A nanosized metal-organic framework of Fe-MIL-88NH₂ as a novel peroxidase mimic used for colorimetric detection of glucose

A Metal-Organic Framework (MOF) Fenton Nanoagent-Enabled Nanocatalytic Cancer Therapy in Synergy with Autophagy Inhibition

Nanocatalytic medicine has been developed recently to trigger intratumoral generation of highly toxic reactive oxygen species (ROS) for cancer therapy, which, unfortunately, suffers from compromised therapeutic efficacy due to a self-protective mechanism, autophagy, of cancer cells to mitigate oxidative damage. In this work, during the efforts of ROS generation by nanocatalytic medicine, a pharmacological autophagy inhibition strategy is implemented for augmenting ROS-induced oxidative damage for synergetic cancer therapy. An iron-containing metal-organic framework [MOF(Fe)] nanocatalyst as a peroxidase mimic is used to catalyze the generation of highly oxidizing •OH radicals specifically within cancer cells, while chloroquine is applied to deacidify lysosomes and inhibit autophagy, cutting off the self-protection pathway under severe oxidative stress. Cancer cells fail to extract their components to detoxicate and strengthen themselves, finally succumbing to the ROS-induced oxidative damage during nanocatalytic therapy. Both in vitro and in vivo results demonstrate the synergy between nanocatalytic therapy and autophagy inhibition, suggesting that such a combined strategy is applicable to amplify tumor-specific oxidative damage and may be informative to future design of therapeutic regimen.

MOF@PEDOT Composite Films for Impedimetric Pesticide Sensors

Due to its deleterious effects on health, development of new methods for detection and removal of pesticide residues in primary and derived agricultural products is a research topic of great importance. Among them, imazalil (IMZ) is a widely used post-harvest fungicide with good performances in general, and is particularly applied to prevent green mold in citrus fruits. In this work, a composite film for the impedimetric sensing of IMZ built from metal-organic framework nanocrystallites homogeneously distributed on a conductive poly(3,4-ethylene dioxythiophene) (PEDOT) layer is presented. The as-synthetized thin films are produced via spin-coating over poly(ethylene terephtalate (PET) substrate following a straightforward, cost-effective, single-step procedure. By means of impedance spectroscopy, electric transport properties of the films are studied, and high sensitivity towards IMZ concentration in the range of 15 ppb to 1 ppm is demonstrated (featuring 1.6 and 4.2 ppb limit of detection, when using signal modulus and phase, respectively). The sensing platform hereby presented could be used for the construction of portable, miniaturized, and ultrasensitive devices, suitable for pesticide detection in food, wastewater effluents, or the assessment of drinking-water quality.

Nanoscale metal-organic frameworks in detecting cancer biomarkers

Following the efficient performance of metal-organic frameworks (MOFs) as recognition elements in gas sensors, biosensors based on MOFs are now being investigated to capture and quantify potential cancer biomarkers, such as circulating tumor cells (CTCs), nucleic acids and proteins. The current status of MOF-based biosensors in the detection of early stages of cancer is in its infancy, although it has significantly emerged since the beginning of this decade. That said, salient research has been conducted in the past five years to utilize the distinctive porous crystalline structure of MOFs for highly sensitive and selective detection of cancer biomarkers. In this pursual, MOFs designed with bimetallic assembly, doped with magnetic nanoparticles, coated with polymers, and even conjugated with peptides or oligonucleotides have shown promising outcomes in detecting CTCs, nucleic acids and proteins. In particular, aptamer-conjugated MOFs are able to perform at a lower limit of detection down to the femtomolar, implying their efficacy for the point of care testing in clinical trials. In this way, aptasensors based on aptamer-conjugated MOFs present a newer sub-branch, to be coined as a MOFTA sensor in the current review. Considering the emerging progress and promising outcomes of MOFTA sensors as well as a variety of MOF-based techniques of detecting cancer biomarkers, this review will highlight their significant advances and related aspects in the recent five years on the context of detecting CTCs, nucleic acids and proteins for the early-stage detection of cancer.

