Cu-Hemin Metal-Organic-Frameworks/Chitosan-Reduced Graphene Oxide Nanocomposites with Peroxidase-Like Bioactivity for Electrochemical Sensing

Iron protoporphyrin IX-hyaluronan hydrogel-supported luminol chemiluminescence for the detection of nitric oxide in physiological solutions

Due to its role as a free radical signal-transducing agent with a short lifespan, precise measurement of nitric oxide (●NO) levels presents significant challenges. Various analytical techniques offer distinct advantages and disadvantages for ●NO detection. This research aims to simplify the detection process by developing a hydrogel system using iron(III)-protoporphyrin IX (hemin)-loaded hyaluronan for the detection of ●NO in solution. Various hydrogel formulations were created, and the effects of their components on hydrogel-supported luminol chemiluminescence (CL) kinetics, radical scavenging, and physicochemical properties were analysed through factorial analysis. The candidate formulations were then evaluated using two ●NO donors. An increase in the degree of crosslinking in unloaded formulations enhanced interactions with the CL reaction components, hydrogen peroxide (H2O2) and luminol, thereby affecting light generation. However, hemin loading negated these effects, resulting in more prominent luminescence kinetics in formulations with lower crosslinking degrees. Similarly, ●NO influenced the kinetics differently, interacting with both the CL reaction and hydrogel components. Hemin-loaded formulations exhibited enhanced signal propagation when exposed to ●NO, followed by H2O2 and luminol, whereas reversing the order of addition inhibited this propagation. The magnitude of these luminescence changes depended on the type and concentration of the ●NO donor, demonstrating greater sensitivity to ●NO levels compared to amperometric sensing. These findings suggest that the studied hydrogel platform has potential for the facile and accurate detection of ●NO in solution, requiring minimal sample sizes.

Bioinspired molecule-functionalized Cu with high CO adsorption for efficient CO electroreduction to acetate

Electrochemical reduction of carbon dioxide (CO2) or carbon monoxide (CO) to valuable multi-carbon (C2+) products like acetate is a promising approach for a sustainable energy economy. However, it is still challenging to achieve high activity and selectivity for acetate production, especially in neutral electrolytes. Herein, a bioinspired hemin/Cu hybrid catalyst was developed to enhance the surface *CO coverage for highly efficient electroreduction of CO to acetate fuels. The hemin/Cu electrocatalyst exhibits a remarkable faradaic efficiency of 45.2% for CO-to-acetate electroreduction and a high acetate partial current density of 152.3 mA cm-2. Furthermore, the developed hybrid catalyst can operate stably at 200 mA cm-2 for 14.6 hours, producing concentrated acetate aqueous solutions (0.235 M, 2.1 wt%). The results of in situ Raman spectroscopy and theoretical calculations proved that the Fe-N4 structure of hemin could enhance the CO adsorption and enrich the local concentration of CO, thereby improving C-C coupling for acetate production. In addition, compared to the unmodified Cu catalysts, the Cu catalysts functionalized with cobalt phthalocyanine with a Co-N4 structure also exhibit improved acetate performance, proving the universality of this bioinspired molecule-enhanced strategy. This work paves a new way to designing bioinspired electrolysis systems for producing specific C2+ products from CO2 or CO electroreduction.

Simultaneous Electrochemical Detection of Dopamine and Uric Acid via Au@Cu-Metal Organic Framework

The incorporation of noble metals with metal-organic frameworks (MOFs) are conducive to the simultaneous electrochemical detection of analytes owing to multiple accessible reaction sites. Herein, Au@Cu-metal organic framework (Au@Cu-MOF) is successfully synthesized and modified as a screen-printed carbon electrode (SPCE), which serves as an excellent electrocatalyst for the oxidation of dopamine (DA) and uric acid (UA). The sensor shows a linear range from 10 μM to 1000 μM, with sensitivity and detection limit of 0.231 μA μM-1 cm-2 and 3.40 μM for DA, and 0.275 μA μM-1 cm-2 and 10.36 μM for UA. Au@Cu-MOF could realize the individual and simultaneous electrochemical sensing of DA and UA, with distinguishable oxidation peak potentials. Moreover, it exhibits reproducibility, repeatability, and stability. Ultimately, the sensor provides an avenue for an ultrasensitive label-free electrochemical detection of DA and UA.

