2D MOF with electrochemical exfoliated graphene for nonenzymatic glucose sensing: Central metal sites and oxidation potentials

Construction and Tribological Performance of Ag Nanowire-Dotted 2D Ni-BDC Nanocomposites in Oil

The collaborative lubrication effect based on different lubricating nanostructures could not only overcome the respective drawbacks of different nanostructures as nanoadditives but also comprehensively improve friction performance. For this, we first developed a novel collaborative lubrication nanostructure based on Ag nanowires (NWs) and two-dimensional (2D) Ni-BDC nanosheets (Ag NWs/2D Ni-BDC) by the in situ chemical reduction strategy. The structural characterizations corroborated that Ag NWs with a width of approximately 20-30 nm grew on the surface of 2D Ni-BDC nanosheets, which presented the chemical interface between both. As the nanoadditive applied in oils, the tribological finding confirmed that the Ag NWs/2D Ni-BDC enabled the friction coefficient and wear scar diameter to reduce by 38 and 37% at 0.04 wt % additive content, respectively. The worn surface was characterized by a series of analytical techniques, which basically revealed the friction-reducing and antiwear mechanism based on the layered structure and self-repair effect. Consequently, the nanocomposite structure incorporating the nanowire and 2D nanosheets should be taken into account as a new potential lubricating material.

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.

A non-enzymatic glucose sensor based on a mesoporous carbon sphere immobilized Co-MOF-74 nanocomposite

Exploration of credible non-enzymatic glucose sensors with high selectivity and sensitivity is of great significance for early clinical monitoring of glucose concentration and preventing the threat of diabetes to human health. Here, mesoporous carbon (MC) sphere immobilized Co-MOF-74 nanorods (NRs), denoted as Co-MOF-74 NRs/MC, were successfully prepared, in which the nanostructural porous carbon sphere was obtained using cobalt glycolate as the built-in template followed by a subsequent carbonization and acid treatment, and the MC spheres were then in situ deposited on the surface of Co-MOF-74 NRs via a solvothermal method. Benefiting from the good conductivity of the grafted porous carbon spheres and the abundant active sites, as well as the permeability of microporous MOF-74 nanocrystals, the Co-MOF-74 NRs/MC modified glassy carbon electrode (GCE) exhibited effective non-enzymatic glucose sensing performance with a fast response time (less than 3 s) and a glucose sensitivity of 98.0 μA cm-2 mM-1. Furthermore, the Co-MOF-74 NRs/MC/GCE showed a favourable anti-interference capability in the presence of various interferents and good long-term reusability. The applicability of Co-MOF-74 NRs/MC/GCE for glucose sensing in real serum samples was also investigated, verifying the applicability of the electrode for targeted glucose monitoring in practical applications.

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.

Ultra-thin 2D bimetallic MOF nanosheets for highly sensitive and stable detection of glucose in sweat for dancer

The measurement of glucose concentration in sweat is expected to replace the existing blood glucose detection, which realize the effective way of non-invasive monitoring of human glucose concentration in dancing. High precision glucose detection can be achieved by adjusting the electrode material of the sensor. Thus, in this work, the bimetallic organic frameworks (bi-MOFs) materials containing Mn and Ni ions (NiMn-MOF) with ultrathin nanosheets have been exquisitely designed. The ultrathin nanosheet and heterogeneous metal ions in the structure optimize the electronic structure, which improves the electrical conductivity of MOFs. The success of the preparation strategy leads the good electrocatalytic performance of NiMn-MOF for glucose detection. Detailedly, NiMn-MOF shows high sensitivity of 1576 μA mM-1 cm-2 in the linear range from 0 to 0.205 mM and the wide linear region of 0.255-2.655 mM and 3.655-5.655 mM were also observed. In addition, the high repeatability, reproductivity, long-term stability and ultra-low limited of detection (LOD, 0.28 μM, S/N = 3) provide foundation for the practical sensor application of this NiMn-MOF nanosheets. Remarkably, as designed NiMn-MOF sensor can accurately measure glucose in sweat showing great potential in the field of wearable glucose monitoring during dancing.