Fe–Ni metal–organic frameworks with prominent peroxidase-like activity for the colorimetric detection of Sn2+ ions

The synthesized Fe–Ni-MOF could oxidize TMB to produce oxTMB with blue color. The presence of Sn²⁺ ions could make the oxTMB color lighter, hence colorimetric detection of Sn²⁺ ions is realized.

Metal–organic framework based nanozymes: promising materials for biochemical analysis

Metal–organic frameworks with enzyme-like catalytic features (MOF nanozymes) exhibit great promise in detecting various analytes with amplified signal outputs.

Two-dimensional iron MOF nanosheet as a highly efficient nanozyme for glucose biosensing

A 2D Fe-BTC nanosheet was preparedviaa cation exchange route. Its peroxidase-like activity is 2.2 times that of 3D MIL-100(Fe) due to highly accessible surface active sites. This is helpful for substrate contact with the catalyst during the catalytic reaction.

Progress and Trend on the Regulation Methods for Nanozyme Activity and Its Application

Natural enzymes, such as biocatalysts, are widely used in biosensors, medicine and health, the environmental field, and other fields. However, it is easy for natural enzymes to lose catalytic activity due to their intrinsic shortcomings including a high purification cost, insufficient stability, and difficulties of recycling, which limit their practical applications. The unexpected discovery of the Fe3O4 nanozyme in 2007 has given rise to tremendous efforts for developing natural enzyme substitutes. Nanozymes, which are nanomaterials with enzyme-mimetic catalytic activity, can serve as ideal candidates for artificial mimic enzymes. Nanozymes possess superiorities due to their low cost, high stability, and easy preparation. Although great progress has been made in the development of nanozymes, the catalytic efficiency of existing nanozymes is relatively low compared with natural enzymes. It is still a challenging task to develop nanozymes with a precise regulation of catalytic activity. This review summarizes the classification and various strategies for modulating the activity as well as research progress in the different application fields of nanozymes. Typical examples of the recent research process of nanozymes will be presented and critically discussed.

Peroxidase-like Activity of Metal-Organic Framework [Cu(PDA)(DMF)] and Its Application for Colorimetric Detection of Dopamine

A metal-organic framework (MOF) [Cu(PDA)(DMF)] was synthesized under mild mixed solvothermal conditions. It is constructed by 1,10-phenanthroline-2,9-dicarboxylic acid (H₂PDA) and Cu²⁺ ions. The complex exhibits high peroxidase-like activity and can catalytically oxidize the colorless substrate 3,3',5,5'-tetramethylbenzidine to a blue product in the presence of H₂O₂. However, the peroxidase-like activity of [Cu(PDA)(DMF)] can be potently inhibited in the presence of dopamine. Based on this phenomenon, the colorimetric detection of dopamine was demonstrated with good selectivity and high sensitivity. [Cu(PDA)(DMF)] showed good stability and robust catalytic activity, which has been employed in the detection of dopamine in human urine and pharmaceutical samples.

Enzyme-Like Metal-Organic Frameworks in Polymeric Membranes for Efficient Removal of Aflatoxin B1

Biodegradation is a mild and efficient way to protect humans and animals from mycotoxins. However, microbes and enzymes are susceptible to environmental change, lack of stability, and reusability. In this work, three peroxidase-like metal-organic frameworks (MOFs), as artificial substitutes of natural peroxidase, are used for aflatoxin B₁ (AFB₁) removal, demonstrating the strong removal ability for AFB₁ and anti-interference ability toward other substances. There are distinct adsorption and catalytic properties among these MOFs that are mainly because of the differences in structure and Fe ion active sites. Then, we immobilized these MOFs into ultrafiltration membranes to form a multifunctional membrane (i.e., filtration, adsorption, and catalysis) for AFB₁ removal with good reusability that can be operated in simultaneous adsorption/catalysis or adsorption followed by catalysis/regeneration modes. Physicochemical analysis and animal experiments showed that the degradation products are probably several low-carbon substances whose toxic groups are cleaved.