Recent progress of metal-organic framework-based nanozymes with oxidoreductase-like activity

Nanozymes, a class of synthetic nanomaterials possessing enzymatic catalytic properties, exhibit distinct advantages such as exceptional stability and cost-effectiveness. Among them, metal-organic framework (MOF)-based nanozymes have garnered significant attention due to their large specific surface area, tunable pore size and uniform structure. MOFs are porous crystalline materials bridged by inorganic metal ions/clusters and organic ligands, which hold immense potential in the fields of catalysis, sensors and drug carriers. The combination of MOFs with diverse nanomaterials gives rise to various types of MOF-based nanozyme, encompassing original MOFs, MOF-based nanozymes with chemical modifications, MOF-based composites and MOF derivatives. It is worth mentioning that the metal ions and organic ligands in MOFs are perfectly suited for designing oxidoreductase-like nanozymes. In this review, we intend to provide an overview of recent trends and progress in MOF-based nanozymes with oxidoreductase-like activity. Furthermore, the current obstacles and prospective outlook of MOF-based nanozymes are proposed and briefly discussed. This comprehensive analysis aims to facilitate progress in the development of novel MOF-based nanozymes with oxidoreductase-like activity while serving as a valuable reference for scientists engaged in related disciplines.

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.

Beyond Pristine Metal-Organic Frameworks: Preparation of Hollow MOFs and Their Composites for Catalysis, Sensing, and Adsorption Removal Applications

Metal-organic frameworks (MOFs) have been broadly applied to numerous domains with a substantial surface area, tunable pore size, and multiple unsaturated metal sites. Recently, hollow MOFs have greatly attracted the scientific community due to their internal cavities and gradient pore structures. Hollow MOFs have a higher tunability, faster mass-transfer rates, and more accessible active sites when compared to traditional, solid MOFs. Hollow MOFs are also considered to be candidates for some functional material carriers. For example, composite materials such as hollow MOFs and metal nanoparticles, metal oxides, and enzymes have been prepared. These composite materials integrate the characteristics of hollow MOFs with functional materials and are broadly used in many aspects. This review describes the preparation strategies of hollow MOFs and their composites as well as their applications in organic catalysis, electrochemical sensing, and adsorption separation. Finally, we hope that this review provides meaningful knowledge about hollow-MOF composites and their derivatives and offers many valuable references to develop hollow-MOF-based applied materials.

Design and Application of Electrochemical Sensors with Metal-Organic Frameworks as the Electrode Materials or Signal Tags

Metal-organic frameworks (MOFs) with fascinating chemical and physical properties have attracted immense interest from researchers regarding the construction of electrochemical sensors. In this work, we review the most recent advancements of MOF-based electrochemical sensors for the detection of electroactive small molecules and biological macromolecules (e.g., DNA, proteins, and enzymes). The types and functions of MOF-based nanomaterials in terms of the design of electrochemical sensors are also discussed. Furthermore, the limitations and challenges of MOF-based electrochemical sensing devices are explored. This work should be invaluable for the development of MOF-based advanced sensing platforms.

Bortezomib prodrug catalytic nanoreactor for chemo/chemodynamic therapy and macrophage re-education

Chemodynamic therapy (CDT), an emerging tumor-specific therapeutic modality, is frequently restrained by insufficient intratumoral Fenton catalysts and increasingly inefficient catalysis caused by the continuous consumption of limited H₂O₂ within tumors. Herein, we engineered a pH-responsive bortezomib (BTZ) polymer prodrug catalytic nanoreactor (HeZn@HA-BTZ) capable of self-supplying Fenton catalyst and H₂O₂. It is aimed for tumor-specific chemo/chemodynamic therapy via oxidative stress and endoplasmic reticulum (ER) stress dual-amplification and macrophage repolarization. A catechol‑boronate bond-based hyaluronic acid-BTZ prodrug HA-DA-BTZ was modified on Hemin and Zn²⁺ coordination nanoscale framework (HeZn), an innovative CDT inducer, to construct He-Zn@HA-BTZ. He-Zn@HA-BTZ with good stability and superior peroxidase-like activity preferentially accumulated at tumor sites and be actively internalized by tumor cells. Under the cleavage of catechol‑boronate bond in acidic endo/lysosomes, pre-masked BTZ was rapidly released to induce ubiquitinated protein aggregation, robust ER stress and elevated H₂O₂ levels. The amplified H₂O₂ was further catalyzed by HeZn via Fenton-catalytic reactions to produce hypertoxic •OH, enabling cascaded oxidative stress amplification and long-lasting effective CDT, which in turn aggravated BTZ-induced ER stress. Eventually, a dual-amplification of oxidative stress and ER stress was achieved to initiate cell apoptosis/necrosis with reduced BTZ toxicity. Intriguingly, He-Zn@HA-BTZ could repolarize macrophages from M2 to antitumor M1 phenotype for potential tumor therapy. This "all in one" prodrug nanocatalytic reactor not only enriches the CDT inducer library, but provides inspirational strategy for simultaneous oxidative stress and ER stress based excellent cancer therapy.