Hierarchical copper-based metal-organic frameworks nanosheet assemblies for electrochemical ascorbic acid sensing

Noninvasive human health monitoring requires the development of efficient electrochemical sensors for the quantitative analysis of infinitesimal biomolecules. In this work, we reported a novel hierarchical nanosheet assemblies (HSA) of copper-based metal-organic frameworks (MOFs) as an electrochemical sensor for ascorbic acid (AA) detection. Copper 1,4-benzenedicarboxylate (CuBDC) HSA was constructed by three steps of in situ growth on stone paper, including hydrolysis, anion exchange, and heteroepitaxy growth. The monodispersed two-dimensional MOFs nanosheet units were aligned in an orderly manner and arranged into three-dimensional hierarchical assemblies. The CuBDC HSA-based AA sensor displayed a high sensitivity of 396.8 μA mM^-1 cm^-2 and a low detection limit of 0.1 μM. Excellent selectivity, stability and reproducibility were also obtained. Benefiting from the advantages of ultrathin nanosheets and nature-inspired hierarchy, this unique architecture facilitated reactant dispersion and maximized the accessible active sites and charge-transport capability and thus had superior catalytic ability for the electro-oxidation of ascorbic acid compared to bulk MOFs. Moreover, the CuBDC HSA sensor performed AA level detection in juice samples with acceptable accuracy and verified the feasibility for sweat AA sensing. This novel MOFs architecture holds great potential as an electrochemical sensor to detect AA for noninvasive human health monitoring in the future.

Exfoliation of metal-organic framework nanosheets using surface acoustic waves

Two-dimensional (2D) metal-organic framework (MOF) nanosheets have recently received extensive attention due to their ultra-thin thickness, large specific surface area, chemical and functional designability. In this study, an unconventional method using surface acoustic wave (SAW) technology is proposed to exfoliate large quantities and uniform layers of 2D MOF-Zn₂(bim)₄ nanosheets in a microfluidic system. We successfully demonstrated that the thickness of 2D MOF is effectively and accurately controlled by optimizing the SAW parameters. The mechanisms for the efficient exfoliation of 2D MOF nanosheets is attributed to both the electric and acoustic fields generated by the SAWs in the liquid. The electric field ionizes the methanol to produce H⁺ ions, which intercalate Zn₂(bim)₄ sheets and weaken the interlayer bonding, and the strong shear force generated by SAWs separates the MOF sheets. A yield of 66% for monolayer MOFs with a maximum size of 3.5 μm is achieved under the combined effect of electric and acoustic fields. This fast, low-energy exfoliation platform has the potential to provide a simple and scalable microfluidic exfoliation method for production of large-area and quantities of 2D MOFs.

Colorimetric quantification of sodium benzoate in food by using d-amino acid oxidase and 2D metal organic framework nanosheets mediated cascade enzyme reactions

A rapid colorimetric method for detecting sodium benzoate in food products was established based on the d-amino acid oxidase (DAAO) and 2D metal organic framework (2D MOF) nanosheets mediated cascade enzyme reactions. Firstly, the synthesized 2D MOF nanosheets served as high efficient nanozyme with outstanding peroxidase-like catalytic activity and catalyzed the color reaction between H₂O₂ and 3, 3', 5, 5'- tetramethylbenzidine. Secondly, sodium benzoate as a competitive inhibitor of DAAO, could influence the production of H₂O₂ in DAAO mediated oxidation reaction. After a combination of those two reactions, this colorimetric quantitative method was constructed and validated for sodium benzoate determination with wide linear range (2.0-200.0 μM), low limit of detection (2.0 μM), high accuracy (recovery rate in 95.80-108.00%) and satisfied selectivity. Lastly, this method was utilized to analyze sodium benzoate concentration in juice, wine and vinegar by naked eyes.

Cost Effective Synthesis of Graphene Nanomaterials for Non-Enzymatic Electrochemical Sensors for Glucose: A Comprehensive Review

The high conductivity of graphene material (or its derivatives) and its very large surface area enhance the direct electron transfer, improving non-enzymatic electrochemical sensors sensitivity and its other characteristics. The offered large pores facilitate analyte transport enabling glucose detection even at very low concentration values. In the current review paper we classified the enzymeless graphene-based glucose electrocatalysts' synthesis methods that have been followed into the last few years into four main categories: (i) direct growth of graphene (or oxides) on metallic substrates, (ii) in-situ growth of metallic nanoparticles into graphene (or oxides) matrix, (iii) laser-induced graphene electrodes and (iv) polymer functionalized graphene (or oxides) electrodes. The increment of the specific surface area and the high degree reduction of the electrode internal resistance were recognized as their common targets. Analyzing glucose electrooxidation mechanism over Cu- Co- and Ni-(oxide)/graphene (or derivative) electrocatalysts, we deduced that glucose electrochemical sensing properties, such as sensitivity, detection limit and linear detection limit, totally depend on the route of the mass and charge transport between metal(II)/metal(III); and so both (specific area and internal resistance) should have the optimum values.