Competitive electrochemical immunosensor for maduramicin detection by multiple signal amplification strategy via hemin@Fe-MIL-88NH2/AuPt

Maduramicin (MD) is a type of monoglycoside polyether ionophore antibiotic that can effectively treat coccidiosis and facilitate animal growth. However, its extensive and excessive use brings potential risk to human health. Herein, an electrochemical immunosensor based on indirect competitive format was fabricated for analysis of MD residue in eggs by a multiple signal amplification system. Initially, Au nanoparticles were deposited onto glassy carbon electrode surface to load the coating antigen MD-BSA and to improve conductivity. Then the signal amplification platform was constructed by encapsulating hemin into Fe-MIL-88 NH₂ metal-organic frameworks (hemin@MOFs), and then the obtained composites were decorated with AuPt nanoparticles. The synthesized hemin@MOFs/AuPt was not only used as a signal amplification mediator, but also utilized as a carrier for immobilization of horseradish peroxidase-conjugated affinipure goat anti-mouse antibody (Ab₂-HRP) and horseradish peroxidase (HRP). The constructed hemin@MOFs/AuPt-Ab₂-HRP bioconjugates could effectively amplify the current signal since hemin@MOFs, AuPt and HRP all exhibited high catalytic activity towards the hydrogen peroxide. Moreover, the established immunosensor showed high sensitivity and stability during the detection procedure. With the synergistic catalytic effect of hemin@MOFs, AuPt and HRP, a wide detection range of 0.1-50 ng mL^-1 and a low detection limit of 0.045 ng mL^-1 were achieved (S/N = 3), respectively. Ultimately, the developed method displayed excellent performance in practical applications, providing a promising probability to detect other veterinary drug residues to guarantee food safety.

Glucose Oxidase-Integrated Metal-Organic Framework Hybrids as Biomimetic Cascade Nanozymes for Ultrasensitive Glucose Biosensing

Nanozyme/natural enzyme hybrid plays a vital role in biosensing, therapy, and catalysis owing to the integrated advantages in the selectivity of natural enzymes and controllable catalytic activity of nanozymes. Herein, Fe-MIL-88B-NH₂ [(Fe-metal-organic framework (MOF)] with remarkable peroxidase-like activity, ultrahigh stability, and high biocompatibility was utilized for immobilization of glucose oxidase (GOx) via an amidation coupling reaction. On the basis of the excellent selectivity and catalytic activity of Fe-MOF-GOx, a cascade catalysis was performed for the colorimetric detection of glucose. The integrated Fe-MOF-GOx not only exhibited higher stability and reusability than their mixtures including Fe-MOF and free GOx system but also possessed a wide linear range (1-500 μM), with a low detection limit of 0.487 μM for glucose detection.

Magnetic Nanoparticles-Embedded Enzyme-Inorganic Hybrid Nanoflowers with Enhanced Peroxidase-Like Activity and Substrate Channeling for Glucose Biosensing

It is reported that glucose oxidase (GOx)-copper hybrid nanoflowers embedded with Fe₃ O₄ magnetic nanoparticles (MNPs) exhibit superior peroxidase-mimicking activity as well as substrate channeling for glucose detection. This is due to the synergistic integration of GOx, crystalline copper phosphates and MNPs being in close proximity within the nanoflowers. The preparation of MNP-embedded GOx-copper hybrid nanoflowers (MNPs-GOx NFs) begins with the facile conjugation of amine-functionalized MNPs with GOx molecules via electrostatic attraction, followed by the addition of copper sulfate that leads to full blooming of the hybrid nanoflowers. In the presence of glucose, the catalytic action of GOx entrapped in the nanoflowers generates H₂ O₂ , which is subsequently used by peroxidase-mimicking MNPs and copper phosphate crystals, located close to GOx molecules, to convert Amplex UltraRed substrate into a highly fluorescent product. Using this strategy, the target glucose is successfully determined with excellent selectivity, stability, and magnetic reusability. This biosensor based on hybrid nanoflowers also exhibits a high degree of precision and reproducibility when applied to real human blood samples. Such novel MNP-embedded enzyme-inorganic hybrid nanoflowers have a great potential to be expanded to any oxidases, which will be highly beneficial for the detection of various other clinically important target molecules.