Copper-based metal-organic frameworks for biomedical applications

Metal-organic frameworks (MOFs) are a class of important porous, crystalline materials composed of metal ions (clusters) and organic ligands. Owing to the unique redox chemistry, photochemical and electrical property, and catalytic activity of Cu^2+/+, copper-based MOFs (Cu-MOFs) have been recently and extensively explored in various biomedical fields. In this review, we first make a brief introduction to the synthesis of Cu-MOFs and their composites, and highlight the recent synthetic strategies of two most studied representatives, three-dimensional HKUST-1 and two-dimensional Cu-TCPP. The recent advances of Cu-MOFs in the applications of cancer treatment, bacterial inhibition, biosensing, biocatalysis, and wound healing are summarized and discussed. Furthermore, we propose a prospect of the future development of Cu-MOFs in biomedical fields and beyond.

Advanced Metal–Organic Frameworks-Based Catalysts in Electrochemical Sensors

Developing efficient catalysts is vital for the application of electrochemical sensors. Metal–organic frameworks (MOFs), with high porosity, large specific surface area, good conductivity, and biocompatibility, have been widely used in catalysis, adsorption, separation, and energy storage applications. In this invited review, the recent advances of a novel MOF-based catalysts in electrochemical sensors are summarized. Based on the structure–activity–performance relationship of MOF-based catalysts, their mechanism as electrochemical sensor, including metal cations, synthetic ligands, and structure, are introduced. Then, the MOF-based composites are successively divided into metal-based, carbon-based, and other MOF-based composites. Furthermore, their application in environmental monitoring, food safety control, and clinical diagnosis is discussed. The perspective and challenges for advanced MOF-based composites are proposed at the end of this contribution.

Cu-MOF/hemin: a bionic enzyme with excellent dispersity for the determination of hydrogen peroxide released from living cells

The stability, repeatability and sensitivity of an electrochemical biosensor material are closely connected with the dispersibility of metal organic frameworks (MOFs) in aqueous media. Herein, a nanocomposite based on Cu-MOF/hemin, which is not only highly water-soluble but also simple and efficient in synthesis, was used for the construction of a non-enzymatic sensor to detect hydrogen peroxide (H₂O₂). The Cu-MOF/hemin was characterized via scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS)-mapping, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and thermal gravimetric analysis (TGA), which indicate that hemin and the Cu-MOF were successfully combined. As a H₂O₂ electrochemical biomimetic enzyme, the Cu-MOF/hemin exhibited excellent electrocatalytic performance, which was confirmed by the electrochemical experiments and chromogenic reactions, and the possible mechanism of the reactions has been deduced. The electrochemical sensor based on the biomimetic enzyme exhibited an extended linear detection range from 0.01-5.0 mM (R = 0.998), low detection limit of 4.14 μM, and high selectivity and stability under the optimized conditions. More importantly, the practical application ability of the sensor was verified by the test of H₂O₂ in human serum samples and it could be used for the real-time detection of H₂O₂ released from living cells with satisfactory results. Therefore, this novel nanocomposite has certain potential in preparing electrochemical sensing platforms for nonenzymatic biosensing and provides a new method for clinical diagnosis and real-time monitoring.

