Two-Dimensional Metal–Organic Framework Nanosheets as an Enzyme Inhibitor: Modulation of the α-Chymotrypsin Activity

Copper-Based Bio-MOF/GO with Lewis Basic Sites for CO2 Fixation into Cyclic Carbonates and C-C Bond-Forming Reactions

Several measures, including crude oil recovery improvement and carbon dioxide (CO2) conversion into valuable chemicals, have been considered to decrease the greenhouse effect and ensure a sustainable low-carbon future. The Knoevenagel condensation and CO2 fixation have been introduced as two principal solutions to these challenges. In the present study for the first time, bio-metal-organic frameworks (MOF)(Cu)/graphene oxide (GO) nanocomposites have been used as catalytic agents for these two reactions. In view of the attendance of amine groups, biological MOFs with NH2 functional groups as Lewis base sites protruding on the channels' internal surface were used. The bio-MOF(Cu)/20%GO performs efficaciously in CO2 fixation, leading to more than 99.9% conversion with TON = 525 via a solvent-free reaction under a 1 bar CO2 atmosphere. It has been shown that these frameworks are highly catalytic due to the Lewis basic sites, i.e., NH2, pyrimidine, and C═O groups. Besides, the Lewis base active sites exert synergistic effects and render bio-MOF(Cu)/10%GO nanostructures as highly efficient catalysts, significantly accelerating Knoevenagel condensation reactions of aldehydes and malononitrile as substrates, thanks to the high TOF (1327 h-1) and acceptable reusability. Bio-MOFs can be stabilized in reactions using GO with oxygen-containing functional groups that contribute as efficient substitutes, leading to an expeditious reaction speed and facilitating substrate absorption.

Ratiometric electrochemical immunoassay based on 2D Co/Fe MOF decorated with toluidine blue and Fc-labeled Schiff base for accurate assay of alpha-fetoprotein in clinical serum

The high level of alpha-fetoprotein (AFP) expression is closely related to hepatocellular carcinoma (HCC). Herein, a dual signal ratiometric electrochemical immunosensor based on chitosan-ferrocenecarboxaldehyde-spindle gold (Chit-Fc-SAu) and Co/Fe metal-organic framework-toluidine blue/polydopamine (Co/Fe MOF-TB/PDA) was proposed for quantitative analysis of AFP. Specifically, Chit-Fc-SAu worked as a substrate to trap more primary antibodies (Ab1) generating the first electrochemical signal from Fc. Thanks to the large specific surface area, the synergistic and electronic effects of Co/Fe MOF nanosheets, and the rich functional groups of PDA, Co/Fe MOF-TB/PDA could load more secondary antibodies (Ab2) and signal molecules (TB) providing another amplified electrochemical signal. In the presence of AFP, Ab1-AFP-Ab2 formed a sandwich structure, and as the AFP concentration increased, the peak current ratio of TB to Fc (ITB/IFc) also increased. The dual signal ratiometric strategy can avoid environmental signal interference and achieve signal self-calibration, thereby improving the accuracy and reproducibility of detection. After a series of exploration, this self-calibrated ratiometric immunosensor exhibited a wide linear range (0.001-200 ng mL-1), a low detection limit (0.34 pg mL-1), and good repeatability. When applied to the assay of clinical serum samples, the detection results of ratiometric sensor were consistent with that of commercial electrochemiluminescence (ECL) immunoassay, significantly superior to that of non-ratiometric sensor. The self-calibrated strategy based on ratiometric sensor helps to improve the accuracy of AFP in clinical diagnosis.

Fluorescent sensor based on bismuth metal-organic frameworks (Bi-MOFs) mimic enzyme for H2O2 detection in real samples and distinction of phenylenediamine isomers

Although peroxidase-like nano-enzymes have been widely utilized in biosensors, nano-enzyme based biosensors are seldom used for both quantitative analysis of H2O2 and differentiation of isomers of organic compounds simultaneously. In this study, a dual-functional mimetic enzyme-based fluorescent sensor was constructed using metal-organic frameworks (Bi-MOFs) with exceptional oxidase activity and fluorescence properties. This mimetic enzyme sensor facilitated quantitative analysis of H2O2 and accurate discrimination of phenylenediamine isomers. The sensor exhibited a wide linear range (0.5-400 μM) and low detection limit (0.16 μM) for the detection of H2O2. Moreover, the sensor can also be used for the discrimination of phenylenediamine isomers, in which the presence of o-phenylenediamine (OPD) leads to the appearance of a new fluorescence emission peak at 555 nm, while the presence of p-phenylenediamine (PPD) significantly quenched its fluorescence due to the internal filtration effect. The proposed strategy exhibited a commendable capability in distinguishing phenylenediamine isomers, thereby paving the way for novel applications of MOFs in the field of environmental science.

