multifunctional Sensing: A Synthesis-Centric Review

Intelligent wearable sensors based on MXenes hydrogels are rapidly advancing the frontier of personalized healthcare management. MXenes, a new class of transition metal carbon/nitride synthesized only a decade ago, have proved to be a promising candidate for soft sensors, advanced human-machine interfaces, and biomimicking systems due to their controllable and high electrical conductivity, as well as their unique mechanical properties as derived from their atomistically thin layered structure. In addition, MXenes' biocompatibility, hydrophilicity, and antifouling properties render them particularly suitable to synergize with hydrogels into a composite for mechanoelectrical functions. Nonetheless, while the use of MXene as a multifunctional surface or an electrical current collector such as an energy device electrode is prevalent, its incorporation into a gel system for the purpose of sensing is vastly less understood and formalized. This review provides a systematic exposition to the synthesis, property, and application of MXene hydrogels for intelligent wearable sensors. Specific challenges and opportunities on the synthesis of MXene hydrogels and their adoption in practical applications are explicitly analyzed and discussed to facilitate cross gemination across disciplines to advance the potential of MXene multifunctional sensing hydrogels.

Development of Automatic Method for Glucose Detection Based on Platinum Octaethylporphyrin Sol-Gel Film with Long-Term Stability

In this study, an approach has been proposed in response to the urgent need for a sensitive and stable method for glucose detection at low concentrations. Platinum octaethylporphyrin (PtOEP) was chosen as the probe and embedded into the matrix material to yield a glucose-sensing film, i.e., Pt/TE-MTS, through a sol-gel process. The optical parameter (OP) was defined as the ratio of phosphorescence in the absence and presence of glucose, and the relationship between OP and glucose concentration (GC) was established in a theoretical way based on the Stern-Volmer equation and further obtained by photoluminescence measurement. OP exhibited a linear relationship with GC in a range of 0-720 μM. The time required by the photoluminescence of the film to reach equilibrium was measured to ensure the completion of the reaction, and it was found that the equilibrium time decreased as the GC increased. The photobleaching behavior and stabilization of the film were monitored, and the result showed that the film exhibited excellent resistance to photobleaching and was quite stable in an aqueous solution. Additionally, a LabVIEW-based GC-detection system was developed to achieve the practical application of the sensing film. In summary, the Pt/TE-MTS film exhibited high sensitivity in detecting the GC with excellent reproducibility, which is of high value in applications.

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

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

ZnFe(PBA)@Ti3C2Tx nanohybrid-based highly sensitive non-enzymatic electrochemical sensor for the detection of glucose in human sweat

The ZnFe prussian blue analogue [ZnFe(PBA)] was infused with Ti3C2Tx (MXene) denoted as ZnFe(PBA)@Ti3C2Tx and was prepared by an in-situ sonication method to use as a non-enzymatic screen printed electrode sensor. The advantage of non-enzymatic sensors is their excellent sensitivity, rapid detection, low cost and simple design. The synthesized ZnFe(PBA)@Ti3C2Tx was characterized for its physical and chemical characterization by XRD, Raman, XPS, EDAX, and FESEM analysis. It possessed multiple functionalized layers and a cubic structure in the nanohybrid. Further, the sensor was investigated by using electroanalytical studies such as cyclic voltammetry and chronoamperometry analysis. The enhanced surface area with a cubic structure of ZnFe(PBA) and the excellent electrical response of Ti3C2 nanosheet support the advancement of a non-enzymatic electrochemical glucose sensor with improved sensitivity of 973.42 µA mM-1 cm-2 with the limit of detection (LOD) of 3.036 µM (S/N = 3) and linear detection range (LDR) from 0.01 to 1 mM.

Ag@TiO2 nanoribbon array: a high-performance sensor for electrochemical non-enzymatic glucose detection in beverage sample

Developing an accurate, cost-effective, reliable, and stable glucose detection sensor for the food industry poses a significant yet challenging endeavor. Herein, we present a silver nanoparticle-decorated titanium dioxide nanoribbon array on titanium plate (Ag@TiO2/TP) as an efficient electrode for non-enzymatic glucose detection in alkaline environments. Electrochemical evaluations of the Ag@TiO2/TP electrode reveal a broad linear response range (0.001 mM - 4 mM), high sensitivity (19,106 and 4264 μA mM-1 cm-2), rapid response time (6 s), and a notably low detection limit (0.18 μM, S/N = 3). Moreover, its efficacy in measuring glucose in beverage samples shows its practical applicability. The impressive performance and structural benefits of the Ag@TiO2/TP electrode highlight its potential in advancing electrochemical sensors for small molecule detection.

