A Novel CuxO Nanoparticles@ZIF-8 Composite Derived from Core-Shell Metal-Organic Frameworks for Highly Selective Electrochemical Sensing of Hydrogen Peroxide

Recent Advances in MOF-Based Materials for Biosensing Applications

Metal-organic frameworks (MOFs) or coordination polymers have gained enormous interest in recent years due to their extraordinary properties, including their high surface area, tunable pore size, and ability to form nanocomposites with various functional materials. MOF materials possess redox-active properties that are beneficial for electrochemical sensing applications. Furthermore, the tunable pore size and high surface area improve the adsorption or immobilization of enzymes, which can enhance the sensitivity and selectivity for specific analytes. Additionally, MOF-derived metal sulfides, phosphides, and nitrides demonstrate superior electrical conductivity and structural stability, ideal for electrochemical sensing. Moreover, the functionalization of MOFs further increases sensitivity by enhancing electrode-analyte interactions. The inclusion of carbon materials within MOFs enhances their electrical conductivity and reduces background current through optimized loading, preventing agglomeration and ensuring uniform distribution. Noble metals immobilized on MOFs offer improved stability and catalytic performance, providing larger surface areas and uniform nanoparticle dispersion. This review focuses on recent developments in MOF-based biosensors specifically for glucose, dopamine, H2O2, ascorbic acid, and uric acid sensing.

Electrochemical detection of myoglobin using an ultrasensitive label-free sensor derived from cubic-ZIF67@Au-rGOF-NH2 composite of MOF and GOF

Markers of myocardial injury, such as myoglobin (Mb), are substances swiftly released into the peripheral bloodstream upon myocardial cell injury or altered cardiac activity. During the onset of acute myocardial infarction, patients experience a significant surge in serum Mb levels. Given this, precise detection of Mb is essential, necessitating the development of innovative assays to optimize detection capabilities. This study introduces the synthesis of a three-dimensional hierarchical nanocomposite, Cubic-ZIF67@Au-rGOF-NH2, utilizing aminated reduced graphene oxide and zeolite imidazolium ester framework-67 (ZIF67) as foundational structures. Notably, this novel material, applied in a label-free electrochemical immunosensor, presents a groundbreaking approach for detecting myocardial injury markers. Experimental outcomes revealed ZIF67 and AuNPs exhibit enhanced affinity and growth on the 3D-rGOF-NH2 matrix, thus amplifying electrical conductivity while preserving the inherent electrochemical attributes of ZIF67. As a result, the Cubic-ZIF67@Au-rGOF-NH2 label-free electrochemical immunosensor exhibited a broad detection range and high sensitivity for Mb. The derived standard curve was ΔIp = 16.67552lgC+275.245 (R = 0.993) with a detection threshold of 3.47 fg/ml. Moreover, recoveries of standards spiked into samples ranged between 96.3% and 108.7%. Importantly, the devised immunosensor retained notable selectivity against non-target proteins, proving its potential clinical utility based on exemplary sample analysis performance.

Surface modification prepared porous copper oxide/(Cu-S)n metal-organic framework/reduced graphene oxide hierarchical structure for highly selective electrochemical quercetin detection

Electrochemical alkalization of (Cu-S)n metal-organic framework (MOF) and graphene oxide ((Cu-S)n MOF/GO) composite yields a new CuO/(Cu-S)n MOF/RGO (reduced GO) composite with porous morphology on screen printed carbon electrode (SPCE) which facilitated the electron transfer properties in electrochemical quercetin (QUE) detection. A selective QUE detection ability has been demonstrated by the constructed electrochemical sensor (CuO/(Cu-S)n MOF/RGO/SPCE), which also has a broad dynamic range of 0.5 to 115 µM in pH 3 by differential pulse voltammetry. The detection limit is 0.083 µM (S/N = 3). In this study, it was  observed that the real samples contained 0.34 mg mL-1 and 27.7 µg g-1 QUE in wine and onion, respectively.

A MOF@Metal Oxide Heterostructure Induced by Post-Synthetic Gamma-Ray Irradiation for Catalytic Reduction

Metal-organic framework (MOF) based heterostructures, which exhibit enhanced or unexpected functionality and properties due to synergistic effects, are typically synthesized using post-synthetic strategies. However, several reported post-synthetic strategies remain unsatisfactory, considering issues such as damage to the crystallinity of MOFs, presence of impure phases, and high time and energy consumption. In this work, we demonstrate for the first time a novel route for constructing MOF based heterostructures using radiation-induced post-synthesis, highlighting the merits of convenience, ambient conditions, large-scale production, and notable time and energy saving. Specifically, a new HKUST-1@Cu2O heterostructure was successfully synthesized by simply irradiating a methanol solution dispersed of HKUST-1 with gamma ray under ambient conditions. The copper source of Cu2O was directly derived from in situ radiation etching and reduction of the parent HKUST-1, without the use of any additional copper reagents. Significantly, the resulting HKUST-1@Cu2O heterostructure exhibits remarkable catalytic performance, with a catalytic rate constant nearly two orders of magnitude higher than that of the parent HKUST-1.