Nanobiohybrids: Synthesis strategies and environmental applications from micropollutants sensing and removal to global warming mitigation

Micropollutants contamination and global warming are critical environmental issues that require urgent attention due to natural and anthropogenic activities posing serious threats to human health and ecosystems. However, traditional technologies (such as adsorption, precipitation, biodegradation, and membrane separation et al.) are facing challenges of low utilization efficiency of oxidants, poor selectivity, and complex in-situ monitoring operations. To address these technical bottlenecks, nanobiohybrids, synthesized by interfacing the nanomaterials and biosystems, have recently emerged as eco-friendly technologies. In this review, we summarize the synthesis approaches of nanobiohybrids and their utilization as emerging environmental technologies for addressing environmental problems. Studies demonstrate that enzymes, cells, and living plants can be integrated with a wide range of nanomaterials including reticular frameworks, semiconductor nanoparticles and single-walled carbon nanotubes. Moreover, nanobiohybrids demonstrate excellent performance for micropollutant removal, carbon dioxide conversion, and sensing of toxic metal ions and organic micropollutants. Therefore, nanobiohybrids are expected to be environmental friendly, efficient, and cost-effective techniques for addressing environmental micropollutants issues and mitigating global warming, benefiting both humans and ecosystems alike.

Supramolecular framework membrane for precise sieving of small molecules, nanoparticles and proteins

Synthetic framework materials have been cherished as appealing candidates for separation membranes in daily life and industry, while the challenges still remain in precise control of aperture distribution and separation threshold, mild processing methods, and extensive application aspects. Here, we show a two-dimensional (2D) processible supramolecular framework (SF) by integrating directional organic host-guest motifs and inorganic functional polyanionic clusters. The thickness and flexibility of the obtained 2D SFs are tuned by the solvent modulation to the interlayer interactions, and the optimized SFs with limited layers but micron-sized areas are used to fabricate the sustainable membranes. The uniform nanopores allow the membrane composed of layered SF to exhibit strict size retention for substrates with the rejection value of 3.8 nm, and the separation accuracy within 5 kDa for proteins. Furthermore, the membrane performs high charge selectivity for charged organics, nanoparticles, and proteins, due to the insertion of polyanionic clusters in the framework skeletons. This work displays the extensional separation potentials of self-assembled framework membranes comprising of small-molecules and provides a platform for the preparation of multifunctional framework materials due to the conveniently ionic exchange of the counterions of the polyanionic clusters.

Construction of Macroporous β-Glucosidase@MOFs by a Metal Competitive Coordination and Oxidation Strategy for Efficient Cellulose Conversion at 120 °C

Metal-organic frameworks (MOFs) have become promising accommodation for enzyme immobilization in recent years. However, the microporous nature of MOFs affects the accessibility of large molecules, resulting in a significant decline in biocatalysis efficiency. Herein, a novel strategy is reported to construct macroporous MOFs by metal competitive coordination and oxidation with induced defect structure using a transition metal (Fe²⁺) as a functional site. The feasibility of in situ encapsulating β-glucosidase (β-G) within the developed macroporous MOFs endows an enzyme complex (β-G@MOF-Fe) with remarkably enhanced synergistic catalysis ability. The 24 h hydrolysis rate of β-G@MOF-Fe (with respect to cellobiose) is as high as approximately 99.8%, almost 32.2 times that of free β-G (3.1%). Especially, the macromolecular cellulose conversion rate of β-G@MOF-Fe reached 90% at 64 h, while that of β-G@MOFs (most micropores) was only 50%. This improvement resulting from the expansion of pores (significantly increased at 50-100 nm) can provide enough space for the hosted biomacromolecules and accelerate the diffusion rate of reactants. Furthermore, unexpectedly, the constructed β-G@MOF-Fe showed a superior heat resistance of up to 120 °C, attributing to the new strong coordination bond (Fe²⁺-N) formation through the metal competitive coordination. Therefore, this study offers new insights to solve the problem of the high-temperature macromolecular substrate encountered in the actual reaction.

2D Cu-Bipyridine MOF Nanosheet as an Agent for Colon Cancer Therapy: A Three-in-One Approach for Enhancing Chemodynamic Therapy

Chemodynamic therapy (CDT) is a highly tumor-specific and minimally invasive treatment that is widely used in cancer therapy. However, its therapeutic effect is limited by the poor efficiency of hydroxyl radical generation. In colon cancer in particular, the high expression of hydrogen sulfide (H₂S), which has strong reducibility, results in the consumption of generated hydroxyl radicals, further weakening the efficacy of CDT. To overcome this problem, we developed a novel two-dimensional (2D) Cu-bipyridine metal-organic framework (MOF) nanosheet [Cu(bpy)₂(OTf)₂] for colon cancer CDT. The therapeutic effect of Cu(bpy)₂(OTf)₂ is enhanced based on three factors. First, the developed 2D Cu-MOF rapidly consumes H₂S to inhibit the consumption of generated hydroxyl radicals. Second, the ultrasmall CuS generated after H₂S depletion facilitates Fenton-like reactions. Third, the generated CuS exhibits good photothermal performance in the second near-infrared window, allowing for photothermal-enhanced CDT. The ability of Cu(bpy)₂(OTf)₂ to improve the CDT effect was demonstrated through both in vitro and in vivo experiments. This work demonstrates the applicability of 2D Cu-MOF in the CDT of colon cancer and provides a novel strategy for constructing CDT agents for colon cancer.