All-Fiber Flexible Electrochemical Sensor for Wearable Glucose Monitoring

Wearable sensors, specifically microneedle sensors based on electrochemical methods, have expanded extensively with recent technological advances. Today's wearable electrochemical sensors present specific challenges: they show significant modulus disparities with skin tissue, implying possible discomfort in vivo, especially over extended wear periods or on sensitive skin areas. The sensors, primarily based on polyethylene terephthalate (PET) or polyimide (PI) substrates, might also cause pressure or unease during insertion due to the skin's irregular deformation. To address these constraints, we developed an innovative, wearable, all-fiber-structured electrochemical sensor. Our composite sensor incorporates polyurethane (PU) fibers prepared via electrospinning as electrode substrates to achieve excellent adaptability. Electrospun PU nanofiber films with gold layers shaped via thermal evaporation are used as base electrodes with exemplary conductivity and electrochemical catalytic attributes. To achieve glucose monitoring, gold nanofibers functionalized by gold nanoflakes (AuNFs) and glucose oxidase (GOx) serve as the working electrode, while Pt nanofibers and Ag/AgCl nanofibers serve as the counter and reference electrode. The acrylamide-sodium alginate double-network hydrogel synthesized on electrospun PU fibers serves as the adhesive and substance-transferring layer between the electrodes. The all-fiber electrochemical sensor is assembled layer-by-layer to form a robust structure. Given the stretchability of PU nanofibers coupled with a high specific surface area, the manufactured porous microneedle glucose sensor exhibits enhanced stretchability, superior sensitivity at 31.94 μA (lg(mM))-1 cm-2, a broad detection range (1-30 mM), and a significantly low detection limit (1 mM, S/N = 3), as well as satisfactory biocompatibility. Therefore, the novel electrochemical microneedle design is well-suited for wearable or even implantable continuous monitoring applications, thereby showing promising significant potential within the global arena of wearable medical technology.

Conductive Polymer-Based Hydrogels for Wearable Electrochemical Biosensors

Hydrogels are gaining popularity for use in wearable electronics owing to their inherent biomimetic characteristics, flexible physicochemical properties, and excellent biocompatibility. Among various hydrogels, conductive polymer-based hydrogels (CP HGs) have emerged as excellent candidates for future wearable sensor designs. These hydrogels can attain desired properties through various tuning strategies extending from molecular design to microstructural configuration. However, significant challenges remain, such as the limited strain-sensing range, significant hysteresis of sensing signals, dehydration-induced functional failure, and surface/interfacial malfunction during manufacturing/processing. This review summarizes the recent developments in polymer-hydrogel-based wearable electrochemical biosensors over the past five years. Initially serving as carriers for biomolecules, polymer-hydrogel-based sensors have advanced to encompass a wider range of applications, including the development of non-enzymatic sensors facilitated by the integration of nanomaterials such as metals, metal oxides, and carbon-based materials. Beyond the numerous existing reports that primarily focus on biomolecule detection, we extend the scope to include the fabrication of nanocomposite conductive polymer hydrogels and explore their varied conductivity mechanisms in electrochemical sensing applications. This comprehensive evaluation is instrumental in determining the readiness of these polymer hydrogels for point-of-care translation and state-of-the-art applications in wearable electrochemical sensing technology.