A three-dimensional hydrogel-modified indium tin oxide electrode with enhanced performance for in situ electrochemical detection of extracellular H2O2

Two different electrochemical sensors (Hemin-G4/Au/GCE and Hemin-G4/Au/ITO) were developed and applied to explore the electrocatalytic capacity of H₂O₂ reduction. Due to the excellent catalytic activity of Hemin-G4 and high conductivity of gold nanoparticles, both electrodes show excellent electrochemical performances towards H₂O₂ with a low LOD (0.67 μM for Hemin-G4/Au/GCE and 0.65 μM for Hemin-G4/Au/ITO), rapid response (<4 s), and high selectivity and sensitivity (314.33 μA mM^-1 cm^-2 for Hemin-G4/Au/GCE and 322.22 μA mM^-1 cm^-2 for Hemin-G4/Au/ITO). The two electrodes allow sensitive capture of H₂O₂ produced by A549 cells. Compared with the conventional method of detection in cell suspensions, an ITO electrode with a large specific surface area and good biocompatibility can provide a promising platform for cell adhesion, so as to realize real-time and in situ detection of extracellular H₂O₂. The experimental results show that A549 cells can adhere to the surface of the Hemin-G4/Au/ITO electrode and grow well. This is benefitted from the three-dimensional structure of the Hemin-G4/Au hydrogel, which provides a suitable microenvironment for cell adhesion and growth. Furthermore, the in situ detection shows a faster response time than that of in-solution detection. This is because the H₂O₂ generated by the cells can be directly captured by the ITO electrode, which avoids diffusion from the solution to the electrode. These results indicate that the self-supporting hydrogel modified ITO electrode has great application prospects in basic biomedical research and continuous dynamic surveillance of diseases.

A novel nonenzymatic ascorbic acid electrochemical sensor based on gold nanoparticals-chicken egg white-copper phosphate-graphene oxide hybrid nanoflowers

Au-CEW-Cu₃(PO₄)₂-GO nanoflowers (HNFs), which were assembled of gold nanoparticals (Au NPs), chicken egg white (CEW), copper phosphate (Cu₃(PO₄)₂) and graphene oxide (GO) together to form a flower-like organic/inorganic hybrid nanocomposite, were synthesized through a simple and gentle one-pot co-precipitation method. The prepared samples were well characterized by scanning electron microscope, transmission electron microscope, energy dispersive x-ray spectrometer, x-ray diffraction and Raman spectrometer. The prepared Au-CEW-Cu₃(PO₄)₂-GO HNFs was used to modify glassy carbon electrode to fabricate an electrochemical sensor for detection of ascorbic acid (AA). The electrochemical test results show that the linear range of the developed sensor is 8-300μM and the detection limit is 2.67μM (S/N = 3). While this sensor displays high sensitivity of 6.01 × 10^-3μAμM^-1cm^-2and low detection potential of 35 mV due to the combination of the high conductivity of Au NPs, the larger specific surface area of GO and the intrinsic electrocatalytic activity of CEW-Cu₃(PO₄)₂HNFs. Moreover, the Au-CEW-Cu₃(PO₄)₂-GO HNFs-based sensor was successfully developed for application in electrochemical detection of AA in vitamin C tablets.

A stepwise recognition strategy for the detection of telomerase activity via direct electrochemical analysis of metal-organic frameworks

The detection of telomerase is of great significance for monitoring cell canceration. The conventional methods depend on the extension of telomerase towards its primer to conduct signal transduction. Herein, a specific and reliable detection strategy based on stepwise recognition was developed for tandem detection of metal ions and enzymes. We first synthesized an electrically active metal-organic framework (MIL-101(Fe)), which can act directly as a signal reporter in phosphate buffered saline after being modified with capture DNA (cDNA). When the zinc ion is added as a coenzyme factor, the modified hairpin DNA on the electrode is cleaved by DNAzyme to yield the activated primer. After the addition of telomerase, the cleaved DNA strand would be extended, and the resulting sequence will be hybridized with the signal label of MIL-101(Fe)-cDNA. Therefore, a signal-on strategy for the detection of telomerase was achieved based on the direct electrochemical analysis of MIL-101(Fe). Moreover, this electrochemical biosensor can discriminate telomerase activity among different cell lines. The stepwise recognition ensured the advantages of an electrochemical biosensor such as high sensitivity and specificity during the detection process, providing a novel method for monitoring and diagnosis of diseases.