Advances in Metal-Organic Framework (MOFs) based biosensors for diagnosis: An update

Metal-organic frameworks (MOFs) have significant advantages over other candidate classes of chemo-sensory materials owing to their extraordinary structural tunability and characteristics. MOF-based biosensing is a simple, and convenient method for identifying various species. Biomarkers are molecular or cellular processes that link environmental exposure to a health outcome. Biomarkers are important in understanding the links between environmental chemical exposure and the development of chronic diseases, as well as in identifying disease-prone subgroups. Until now, several species, including nanoparticles (NPs) and their nanocomposites, small molecules, and unique complex systems, have been used for the chemical sensing of biomarkers. Following the overview of the field, we discussed the various fabrication methods for MOFs development in this review. We provide a thorough overview of the previous five years of progress to broaden the scope of analytes for future research. Several enzymatic and non-enzymatic sensors are offered, together with a mandatory measuring method that includes detection range and dynamic range. In addition, we reviewed the comparison of enzymatic and non-enzymatic biosensors, inventive edges, and the difficulties that need to be solved. This work might open up new possibilities for material production, sensor development, medical diagnostics, and other sensing fields.

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.

Nanoscale Metal−Organic Frameworks and Their Nanomedicine Applications

Abundant connectivity among organic ligands and inorganic metal ions makes the physical and chemical characters of metal-organic frameworks (MOFs) could be precisely devised and modulated for specific applications. Especially nanoscale MOFs (NMOFs), a unique family of hybrid nanomaterials, with merits of holding the nature as the mainstay MOFs and demonstrating particle size in nanoscale range which enable them prospect platform in clinic. Adjustability of composition and structure allows NMOFs with different constituents, shapes, and characteristics. Oriented frameworks and highly porous provide enough space for packing therapeutic cargoes and various imaging agents efficiently. Moreover, the relatively labile metal-ligand bonds make NMOFs biodegradable in nature. So far, as a significant class of biomedically relevant nanomaterials, NMOFs have been explored as drug carriers, therapeutic preparation, and biosensing and imaging preparation owing to their high porosity, multifunctionality, and biocompatibility. This review provides up-to-date developments of NMOFs in biomedical applications with emphasis on size control, synthetic approaches, and surfaces functionalization as well as stability, degradation, and toxicity. The outlooks and several crucial issues of this area are also discussed, with the expectation that it may help arouse widespread attention on exploring NMOFs in potential clinical applications.

Preparation of a boronate affinity-functionalized metal–organic framework material for selective recognition and separation of glycoproteins at physiological pH

A boronate affinity functionalized metal–organic framework material was successfully prepared for the efficient and selective extraction of OVA glycoprotein from egg white samples and protein powder.

Advances and challenges in the development of nanosheet membranes

The development of highly efficient separation membranes utilizing emerging materials with controllable pore size and minimized thickness could greatly enhance the broad applications of membrane-based technologies. Having this perspective, many studies on the incorporation of nanosheets in membrane fabrication have been conducted, and strong interest in this area has grown over the past decade. This article reviews the development of nanosheet membranes focusing on two-dimensional materials as a continuous phase, due to their promising properties, such as atomic or nanoscale thickness and large lateral dimensions, to achieve improved performance compared to their discontinuous counterparts. Material characteristics and strategies to process nanosheet materials into separation membranes are reviewed, followed by discussions on the membrane performances in diverse applications. The review concludes with a discussion of remaining challenges and future outlook for nanosheet membrane technologies.

Structural and Electrochemical Studies of Cobalt(II) and Nickel(II) Coordination Polymers with 6-Oxonicotinate and 4,4′-Bipyridine

The 6-oxonicotinate (6-Onic) salts of a one-dimensional cationic cobalt(II) or nickel(II) coordination polymers with 4,4′-bipyridine (4,4′-bpy), namely {[Co(4,4′-bpy)(H2O)4](6-Onic)2·2H2O}n (1) and {[Ni(4,4′-bpy)(H2O)4](6-Onic)2·2H2O}n (2), were prepared hydrothermally by reactions of cobalt(II) nitrate hexahydrate or nickel(II) nitrate hexahydrate, respectively, 6-hydroxynicotinic acid and 4,4′-bipyridine in a mixture of ethanol and water. In the hydrogen-bonded frameworks of 1 and 2, the one-dimensional polymeric chains of {[M(4,4′-bpy)(H2O)4]2+}n (M = Co, Ni), the 6-oxonicotinate anions and the lattice water molecules were assembled via strong intermolecular O–H···O and N–H···O hydrogen bonds and π–π interactions, leading to the formation of the representative hydrogen-bond ring motifs: trimeric R23(10) motif, the centrosymmetric tetrameric R24(8) and R24(12) motifs and the pentameric R45(12) motif. The isostructural coordination polymers 1 and 2 exhibited a different electrochemical behavior, as observed by cyclic voltammetry, which can be attributed to the nature of the metal ions (cobalt(II) vs. nickel(II)).