In Situ Exfoliation Growth Strategy Realizing Controlled Synthesis of 3D to 2D MOF Materials as High-Performance Electrochemical Biosensors

Two-dimensional (2D) metal-organic framework (MOF) nanosheets with large surface area, ultrathin thickness, and highly accessible active sites have attracted great research attention. Developing efficient approaches to realize the controllable synthesis of well-defined 2D MOFs with a specific composition and morphology is critical. However, it is still a significant challenge to construct thin and uniform 2D MOF nanosheets and resolve the reagglomeration as well as poor stability of target 2D MOF products. Here, an "in situ exfoliation growth" strategy is proposed, where a one-step synthetic process can realize the successful fabrication of PBA/MIL-53(NiFe)/NF nanosheets on the surface of nickel foam (NF) via in situ conversion and exfoliation growth strategies. The PBA/MIL-53(NiFe)/NF nanosheets combine the individual advantages of MOFs, Prussian blue analogues (PBAs), and 2D materials. As expected, the resulting PBA/MIL-53(NiFe)/NF as a glucose electrode exhibits an extremely high sensitivity of 25.74 mA mM-1 cm-2 in a very wide concentration range of 180 nM to 4.8 μM. The present exciting work provides a simple and effective strategy for the construction of high-performance nonenzymatic glucose electrochemical biosensors.

A Review on Recent Trends and Future Developments in Electrochemical Sensing

Electrochemical methods and devices have ignited prodigious interest for sensing and monitoring. The greatest challenge for science is far from meeting the expectations of consumers. Electrodes made of two-dimensional (2D) materials such as graphene, metal-organic frameworks, MXene, and transition metal dichalcogenides as well as alternative electrochemical sensing methods offer potential to improve selectivity, sensitivity, detection limit, and response time. Moreover, these advancements have accelerated the development of wearable and point-of-care electrochemical sensors, opening new possibilities and pathways for their applications. This Review presents a critical discussion of the recent developments and trends in electrochemical sensing.

MOFs for Ultrahigh Efficiency Pulsed Laser Micropropulsion

Conventional propellant materials, such as polymers and single metal elements, have long been investigated for their potential in pulsed laser micropropulsion (LMP) technology. However, achieving superior LMP efficiency through physical mixing of these materials remains a significant challenge. This study presents a paradigm shift by introducing porous crystalline polymers, known as metal-organic frameworks (MOFs), as novel propellants in pulsed LMP. MOFs are composed of metal cations and organic ligands that form ordered structures through coordination, eliminating the problem of local hot zones arising from uneven physical mixing encountered in LMP. In direct comparison to conventional polymers and single element targets, MOFs exhibit substantially higher LMP efficiency. By precisely tailoring the metal atom fraction within MOFs, an extraordinary ultrahigh efficiency of 51.15% is achieved in pulsed LMP, surpassing the performance of similar materials previously reported in the literature. This pioneering application of MOFs not only revolutionizes the field of LMP but also opens up new frontiers for MOF utilization in various energy applications.

Construction of continuous flow catalytic reactor-HPLC system with ultrahigh catalytic activity using 2D nanoflower MOF-derived Cu2O/Cu/PDA/CF catalyst

Currently, metal-organic frameworks (MOFs) derived materials have been widely concerned for the reduction of 4-nitrophenol (4-NP). However, complex recovery of powder catalysts and low utilization ratio of active sites make their application challenging. Herein, a novel Cu2O/Cu/PDA/CF catalyst has been developed for the rapid reduction of 4-NP to 4-aminophenol (4-AP). The catalyst was constructed by compositing a two-dimensional nanoflower MOF-derived nanoporous Cu2O/Cu network on a polydopamine (PDA)-modified porous copper foam by a mild and controllable in-situ reduction synthesis. Notably, an enhanced catalytic performance of Cu2O/Cu/PDA/CF was obtained for 4-NP reduction with a rate constant (k) of 0.8001 min-1, outperforming Cu/PDA/CF-X (X = 400, 500 and 600 ℃ pyrolysis temperature) catalysts (2.3-6.4 folds), and even many reported catalysts (2.3-46.5 folds). The ultrafast degradation of 4-NP was completed in 70 s. Moreover, an ingenious online continuous flow catalytic reactor (CFCR)-high performance liquid chromatography (HPLC) system was constructed for automatic and real-time monitoring of the reduction reaction. System stability experiments over 300 min revealed a surprisingly high reaction k value of 76.68 min-1 at low NaBH4 usage, significant increasing by 2-3 orders of magnitude compared with Cu2O/Cu/PDA/CF batch catalysis, due to the high aspect ratio of 2D nanoflower MOF and convection-accelerated mass transfer. This work offers new insights for the rational design of catalytic reactor and its potential application in wastewater treatment.

Gram-scale synthesis of MIL-125 nanoparticles and their solution processability

Although metal-organic framework (MOF) photocatalysts have become ubiquitous, basic aspects of their photoredox mechanisms remain elusive. Nanosizing MOFs enables solution-state techniques to probe size-dependent properties and molecular reactivity, but few MOFs have been prepared as nanoparticles (nanoMOFs) with sufficiently small sizes. Here, we report a rapid reflux-based synthesis of the photoredox-active MOF Ti8O8(OH)4(terephthalate)6 (MIL-125) to achieve diameters below 30 nm in less than 2 hours. Whereas MOFs generally require ex situ analysis by solid-state techniques, sub-30 nm diameters ensure colloidal stability for weeks and minimal light scattering, permitting in situ analysis by solution-state methods. Optical absorption and photoluminescence spectra of free-standing colloids provide direct evidence that the photoredox chemistry of MIL-125 involves Ti3+ trapping and charge accumulation onto the Ti-oxo clusters. Solution-state potentiometry collected during the photochemical process also allows simultaneous measurement of MOF Fermi-level energies in situ. Finally, by leveraging the solution-processability of these nanoparticles, we demonstrate facile preparation of mixed-matrix membranes with high MOF loadings that retain the reversible photochromism. Taken together, these results demonstrate the feasibility of a rapid nanoMOF synthesis and fabrication of a photoactive membrane, and the fundamental insights they offer into heterogeneous photoredox chemistry.