Porphyrin-Based Metal-Organic Frameworks for Biomedical Applications

Porphyrins and porphyrin derivatives have been widely explored for various applications owing to their excellent photophysical and electrochemical properties. However, inherent shortcomings, such as instability and self-quenching under physiological conditions, limit their biomedical applications. In recent years, metal-organic frameworks (MOFs) have received increasing attention. The construction of porphyrin-based MOFs by introducing porphyrin molecules into MOFs or using porphyrins as organic linkers to form MOFs can combine the unique features of porphyrins and MOFs as well as overcome the limitations of porphyrins. This Review summarizes important synthesis strategies for porphyrin-based MOFs including porphyrin@MOFs, porphyrinic MOFs, and composite porphyrinic MOFs, and highlights recent achievements and progress in the development of porphyrin-based MOFs for biomedical applications in tumor therapy and biosensing. Finally, the challenges and prospects presented by this class of emerging materials for biomedical applications are discussed.

Detection Technologies for Reactive Oxygen Species: Fluorescence and Electrochemical Methods and Their Applications

Reactive oxygen species (ROS) have been found in plants, mammals, and natural environmental processes. The presence of ROS in mammals has been linked to the development of severe diseases, such as diabetes, cancer, tumors, and several neurodegenerative conditions. The most common ROS involved in human health are superoxide (O2•-), hydrogen peroxide (H2O2), and hydroxyl radicals (•OH). Organic and inorganic molecules have been integrated with various methods to detect and monitor ROS for understanding the effect of their presence and concentration on diseases caused by oxidative stress. Among several techniques, fluorescence and electrochemical methods have been recently developed and employed for the detection of ROS. This literature review intends to critically discuss the development of these techniques to date, as well as their application for in vitro and in vivo ROS detection regarding free-radical-related diseases. Moreover, important insights into and further steps for using fluorescence and electrochemical methods in the detection of ROS are presented.

Hemin-doped metal-organic frameworks based nanozyme electrochemical sensor with high stability and sensitivity for dopamine detection

This study reports a new type of artificial nanozyme based on Hemin-doped-HKUST-1 (HKUST-1, also referred to as MOF-199; a face-centered-cubic MOF containing nanochannels) as a redox mediator for the detection of dopamine (DA). Hemin-doped-HKUST-1 was successfully synthesized by one-pot hydrothermal method, which was combined with reduced graphene oxide (rGO) modified on a glassy carbon electrode (GCE) to construct a sensor (Hemin-doped HKUST-1/rGO/GCE). The morphology and structure of Hemin-doped-HKUST-1 were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and infrared spectra (IR) techniques. The Hemin-doped HKUST-1/rGO nanozyme showed an excellent electrocatalytic activity for DA oxidation, which is due to the enhanced Hemin activity through the formation of a metal-organic framework (MOFs) and the synergy between the Hemin-doped HKUST-1 and rGO in nanozyme. The resulted sensor exhibited a high sensitivity of 1.224 μA μM-1, with a lower detection limit of 3.27 × 10-8 M (S/N = 3) and a wide linear range of 0.03-10 μM for DA detection. In addition, due to the stabilizing effect of MOFs on heme, the sensor showed satisfactory stability and has been successfully applied to the detection of DA in serum samples, indicating that this work has potential value in clinical work.

Metal–organic frameworks/biopolymer nanocomposites: from fundamentals toward recent applications in modern technology

Bio–nanocomposite compounds based on biopolymers and MOFs have presented great potential in various applications for modern technology.

Recent Advances in the Design and Sensing Applications of Hemin/Coordination Polymer-Based Nanocomposites

The fabrication of biomimetic catalysts as substituents for enzymes is of critical interest in the field due to the problems associated with the extraction, purification, and storage of enzymes in sensing applications. Of these mimetics, hemin/coordination polymer-based nanocomposites, mainly hemin/metal-organic frameworks (MOF), have been developed for various biosensing applications because of the unique properties of each component, while trying to mimic the normal biological functions of heme within the protein milieu of enzymes. This critical review first discusses the different catalytic functions of heme in the body in the form of enzyme/protein structures. The properties of hemin dimerization are then elucidated with the supposed models of hemin oxidation. After that, the progress in the fabrication of hemin/MOF nanocomposites for the sensing of diverse biological molecules is discussed. Finally, the challenges in developing this type of composites are examined as well as possible proposals for future directions to enhance the sensing performance in this field further.