A bifunctional metal organic framework of type Fe(III)-BTC for cascade (enzymatic and enzyme-mimicking) colorimetric determination of glucose

A metal organic framework (MOF) of type Fe(III)-BTC (where BTC is 1,3,5-benzenetricarboxylic acid) was utilized to construct an integrated system for cascade colorimetric determination of glucose. The MOF performs a dual function in acting (a) as a peroxidase (POx) mimic, and (b) as a solid support for immobilization of glucose oxidase (GOx). The MOF was prepared by a one-pot method. Glucose is consumed while H₂O₂ is produced during the enzymatic oxidation by GOx. In the presence of H₂O₂, the POx mimic catalytically oxidizes 3,3',5,5'-tetramethylbenzidine (TMB) to form a blue-green product. The absorbance of oxidized TMB (measured at 652 nm) increases linearly in the 5.0-100 μM glucose concentration range, and the detection limit is 2.4 μM. The GOx@Fe-BTC MOF was successfully applied to the determination of glucose in serum. Graphical abstract Schematic presentation of a bifunctional metal organic framework of type Fe-BTC for cascade (enzymatic and enzyme-mimicking) colorimetric determination of glucose. The Fe-BTC performs a dual function in acting as both a peroxidase mimic and support for immobilizing glucose oxidase. Using the integrated enzyme, a colorimetric method was successfully applied to one-step detection of glucose in human serum.

Nanozymes: Classification, Catalytic Mechanisms, Activity Regulation, and Applications

Because of the high catalytic activities and substrate specificity, natural enzymes have been widely used in industrial, medical, and biological fields, etc. Although promising, they often suffer from intrinsic shortcomings such as high cost, low operational stability, and difficulties of recycling. To overcome these shortcomings, researchers have been devoted to the exploration of artificial enzyme mimics for a long time. Since the discovery of ferromagnetic nanoparticles with intrinsic horseradish peroxidase-like activity in 2007, a large amount of studies on nanozymes have been constantly emerging in the next decade. Nanozymes are one kind of nanomaterials with enzymatic catalytic properties. Compared with natural enzymes, nanozymes have the advantages such as low cost, high stability and durability, which have been widely used in industrial, medical, and biological fields. A thorough understanding of the possible catalytic mechanisms will contribute to the development of novel and high-efficient nanozymes, and the rational regulations of the activities of nanozymes are of great significance. In this review, we systematically introduce the classification, catalytic mechanism, activity regulation as well as recent research progress of nanozymes in the field of biosensing, environmental protection, and disease treatments, etc. in the past years. We also propose the current challenges of nanozymes as well as their future research focus. We anticipate this review may be of significance for the field to understand the properties of nanozymes and the development of novel nanomaterials with enzyme mimicking activities.

A DNA functionalized porphyrinic metal-organic framework as a peroxidase mimicking catalyst for amperometric determination of the activity of T4 polynucleotide kinase