Metal-organic framework glass composites

The melting phenomenon in metal-organic frameworks (MOFs) has been recognised as one of the fourth generation MOF paradigm behaviours. Molten MOFs have high processibility for producing mechanically robust glassy MOF macrostructures, and they also offer highly tunable interfacial characteristics when combined with other types of functional materials, such as crystalline MOFs, inorganic glass and metal halide perovskites. As a result, MOF glass composites have emerged as a family of functional materials with dynamic properties and hierarchical structural control. These nanocomposites allow for sophisticated materials science studies as well as the fabrication of next-generation separation, catalysis, optical, and biomedical devices. Here, we review the approaches for designing, fabricating, and characterising MOF glass composites. We determine the key application opportunities enabled by these composites and explore the remaining hurdles, such as improving thermal and chemical compatibility, regulating interfacial properties, and scalability.

Electrochemical aptasensor based on the engineered core-shell MOF nanostructures for the detection of tumor antigens

It is essential to develop ultrasensitive biosensors for cancer detection and treatment monitoring. In the development of sensing platforms, metal-organic frameworks (MOFs) have received considerable attention as potential porous crystalline nanostructures. Core-shell MOF nanoparticles (NPs) have shown different diversities, complexities, and biological functionalities, as well as significant electrochemical (EC) properties and potential bio-affinity to aptamers. As a result, the developed core-shell MOF-based aptasensors serve as highly sensitive platforms for sensing cancer biomarkers with an extremely low limit of detection (LOD). This paper aimed to provide an overview of different strategies for improving selectivity, sensitivity, and signal strength of MOF nanostructures. Then, aptamers and aptamers-modified core-shell MOFs were reviewed to address their functionalization and application in biosensing platforms. Additionally, the application of core-shell MOF-assisted EC aptasensors for detection of several tumor antigens such as prostate-specific antigen (PSA), carbohydrate antigen 15-3 (CA15-3), carcinoembryonic antigen (CEA), human epidermal growth factor receptor-2 (HER2), cancer antigen 125 (CA-125), cytokeratin 19 fragment (CYFRA21-1), and other tumor markers were discussed. In conclusion, the present article reviews the advancement of potential biosensing platforms toward the detection of specific cancer biomarkers through the development of core-shell MOFs-based EC aptasensors.

Electrochemical-Based Sensing Platforms for Detection of Glucose and H2O2 by Porous Metal-Organic Frameworks: A Review of Status and Prospects

Establishing enzyme-free sensing assays with great selectivity and sensitivity for glucose and H₂O₂ detection has been highly required in biological science. In particular, the exploitation of nanomaterials by using noble metals of high conductivity and surface area has been widely investigated to act as selective catalytic agents for molecular recognition in sensing platforms. Several approaches for a straightforward, speedy, selective, and sensitive recognition of glucose and H₂O₂ were requested. This paper reviews the current progress in electrochemical detection using metal-organic frameworks (MOFs) for H₂O₂ and glucose recognition. We have reviewed the latest electrochemical sensing assays for in-place detection with priorities including straightforward procedure and manipulation, high sensitivity, varied linear range, and economic prospects. The mentioned sensing assays apply electrochemical systems through a rapid detection time that enables real-time recognition. In profitable fields, the obstacles that have been associated with sample preparation and tool expense can be solved by applying these sensing means. Some parameters, including the impedance, intensity, and potential difference measurement methods have permitted low limit of detections (LODs) and noticeable durations in agricultural, water, and foodstuff samples with high levels of glucose and H₂O₂.

Recent advances in metal-based nanoporous materials for sensing environmentally-related biomolecules

Highly sensitive, stable, selective, efficient, and short reaction time sensors play a substantial role in daily life/industry and are the need of the day. Due to the rising environmental issues, nanoporous carbon and metal-based materials have attracted significant attention in environmental analysis owing to their intriguing and multifunctional properties and cost-effective and rapid detection of different analytes by sensing applications. Environmental-related issues such as pollution have been a significant threat to the world. Therefore, it is necessary to fabricate highly promising performance-based sensor materials with excellent reliability, selectivity and good sensitivity for monitoring various analytes. In this regard, different methods have been employed to fabricate these sensors comprising metal, metal oxides, metal oxide carbon composites and MOFs leading to the formation of nanoporous metal and carbon composites. These composites have exceptional properties such as large surface area, distinctive porosity, and high conductivity, making them promising candidates for several versatile sensing applications. This review covers recent advances and significant studies in the sensing field of various nanoporous metal and carbon composites. Key challenges and future opportunities in this exciting field are also part of this review.