Recent advances in enzyme-enhanced immunosensors

Among the products for rapid detection in different fields, enzyme-based immunosensors have received considerable attention. Recently, great efforts have been devoted to enhancing the output signals of enzymes through different strategies that can significantly improve the sensitivity of enzyme-based immunosensors for the need of practical applications. In this manuscript, the significance of enzyme-based signal transduction patterns in immunoassay and the central role of enzymes in achieving precise control of reaction systems are systematically described. In view of the rapid development of this field, we classify these strategies based on the combination of immune recognition and enzyme amplification into three categories, namely enzyme-based enhancement strategies, combination of the catalytic amplification of enzymes with other signal amplification methods, and substrate-based enhancement strategies. The current focus and future direction of enzyme-based immunoassays are also discussed. This article is not exhaustive, but focuses on the latest advances in different signal generation methods based on enzyme-initiated catalytic reactions and their applications in the detection field, which could provide an accessible introduction of enzyme-based immunosensors for the community with a view to further improving its application efficiency.

Fabrication of Ultrathin Membranes Using 2D-MOF Nanosheets for Tunable Gas Separation

Two-dimensional (2D) metal-organic frameworks (MOF) nanosheets have emerged as novel membrane materials for gas separation. However, the development of ultrathin MOF membranes with tunable separation performances is still a challenge. Herein, we developed a facile GO-assisted restacking method to fabricate defect-free membranes with monolayer Zr-BTB nanosheets. Obtained ultrathin membranes ranging from 130 nm to 320 nm show tunable separation performances and exceed the 2008 Robeson upper bound by changing the amount of nanolayers in vertical stacking direction. Furthermore, a heating filtration method was used to change the restacking process of nanosheets in the horizontal direction. As a result, H₂ /CO₂ selectivity can be enhanced by two times with the same membrane thickness (130 nm) and H₂ permeance is almost maintained to be 7.0×10^-7  mol m^-2  s^-1  pa^-1 . This method may provide a possible way to efficiently tune the gas separation performances of MOF membranes.

Programmable Logic in Metal-Organic Frameworks for Catalysis

Metal-organic frameworks (MOFs) have emerged as one of the most widely investigated materials in catalysis mainly due to their excellent component tunability, high surface area, adjustable pore size, and uniform active sites. However, the overwhelming number of MOF materials and complex structures has brought difficulties for researchers to select and construct suitable MOF-based catalysts. Herein, a programmable design strategy is presented based on metal ions/clusters, organic ligands, modifiers, functional materials, and post-treatment modules, which can be used to design the components, structures, and morphologies of MOF catalysts for different reactions. By establishing the corresponding relationship between these modules and functions, researchers can accurately and efficiently construct heterometallic MOFs, chiral MOFs, conductive MOFs, hierarchically porous MOFs, defective MOFs, MOF composites, and MOF-derivative catalysts. Further, this programmable design approach can also be used to regulate the physical/chemical microenvironments of pristine MOFs, MOF composites, and MOF-derivative materials for heterogeneous catalysis, electrocatalysis, and photocatalysis. Finally, the challenging issues and opportunities for the future research of MOF-based catalysts are discussed. Overall, the modular design concept of this review can be applied as a potent tool for exploring the structure-activity relationships and accelerating the on-demand design of multicomponent catalysts.

Precise Spatial-Designed Metal-Organic-Framework Nanosheets for Efficient Energy Transfer and Photocatalysis

High-efficiency photocatalysis in metal-organic frameworks (MOF) and MOF nanosheets (NSs) are often limited by their short-lived charge separation as well as self-quenching. Here, we propose to use the energy-transfer process (EnT) to increase charge separation, thus enhancing the catalytic performance of a series of MOF NSs. With the use of NS, the photocatalyst can also be well isolated to reduce self-quenching. Tetrakis(4-carboxyphenyl) porphyrin (H₄ TCPP) and 1,3,6,8-tetrakis(p-benzoic acid)pyrene (H₄ TBAPy) linkers were chosen as the acceptor and donor moieties, respectively. Accounting for the precise spatial design afforded by the MOF NSs, the donor and acceptor moieties could be closely positioned on the NSs, allowing for an efficient EnT process as well as a high degree of site isolation. Two templates, donor-on-acceptor NS and acceptor-on-donor NS catalysts, were successfully synthesized, and the results show that the second one has much enhanced catalytic performances over the first one due to site-isolated active photocatalysts.