Biomimetic Au/CeO2 Catalysts Decorated with Hemin or Ferrous Phthalocyanine for Improved CO Oxidation via Local Synergistic Effects

Biomimetic catalysts have drawn broad research interest owing to both high specificity and excellent catalytic activity. Herein, we report a series of biomimetic catalysts by the integration of biomolecules (hemin or ferrous phthalocyanine) onto well-defined Au/CeO₂, which leads to the high-performance CO oxidation catalysts. Strong electronic interactions among the biomolecule, Au, and CeO₂ were confirmed, and the CO uptake over hemin-Au/CeO₂ was roughly about 8 times greater than Au/CeO₂. Based on the Au/CeO₂(111) and hemin-Au/CeO₂(111) models, the density functional theory calculations reveal the mechanisms of the biomolecules-assisted catalysis process. The theoretical prediction suggests that CO and O₂ molecules preferentially bind to the surface of noncontacting Au atoms (low-coordinated sites) rather than the biomolecule sites, and the accelerating oxidation of Au-bound CO occurs via either the Langmuir-Hinshelwood mechanism or the Mars-van Krevelen mechanism. Accordingly, the findings provide useful insights into developing biomimetic catalysts with low cost and high activity.

Hemin-Bridged MOF Interface with Double Amplification of G-Quadruplex Payload and DNAzyme Catalysis: Ultrasensitive Lasting Chemiluminescence MicroRNA Imaging

Here, we report a double-amplified sensing platform for ultrasensitive chemiluminescence (CL) miRNA detection in real patients' blood in which a hemin-bridged metal-organic framework (MOF) is employed as a functional interface to boost the payload and catalysis of G-quadruplex (G4) DNAzymes. Hemin is here used as the organic ligand for the MOF synthesis, which endows the MOF with an intrinsic peroxidase-like catalytic activity. Most importantly, the MOF surface provides a large amount of binding sites for polymeric G4 DNAzymes that are produced by miRNA-triggered rolling circle amplification reactions, and meanwhile, the interfaced G4 DNAzymes on MOFs (G4/MOFzymes) display an about 100-fold higher catalytic activity than those in solution. By using the G4/MOFzyme catalysts in the luminol/H₂O₂ CL system, the amplification detection of two acute myocardial infarction (AMI)-related miRNAs (low to 1 fM seen with naked eyes) is achieved in human serum with a smartphone as a portable imaging detector, which provides a facile methodology for point-of-care (POC) diagnosis of AMI. Compared with previous smartphone-based counterparts not requiring sophisticated equipment, this new facile methodology shows both 6 orders of magnitude higher sensitivity and an ∼50-fold longer duration for CL miRNA imaging. These unique features allow our developed G4/MOFzymes to be further employed as a novel luminescent ink for printing commonly used patterns.

Cu-based metal–organic framework HKUST-1 as effective catalyst for highly sensitive determination of ascorbic acid

In this work, a Cu-based nanosheet metal–organic framework (MOF), HKUST-1, was synthesised using a solvent method at room temperature. Its morphology, structure and composition were characterised by scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), powder X-ray diffraction (XRD), Fourier transform infrared (FTIR), Raman spectroscopy, nitrogen adsorption and desorption isotherms, energy dispersive X-ray spectroscopy (EDS) and elemental analysis (EA). This material was then loaded onto the surface of an indium tin oxide (ITO) electrode to catalyse the electrochemical oxidation of ascorbic acid (AA). An equal-electron-equal-proton reaction was deduced from the pH investigation, and a diffusion-controlled process was reinforced by the dynamics study. Under optimal conditions, the oxidation peak current at +0.02 V displayed a linear relationship with the concentration of AA within the ranges of 0.01–25 and 25–265 mM, respectively. The limit of detection (LOD) was 3 μM at S/N of 3. The superb response could be ascribed to the porous nanosheet structure of HKUST-1, which enhanced both the effective surface area and the electron transfer ability significantly. Moreover, the novel AA sensor demonstrated good reproducibility, favourable stability and high sensitivity towards glucose, uric acid (UA), dopamine (DA) and several amino acids. It was also successfully applied to the real sample testing of various AA-containing tablets.

In this work, a Cu-based nanosheet metal–organic framework (MOF), HKUST-1, was synthesised using a solvent method at room temperature and it demonstrated high capability and sensitivity towards the oxidation of ascorbic acid (AA).