Ultrasmall Copper Nanoclusters in Zirconium Metal-Organic Frameworks for the Photoreduction of CO2

Encapsulating ultrasmall Cu nanoparticles inside Zr-MOFs to form core-shell architecture is very challenging but of interest for CO₂ reduction. We report for the first time the incorporation of ultrasmall Cu NCs into a series of benchmark Zr-MOFs, without Cu NCs aggregation, via a scalable room temperature fabrication approach. The Cu NCs@MOFs core-shell composites show much enhanced reactivity in comparison to the Cu NCs confined in the pore of MOFs, regardless of their very similar intrinsic properties at the atomic level. Moreover, introducing polar groups on the MOF structure can further improve both the catalytic reactivity and selectivity. Mechanistic investigation reveals that the Cu^I sites located at the interface between Cu NCs and support serve as the active sites and efficiently catalyze CO₂ photoreduction. This synergetic effect may pave the way for the design of low-cost and efficient catalysts for CO₂ photoreduction into high-value chemical feedstock.

Sensing performance and mechanism of carbon dots encapsulated into metal-organic frameworks

Metal-organic frameworks (MOFs) can be combined with nanomaterials and the combined composites have excellent optical properties. Carbon dots (CDs) with tiny particle size, non-toxic and rich surface functional groups are novel fluorescent materials. Carbon dots@metal-organic frameworks (CDs@MOFs) are synthesized by encapsulating CDs into MOFs. CDs@MOFs are promising composites for the preparation of a new generation of fluorescence sensors, which combine the hybrid properties of MOFs and the special optical properties of CDs. Urged as such, we are encouraged to categorize according to the sensing mechanisms. These include fluorescence resonance energy transfer (FRET), aggregation-caused quenching (ACQ), static quenching, dynamic quenching, photo-induced electron transfer (PET), inner filter effect (IFE) and so on. Based on the above mechanisms, CDs@MOFs can specifically interact with target analytes to generate fluorescence quenching. This review covers the research progress of CDs@MOFs in recent five years (with 103 refs), synthetic design of CDs@MOFs and introduces the sensing mechanism. The current challenges and future research directions are discussed briefly. The sensing mechanism and applications of CDs@MOFs.

In situ electrochemical reductive construction of metal oxide/metal-organic framework heterojunction nanoarrays for hydrogen peroxide sensing

Transition metal oxide/metal-organic framework heterojunctions (TMO@MOF) that combine the large specific surface area of MOFs with TMOs' high catalytic activity and multifunctionality, show excellent performances in various catalytic reactions. Nevertheless, the present preparation approaches of TMO@MOF heterojunctions are too complex to control, stimulating interests in developing simple and highly controllable methods for preparing such heterojunction. In this study, we propose an in situ electrochemical reduction approach to fabricating Cu₂O nanoparticle (NP)@CuHHTP heterojunction nanoarrays with a graphene-like conductive MOF CuHHTP (HHTP is 2,3,6,7,10,11-hexahydroxytriphenylene). We have discovered that size-controlled Cu₂O nanoparticles could be in situ grown on CuHHTP by applying different electrochemical reduction potentials. Also, the obtained Cu₂O NP@CuHHTP heterojunction nanoarrays show high H₂O₂ sensitivity of 8150.6 μA·mM^-1·cm² and satisfactory detection performances in application of measuring H₂O₂ concentrations in urine and serum samples. This study offers promising guidance for the synthesis of MOF-based heterojunctions for early cancer diagnosis.

Recent advancements in metal-organic frameworks composites based electrochemical (bio)sensors

Metal-organic frameworks (MOFs) are a novel class of crystalline materials which find widespread applications in the field of microporous conductors, catalysis, separation, biomedical engineering, and electrochemical sensing. With a specific emphasis on the MOF composites for electrochemical sensor applications, this review summarizes the recent construction strategies on the development of conductive MOF composites (post-synthetic modification of MOFs, in situ synthesis of functional materials@MOFs composites, and incorporating electroactive ligands). The developed composites are revealed to have excellent electrochemical sensing activity better than their pristine forms. Notably, the applicable functionalized MOFs to electrochemical sensing/biosensing of various target species are discussed. Finally, we highlight the perspectives and challenges in the field of electrochemical sensors and biosensors for potential directions of future development.

Core-shell Cu@C@ZIF-8 composite: a high-performance electrode material for electrochemical sensing of nitrite with high selectivity and sensitivity

Herein, an efficient electrochemical sensing platform is proposed for selective and sensitive detection of nitrite on the basis of Cu@C@Zeolitic imidazolate framework-8 (Cu@C@ZIF-8) heterostructure. core-shell Cu@C@ZIF-8 composite was synthesized by pyrolysis of Cu-metal-organic framework@ZIF-8 (Cu-MOF@ZIF-8) in Ar atmosphere on account of the difference of thermal stability between Cu-MOF and ZIF-8. For the sensing system of Cu@C@ZIF-8, ZIF-8 with proper pore size allows nitrite diffuse through the shell, while big molecules cannot, which ensures high selectivity of the sensor. On the other hand, Cu@C as electrocatalyst promotes the oxidation of nitrite, thereby resulting high sensitivity of the sensor. Accordingly, the Cu@C@ZIF-8 based sensor presents excellent performance for nitrite detection, which achieves a wide linear response range of 0.1-300.0μM, and a low limit of detection of 0.033μM. In addition, the Cu@C@ZIF-8 sensor possesses excellent stability and reproducibility, and was employed to quantify nitrite in sausage samples with recoveries of 95.45%-104.80%.