AuNi bimetallic aerogel with ultra-high stability applied in smart and portable biosensing

Glucose detection is of significant importance in providing information to the human health management. However, conventional enzymatic glucose sensors suffer from a limited long-term stability due to the losing activity of the enzymes. In this work, the AuNi bimetallic aerogel with a well-defined nanowire network is synthesized and applied as the sensing nanomaterial in the non-enzymatic glucose detection. The three-dimensional (3D) hierarchical porous structure of the AuNi bimetallic aerogel ensures the high sensitivity of the sensor (40.34 μA mM-1 cm-2). Theoretical investigation unveiled the mechanism of the boosting electrocatalytic activity of the AuNi bimetallic aerogel toward glucose. A better adhesion between the sensing nanomaterial and the screen-printing electrodes (SPEs) is obtained after the introduction of Ni. On the basis of a wide linearity in the range of 0.1-5 mM, an excellent selectivity, an outstanding long-term stability (90 days) as well as the help of the signal processing circuit and an M5stack development board, the as-prepared glucose sensor successfully realizes remote monitoring of the glucose concentration. We speculate that this work is favorable to motivating the technological innovations of the non-enzymatic glucose sensors and intelligent sensing devices.

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.

Advances of Transition Metal-Based Electrochemical Non-enzymatic Glucose Sensors for Glucose Analysis: A Review

Glucose concentration is a crucial parameter for assessing human health. Over recent years, non-enzymatic electrochemical glucose sensors have drawn considerable attention due to their substantial progress. This review explores the common mechanism behind the transition metal-based electrocatalytic oxidation of glucose molecules through classical electrocatalytic frameworks like the Pletcher model and the Hydrous Oxide-Adatom Mediator model (IHOAM), as well as the redox reactions at the transition metal centers. It further compiles the electrochemical characterization techniques, associated formulas, and their ensuing conclusions pertinent to transition metal-based non-enzymatic electrochemical glucose sensors. Subsequently, the review covers the latest advancements in the field of transition metal-based active materials and support materials used in non-enzymatic electrochemical glucose sensors in the last decade (2014-2023). Additionally, it presents a comprehensive classification of representative studies according to the active metal catalysts components involved.

Facile preparation of a CoNiS/CF electrode by SILAR for a high sensitivity non-enzymatic glucose sensor

The nanomaterials for non-enzymatic electrochemical sensors are usually pre-synthesized and coated onto electrodes by ex situ methods. In this work, amorphous cobalt-nickel sulfide (CoNiS) nanoparticles were facilely prepared on copper foam (CF) by the in situ successive ionic layer adsorption and reaction (SILAR) method, and as-prepared CoNiS/CF was studied as an electrode for non-enzymatic glucose sensing. It was analyzed by field emission scanning electron microscopy (FESEM), energy dispersive X-ray analysis (EDAX) and X-ray photoelectron spectroscopy (XPS). The electrochemical performance was investigated by cyclic voltammetry (CV) and chronoamperometry (CA). This binary sulfide electrode showed better performance toward glucose oxidation compared to the corresponding single sulfide and showed a wide linear range of 0.005 to 3.47 mM, a high sensitivity of 2298.7 μA mM-1 cm-2 and a low detection limit of 2.0 μM. The sensor exhibited high sensitivity and good repeatability and stability and was able to detect glucose in an actual sample. This work provides a simple and fast in situ electrode preparation method for a high-sensitivity glucose sensor.

Electrochemical biosensor based on PAMAM functionalized MXene nanoplatform for detection of folate receptor

The level of folate receptor (FR) has become one of the independent factors for measuring human tumor diseases. The precise quantification of FR is helpful for the early diagnosis and subsequent treatment of tumors. The modification of electrodes is a key issue in ensuring and enhancing the electrochemical biosensing ability. In this study, we in-situ synthesized a nanocomposite material with excellent conductivity and stability by grafting first-generation poly(amidoamine) dendrimers onto the MXene (Ti3C2TX) as the immobilized matrix (PAMAM@MXene). An electrochemical sensor was developed for FR monitor by loading the PAMAM@MXene on screen-printed carbon electrodes (SPCEs). Scanning electron microscopy (SEM) supported the effective synthesis of PAMAM@MXene. Under optimal conditions, the prepared sensor achieved the quantification of FR with a wide range of concentrations from 10 ng/mL to 1000 ng/mL with a detection limit (LOD) of 5.6 ng/mL. It also exhibited satisfactory selectivity, reproducibility, and stability, which provided the possibility for expanding new pathways in the detection of clinical FR.