Ultrasmall Au nanoparticles modified 2D metalloporphyrinic metal-organic framework nanosheets with high peroxidase-like activity for colorimetric detection of organophosphorus pesticides

Ultrasmall Au nanoparticles (UsAuNPs) in the size range of 4.0-7.0 nm was successfully immobilized on the surface of 2D metalloporphyrinic metal-organic framework nanosheets (2D MOF). Firstly, The obtained hybrid nanomaterial, UsAuNPs/2D MOF, was fully characterized by TEM, HRTEM, element mapping images and XPS. Then, the peroxidase-like activity of UsAuNPs/2D MOF was comparatively studied with other hybrid nanozyme to explore the influence of AuNPs size on peroxidase-like activity. Further, UsAuNPs/2D MOF with outstanding peroxidase-like activity was selected to form ternary cascade enzyme reaction with acetylcholinesterase (AChE) and choline oxidase (ChOx). Based on the inhibitory effect of organophosphorus pesticides on AChE, a fast and sensitive colorimetric method was established for trichlorfon detection with the advantages of simple operation, low detection limit (1.7 μM), good linear range (1.7-42.4 μM) and high accuracy (recovery rate of 96.6-105.3%). Finally, this method was applied to visual analysis of trichlorfon concentration in tomatoes, cucumbers and eggplants.

MOF@COF Heterostructure Hybrid for Dual-Mode Photoelectrochemical-Electrochemical HIV-1 DNA Sensing

We developed a novel metal-organic framework (MOF)@covalent-organic framework (COF) hybrid with a hierarchical nanostructure and excellent photoactivity, which further acted as the bifunctional platform of a dual-mode photoelectrochemical (PEC) and electrochemical (EC) biosensor for detecting HIV-1 DNA via immobilizing the HIV-1 DNA probe. First, the presynthesized Cu-MOF nanoellipsoids were used as the template for the in situ growth of the COF network, which was synthesized using copper-phthalocyanine tetra-amine (CoPc-TA) and 2,9-bis[p-(formyl)phenyl]-1,10-phenanthroline as building blocks through the Schiff base condensation. In view of the large specific surface area, abundant reserved amino group, excellent electrochemical activity, and high photoactivity, the obtained Cu-MOF@CuPc-TA-COF heterostructure not only can serve as the sensitive platform for anchoring the HIV-1 DNA probe strands but also can be utilized as the signal transducers for PEC and EC biosensors. Thereby, the constructed biosensor shows the sensitive and selective analysis ability toward the HIV-1 target DNA via the complementary hybridization between probe and target DNA strands. The dual-mode PEC and EC measurements revealed that the Cu-MOF@CuPc-TA-COF-based biosensor displayed a wide linear detection range from 1 fM to 1 nM and an extremely low limit of detection (LOD) of 0.07 and 0.18 fM, respectively. In addition, the dual-mode PEC-EC biosensor also demonstrated remarkable selectivity, high stability, good reproducibility, and preferable regeneration ability, as well as acceptable applicability, for which the detected HIV-1 DNA in human serum showed good consistency with real concentrations. Thereby, the present work can open a new dual-mode PEC-EC platform for detecting HIV-1 DNA based on the porous-organic framework heterostructure.

Metal-Organic-Framework- and MXene-Based Taste Sensors and Glucose Detection

Taste sensors can identify various tastes, including saltiness, bitterness, sweetness, sourness, and umami, and have been useful in the food and beverage industry. Metal-organic frameworks (MOFs) and MXenes have recently received considerable attention for the fabrication of high-performance biosensors owing to their large surface area, high ion transfer ability, adjustable chemical structure. Notably, MOFs with large surface areas, tunable chemical structures, and high stability have been explored in various applications, whereas MXenes with good conductivity, excellent ion-transport characteristics, and ease of modification have exhibited great potential in biochemical sensing. This review first outlines the importance of taste sensors, their operation mechanism, and measuring methods in sensing utilization. Then, recent studies focusing on MOFs and MXenes for the detection of different tastes are discussed. Finally, future directions for biomimetic tongues based on MOFs and MXenes are discussed.

Nanosized CuO encapsulated Ni/Co bimetal Prussian blue with high anti-interference and stability for electrochemical non-enzymatic glucose detection

Non-enzymatic glucose sensors based on metal oxides are receiving remarkable attention owing to their outstanding characteristics of being easy-to use, low cost, and reusability. However, the disadvantage of weak anti-interference associated with poor selectivity significantly restricts their applicability. Herein, we report a two-step in situ fabrication of nanosized CuO encapsulated Ni/Co bimetal Prussian blue (PB) with a typical core-shell structure, which can be efficiently used for non-enzymatic glucose detection, ascribing to the permeability and abundant active sites of out-shelled crystalline porous Ni/Co PB and the high catalytic activity and conductivity of embedded CuO nanoparticles, afforded by their mutual synergistic interactions. The glassy carbon electrode modified with the hybrid of the CuO-encapsulated Ni/Co PB (simplified as the Ni/Co-PB/CuO/GCE electrode) exhibited a high glucose sensitivity of 600 μA mM-1 cm-2 with a low detection limit of 0.69 μM (S/N = 3), a fast response time (less than 3 s), and excellent long-term stability. In addition, the CuO-encapsulated Ni/Co PB showed favorable anti-interference ability in the presence of ascorbic acid (AA), L-lysine (Lys), dopamine (DA), cysteine (Cys), dopamine (DA), and KCl interferences. The reusability and long-term stability, as well as the practicability of the Ni/Co-PB/CuO/GCE sensing electrode verified by testing real serum samples were also investigated, and the experimental results demonstrated the applicability of the core-shell NiCo-PB/CuO based flexible electrochemical sensor for non-enzymatic glucose sensing in practical applications.

