In situ formation of Co3O4 hollow nanocubes on carbon cloth-supported NiCo2O4 nanowires and their enhanced performance in non-enzymatic glucose sensing

A review of zeolitic imidazolate frameworks (ZIFs) as electrochemical sensors for important small biomolecules in human body fluids

Small biomolecules play a critical role in the fundamental processes that sustain life and are essential for the proper functioning of the human body. The detection of small biomolecules has garnered significant interest in various fields, including disease diagnosis and medicine. Electrochemical techniques are commonly employed in the detection of critical biomolecules through the principle of redox reactions. It is also a very convenient, cheap, simple, fast, and accurate measurement method in analytical chemistry. Zeolitic imidazolate frameworks (ZIFs) are a unique type of metal-organic framework (MOF) composed of porous crystals with extended three-dimensional structures. These frameworks are made up of metal ions and imidazolate linkers, which form a highly porous and stable structure. In addition to their many advantages in other applications, ZIFs have emerged as promising candidates for electrochemical sensors. Their large surface area, pore diameter, and stability make them ideal for use in sensing applications, particularly in the detection of small molecules and ions. This review summarizes the critical role of small biomolecules in the human body, the standard features of electrochemical analysis, and the utilization of various types of ZIF materials (including carbon composites, metal-based composites, ZIF polymer materials, and ZIF-derived materials) for the detection of important small biomolecules in human body fluids. Lastly, we provide an overview of the current status, challenges, and future outlook for research on ZIF materials.

Recent Progress in MOF-Based Electrochemical Sensors for Non-Enzymatic Glucose Detection

In recent years, substantial advancements have been made in the development of enzyme-free glucose sensors utilizing pristine metal-organic frameworks (MOFs) and their combinations. This paper provides a comprehensive exploration of various MOF-based glucose sensors, encompassing monometallic MOF sensors as well as multi-metal MOF combinations. These approaches demonstrate improved glucose detection capabilities, facilitated by the augmented surface area and availability of active sites within the MOF structures. Furthermore, the paper delves into the application of MOF complexes and derivatives in enzyme-free glucose sensing. Derivatives incorporating carbon or metal components, such as carbon cloth synthesis, rGO-MOF composites, and core-shell structures incorporating noble metals, exhibit enhanced electrochemical performance. Additionally, the integration of MOFs with foams or biomolecules, such as porphyrins, enhances the electrocatalytic properties for glucose detection. Finally, this paper concludes with an outlook on the future development prospects of enzyme-free glucose MOF sensors.

Recent Advances in Metal-Organic Frameworks (MOFs) and Their Composites for Non-Enzymatic Electrochemical Glucose Sensors

In recent years, with pressing needs such as diabetes management, the detection of glucose in various substrates has attracted unprecedented interest from researchers in academia and industry. As a relatively new glucose sensor, non-enzymatic target detection has the characteristics of high sensitivity, good stability and simple manufacturing process. However, it is urgent to explore novel materials with low cost, high stability and excellent performance to modify electrodes. Metal-organic frameworks (MOFs) and their composites have the advantages of large surface area, high porosity and high catalytic efficiency, which can be utilized as excellent materials for electrode modification of non-enzymatic electrochemical glucose sensors. However, MOFs and their composites still face various challenges and difficulties that limit their further commercialization. This review introduces the applications and the challenges of MOFs and their composites in non-enzymatic electrochemical glucose sensors. Finally, an outlook on the development of MOFs and their composites is also presented.

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.

Electrospun nanofiber-based glucose sensors for glucose detection

Diabetes is a chronic, systemic metabolic disease that leads to multiple complications, even death. Meanwhile, the number of people with diabetes worldwide is increasing year by year. Sensors play an important role in the development of biomedical devices. The development of efficient, stable, and inexpensive glucose sensors for the continuous monitoring of blood glucose levels has received widespread attention because they can provide reliable data for diabetes prevention and diagnosis. Electrospun nanofibers are new kinds of functional nanocomposites that show incredible capabilities for high-level biosensing. This article reviews glucose sensors based on electrospun nanofibers. The principles of the glucose sensor, the types of glucose measurement, and the glucose detection methods are briefly discussed. The principle of electrospinning and its applications and advantages in glucose sensors are then introduced. This article provides a comprehensive summary of the applications and advantages of polymers and nanomaterials in electrospun nanofiber-based glucose sensors. The relevant applications and comparisons of enzymatic and non-enzymatic nanofiber-based glucose sensors are discussed in detail. The main advantages and disadvantages of glucose sensors based on electrospun nanofibers are evaluated, and some solutions are proposed. Finally, potential commercial development and improved methods for glucose sensors based on electrospinning nanofibers are discussed.