Flexible molecularly imprinted glucose sensor based on graphene sponge and Prussian blue

To enhance the sensitivity of flexible glucose sensors made with 3-aminophenylboronic acid and pyrrole as functional molecules and a carbon tri-electrode as substrate, graphene sponge (GS) and Prussian blue (PB) were used to enhance the charge transfer between the molecularly imprinted cavities and the electrodes. Electrochemical impedance spectroscopy and cyclic voltammetry showed that modifying the electrode with GS and PB significantly reduced the charge transfer impedance and increased the redox current of the sensor. The sensor has a sensitivity of up to 25.81 µA⋅loge (µM)-1⋅cm-2 for the detection of glucose using differential pulse voltammetry in the range of 7.78 to 600 µM, with a low detection limit of 1.08 μM (S/N = 3). When the pH varies in the range of 5.5 to 7.5, the sensor maintains a certain level of stability for glucose detection. The presence of lactic acid, urea, and ascorbic acid had minimal impact on glucose detection by the sensor. After 20 days of storage at room temperature, the sensor maintains 80 % efficiency. This study supports the development of wearable glucose sensors with high sensitivity, specificity, and stability through molecular imprinting.

Disease diagnosis and application analysis of molecularly imprinted polymers (MIPs) in saliva detection

Saliva has significantly evolved as a diagnostic fluid in recent years, giving a non-invasive alternative to blood analysis. A high protein concentration in saliva is delivered directly from the bloodstream, making it a "human mirror" that reflects the body's physiological state. It plays an essential role in detecting diseases in biomedical and fitness monitoring. Molecularly imprinted polymers (MIPs) are biomimetic materials with custom-designed synthetic recognition sites that imitate biological counterparts renowned for sensitive analyte detection. This paper reviews the progress made in research about MIP biosensors for detecting saliva biomarkers. Specifically, we investigate the link between saliva biomarkers and various diseases, providing detailed insights into the corresponding biosensors. Furthermore, we discuss the principles of molecular imprinting for disease diagnostics and application analysis, including recent advances in integrated MIP-sensor technologies for high-affinity analyte detection in saliva. Notably, these biosensors exhibit high discrimination, allowing for the detection of saliva biomarkers linked explicitly to chronic stress disorders, diabetes, cancer, bacterial or viral-induced illnesses, and exposure to illicit toxic substances or tobacco smoke. Our findings indicate that MIP-based biosensors match and perhaps surpass their counterparts featuring integrated natural antibodies in terms of stability, signal-to-noise ratios, and detection limits. Additionally, we highlight the design of MIP coatings, strategies for synthesizing polymers, and the integration of advanced biodevices. These tailored biodevices, designed to assess various salivary biomarkers, are emerging as promising screening or diagnostic tools for real-time monitoring and self-health management, improving quality of life.

MXene-Embedded Porous Carbon-Based Cu2O Nanocomposites for Non-Enzymatic Glucose Sensors

This work explores the use of MXene-embedded porous carbon-based Cu2O nanocomposite (Cu2O/M/AC) as a sensing material for the electrochemical sensing of glucose. The composite was prepared using the coprecipitation method and further analyzed for its morphological and structural characteristics. The highly porous scaffold of activated (porous) carbon facilitated the incorporation of MXene and copper oxide inside the pores and also acted as a medium for charge transfer. In the Cu2O/M/AC composite, MXene and Cu2O influence the sensing parameters, which were confirmed using electrochemical techniques such as cyclic voltammetry, electrochemical impedance spectroscopy, and amperometric analysis. The prepared composite shows two sets of linear ranges for glucose with a limit of detection (LOD) of 1.96 μM. The linear range was found to be 0.004 to 13.3 mM and 15.3 to 28.4 mM, with sensitivity values of 430.3 and 240.5 μA mM-1 cm-2, respectively. These materials suggest that the prepared Cu2O/M/AC nanocomposite can be utilized as a sensing material for non-enzymatic glucose sensors.