Study on Chemical Modifications of Glutathione by Cold Atmospheric Pressure Plasma (Cap) Operated in Air in the Presence of Fe(II) and Fe(III) Complexes

Cold atmospheric pressure plasma is an attractive new research area in clinical trials to treat skin diseases. However, the principles of plasma modification of biomolecules in aqueous solutions remain elusive. It is intriguing how reactive oxygen and nitrogen species (RONS) produced by plasma interact on a molecular level in a biological environment. Previously, we identified the chemical effects of dielectric barrier discharges (DBD) on the glutathione (GSH) and glutathione disulphide (GSSG) molecules as the most important redox pair in organisms responsible for detoxification of intracellular reactive species. However, in the human body there are also present redox-active metals such as iron, which is the most abundant transition metal in healthy humans. In the present study, the time-dependent chemical modifications on GSH and GSSG in the presence of iron(II) and iron(III) complexes caused by a dielectric barrier discharge (DBD) under ambient conditions were investigated by IR spectroscopy, mass spectrometry and High Performance Liquid Chromatography (HPLC). HPLC chromatograms revealed one clean peak after treatment of both GSH and GSSH with the dielectric barrier discharge (DBD) plasma, which corresponded to glutathione sulfonic acid GSO₃H. The ESI-MS measurements confirmed the presence of glutathione sulfonic acid. In our experiments, involving either iron(II) or iron(III) complexes, glutathione sulfonic acid GSO₃H appeared as the main oxidation product. This is in sharp contrast to GSH/GSSG treatment with DBD plasma in the absence of metal ions, which gave a wild mixture of products. Also interesting, no nitrosylation of GSH/GSSG was oberved in the presence of iron complexes, which seems to indicate a preferential oxygen activation chemistry by this transition metal ion.

Metal–Organic Frameworks Toward Electrocatalytic Applications

Metal–organic frameworks (MOFs) are a class of porous materials constructed from metal-rich inorganic nodes and organic linkers. Because of their regular porosity in microporous or mesoporous scale and periodic intra-framework functionality, three-dimensional array of high-density and well-separated active sites can be built in various MOFs; such characteristics render MOFs attractive porous supports for a range of catalytic applications. Furthermore, the electrochemically addressable thin films of such MOF materials are reasonably considered as attractive candidates for electrocatalysis and relevant applications. Although it still constitutes an emerging subfield, the use of MOFs and relevant materials for electrocatalytic applications has attracted much attention in recent years. In this review, we aim to focus on the limitations and commonly seen issues for utilizing MOFs in electrocatalysis and the strategies to overcome these challenges. The research efforts on utilizing MOFs in a range of electrocatalytic applications are also highlighted.

Facile synthesis of a zeolitic imidazolate framework-8 with reduced graphene oxide hybrid material as an efficient electrocatalyst for nonenzymatic H2O2 sensing

A zeolitic imidazolate framework-8 (ZIF-8)/reduced graphene oxide (rGO) nanocomposite was formed by using an efficient synthetic method. The morphology and structure of the ZIF-8/rGO nanocomposite were characterized by scanning electron spectroscopy (SEM), X-ray diffraction (XRD) and thermogravimetric analysis (TGA) mapping. The ZIF-8/rGO nanocomposites were immobilized on a carbon paste electrode (CPE) to construct a high-performance nonenzymatic electrochemical H2O2 sensor. A cyclic voltammetry (CV) study showed that the ZIF-8/rGO nanocomposites displayed better electrocatalytic activity toward H2O2 reduction compared to that of ZIF-8. An amperometric study indicated that the H2O2 sensor displayed high performance, which offered a low detection limit (0.05 μM) (S/N = 3), a high sensitivity (4.01 μA mM-1 cm-2), and a wide linear range (from 1.0 to 625 μM). An electrochemical reaction mechanism was proposed for H2O2 reduction on the ZIF-8/rGO/CPE. Importantly, the as-fabricated H2O2 sensor exhibited good reproducibility and excellent selectivity. Furthermore, the constructed high-performance sensor was utilized to monitor the H2O2 levels in real samples, and satisfactory results were obtained. These results demonstrated that the ZIF-8/rGO nanocomposite can be used as a good electrochemical sensor material in practical applications.

Nitro-functionalized metal–organic frameworks with catalase mimic properties for glutathione detection

Herein, four copper-based metal–organic frameworks were synthesized to investigate the effects of the substituents in ligands on the enzyme-like catalytic activity of these frameworks.

Nanomaterials with enzyme-like characteristics (nanozymes): next-generation artificial enzymes (II)

An updated comprehensive review to help researchers understand nanozymes better and in turn to advance the field.