Electrochemical sensors based on metal nanoparticles with biocatalytic activity

Biosensors have attracted a great deal of attention, as they allow for the translation of the standard laboratory-based methods into small, portable devices. The field of biosensors has been growing, introducing innovations into their design to improve their sensing characteristics and reduce sample volume and user intervention. Enzymes are commonly used for determination purposes providing a high selectivity and sensitivity; however, their poor shelf-life is a limiting factor. Researchers have been studying the possibility of substituting enzymes with other materials with an enzyme-like activity and improved long-term stability and suitability for point-of-care biosensors. Extra attention is paid to metal and metal oxide nanoparticles, which are essential components of numerous enzyme-less catalytic sensors. The bottleneck of utilising metal-containing nanoparticles in sensing devices is achieving high selectivity and sensitivity. This review demonstrates similarities and differences between numerous metal nanoparticle-based sensors described in the literature to pinpoint the crucial factors determining their catalytic performance. Unlike other reviews, sensors are categorised by the type of metal to study their catalytic activity dependency on the environmental conditions. The results are based on studies on nanoparticle properties to narrow the gap between fundamental and applied research. The analysis shows that the catalytic activity of nanozymes is strongly dependent on their intrinsic properties (e.g. composition, size, shape) and external conditions (e.g. pH, type of electrolyte, and its chemical composition). Understanding the mechanisms behind the metal catalytic activity and how it can be improved helps designing a nanozyme-based sensor with the performance matching those of an enzyme-based device.

Rationally designed NiMn LDH@NiCo2O4core-shell structures for high energy density supercapacitor and enzyme-free glucose sensor

Exploring high-efficiency and low-cost bifunctional electrodes for supercapacitors and sensors is significant but challenging. Most of the existing electrodes are mostly single-functional materials with simple structure. Herein, NiCo₂O₄nanowires as the core and NiMn layered double hydroxide (LDH) as the shell is directly grownin situon carbon cloth (CC) to form a heterostructure (NiMn LDH@NiCo₂O₄/CC). The performance in supercapacitors and enzyme-free glucose sensing has been systematically studied. Compared with a single NiCo₂O₄nanowire or NiMn LDH nanosheet, the heterogeneous interface produced by the unique core-shell structure has stronger electronic interaction and abundant active surface area, which shows excellent electrochemical performance. Electrochemical tests demonstrate that the NiMn LDH@NiCo₂O₄/CC core-shell electrode possesses an area specific capacitance of 2.40 F cm^-2and a rate capability of 76.22% at 20 mA cm^-2. Simultaneously, asymmetric supercapacitor is assembled with it as the positive electrode and NiFe LDH@NiCo₂O₄/CC as the negative electrode. The supercapacitor possesses an energy density of 47.74 Wh kg^-1when the power density is 175 W kg^-1, revealing excellent performance and maintains cycle stability of 93.48% after 6000 cycles at 10 mA cm^-2. Additionally, the electrode applied as enzyme-free glucose sensor electrode also displays outstanding sensitivity of 2139μA mM^-1cm^-2, wide detection range (2μM^-3mM and 4-8 mM) and low detection limit of 210 nM, representing good anti-interference performance. This work reveals the multi-metal synergy and rationally designed core-shell structure is critical to the electrochemical performance of bifunctional electrodes.

Developments of the Electroactive Materials for Non-Enzymatic Glucose Sensing and Their Mechanisms

A comprehensive review of the electroactive materials for non-enzymatic glucose sensing and sensing devices has been performed in this work. A general introduction for glucose sensing, a facile electrochemical technique for glucose detection, and explanations of fundamental mechanisms for the electro-oxidation of glucose via the electrochemical technique are conducted. The glucose sensing materials are classified into five major systems: (1) mono-metallic materials, (2) bi-metallic materials, (3) metallic-oxide compounds, (4) metallic-hydroxide materials, and (5) metal-metal derivatives. The performances of various systems within this decade have been compared and explained in terms of sensitivity, linear regime, the limit of detection (LOD), and detection potentials. Some promising materials and practicable methodologies for the further developments of glucose sensors have been proposed. Firstly, the atomic deposition of alloys is expected to enhance the selectivity, which is considered to be lacking in non-enzymatic glucose sensing. Secondly, by using the modification of the hydrophilicity of the metallic-oxides, a promoted current response from the electro-oxidation of glucose is expected. Lastly, by taking the advantage of the redistribution phenomenon of the oxide particles, the usage of the noble metals is foreseen to be reduced.