Metal organic frameworks for electrochemical sensor applications: A review

Metal-organic frameworks (MOFs) are broadly known as porous coordination polymers, synthesized by metal-based nodes and organic linkers. MOFs are used in various fields like catalysis, energy storage, sensors, drug delivery etc., due to their versatile properties (tailorable pore size, high surface area, and exposed active sites). This review presents a detailed discussion of MOFs as an electrochemical sensor and their enhancement in the selectivity and sensitivity of the sensor. These sensors are used for the detection of heavy metal ions like Cd²⁺, Pb²⁺, Hg²⁺, and Cu²⁺ from groundwater. Various types of organic pollutants are also detected from the water bodies using MOFs. Furthermore, electrochemical sensing of antibiotics, phenolic compounds, and pesticides has been explored. In addition to this, there is also a detailed discussion of metal nano-particles and metal-oxide based composites which can sense various compounds like glucose, amino acids, uric acid etc. The review will be helpful for young researchers, and an inspiration to future research as challenges and future opportunities of MOF-based electrochemical sensors are also reported.

Process of metal-organic framework (MOF)/covalent-organic framework (COF) hybrids-based derivatives and their applications on energy transfer and storage

The fossil-fuel shortage and severe environmental issues have posed ever-increasing demands on clean and renewable energy sources, for which the exploration of electrocatalysts has been a big challenge toward energy transfer and storage. Some indispensable features of electrocatalysts, such as large surface area, controlled structure, high porosity, and effective functionalization, have been proved to be critical for the improvement of electrocatalytic activities. Recently, the rapid expansion of metal-organic frameworks (MOFs), covalent-organic frameworks (COFs), and porous-organic polymers has provided extensive opportunities for the development of various electrocatalysts. Moreover, combining diverse descriptions of porous-organic frameworks (such as MOFs and COFs) can generate amazing and fantastic properties, affording the formed MOF/COF (including core-shell MOF@MOF and MOF@COF and layer-on-layer MOF-on-MOF or COF-on-MOF) heterostructures wide applications in diverse fields, especially in clean energy and energy transfer. To further boosts electronic conductivity, catalytic performances, and energy storage abilities, these MOF/COF hybrid materials have been widely utilized as versatile precursors for the manufacture of transition metal catalysts embedded within mesoporous carbon nitrides (M@CN_x) and porous carbon nitride frameworks (CN_x) via a facile pyrolysis process. Given that these M@CN_x and CN_x hybrids are composed of abundant catalytic centers, rich functionalities, and large specific surface areas, vast applications in energy transfer and energy storage fields can be realized. In this mini-review, we summarize the preparation strategies of MOF/COF-based hybrids, as well as their derivatives, nanostructure formation mechanism of M@CN_x and CN_x hybrids from MOF/COF-based hybrid materials, and their applications as catalysts for driving diverse reactions and electrode materials for energy storage. Further, current challenges and future prospects of applying these derivatives into energy conversion and storage devices are also discussed.

Mo and Zn-Dual doped CuxO nanocrystals confined High-Conductive Cu arrays as novel sensitive sensor for neurotransmitter detection

The development of sensitive and selective sensors using facile and low-cost methods for detecting neurotransmitter molecules is a critical factor in the health care system in regard to early diagnosis. In this research, an electrocatalyst derived from Mo,Zn dual-doped Cu_xO nanocrystals-based layer coating over one-dimensional copper nanowire arrays (Mo,Zn-Cu_xO/CuNWs) was successfully designed using a facile electrodeposition approach and used as an electrochemical sensor for non-enzymatic dopamine (DA) neurotransmitter detection. The synergistic effect caused by the dual-doping effect along with its excellent conductivity produced a large electroactive surface area and an improved hetero-charge transfer, thereby boosting DA sensing ability with a low limit detection of 0.32 µM, wide-range of detection (0.5 µM - 3.9 mM), long-term stability (5 weeks), and high selectivity in phosphate buffer solution (pH 7.4). Also, the sensor accurately determined DA in real blood serum-spiked solutions. The achieved results evidenced that the Mo,Zn-Cu_xO/CuNWs derived sensor is highly suitable for DA detection. Therefore, it also opens new windows for the development of low-cost, accurate, high-performance, and stable sensors for other neurotransmitter sensing for the purposes of better health care and early diagnosis.

Metal–organic framework functionalized sulphur doped graphene: a promising platform for selective and sensitive electrochemical sensing of acetaminophen, dopamine and H2O2

We present a simple in situ self-assembly approach for crafting a heteroatom doped graphene supported MOF nanocomposite with excellent potential for selective and sensitive electrochemical sensing of clinically important molecules.

Rational design of ZnO@ZIF-8 nanoarrays for improved electrochemical detection of H2O2

Core–shell ZnO@ZIF-8 nanoarrays demonstrate remarkable electrochemical performance for detection of H2O2.