Fast and In-Depth Reconstruction of Two-Dimension Cobalt-Based Zeolitic Imidazolate Framework in Glucose Oxidation Processes

Currently, metal-organic frameworks (MOFs) have emerged as viable candidates for enduring electrode materials in nonenzyme glucose sensing. However, given the inherent water susceptibility of MOFs and their complete self-reconstruction during the process of electrochemical oxygen evolution in alkaline conditions, we are motivated to explore the truth of MOFs catalyzing glucose oxidation. In this work, we fabricated a two-dimensional cobalt-based zeolitic imidazolate framework (ZIF-L) as the electrode material for catalyzing glucose oxidation in alkaline conditions. Our explorations revealed that while the initial glucose catalytic response varied among ZIF-L samples with differing thicknesses, the ultimate steady-state catalytic performance remained largely consistent. This phenomenon arose from the transformation of ZIF-L with distinct thicknesses into CoOOH with uniform morphological and structural characteristics during the glucose catalysis process. And in situ Raman spectroscopy elucidated the sustained equilibrium within the glucose catalytic system, wherein the dynamic interconversion between CoOOH and Co(OH)2 governs the overall process. This study contributes to an enhanced understanding of the glucose catalytic mechanism aspects of nonenzymatic glucose sensor electrode materials, offering insights that serve as inspiration for the development of advanced glucose electrode materials.

Integration of MXene and Microfluidics: A Perspective

The fusion of MXene-based materials with microfluidics not only presents a dynamic and promising avenue for innovation but also opens up new possibilities across various scientific and technological domains. This Perspective delves into the intricate synergy between MXenes and microfluidics, underscoring their collective potential in material science, sensing, energy storage, and biomedical research. This intersection of disciplines anticipates future advancements in MXene synthesis and functionalization as well as progress in advanced sensing technologies, energy storage solutions, environmental applications, and biomedical breakthroughs. Crucially, the manufacturing and commercialization of MXene-based microfluidic devices, coupled with interdisciplinary collaborations, stand as pivotal considerations. Envisioning a future where MXenes and microfluidics collaboratively shape our technological landscape, addressing intricate challenges and propelling innovation forward necessitates a thoughtful approach. This viewpoint provides a comprehensive assessment of the current state of the field while outlining future prospects for the integration of MXene-based entities and microfluidics.

Pristine Ti3C2Tx MXene Enables Flexible and Transparent Electrochemical Sensors

In the era of the internet of things, there exists a pressing need for technologies that meet the stringent demands of wearable, self-powered, and seamlessly integrated devices. Current approaches to developing MXene-based electrochemical sensors involve either rigid or opaque components, limiting their use in niche applications. This study investigates the potential of pristine Ti3C2Tx electrodes for flexible and transparent electrochemical sensing, achieved through an exploration of how material characteristics (flake size, flake orientation, film geometry, and uniformity) impact the electrochemical activity of the outer sphere redox probe ruthenium hexamine using cyclic voltammetry. The optimized electrode made of stacked large Ti3C2Tx flakes demonstrated excellent reproducibility and resistance to bending conditions, suggesting their use for reliable, robust, and flexible sensors. Reducing electrode thickness resulted in an amplified faradaic-to-capacitance signal, which is advantageous for this application. This led to the deposition of transparent thin Ti3C2Tx films, which maintained their best performance up to 73% transparency. These findings underscore its promise for high-performance, tailored sensors, marking a significant stride in advancing MXene utilization in next-generation electrochemical sensing technologies. The results encourage the analytical electrochemistry field to take advantage of the unique properties that pristine Ti3C2Tx electrodes can provide in sensing through more parametric studies.

Recent Advances in Electrochemical Detection of Cell Energy Metabolism

Cell energy metabolism is a complex and multifaceted process by which some of the most important nutrients, particularly glucose and other sugars, are transformed into energy. This complexity is a result of dynamic interactions between multiple components, including ions, metabolic intermediates, and products that arise from biochemical reactions, such as glycolysis and mitochondrial oxidative phosphorylation (OXPHOS), the two main metabolic pathways that provide adenosine triphosphate (ATP), the main source of chemical energy driving various physiological activities. Impaired cell energy metabolism and perturbations or dysfunctions in associated metabolites are frequently implicated in numerous diseases, such as diabetes, cancer, and neurodegenerative and cardiovascular disorders. As a result, altered metabolites hold value as potential disease biomarkers. Electrochemical biosensors are attractive devices for the early diagnosis of many diseases and disorders based on biomarkers due to their advantages of efficiency, simplicity, low cost, high sensitivity, and high selectivity in the detection of anomalies in cellular energy metabolism, including key metabolites involved in glycolysis and mitochondrial processes, such as glucose, lactate, nicotinamide adenine dinucleotide (NADH), reactive oxygen species (ROS), glutamate, and ATP, both in vivo and in vitro. This paper offers a detailed examination of electrochemical biosensors for the detection of glycolytic and mitochondrial metabolites, along with their many applications in cell chips and wearable sensors.