Two-dimensional biomaterials: material science, biological effect and biomedical engineering applications

To date, nanotechnology has increasingly been identified as a promising and efficient means to address a number of challenges associated with public health. In the past decade, two-dimensional (2D) biomaterials, as a unique nanoplatform with planar topology, have attracted explosive interest in various fields such as biomedicine due to their unique morphology, physicochemical properties and biological effect. Motivated by the progress of graphene in biomedicine, dozens of types of ultrathin 2D biomaterials have found versatile bio-applications, including biosensing, biomedical imaging, delivery of therapeutic agents, cancer theranostics, tissue engineering, as well as others. The effective utilization of 2D biomaterials stems from the in-depth knowledge of structure-property-bioactivity-biosafety-application-performance relationships. A comprehensive summary of 2D biomaterials for biomedicine is still lacking. In this comprehensive review, we aim to concentrate on the state-of-the-art 2D biomaterials with a particular focus on their versatile biomedical applications. In particular, we discuss the design, fabrication and functionalization of 2D biomaterials used for diverse biomedical applications based on the up-to-date progress. Furthermore, the interactions between 2D biomaterials and biological systems on the spatial-temporal scale are highlighted, which will deepen the understanding of the underlying action mechanism of 2D biomaterials aiding their design with improved functionalities. Finally, taking the bench-to-bedside as a focus, we conclude this review by proposing the current crucial issues/challenges and presenting the future development directions to advance the clinical translation of these emerging 2D biomaterials.

Functionalized Tumor-Targeting Nanosheets Exhibiting Fe(II) Overloading and GSH Consumption for Ferroptosis Activation in Liver Tumor

Liver tumor is difficult to cure for its high degree of malignancy and rapid progression characteristics. Ferroptosis as a new model of inducing cell death is expected to break the treatment bottleneck of liver tumors. Here, a strategy to induce ferroptosis in HepG2 cells with acid-degradable tumor targeted nanosheets Cu-Hemin-PEG-Lactose acid (Cu-Hemin-PEG-LA) is proposed. After highly ingested by HepG2 cells, Cu-Hemin-PEG-LA nanosheets are degraded by weak acid and release Cu(II) and hemin, which consuming intracellular glutathione (GSH) content and increasing the expression of heme oxygenase 1 (HMOX1) protein, respectively. Furthermore, the expression of glutathione peroxidase 4 protein (GPX4) is down-regulated by consumption intracellular GSH content via converting GSH into glutathione oxidized (GSSG), which is named the classical mode. The intracellular Fe²⁺ content is overloaded by the significant up-regulation of HMOX1 expression, which is denoted as nonclassical mode. The synergistic effect of classical and nonclassical mode increased the intracellular lipid reactive oxide species, induced the occurrence of ferroptosis and up-regulated the expression of BH3 interacting domain death agonist (BID), apoptosis-inducing factor (AIF), and endonuclease G proteins (EndoG). The synergistic strategy demonstrate the excellent ferroptosis induction ability and antitumor efficacy in vivo, which provides great potential for the clinical transformation of ferroptosis.

Recent advances in Cu(II)/Cu(I)-MOFs based nano-platforms for developing new nano-medicines

With increasing world population, life-span of humans and spread of viruses, myriad of diseases in human beings are becoming more and more common. Because of the interesting chemical and framework versatility and porosity of metal organic frameworks (MOFs) they find application in varied areas viz. catalysis, sensing, metal ion/gas storage, chemical separation, drug delivery, bio-imaging. This subclass of coordination polymers having interesting three-dimensional framework exhibits inordinate potential and hence may find application in treatment and cure of cancer, diabetes Alzheimer's and other diseases. The presented review focuses on the diverse mechanism of action, unique biological activity and advantages of copper-based metal organic framework (MOF) nanomaterials in medicine. Also, different methods used in the treatment of cancer and other diseases have been presented and the applications as well as efficacy of copper MOFs have been reviewed and discussed. Eventually, the current-status and potential of copper based MOFs in the field of anti-inflammatory, anti-bacterial and anti-cancer therapy as well as further investigations going on for this class of MOF-based multifunctional nanostructures in for developing new nano-medicines have been presented.

Environment Responsive Metal-Organic Frameworks as Drug Delivery System for Tumor Therapy

Nanoparticles as drug delivery systems can alter the drugs' hydrophilicity to affect drug uptake and efflux in tissues. They prevent drugs from non-specifically binding with bio-macromolecules and enhance drug accumulation at the lesion sites, improving therapy effects and reducing unnecessary side effects. Metal-organic frameworks (MOFs), the typical nanoparticles, a class of crystalline porous materials via self-assembled organic linkers and metal ions, exhibit excellent biodegradability, pore shape and sizes, and finely tunable chemical composition. MOFs have a rigid molecular structure, and tunable pore size can improve the encapsulation drug's stability under harsh conditions. Besides, the surface of MOFs can be modified with small-molecule ligands and biomolecule, and binding with the biomarkers which is overexpressed on the surface of cancer cells. MOFs formulations for therapeutic have been developed to effectively respond to the unique tumor microenvironment (TEM), such as high H2O2 levels, hypoxia, and high concentration glutathione (GSH). Thus, MOFs as a drug delivery system should avoid drugs leaking during blood circulation and releasing at the lesion sites via a controlling manner. In this article, we will summary environment responsive MOFs as drug delivery systems for tumor therapy under different stimuli.