Metal-Organic Framework-Based Composites for the Detection and Monitoring of Pharmaceutical Compounds in Biological and Environmental Matrices

The production of synthetic drugs is considered a huge milestone in the healthcare sector, transforming the overall health, aging, and lifestyle of the general population. Due to the surge in production and consumption, pharmaceutical drugs have emerged as potential environmental pollutants that are toxic with low biodegradability. Traditional chromatographic techniques in practice are time-consuming and expensive, despite good precision. Alternatively, electroanalytical techniques are recently identified to be selective, rapid, sensitive, and easier for drug detection. Metal-organic frameworks (MOFs) are known for their intrinsic porous nature, high surface area, and diversity in structural design that provides credible drug-sensing capacities. Long-term reusability and maintaining chemo-structural integrity are major challenges that are countered by ligand-metal combinations, optimization of synthetic conditions, functionalization, and direct MOFs growth over the electrode surface. Moreover, chemical instability and lower conductivities limited the mass commercialization of MOF-based materials in the fields of biosensing, imaging, drug release, therapeutics, and clinical diagnostics. This review is dedicated to analyzing the various combinations of MOFs used for electrochemical detection of pharmaceutical drugs, comprising antibiotics, analgesics, anticancer, antituberculosis, and veterinary drugs. Furthermore, the relationship between the composition, morphology and structural properties of MOFs with their detection capabilities for each drug species is elucidated.

Gold Nanorods (AuNRs) and Zeolitic Imidazolate Framework-8 (ZIF-8) Core-Shell Nanostructure-Based Electrochemical Sensor for Detecting Neurotransmitters

The development of novel electrode materials for rapid and sensitive detection of neurotransmitters in the human body is of great significance for early disease diagnosis and personalized therapy. Herein, gold nanorod@zeolitic imidazolate framework-8 (AuNR@ZIF-8) core-shell nanostructures were prepared by controlled encapsulation of gold nanorods within a ZIF-8 assembly. The designed AuNR@ZIF-8 nanostructures have uniform morphology, good dispersion, a large specific surface area, and an average size of roughly 175 nm. Compared with individual ZIF-8 and AuNR-modified electrodes, the obtained core-shell-structured AuNR@ZIF-8 nanocomposite structure-modified electrode shows excellent electrocatalytic performance in the determination of dopamine (DA) and serotonin (ST). The designed AuNR@ZIF-8 exhibited a wide linear range of 0.1-50 μM and low detection limit (LOD, 0.03 μM, S/N = 3) for the determination of DA, as well as a linear range of 0.1-25 μM and low LOD (0.007 μM, S/N = 3) for monitoring ST. The improved performance is attributed to the synergistic effect of the high conductivity of AuNRs and multiple catalytic sites of ZIF-8. The good electroanalytical ability of AuNR@ZIF-8 for detection of DA and ST can provide a guide to efficiently and rapidly monitor other neurotransmitters and construct novel electrochemical sensors.

Rational Design and Growth of MOF-on-MOF Heterostructures

Multiporous metal-organic frameworks (MOFs) have emerged as a subclass of highly crystalline inorganic-organic materials, which are endowed with high surface areas, tunable pores, and fascinating nanostructures. Heterostructured MOF-on-MOF composites are recently becoming a research hotspot in the field of chemistry and materials science, which focus on the assembly of two or more different homogeneous or heterogeneous MOFs with various structures and morphologies. Compared with one single MOF, the dual MOF-on-MOF composites exhibit unprecedented tunability, hierarchical nanostructure, synergistic effect, and enhanced performance. Due to the difference of inorganic metals and organic ligands, the lattice parameters in a, b, and c directions in the single crystal cells could bring about subtle or large structural difference. It will result in the composite material with distinct growth methods to obtain secondary MOF grown from the initial MOF. In this review, the authors wish to mainly outline the latest synthetic strategies of heterostructured MOF-on-MOFs and their derivatives, including ordered epitaxial growth, random epitaxial growth, etc., which show the tutorial guidelines for the further development of various MOF-on-MOFs.

Interwrapping Distinct Metal-Organic Frameworks in Dual-MOFs for the Creation of Unique Composite Catalysts

Incorporating metal nanoparticles (MNPs) inside metal-organic frameworks (MOFs) demonstrates superior catalytic properties in numerous reactions; however, the size and distribution of MNPs could not be well controlled, resulting in low product selectivity in catalysis by undergoing different catalytic reaction pathways. We report herein a facile strategy for integrating lattice-mismatched MOFs together to fabricate homogeneously distributed “dual-MOFs,” which are the ideal precursors for the preparation of MNPs@MOFs with unique catalytic properties. As a proof of concept, we successfully synthesize a dual-MOF HKUST-1/ZIF-8 for in situ creation of redox-active Cu NPs inside hierarchical porous ZIF-8 under controlled pyrolytic conditions. Combining the advantages of size-tunable Cu NPs in the molecular sieving matrix of ZIF-8, Cu@ZIF-8 demonstrates high activity and selectivity for transformation of alkynes into alkenes without overhydrogenation, which surpasses most of the catalysts in the literature. Therefore, this work paves a new pathway for developing highly efficient and selective heterogeneous catalysts to produce highly value-added chemicals.

Conductive Metal-Organic Frameworks: Electronic Structure and Electrochemical Applications

Smarter and minimization of devices are consistently substantial to shape the energy landscape. Significant amounts of endeavours have come forward as promising steps to surmount this formidable challenge. It is undeniable that material scientists were contemplating smarter material beyond purely inorganic or organic materials. To our delight, metal-organic frameworks (MOFs), an inorganic-organic hybrid scaffold with unprecedented tunability and smart functionalities, have recently started their journey as an alternative. In this review, we focus on such propitious potential of MOFs that was untapped over a long time. We cover the synthetic strategies and (or) post-synthetic modifications towards the formation of conductive MOFs and their underlying concepts of charge transfer with structural aspects. We addressed theoretical calculations with the experimental outcomes and spectroelectrochemistry, which will trigger vigorous impetus about intrinsic electronic behaviour of the conductive frameworks. Finally, we discussed electrocatalysts and energy storage devices stemming from conductive MOFs to meet energy demand in the near future.