MXene-based electrochemical devices applied for healthcare applications

The initial part of the review provides an extensive overview about MXenes as novel and exciting 2D nanomaterials describing their basic physico-chemical features, methods of their synthesis, and possible interfacial modifications and techniques, which could be applied to the characterization of MXenes. Unique physico-chemical parameters of MXenes make them attractive for many practical applications, which are shortly discussed. Use of MXenes for healthcare applications is a hot scientific discipline which is discussed in detail. The article focuses on determination of low molecular weight analytes (metabolites), high molecular weight analytes (DNA/RNA and proteins), or even cells, exosomes, and viruses detected using electrochemical sensors and biosensors. Separate chapters are provided to show the potential of MXene-based devices for determination of cancer biomarkers and as wearable sensors and biosensors for monitoring of a wide range of human activities.

Synthesis of unique three-dimensional CoMn2O4@Ni(OH)2 nanocages via Kirkendall effect for non-enzymatic glucose sensing

Transition metal oxides / hydroxides, which have the advantages of wide distribution, low price, low toxicity, and stable chemical properties, have attracted much attention from researchers. Therefore, this work reports the construction of the unique CoMn2O4 nanocages assisted by the Kirkendall effect, and worm-like Ni(OH)2 nanoparticles were grown on the surface via hydrothermal method, the final product CoMn2O4@Ni(OH)2 nanocages were applied to construct efficient and sensitive non-enzymatic glucose electrochemical sensing. The stable three-dimensional hollow CoMn2O4 nanocages structure, not only can provide a wider specific surface area and more abundant active sites, its porous structure also can effectively inhibit the aggregation of nanoparticles, increase the ion diffusion path, shorten the electron transport distance, and improve the electrical conductivity. Loading Ni(OH)2 nanoparticles on the CoMn2O4 nanocages can increase catalytic sites, and further strengthen the electrocatalytic performance. Due to the good synergistic effect between CoMn2O4 and Ni(OH)2, CoMn2O4@Ni(OH)2 nanocages electrochemical sensor can achieve sensitive and rapid detection of trace glucose, with excellent linear range (8.5-1830.5 μM), low limit of detection (0.264 μM), high sensitivity of 0.00646 μA mM-1 cm-2, and outstanding repeatability. More importantly, the sensor has been successfully applied to the determination of blood glucose in human serum with good recoveries (95.64-104.3 %). This work provides a novel scheme for blood glucose detection and expands the application of transition metal oxides / hydroxides in the field of electrochemical sensing.

Advances in Non-Electrochemical Sensing of Human Sweat Biomarkers: From Sweat Sampling to Signal Reading

Sweat, commonly referred to as the ultrafiltrate of blood plasma, is an essential physiological fluid in the human body. It contains a wide range of metabolites, electrolytes, and other biologically significant markers that are closely linked to human health. Compared to other bodily fluids, such as blood, sweat offers distinct advantages in terms of ease of collection and non-invasive detection. In recent years, considerable attention has been focused on wearable sweat sensors due to their potential for continuous monitoring of biomarkers. Electrochemical methods have been extensively used for in situ sweat biomarker analysis, as thoroughly reviewed by various researchers. This comprehensive review aims to provide an overview of recent advances in non-electrochemical methods for analyzing sweat, including colorimetric methods, fluorescence techniques, surface-enhanced Raman spectroscopy, and more. The review covers multiple aspects of non-electrochemical sweat analysis, encompassing sweat sampling methodologies, detection techniques, signal processing, and diverse applications. Furthermore, it highlights the current bottlenecks and challenges faced by non-electrochemical sensors, such as limitations and interference issues. Finally, the review concludes by offering insights into the prospects for non-electrochemical sensing technologies. By providing a valuable reference and inspiring researchers engaged in the field of sweat sensor development, this paper aspires to foster the creation of innovative and practical advancements in this domain.