Monodispersed Ni active sites anchored on N-doped porous carbon nanosheets as high-efficiency electrocatalyst for hydrogen peroxide sensing

Metal active species combined with N-doped porous carbon nanosheets usually own excellent electrochemical activity and sensing performance owing to its unique microstructure and composition. In this work, monodispersed Ni active sites anchored on N-doped porous carbon nanosheets (Ni@N-PCN) were facilely prepared via rational metal-organic frameworks (MOFs) route. Firstly, zeolitic imidazolate frameworks-8 (ZIF-8) was in situ grown on physically-exfoliated graphene nanosheets (GN) with homogeneous sandwich-like structure (ZIF-8@GN). Secondly, nickel bonded ZIF-8@GN hybrids (Ni/ZIF-8@GN) were obtained by ionic exchange reaction, and then transformed into Ni@N-PCN by high-temperature pyrolysis. Benefiting from the monodispersed Ni active sites and highly reactive N-doped porous carbon nanosheets (N-PCN), the as-prepared Ni@N-PCN hybrids displayed superior catalytic performance toward hydrogen peroxide (H₂O₂) sensing. As a result, a highly sensitive electrochemical sensing platform for H₂O₂ was fabricated with low detection limit (0.032 μM), wide detection linearity (0.2-2332.8 μM), and high sensitivity (6085 μA cm^-2 mM^-1). Besides, the as-developed electrochemical sensing platform was successfully applied to detect H₂O₂ contents in biological medicine and food specimens with satisfied results. This study will provide effective guidance for the preparation of novel metal/N-doped carbon nanomaterials and establishment of high-performance electrochemical sensors.

Facile synthesis of Cu/Co-ZIF nanoarrays for non-enzymatic glucose detection

Cu/Co-ZIF nanoflake arrays on carbon cloth are fabricated by controlling the introducing of Cu²⁺ions during the growth of Co-ZIF. The Cu/Co-ZIF-20 electrode prepared with 20 mM Cu²⁺possesses large electrochemically active surface area and bimetallic active sites, which can be revealed by cyclic voltammetry tests. The amperometrici-tmeasurements demonstrate that the Cu/Co-ZIF-20 electrode displays a wide linear range from 0.05 mM to 6.0 mM, and a high sensitivity of 1.03 mA mM^-1cm^-2. Good selectivity, repeatability and practical applicability indicate its promising application in enzyme-free glucose sensing.

Magnetic mesoporous carbon nanosheets derived from two-dimensional bimetallic metal-organic frameworks for magnetic solid-phase extraction of nitroimidazole antibiotics

We prepared two-dimensional (2D) bimetallic metal-organic frameworks (Ni-ZIF-8) nanosheets by a simple solvent-free method at room temperature. The morphology and composition of Ni-ZIF-8 can be controlled through adding different amounts of Ni. And then, the 2D magnetic mesoporous nanosheets (Ni/ZnO@C) were synthesized by directly pyrolyzing Ni-ZIF-8 under argon atmosphere and explored as magnetic solid phase extraction (MSPE) adsorbents for the determination of nitroimidazole antibiotics (NIABs). Magnetic Ni nanoparticles embedded in carbon nanosheets uniformly resulted in high magnetization saturation of Ni/ZnO@C for easy separation. The Ni/ZnO@C can form hydrogen bond and π-π interaction with three NIABs resulting from their rich N-H containing imidazole, π-electron. Due to the high specific surface area and high mass transfer rate of 2D Ni/ZnO@C, the materials showed satisfactory adsorption capacity and rapid adsorption kinetics for NIABs. A rapid and effective method of Ni/ZnO@C-MSPE combined with high-performance liquid chromatography was proposed for the determination of NIABs. Several main parameters affecting MSPE were investigated. Under the optimal conditions, wide linear was achieved ranging from 0.1 to 500 µg⋅L^-1 with a low detection limit of 0.025-0.05 µg⋅L^-1. The established method has been successfully applied to analyze NIABs from environmental water samples with satisfactory recovery from 74.33 to 105.71%.

A high-performance Co-MOF non-enzymatic electrochemical sensor for glucose detection

The non-enzymatic [Ch]2[Co3(BDC)3Cl2]/GCE electrocatalyst can rapidly detect glucose with high accuracy and reliability in both human serum and orange juice.