In situ construction of multi-dimensional Co3O4/NiCo2O4 hierarchical flakes on self-supporting carbon substrate with ultra-high capacitance for hybrid supercapacitors

Research on environmentally friendly energy storage devices is an important strategy to solve the energy crisis and environmental pollution. Herein, a novel self-supporting electrode based on multi-dimensional Co₃O₄/NiCo₂O₄ hierarchical flakes coating on graphene/carbon sphere (rGO/CS) conductive substrate is reasonably designed. Firstly, a simple hydrothermal method is used to synthesize NiCo₂O₄ with both flake and nanoneedle morphology on the rGO/CS substrate. Subsequently, Co₃O₄/NiCo₂O₄@rGO/CS is obtained by in-situ growth of metal organic frameworks polyhedrons on the surface of NiCo₂O₄ flakes followed by calcination. In the unique structure, benefitting from the synergy between the substrate and multi-element transition metal oxides, the integrated film shows good conductivity, high specific surface area and abundant active sites. Thus, the binder-free electrode exhibits an ultra-high specific capacitance of 3876.6 F g^-1 (538.4 mA h g^-1) at 1 A g^-1. A hybrid supercapacitor is assembled with activated carbon as the negative electrode and Co₃O₄/NiCo₂O₄@rGO/CS as the positive electrode, the device shows a highest energy density of 56.5 Wh kg^-1 at a power density of 800 W kg^-1. After 6000 charge-discharge cycles, 92.5% of the initial capacitance can be still maintained, indicating its good application prospects in energy storage materials.

Multifunctional book-like CuCo-MOF for highly sensitive glucose detection and electrocatalytic oxygen evolution

Bimetallic book-like CuCo-MOF were fixed on carbon fiber paper as efficient catalyst for electrochemical glucose detection and oxygen evolution reaction.

Synthesis of NiCo2O4 Nanostructures and Their Electrochemial Properties for Glucose Detection

In this work, we prepared spinel-type NiCo2O4 (NCO) nanopowders as a low-cost and sensitive electrochemical sensor for nonenzymatic glucose detection. A facile and simple chemical bath method to synthesize the NCO nanopowders is demonstrated. The effect of pH and annealing temperature on the formation mechanism of NCO nanoparticles was systematically investigated. Our studies show that different pHs of the precursor solution during synthesis result in different intermediate phases and relating chemical reactions for the formation of NCO nanoparticles. Different morphologies of the NCO depending on pHs are also discussed based on the mechanism of growth. Electrochemical performance of the prepared NCO was characterized towards glucose, which reveals that sensitivity and selectivity of the NCO are significantly related with the final microstructure combined with constituent species with multiple oxidation states in the spinel structure.

Nitrogen-doped carbon dodecahedron embedded with cobalt nanoparticles for the direct electro-oxidation of glucose and efficient nonenzymatic glucose sensing

Developing high-performance sensors for glucose detection is extremely desirable for clinical diagnostics and life sciences. Particularly, it is greatly attractive to exploit composite materials with large surface area, doped heterojunction and non-precious metal as highly active electro-catalysts for nonenzymatic glucose sensing. Herein, we reported a N-doped carbon dodecahedron embedded with Co nanoparticles (Co@NCD) for the direct electro-oxidation of glucose and efficient nonenzymatic glucose detection. Co@NCD was synthesized by the pyrolysis of zeolitic imidazolate framework (ZIF). Field emission scanning electron microscope, high-resolution transmission electron microscope, powder X-ray diffraction, X-ray photoelectron spectroscopy and nitrogen adsorption-desorption experiments were performed to investigate Co@NCD. A well-defined dodecahedron morphology with uniform size and shape was observed. Besides, the original framework was carbonized after pyrolysis leading to a hollow and porous graphite dodecahedron containing N-doped carbon heterojunction. Moreover, Co nanoparticles were evenly distributed into the dodecahedron. With porous structure, N-doped carbon and embedded Co nanoparticles, Co@NCD displayed a notable electro-catalysis towards the direct oxidation of glucose (onset potential: 0.20 V). By using Co@NCD as electro-catalyst, an efficient nonenzymatic glucose sensor was obtained with a rapid amperometric response (within 1 s), low detection limit (0.11 μM) and broad detection range (0.2 μM-12.0 mM). In addition, remarkable selectivity, repeatability, reproducibility and long-term stability were also observed. Finally, Co@NCD prepared sensor was also successfully applied to the detection of glucose in human serum. Our results suggested that ZIF templated method could be an innovative solution for active composite catalysts in biomolecular electro-catalysis and Co@NCD prepared sensor could be a substantial preferable sensing platform for the nonenzymatic glucose detection.