One-pot bottom-up synthesis of a 2D graphene derivative: application in biomolecular recognition and nanozyme activity

The synthesis of two-dimensional (2D) nanosheets such as graphene and its derivatives through a bottom-up approach has many advantages such as growth control and functionalization, but it is always challenging to get the desired material. Herein, we have reported the synthesis of water soluble 2D-nanosheets through a bottom-up approach from 2,4,6-tribromo-3-hydroxybenzoic acid via a self-coupling pathway and characterized them using several techniques. AFM and TEM analyses reveal that the synthesized material has a layered structure with a thickness of ∼1.2 nm. Also, the prepared nanosheets are amorphous in nature with high negative charge (-38 ± 2.5 mV). The flexible nature of 2D-nanosheets and their functionality can be used in many related applications. Therefore, we have utilized the synthesized 2D-nanosheets in biomolecular recognition studies. It was found that the enzymatic activity of α-chymotrypsin can be controlled reversibly in the presence of the synthesized 2D-nanosheets. The kinetic study revealed that the nanosheet surface selectively binds to the active sites of the enzyme through a competitive pathway. Furthermore, we explored the nanozyme activity of the material in a peroxidase-like activity assay of two bio-active molecules: Nicotinamide Adenine Dinucleotide Phosphate (NADH) and dopamine. The results suggest that the prepared material efficiently catalyzed the oxidation of NADH to biological cofactor NAD⁺ and dopamine to aminochrome in the presence of H₂O₂. These synthesized graphene-like 2D-nanosheets with functional groups can be further tuned with other functionalities, which can open a new window for other related applications.

Facet Selectivity Guided Assembly of Nanoarchitectures onto Two-Dimensional Metal-Organic Framework Nanosheets

Facet-selective nanostructures in living systems usually exhibit outstanding optical and enzymatic properties, playing important roles in photonics, matter exchange, and biocatalysis. Bioinspired construction of facet-selective nanostructures offers great opportunities for sophisticated nanomaterials, but remains a formidable task. We have developed a macromolecule-mediated strategy for the assembly of upconversion nanoparticles (UCNPs)/two-dimensional metal-organic frameworks (2DMOFs) heterostructures with facet selectivity. Both experimental and theoretical results demonstrate that polyvinylpyrrolidone (PVP) can be utilized as an interface-selective mediator to further promote the facet-selective assembly of MOFs onto the surface of UCNPs. The UCNPs/2DMOFs nanostructures with facet selectivity display specific optical properties and show great advantages in anti-counterfeiting. Our demonstration of UCNPs/2DMOFs provides a vivid example for the controlled fabrication of facet-selective nanostructures and can promote the development of advanced functional materials for applications in biosensing, energy conversion, and information assurance.

Three Polyoxovanadates-Based Organic-Inorganic Hybrids: Structural Variation, Bifunctional Electrocatalytic Activities, and Computational Studies

Three bimetallic organic-inorganic hybrids based on the [V₂O₆]^2- building unit, [Cu(pty)(V₂O₆)]·H₂O (1), [Cu(pty)(V₂O₆)] (2), [Cu(tpy)(V₂O₆)] (3), (pty = 4'-(4″-pyridyl)-2,2':6',2″-terpyridine, tpy = 2,2':6',2″-terpyridine), were synthesized via a one-pot method. Hybrid 1 has a 1D straight chain architecture with [V₂O₆]^2- clusters and Cu-pty complexes; hybrids 2 and 3 possess a 2D sheet structure including 10-membered rings assembled from four [Cu(pty)]²⁺ motifs and six [V₂O₆]^2- clusters in 2, and two [Cu(tpy)]²⁺ units and eight [V₂O₆]^2- clusters in 3. Noteworthy, hybrids 1-3 can be employed as bifunctional electrocatalysts for electroreduction of nitrite and electrooxidation of ascorbic acid. Additionally, theoretical calculations including the molecular electrostatic potential and the frontier molecular orbital were performed to estimate the electronic structure of hybrids 1-3. The natural bond orbital analysis was also calculated to interpret the electron charge distribution.

Enhancing the enzymatic inhibition performance of Cu-based metal-organic frameworks by shortening the organic ligands

Creating more exposed active sites on the metal-organic framework (MOF) surface is crucial for enhancing the recognition ability of MOF artificial receptors. Here, a copper-based MOF Cu(im)₂ (im = imidazole) was utilized to act as an artificial receptor, inhibiting the activity of α-chymotrypsin. The shortest diazole ligand reduced the distance between regenerative copper sites, creating as many active sites as possible on the MOF unit surface. The amount of copper(ii) centers on the Cu(im)₂ surface was calculated to be 4.96 × 10⁶μm^-2. Thus, Cu(im)₂ showed exceedingly higher inhibition performance than other copper-based MOFs. The ChT activity was almost inhibited (88.8%) after the incubation with only 20 μg mL^-1 Cu(im)₂ for 10 min. The binding between ChT and Cu(im)₂ was very fast with high affinity. Further results proved that Cu(im)₂ inhibited the activity of ChT through electrostatic interactions and coordination interactions via the mixed inhibition mode. This strategy to use short ligands to create more active sites on the MOF surface provides a new direction to enhance the inhibition efficiency.