Novel SnO2@ZIF-8/gC3N4 nanohybrids for excellent electrochemical performance towards sensing of p-nitrophenol

Herein, a novel synthetic strategy has been proposed to prepare engineered SnO₂@ZIF-8/gC₃N₄ nanohybrids for electrochemical sensing of p-nitrophenol (p-NP). The electrochemical properties were investigated using cyclic voltammetry (CV), chronoamperometry (CA), and differential pulse voltammetry (DPV). The developed nanohybrid sensor displayed an excellent electrochemical performance towards sensing of p-NP with a detection limit of 0.565 μM. The sensitivity of the prepared nanohybrid was found to be 2.63 μAcm^-2μM^-1. Moreover, the newly fabricated sensor exhibited remarkable selectivity (over tenfold excess) in the presence of common interferents. The simultaneous detection of isomers of nitrophenol is difficult using the developed sensor. However, other common interferents, such as phenol and aminophenol have negligible effects on the sensitivity of SnO₂@ZIF-8/gC₃N₄ towards the detection of p-nitrophenol. Further, the newly developed sensor showed consistency of sensing response up to 30 days. Thus, implementation of SnO₂@ZIF-8/gC₃N₄ nanohybrids as a p-NP electrochemical sensor offers the advantages of simplicity, selectivity, and stability.

Catalytic amplification based on hierarchical heterogeneity bimetal-organic nanostructures with peroxidase-like activity

In this paper, integrating heterometallic units and nanostructures into metal-organic frameworks (MOFs) were applied to improve the sensitivity of detecting hydrogen peroxide (H₂O₂) in neutral solution. The bimetal-MOFs (CuCo-BDC) and GO composite (CuCo-BDC/GO) were first synthesized via an ordinary one-step solvothermal synthesis. The CuCo-BDC/GO with admirable peroxidase-like catalytic activity could be applied to detect H₂O₂. The results have low detection limit of 69 nM (S/N = 3) and a wide linear detection range, from 100 nM to 3.5 mM. This is superior to recently published biosensors based on noble metal nanomaterials, which confirms CuCo-BDC/GO as the MOF electrocatalysts with high performance. The remarkable electroanalytical performance of CuCo-BDC/GO is due to the presence of numerous open metal active sites, the synergistic effect of Cu²⁺ and Co²⁺, hierarchical structure with high-specific surface areas and the marvelous electrochemical properties of GO. Therefore, CuCo-BDC/GO is a powerful candidate for detecting H₂O₂ in electrochemical biosensing fields. Moreover, H₂O₂ detection in real samples can be done with the CuCo-BDC/GO, including human serum samples. Therefore, the novel CuCo-BDC/GO is a promising catalyst that can be applied in biotechnological and environmental applications.

In situ growth of ZIF-8 on gold nanoparticles/magnetic carbon nanotubes for the electrochemical detection of bisphenol A

We herein report a facile and scalable strategy for the fabrication of a metal-organic framework (MOF) based composite by in situ growing ZIF-8 on gold nanoparticle (AuNP) loaded magnetic carbon nanotubes (mCNTs). AuNPs were firstly loaded on PEI (polyethylenimine) modified mCNTs by electrostatic forces, and then AuNPs/mCNTs were encapsulated into the ZIF-8 frame through in situ self-assembling of zinc ions and 2-methylimidazole. The morphology, spectroscopy and structural properties of the AuNP/mCNT@ZIF-8 nanocomposites were systematically characterized. The conductivity-strain tests revealed that the in situ insertion of AuNPs/mCNTs in ZIF-8 could not only shorten the electron transfer distance between active sites and mCNTs, but also increase the dispersion of mCNTs, which would benefit the electron and mass transfer. Besides, by adopting the AuNP/mCNT@ZIF-8 nanocomposite-modified glassy carbon electrode (GCE) as the working electrode, a novel electrochemical sensor was successfully developed for the detection of bisphenol A (BPA). A linear range of BPA detection from 1 μM to 100 μM with a limit of detection of 690 nM was favorably obtained. Moreover, the developed sensor exhibited satisfactory reproducibility and superior stability with excellent anti-interference ability, and was successfully applied in the detection of BPA in real samples.

Nano-spinel cobalt decorated sulphur doped graphene: an efficient and durable electrocatalyst for oxygen evolution reaction and non-enzymatic sensing of H2O2

We report the synthesis of a nano-spinel cobalt decorated sulphur doped reduced graphene oxide (Co@S–rGO) composite exhibiting excellent electrocatalytic performance and electrochemical stability toward oxygen evolution reaction in an alkaline medium.