Optimized Copper-Based Microfeathers for Glucose Detection

Diabetes is expected to rise substantially by 2045, prompting extensive research into accessible glucose electrochemical sensors, especially those based on non-enzymatic materials. In this context, advancing the knowledge of stable metal-based compounds as alternatives to non-enzymatic sensors becomes a scientific challenge. Nonetheless, these materials have encountered difficulties in maintaining stable responses under physiological conditions. This work aims to advance knowledge related to the synthesis and characterization of copper-based electrodes for glucose detection. The microelectrode presented here exhibits a wide linear range and a sensitivity of 1009 µA∙cm-2∙mM-1, overperfoming the results reported in literature so far. This electrode material has also demonstrated outstanding results in terms of reproducibility, repeatability, and stability, thereby meeting ISO 15197:2015 standards. Our study guides future research on next-generation sensors that combine copper with other materials to enhance activity in neutral media.

Enzyme-free electrochemical sensor platforms based on transition metal nanostructures for clinical diagnostics

The detection of emergent biomarkers is of key significance in numerous clinical, biological, and biomedical fields. Specifically, the design and development of potent electrochemical lactic acid and glucose sensing platforms are especially in great demand in a variety of industries, including those involved in clinical analysis, biomedicine, biological, food, cosmetics, pharmaceuticals, leather, sports, and chemical industries. Nanostructured transition metal-derived materials have opened the door to electrochemical sensors and biosensors due to their advantages of high surface-to-volume ratio, surface reaction activity, catalytic activity, and strong adsorption capability. The primary aim of the present minireview is to highlight the advancement of enzyme-free electrochemical sensor platforms based on transition metal-derived nanostructures with high electrocatalytic activity and sensing performance towards lactic acid and glucose in practical samples. The preparation approaches, structural and composition monitoring, fabrication of sensing electrodes, catalytic activity, sensing performance in real samples, and the exploration of sensing mechanisms are majorly concentrated on in most of our recent research studies. Moreover, state-of-the-art transition metal-derived nanostructure-derived electrochemical sensor platforms, critical comparison of the analytical performance of the sensor platforms, and the future perspectives of the enzyme-free electrochemical sensor for clinical diagnostics are described.

A proof-of-concept electroreduction-free anodic stripping voltammetry analysis of Ag(I) based on S,N-Ti3C2Tx MXene nanoribbons

Herein, by preparing sulfur and nitrogen co-doped Ti3C2Tx MXene nanoribbons (S,N-Ti3C2TxR) as a sensing material, a sensitive and novel electroreduction-free anodic stripping voltammetry strategy was designed to detect Ag(I) (Ag+) for the first time, which can successfully avoid the power-consuming electroreduction step, achieving simple, sensitive and efficient detection for Ag+ with a low detection limit and wide linearity.

Chemresistor Smart Sensors from Silk Fibroin-Graphene Composites for Touch-free Wearables

With the rapid development of wearable electronics, low-cost, multifunctional, ultrasensitive touch-free wearables for human-machine interaction and human/plant healthcare management have attracted great attention. The experience of fighting the COVID-19 epidemic has also confirmed the great significance of contactless sensation. Herein, a wearable smart-sensing platform using silk fibroin-reduced graphene oxide (SF-rGO) as bifunctional sensing active layers has been fabricated and integrated with a noncontact moisture/thermo sensor and Joule heater. As a result, the as-prepared smart sensor operated at 0.1 V exhibits good stability and sensitivity (sensor response of 60 for 97% RH) under a wide linear range of 6-97% RH, fast response/recover speed (real test: 21.51 s/85.62 s) toward touch-free humidity/temperature sensing for wearables, and thermal readings that can be accurately corrected by Joule heater. Impressively, it can achieve breath monitoring, mental state prediction, or elevator switching by identifying fingertip humidity variation. Prospectively, this all-in-one wearable smart sensor would set an example for improving sensing performance from structure-function relationship points of view and building a noncontact sensing system for daily life.