An electrochemical method is described for the sensitive detection of the activity of the enzyme T4 polynucleotide kinase (PNK) by using a DNA functionalized porphyrinic metal-organic framework (L/(Fe-P)n-MOF). In the presence of PNK, the hairpin oligonucleotide (HP1) becomes phosphorylated, and the trigger is released by lambda exonuclease (λ exo). The trigger DNA hybridizes with hairpin probe (immobilized on the gold electrode) to form a nicking endonuclease cleavage site. Thus, a single-strand capture probe is employed to hybridize with L/(Fe-P)n-MOF. The (Fe-P)n-MOF is a peroxidase mimicking material with high catalytic efficiency. By using this amplification strategy, an electrochemical signal is procured that allows for the determination of T4 PNK in the 1.0 mU·mL^-1 to 1.0 U·mL^-1 with a detection limit of 0.62 mU·mL^-1. The method is selective and can be used to screen for enzyme inhibitors. Conceivably, the (Fe-P)n-MOF can also be used to detect other analytes via its peroxidase-mimicking activity. Graphical abstract Schematic presentation of T4 polynucleotide kinase (PNK) detection. Two hairpin DNAs (HP) and a porphyrinic metal-organic framework with peroxidase-mimicking activity are used. The detection limit is 0.62 mU mL^-1 with enzyme assisted signal amplification. This method is selective and can be used to screen for enzyme inhibitors.

Paper-based microfluidic devices for glucose assays employing a metal-organic framework (MOF)

This paper describes the development of two microfluidic paper-based analytical devices (μPADs), one well-based and the other based on a lateral flow assay (LFA) configuration, to detect glucose via a colorimetric assay using the solid metal-organic framework (MOF) Zr-PCN-222(Fe), to encapsulate glucose oxidase (GOx). The well-based platform consisted of laminate sheets and multiple layers of wax-printed chromatography paper. Solutions of KI and glucose placed into the well flowed through the device and reacted with the GOx@MOF species sandwiched between the paper layers realizing a yellow-brown color. The LFA platform consisted of chromatography paper between parafilm and polyvinyl acetate (PVA) layers. GOx@MOFs spotted on the paper subjected to solutions of KI and glucose yielded a brown color. The devices were then dried, scanned, and analyzed yielding a correlation between average inverse yellow intensity and glucose concentrations. The development of these devices employing MOFs as biomimetic catalysts should further expand the applications of microfluidic technologies for sensors a variety of analytes.

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.

Functional nanomaterials with unique enzyme-like characteristics for sensing applications

We highlight the recent developments in functional nanomaterials with unique enzyme-like characteristics for sensing applications.

Colorimetric determination of mercury(II) via the inhibition by ssDNA of the oxidase-like activity of a mixed valence state cerium-based metal-organic framework

This work demonstrates the inhibition effects of single-stranded (ssDNA) on the oxidase-like activity of a mixed-valence state cerium-based metal-organic framework, denoted as MVC-MOF. The MVC-MOF was synthesized by partial oxidation of cerium(III) which leads to the presence of both Ce(III) and Ce(IV) ions. The latter endows the MVC-MOF with a typical oxidase-like activity. However, on addition of ssDNA, the catalytic activity of the MVC-MOF is inhibited because it binds the MVC-MOF and thereby shield its active sites. This prevents the access of substrates. The inhibition by ssDNA depends on its length but not its sequence. By contrast, negligible changes in the oxidase-mimicking activity are observed if double-stranded DNA (dsDNA) is added. By employing a thymine-rich ssDNA (T-ssDNA) as a model DNA, a colorimetric assay was developed for the determination of Hg(II). This ion binds to T-ssDNA and causes the formation of T-dsDNA. Hence, the oxidase-mimicking activity is compromised. By using the oxidase substrate 3,3',5,5'-tetramethylbenzidine that gives a colored product in the presence of oxygen, the assay has a linear response that covers 0.05 to 6 μM Hg(II) with a detection limit of 10.5 nM, and exhibits high selectivity over other metal ions. The assay was successfully applied to the determination of Hg(II) in environmental water samples. Graphical abstract Schematic of the inhibition effect of ssDNA on the oxidase-like activity of MVC-MOF that converts colorless TMB to oxTMB with blue color in the presence of oxygen, and its application in the construction of a colorimetric assay for Hg(II) determination.