Core-Shell MOFs@MOFs: Diverse Designability and Enhanced Selectivity

Metal-Organic frameworks (MOFs), especially MOF-based composites, performed an irreplaceable role in the material fields. By virtue of the tailorability of MOFs, core-shell MOFs@MOFs composites with diverse designability and enhanced selectivity have inspired infinite scientific interest. This review will highlight an up-to-date overview of the designability and enhanced selectivity of core-shell MOFs@MOFs composites, covering the synthetic strategies of an epitaxial growth method, postsynthetic modification, and one-pot synthesis as well as the synergistic selective performance of the synthesized MOFs@MOFs in catalysis, adsorption and separation, and molecular recognition. Finally, the potential development trend and challenges toward core-shell MOFs@MOFs are addressed.

Sn-MOF@CNT nanocomposite: An efficient electrochemical sensor for detection of hydrogen peroxide

A novel approach for the assembly of Sn-based metal organic framework (Sn-MOF) via solvothermal method and its composite (Sn-MOF@CNT) with electroactive material, carbon nanotubes (CNT) by sonochemical means, is described that is useful for hydrogen peroxide sensing; large surface area and pore volume of Sn-MOF were exploited where in the crystallinity of the Sn-MOF was preserved upon inclusion of CNT over its surface. The surface morphology and structural analysis of Sn-MOF and its composite form, Sn-MOF@CNT, were determined analytically through Fourier-transform infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD), Scanning electron microscopy (SEM), Brunauer-Emmett-Teller and Energy-dispersive X-ray spectroscopy (EDX). The developed Sn-MOF@CNT sensor was expansively used to determine and optimize the effect of scan rate, concentration and detection limits including the EDX and SEM analysis of used Sn-MOF@CNT nanocomposite's post hydrogen peroxide sensing. The electrochemical sensing with Sn-MOF@CNT revealed a lower limit of detection ~4.7 × 10^-3 μM with wide linear range between 0.2 μM and 2.5 mM. This study has explored a new strategy for the deposition of CNT over Sn-MOF via a simple sonochemical methodology for successful electrochemical detection of H₂O₂, an approach that can be imitated for other applications.

Ultrasensitive electrochemical detection of neuron-specific enolase based on spiny core-shell Au/CuxO@CeO2 nanocubes

As a specific biomarker, neuron-specific enolase (NSE) is an essential clinical indicator for diagnosing small cell lung cancer. In this paper, a sandwich-type electrochemical immunosensor was designed for the quantitative detection of NSE. AuPt nanoblock spherical nanoarchitectonics (AuPt NSNs), a bimetallic nanoparticle with a rugged morphology, were utilized as the substrate, which could enhance the electronic conduction and increase the immobilization capacity of the primary antibody (Ab₁). Moreover, through a simple hydrothermal method, Au/Cu_xO@CeO₂ was prepared as a spiny core-shell nanocube with cerium dioxide (CeO₂) and gold nanoparticles (Au NPs) loading. The combination of Cu₂O, CuO, and CeO₂ showed favorable catalytic activity toward hydrogen peroxide (H₂O₂). Furthermore, the deposition of Au NPs on the spiny surface structure enhanced the specific surface area and biocompatibility, thereby rendering it more effective for loading the second antibody (Ab₂). As the label material, the Au/Cu_xO@CeO₂ achieved signal amplification and sensitive detection with the immunosensor. Under optimal conditions, the designed immunosensor possessed a broad linear range of 50 fg mL^-1 to 100 ng mL^-1 and a limit of detection of 31.3 fg mL^-1, along with satisfactory performance in sensitivity, selectivity, and stability.

The function of metal-organic frameworks in the application of MOF-based composites

In the last two decades, metal-organic frameworks (MOFs), as a class of porous crystalline materials formed by organic linkers coordinated-metal ions, have attracted increasing attention due to their unique structures and wide applications. Compared to single components, various well-designed MOF-based composites combining MOFs with other functional materials, such as nanoparticles, quantum dots, natural enzymes and polymers with remarkably enhanced or novel properties have recently been reported. To efficiently and directionally synthesize high-performance MOF-based composites for specific applications, it is vital to understand the structural-functional relationships and role of MOFs. In this review, preparation methods of MOF-based composites are first summarized and then the relationship between the structure and performance is determined. The functions of MOFs in practical use are classified and discussed through various examples, which may help chemists to understand the structural-functional relationship in MOF-based composites from a new perspective.

Surface-coordinated metal-organic framework thin films (SURMOFs) for electrocatalytic applications

The design and development of highly efficient electrocatalysts are very important in energy storage and conversion. As a kind of inorganic organic hybrid material, metal-organic frameworks (MOFs) have been used as electrocatalysts in electrocatalytic reactions due to their structural diversities and fascinating functionalities. Particularly, MOF thin films are coordinated on substrate surfaces by a liquid phase epitaxial (LPE) layer by layer (LBL) growth method (called surface-coordinated MOF thin films, SURMOFs), and recently have been studied in various applications due to their precisely controlled thickness, preferred growth orientation and homogeneous surface. In this review, we will summarize the preparation and electrocatalysis of SURMOFs and their derived thin films (SURMOF-D). The SURMOF based thin films possess diverse topological structures and flexible properties, providing abundant catalytically active sites and fast charge transfer for efficient electrocatalytic performance in the oxygen evolution reaction (OER), oxygen reduction reaction (ORR), hydrogen evolution reaction (HER), carbon dioxide reduction reaction (CRR), supercapacitors, tandem electrocatalysis and so on. The research challenges and problems of SURMOFs for electrocatalytic applications are also discussed at the end of the review.