Regulating metal-organic frameworks as stationary phases and absorbents for analytical separations

Metal-organic frameworks (MOFs) are highly ordered framework systems composed of metal centers and organic linkers formed through coordination bonds. The diversity of metal elements and easily modified organic ligands, together with controllable synthetic approaches, gives rise to the designability of various MOF structures and topologies and the capability of MOFs to be functionalized. Their structural diversity provides MOFs with many unique properties, such as permanent porosity, flexible structures, thermostability, and high adsorption capacity, leading to great practicability in technical applications. In this review, we concentrate on the applications of MOFs in the field of gas chromatography, high-performance liquid chromatography, and the enrichment of biomolecules, based on rational arrangements in the structures and functions of MOFs. Moreover, we emphasize the importance of structural and chemical regulations for the improvement of separation efficiency.

Biomimetic catalysts of iron-based metal-organic frameworks with high peroxidase-mimicking activity for colorimetric biosensing

The field of metal-organic framework (MOF)-based biomimetic catalysts has achieved great progress but is still in its infancy. The systematic investigation of the tailored construction of MOF-based biomimetic catalysts is required for further development. Herein, two iron-based MOFs, namely, [(Fe₃O)₂(H₂O)₄(HCOO)(L)₂]_n (HUST-5: H₆L = hexakis(4-formylphenoxy) cyclotriphosphazene; HUST = Huazhong University of Science and Technology) and [(Fe₃O)(H₂O)₃(L)]_n (HUST-7) have been fabricated through the assembly of different iron clusters and hexa-carboxylate ligand under the control of the added acid species. The two MOFs exhibit distinct secondary building units (SBUs) and topological structures, which could be used as biomimetic catalysts for the systematic comparisons of structural characteristics and the catalytic activity. Both MOFs possess catalytic activity similar to that of natural peroxidases towards the catalysis of the oxidation of a variety of substrates. Significantly, HUST-5 and HUST-7 can effectively catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) by H₂O₂ accompanied by significant colorimetric biosensing. With same compositions, different catalytic performances were obtained due to differences in the porous structures and characteristics of SBUs in two Fe-MOFs, which was also validated by theoretical calculation results. Furthermore, the phenomenon of colorimetric biosensing could be significantly suppressed by the addition of ascorbic acid (AA) during the oxidation process of TMB. It was observed from these findings that a facile colorimetric biosensing platform for detecting H₂O₂ and ascorbic acid has been successfully explored. Therefore, this work provides another unique perspective for the tailor-made preparation of stable MOF-based peroxidase mimics with excellent catalytic performance and colorimetric biosensing.

Metal-Organic Frameworks for Liquid Phase Applications

In the last two decades, metal-organic frameworks (MOFs) have attracted overwhelming attention. With readily tunable structures and functionalities, MOFs offer an unprecedentedly vast degree of design flexibility from enormous number of inorganic and organic building blocks or via postsynthetic modification to produce functional nanoporous materials. A large extent of experimental and computational studies of MOFs have been focused on gas phase applications, particularly the storage of low-carbon footprint energy carriers and the separation of CO2-containing gas mixtures. With progressive success in the synthesis of water- and solvent-resistant MOFs over the past several years, the increasingly active exploration of MOFs has been witnessed for widespread liquid phase applications such as liquid fuel purification, aromatics separation, water treatment, solvent recovery, chemical sensing, chiral separation, drug delivery, biomolecule encapsulation and separation. At this juncture, the recent experimental and computational studies are summarized herein for these multifaceted liquid phase applications to demonstrate the rapid advance in this burgeoning field. The challenges and opportunities moving from laboratory scale towards practical applications are discussed.

Single-Crystalline Ultrathin 2D Porous Nanosheets of Chiral Metal-Organic Frameworks

Two-dimensional (2D) materials with highly ordered in-plane nanopores are crucial for numerous applications, but their rational synthesis and local structural characterization remain two grand challenges. We illustrate here that single-crystalline ultrathin 2D MOF nanosheets (MONs) with intrinsic porosity can be prepared by exfoliating layered metal-organic frameworks (MOFs), whose layers are stabilized by sterically bulky groups. As a result, three three-dimensional (3D) isostructural lanthanide MOFs possessing porous layer structures are constructed by coordinating metal ions with an angular dicarboxylate linker derived from chiral 1,1'-biphenyl phosphoric acid with pendant mesityl groups. The Eu-MOF is readily ultrasonic exfoliated into single-crystalline nanosheets with a thickness of ca. 6.0 nm (2 layers) and a lateral size of 1.5 × 3.0 μm². The detailed structural information, i.e., the pore channels and individual organic and inorganic building units in the framework, is clearly visualized by a low-dose high-resolution transmission electron microscopy (HRTEM) technique. Benefiting from their ultrathin feature, the nanosheets are well embedded into the polymer matrix to form free-standing mixed-matrix membranes. In both the solution and membrane phase, the fluorescence of the MONs can be effectively quenched by a total of 17 chiral terpenes and terpenoids through supramolecular interactions with uncoordinated chiral phosphoric acids, leading to a chiral optical sensor for detecting vapor enantiomers, which is among the most challenging molecular recognition tasks.