Hemin-Modified SnO2/Metglas Electrodes for the Simultaneous Electrochemical and Magnetoelastic Sensing of H2O2

In this work, we present a simple and efficient method for the preparation of hemin-modified SnO2 films on Metglas ribbon substrates for the development of a sensitive magneto-electrochemical sensor for the determination of H2O2. The SnO2 films were prepared at low temperatures, using a simple hydrothermal method, compatible with the Metglas surface. The SnO2 film layer was fully characterized by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), photoluminescence (PL) and Fourier Transform-Infrared spectroscopy (FT-IR). The properties of the films enable a high hemin loading to be achieved in a stable and functional way. The Hemin/SnO2-Metglas system was simultaneously used as a working electrode (WE) for cyclic voltammetry (CV) measurements and as a magnetoelastic sensor excited by external coils, which drive it to resonance and interrogate it. The CV scans reveal direct reduction and oxidation of the immobilized hemin, as well as good electrocatalytic response for the reduction of H2O2. In addition, the magnetoelastic resonance (MR) technique allows the detection of any mass change during the electroreduction of H2O2 by the immobilized hemin on the Metglas surface. The experimental results revealed a mass increase on the sensor during the redox reaction, which was calculated to be 767 ng/μM. This behavior was not detected during the control experiment, where only the NaH2PO4 solution was present. The following results also showed a sensitive electrochemical sensor response linearly proportional to the concentration of H2O2 in the range 1 × 10−6–72 × 10−6 M, with a correlation coefficient of 0.987 and detection limit of 1.6 × 10−7 M. Moreover, the Hemin/SnO2-Metglas displayed a rapid response (30 s) to H2O2 and exhibits good stability, reproducibility and selectivity.

Heterogeneous catalysis with encapsulated haem and other synthetic porphyrins: Harnessing the power of porphyrins for oxidation reactions

Encapsulated metalloporphyrins have been widely studied for their use as efficient heterogeneous catalysts, inspired by the known catalytic activity of porphyrins in haemoproteins. The oxidation of organic substrates by haemoproteins is one of the well-known roles of these proteins, in which the haem (ferriprotoporphyrin IX = FePPIX) cofactor is the centre of reactivity. While these porphyrins are highly efficient catalysts in the protein environment, once removed, they quickly lose their reactivity. It is for this reason that they have garnered much interest in the field of heterogeneous catalysis of oxidation reactions. This review details current research in the field, focusing on the application of encapsulated haem, and other synthetic metalloporphyrins, applied to oxidation reactions.

Efficient detection of hazardous catechol and hydroquinone with MOF-rGO modified carbon paste electrode

Reduced graphite oxide (rGO) was incorporated into a metal organic framework (MOF) MIL-101(Cr) for the modification of carbon paste electrode. Taking advantages of the large surface area of MOF and the electrical conductivity of rGO, the resulted electrodes exhibited high sensitivity and reliability in the simultaneous electrochemical identification and quantification of catechol (CC) and hydroquinone (HQ). Specifically, in the mixture solution of catechol and hydroquinone (constant concentration of an analyte), the linear response ranges for catechol and hydroquinone were 10-1400 μM and 4-1000 μM, and detection limits were 4 μM and 0.66 μM (S/N = 3) for individual catechol and hydroquinone, respectively. Therefore, the relatively easy fabrication of modified CPE and its fascinating reliability towards HQ and CC detection may simulate more research interest in the applications of MIL-101(Cr)-rGO composites for electrochemical sensors.

Nanoscaled Metal-Organic Frameworks for Biosensing, Imaging, and Cancer Therapy

Owing to the progressive development of metal-organic frameworks (MOFs) synthetic processes and their unique characters associated with the excellent performance-selectable composition, tunable pore scale, large surface area, and good thermal stability, MOFs have captured the interest and the imagination of an increasing number of scientists working in different fields. In the area of biomedical applications, MOFs are especially involved in sensing, molecular imaging, and drug delivery, with strong contributions to the whole nanomedicine area. Recently, these materials have been scaled down to nanometer sizes with the advancement of chemical synthesis gradually reaching an adjustable level. This review mainly discusses and summarizes the general synthesis, properties, and biomedical applications of nanoscaled MOFs and their composites in biosensing, imaging, and cancer therapy within the latest three years. The remaining challenges and future opportunities in this field, in terms of processing techniques, maximizing composite properties, and prospects for clinical applications, are also indicated.