Synergistic effect of bimetallic Pd-Pt nanocrystals for highly efficient methanol oxidation electrocatalysts

Metal nanocrystals (NCs) with controlled compositional and distributional structures have gained increasing attention due to their unique properties and broad applications, particularly in fuel cell systems. However, despite the significant importance of composition in metal NCs and their electrocatalytic behavior, comprehensive investigations into the relationship between atomic distribution and electrocatalytic activity remain scarce. In this study, we present the development of four types of nanocubes with similar sizes and controlled compositions (Pd-Pt alloy, Pd@Pt core-shell, Pd, and Pt) to investigate their influence on electrocatalytic performance for methanol oxidation reaction (MOR). The electrocatalytic activity and stability of these nanocubes exhibited variations based on their compositional structures, potentially affecting the interaction between the surface-active sites of the nanocrystals and reactive molecules. As a result, leveraging the synergistic effect of their alloy nanostructure, the Pd-Pt alloy nanocubes exhibited exceptional performance in MOR, surpassing the catalytic activity of other nanocubes, including Pd@Pt core-shell nanocubes, monometallic Pd and Pt nanocubes, as well as commercial Pd/C and Pt/C catalysts.

Focus Review on Nanomaterial-Based Electrochemical Sensing of Glucose for Health Applications

Diabetes management can be considered the first paradigm of modern personalized medicine. An overview of the most relevant advancements in glucose sensing achieved in the last 5 years is presented. In particular, devices exploiting both consolidated and innovative electrochemical sensing strategies, based on nanomaterials, have been described, taking into account their performances, advantages and limitations, when applied for the glucose analysis in blood and serum samples, urine, as well as in less conventional biological fluids. The routine measurement is still largely based on the finger-pricking method, which is usually considered unpleasant. In alternative, glucose continuous monitoring relies on electrochemical sensing in the interstitial fluid, using implanted electrodes. Due to the invasive nature of such devices, further investigations have been carried out in order to develop less invasive sensors that can operate in sweat, tears or wound exudates. Thanks to their unique features, nanomaterials have been successfully applied for the development of both enzymatic and non-enzymatic glucose sensors, which are compliant with the specific needs of the most advanced applications, such as flexible and deformable systems capable of conforming to skin or eyes, in order to produce reliable medical devices operating at the point of care.

Recent Advances in Two-Dimensional MXene-Based Electrochemical Biosensors for Sweat Analysis

Sweat, a biofluid secreted naturally from the eccrine glands of the human body, is rich in several electrolytes, metabolites, biomolecules, and even xenobiotics that enter the body through other means. Recent studies indicate a high correlation between the analytes' concentrations in the sweat and the blood, opening up sweat as a medium for disease diagnosis and other general health monitoring applications. However, low concentration of analytes in sweat is a significant limitation, requiring high-performing sensors for this application. Electrochemical sensors, due to their high sensitivity, low cost, and miniaturization, play a crucial role in realizing the potential of sweat as a key sensing medium. MXenes, recently developed anisotropic two-dimensional atomic-layered nanomaterials composed of early transition metal carbides or nitrides, are currently being explored as a material of choice for electrochemical sensors. Their large surface area, tunable electrical properties, excellent mechanical strength, good dispersibility, and biocompatibility make them attractive for bio-electrochemical sensing platforms. This review presents the recent progress made in MXene-based bio-electrochemical sensors such as wearable, implantable, and microfluidic sensors and their applications in disease diagnosis and developing point-of-care sensing platforms. Finally, the paper discusses the challenges and limitations of MXenes as a material of choice in bio-electrochemical sensors and future perspectives on this exciting material for sweat-sensing applications.

Research Progress on Biomimetic Nanomaterials for Electrochemical Glucose Sensors

Diabetes has become a chronic disease that necessitates timely and accurate detection. Among various detection methods, electrochemical glucose sensors have attracted much attention because of low cost, real-time detection, and simple and easy operation. Nonenzymatic biomimetic nanomaterials are the vital part in electrochemical glucose sensors. This review article summarizes the methods to enhance the glucose sensing performance of noble metal, transition metal oxides, and carbon-based materials and introduces biomimetic nanomaterials used in noninvasive glucose detection in sweat, tear, urine, and saliva. Based on these, this review provides the foundation for noninvasive determination of trace glucose for diabetic patients in the future.