Metal-Organic Frameworks: Synthetic Methods and Potential Applications

Metal-organic frameworks represent a porous class of materials that are build up from metal ions or oligonuclear metallic complexes and organic ligands. They can be considered as sub-class of coordination polymers and can be extended into one-dimension, two-dimensions, and three-dimensions. Depending on the size of the pores, MOFs are divided into nanoporous, mesoporous, and macroporous items. The latter two are usually amorphous. MOFs display high porosity, a large specific surface area, and high thermal stability due to the presence of coordination bonds. The pores can incorporate neutral molecules, such as solvent molecules, anions, and cations, depending on the overall charge of the MOF, gas molecules, and biomolecules. The structural diversity of the framework and the multifunctionality of the pores render this class of materials as candidates for a plethora of environmental and biomedical applications and also as catalysts, sensors, piezo/ferroelectric, thermoelectric, and magnetic materials. In the present review, the synthetic methods reported in the literature for preparing MOFs and their derived materials, and their potential applications in environment, energy, and biomedicine are discussed.

Molecular interaction of fluorescent carbon dots from mature vinegar with human hemoglobin: Insights from spectroscopy, thermodynamics and AFM

Foodborne nanoparticles have attracted considerable interest due to their distinctive fluorescence and physicochemical properties. The discovery of vinegar carbon dots (VCDs) has drawn our attention to study their effect on human plasma protein. Herein, spectral, constructional, morphological, and enzymatic activity assessments were carried out to investigate the interaction of VCDs with human hemoglobin (HHb). The intrinsic fluorescence of HHb was quenched significantly by the VCDs through a static quenching process. Furthermore, binding constants and important thermodynamic parameters were calculated, the negative enthalpy and entropy changes were accompanied by a negative Gibbs energy, which proposed the binding between VCDs with HHb was spontaneous. Moreover, negative enthalpy and entropy change corroborated the involvement of van der Waals force and hydrogen bonds in the binding process. Results from FTIR, atomic force microscopy and circular dichroism revealed change of HHB after binding with VCDs although their essential morphological features were unaffected. The esterase activity of HHb decreased after VCDs treatment in a dose-dependent manner, which further confirmed the effect of VCDs on HHb. The results offered detailed information about the interaction between VCDs and HHb.

Two-dimensional metal organic frameworks for biomedical applications

Two-dimensional (2D) metal organic frameworks (MOFs), are an emerging class of layered nanomaterials with well-defined structure and modular composition. The unique pore structure, high flexibility, tunability, and ability to introduce desired functionality within the structural framework, have led to potential use of MOFs in biomedical applications. This article critically reviews the application of 2D MOFs for therapeutic delivery, tissue engineering, bioimaging, and biosensing. Further, discussion on the challenges and strategies in next generation of 2D MOFs are also included. This article is categorized under: Nanotechnology Approaches to Biology > Nanoscale Systems in Biology.

Lysozyme Adsorption on Porous Organic Cages: A Molecular Simulation Study

Recently, porous organic cages (POCs) have emerged as a novel porous material with many merits and are widely utilized in many application fields. In this work, for the first time, molecular dynamics simulations were performed to investigate the mechanism of lysozyme adsorption onto the CC3 crystal, a kind of widely studied POC material. The simulation results show that lysozyme adsorbs onto the surface of CC3 with "top end-on," "back-on," or "side-on" orientations. It is found that the van der Waals interaction is the primary contribution to the binding; the conformation of the lysozyme is well preserved during the adsorption process. This provides some evidence for its biocompatibility and feasibility in biorelated applications. Arginine plays an important role in mediating the adsorption through nonpolar aliphatic chains. More importantly, the distribution and structure of the water layer on the POC surface has a significant impact on adsorption. This study provides insights into the development of POC materials with defined morphologies for the adsorption of biomolecules and may help the rational design of biorelated systems.

Recent development of two-dimensional metal-organic framework derived electrocatalysts for hydrogen and oxygen electrocatalysis

Developing efficient and low-cost electrocatalysts with unique nanostructures is of great significance for improved electrocatalytic reactions, including the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR). Two-dimensional (2D) metal-organic frameworks (MOFs) have attracted recent attention because of their unique dimension-related properties, such as ultrathin thickness, large specific surface area, and abundant accessible active sites that can act as good precursors for the derivation of a variety of nanocomposites as active materials in electrocatalysis and energy-related devices. In this review, we present recent developments in 2D MOF-derived nanomaterials for hydrogen and oxygen reactions in overall water-splitting and rechargeable Zn-air batteries. The advantages of various synthetic strategies are summarized and discussed in detail. Finally, we discuss the main challenges and future perspectives of the development of 2D MOF-derived electrocatalysts.