Solution-Phase Synthesis of Platinum Nanoparticle-Decorated Metal-Organic Framework Hybrid Nanomaterials as Biomimetic Nanoenzymes for Biosensing Applications

The synthesis of nanomaterials with specific properties and functions as biomimetic nanoenzymes has attracted extensive attention in the past decades due to their great potential to substitute natural enzymes. Herein, a facile and simple method for the preparation of platinum nanoparticle (PtNP)-decorated two-dimensional metal-organic framework (MOF) nanocomposites was developed. A ligand with heme-like structure, Fe(III) tetra(4-carboxyphenyl)porphine chloride (TCPP(Fe)), was applied to synthesize MOF nanosheets (denoted as Cu-TCPP(Fe) nanosheets) in high yield. Ultrathin Cu-TCPP(Fe) nanosheets with thickness less than 10 nm were used as a novel template for the growth of ultrasmall and uniform PtNPs. Significantly, the obtained hybrid nanomaterials (PtNPs/Cu-TCPP(Fe) hybrid nanosheets) exhibit enhanced peroxidase-like activity compared to PtNPs, Cu-TCPP(Fe) nanosheets, and the physical mixture of both due to the synergistic effect. On account of the excellent peroxidase-like activity of PtNPs/Cu-TCPP(Fe) hybrid nanosheets, we established a colorimetric method for sensitive and rapid detection of hydrogen peroxide. Furthermore, by combining with glucose oxidase, a cascade colorimetric method was established to further detect glucose with excellent sensitivity and selectivity.

Photo-Induced Polymerization and Reconfigurable Assembly of Multifunctional Ferrocene-Tyrosine

The photo-induced reconfigurable assembly of nanostructures via the simultaneous noncovalent and covalent polymerization of a functional ferrocene-tyrosine (Fc-Y) molecule is reported. The Fc-Y monomers can directly self-assemble into nanospheres with a smooth surface driven by noncovalent interactions. By covalent photo-crosslinking of the Fc-Y monomers, the nanospheres transform spontaneously into hollow vesicles composed of hierarchically ordered lamellar structures. It is worth noting that the formed nanostructures exhibit both reducing property for in situ mineralization of gold nanoparticles with tunable biocatalytic behavior, and the redox activity for superior energy storage capacity. The measured energy storage capacity is 31 mAh g^-1 for the nanospheres, which is the highest value reported so far for peptide assemblages as supercapacitor. The results offer insights into the dynamic self-assembly of highly ordered multifunctional materials with promising applications in catalysis, sensing, energy and biomedical fields.

A label-free fluorescence assay for hydrogen peroxide and glucose based on the bifunctional MIL-53(Fe) nanozyme

A label-free nanozyme MIL-53(Fe) with the dual-function of catalyzing and emitting fluorescence was utilized for turn-on fluorescence detection of hydrogen peroxide and glucose. The proposed strategy provides a cost-effective, safe and sensitive method for the design and development of multiple enzyme cascade assays for various biomolecules.

Highly efficient Fenton and enzyme-mimetic activities of NH2-MIL-88B(Fe) metal organic framework for methylene blue degradation

Here, we show that NH2-MIL-88B(Fe) can be used as a peroxidase-like catalyst for Fenton-like degradation of methylene blue (MB) in water. The iron-based NH2-MIL-88B(Fe) metal organic framework (MOF) was synthesized by a facile and rapid microwave heating method. It was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, powder X-ray diffraction, and the Brunauer-Emmett-Teller method. The NH2-MIL-88B(Fe) MOF possesses intrinsic oxidase-like and peroxidase-like activities. The reaction parameters that affect MB degradation were investigated, including the solution pH, NH2-MIL-88B(Fe) MOF and H2O2 concentrations, and temperature. The results show that the NH2-MIL-88B(Fe) MOF exhibits a wide working pH range (pH 3.0-11.0), temperature tolerance, and good recyclability for MB removal. Under the optimal conditions, complete removal of MB was achieved within 45 min. In addition, removal of MB was above 80% after five cycles, showing the good recyclability of NH2-MIL-88B(Fe). The NH2-MIL-88B(Fe) MOF has the features of easy preparation, high efficiency, and good recyclability for MB removal in a wide pH range. Electron spin resonance and fluorescence probe results suggest the involvement of hydroxyl radicals in MB degradation. These findings provide new insight into the application of high-efficient MOF-based Fenton-like catalysts for water purification.

Nanostructured silver fabric as a free-standing NanoZyme for colorimetric detection of glucose in urine

Enzyme-mimicking catalytic nanoparticles, more commonly known as NanoZymes, have been at the forefront for the development of new sensing platforms for the detection of a range of molecules. Although solution-based NanoZymes have shown promise in glucose detection, the ability to immobilize NanoZymes on highly absorbent surfaces, particularly on free-standing substrates that can be feasibly exposed and removed from the reaction medium, can offer significant benefits for a range of biosensing and catalysis applications. This work, for the first time, shows the ability of Ag nanoparticles embedded within the 3D matrix of a cotton fabric to act as a free-standing peroxidase-mimic NanoZyme for the rapid detection of glucose in complex biological fluids such as urine. The use of cotton fabric as a template not only allows high number of catalytically active sites to participate in the enzyme-mimic catalytic reaction, the absorbent property of the cotton fibres also helps in rapid absorption of biological molecules such as glucose during the sensing event. This, in turn, brings the target molecule of interest in close proximity of the NanoZyme catalyst enabling accurate detection of glucose in urine. Additionally, the ability to extract the free-standing cotton fabric-supported NanoZyme following the reaction overcomes the issue of potential interference from colloidal nanoparticles during the assay. Based on these unique characteristics, nanostructured silver fabrics offer remarkable promise for the detection of glucose and other biomolecules in complex biological and environmental fluids.

A cobalt-based polyoxometalate nanozyme with high peroxidase-mimicking activity at neutral pH for one-pot colorimetric analysis of glucose

A polyoxometalate (CoPW₁₁O₃₉) with high peroxidase-mimicking activity at physiological pH enables one-pot colorimetric analysis of glucose when coupled with GOx.

Fe3O4-AuNPs anchored 2D metal-organic framework nanosheets with DNA regulated switchable peroxidase-like activity

Two-dimensional (2D) metal-organic framework (MOF) nanosheets emerging as a new member of the 2D family have received significant research interest in recent years. Herein, we have successfully synthesized 2D copper-based MOF nanosheets with bimetallic anchorage using a facile two-step process at room temperature and ambient pressure, denoted as Cu(HBTC)-1/Fe₃O₄-AuNPs nanosheets. The as-synthesized 2D bimetallic MOF nanosheets displayed enhanced peroxidase-like activity with relatively high catalytic velocity and affinity for substrates compared with previously reported peroxidase mimics. Furthermore, their intrinsic peroxidase-like catalytic activity could be flexibly regulated by single-stranded DNA (ssDNA), exhibiting the enhancement of 3,3',5,5'-tetramethylbenzidine (TMB) oxidation or inhibition of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)diammonium salt (ABTS) oxidation due to the adsorption of ssDNA via π-π stacking. Accordingly, on the basis of their peroxidase-like activity, our prepared 2D bimetallic immobilized MOF nanosheets achieved ultra-sensitive detection of H₂O₂ with a linear range of 2.86 to 71.43 nM, and comparable detection performance for glucose with a linear range of 12.86 to 257.14 μM. By means of their controllable peroxidase-like activity, a versatile colorimetric sensing platform was developed which realized the detection of sulfadimethoxine (SDM) with a linear range of 3.57 to 357.14 μg L^-1 and the limit of detection (LOD) of 1.70 μg L^-1. With the multiplexed performance for detecting various targets, our as-synthesized bimetallic MOF nanosheets hold great promise for applications in environmental monitoring, as well as bioassays by virtue of their good biocompatibility.