Bifunctional Hybrid Enzyme-Catalytic Metal Organic Framework Reactors for α-Glucosidase Inhibitor Screening

Design, Synthesis, and Application of Immobilized Enzymes on Artificial Porous Materials

Enzymes have been recognized as highly efficient biocatalysts, whereas characteristics such as poor stability and single reaction type greatly significantly limit their wide application. Hence, the exploitation of suitable carriers for immobilized enzymes enables the provision of a protective layer for the enzyme, with the capability of chemical and biological cascade catalysis. Among the various immobilization carriers, metal-organic frameworks (MOFs), covalent organic frameworks (COFs) and hydrogen-bonded organic frameworks (HOFs) have been emerging as a promising strategy to surpass the inherent instability and other limitations of free enzymes. Specifically, the integration of such artificial porous materials as carriers improves the stability and reusability of enzymes, while simultaneously affording a platform for multifunctional applications. Herein, this review systematically discusses the various preparation strategies and advantages of artificial porous materials, while elucidating the effects of different immobilization methods on enzyme activity. Furthermore, the innovative applications of artificial porous materials as multifunctional carriers in the field of enzyme immobilization fields such as enzyme carriers, photocatalysts, chemical catalysts and sensing are also comprehensively summarized here, thus demonstrating their multifunctional characteristics and promising applications in addressing complex biotransformation challenges.

Unravelling the Potential of Crude Enzyme Extracts for Biocatalyst Entrapment in Metal-Organic Frameworks

To bolster the applicability of enzymes as catalysts, it is imperative not only to address their inherent fragility, particularly when used under harsh organic-synthetic reaction conditions, but also to mitigate deactivation during purification and enable applicability in a broad range of organic-synthetic transformations. Currently, the process of purification of crude enzyme extracts and subsequent heterogenization to obtain immobilized biocatalysts often leads to partial enzyme deactivation and represents, at least in part, a resource-intensive process that is driving up the overall production efforts. To tackle both the enzyme fragility and deactivation during purification and immobilization, we propose the direct use of crude enzyme extracts obtained from cell lysis instead of pure enzymes and their entrapment in metal-organic framework (MOF) structures. We focus on three enzyme types with varying sensitivities: aldoxime dehydratase, imine reductase, and lipase. We evaluate the effects of different metal sources (Al, Fe, Co, Ni, Cu, and Zn), their oxidation state and counterions, and MOF synthesis parameters on enzyme stability and activity during their entrapment in the MOF structures. Based on this, we optimize protocols for enzyme entrapment in Fe-MIL-88A, Fe-MIL-100, Zn-MOF-74, and Zn-ZIF-8 and develop a fast-aqueous room temperature synthesis of Al-MIL-53. Investigation of the biocatalytic performance of the enzyme@MOF biocomposites suggests that enzyme entrapment in MOFs using crude enzyme extracts can effectively maintain enzyme activity and stability in various catalytic reactions, offering a perspective for an efficient pathway for industrial applications.

Host molecules inside metal-organic frameworks: host@MOF and guest@host@MOF (Matrjoschka) materials

The controllable encapsulation of host molecules (such as porphyrin, phthalocyanine, crown ether, calixarene or cucurbituril organic macrocycles, cages, metal-organic polyhedrons and enzymes) into the pores of metal-organic frameworks (MOFs) to form host-in-host (host@MOF) materials has attracted increasing research interest in various fields. These host@MOF materials combine the merits of MOFs as a host matrix and functional host molecules to exhibit synergistic functionalities for the formation of guest@host@MOF materials in sorption and separation, ion capture, catalysis, proton/ion conduction and biosensors. (This guest@host@MOF construction is reminiscent of Russian (Matrjoschka) dolls which are nested dolls of decreasing size placed one inside another.) In this tutorial review, the advantages of MOFs as a host matrix are presented; the encapsulation approaches and general important considerations for the preparation of host@MOF materials are introduced. The state-of-the-art examples of these materials based on different host molecules are shown, and representative applications and general characterization of these materials are discussed. This review will guide researchers attempting to design functional host@MOF and guest@host@MOF materials for various applications.

A colorimetric sensing strategy based on chitosan-stabilized platinum nanoparticles for quick detection of α-glucosidase activity and inhibitor screening

α-Glucosidase (α-Glu) is implicated in the progression and pathogenesis of type II diabetes (T2D). In this study, we developed a rapid colorimetric technique using platinum nanoparticles stabilized by chitosan (Ch-PtNPs) to detect α-Glu activity and its inhibitor. The Ch-PtNPs facilitate the conversion of 3,3',5,5'-tetramethylbenzidine (TMB) into oxidized TMB (oxTMB) in the presence of dissolved O2. The catalytic hydrolysis of 2-O-α-D-glucopyranosyl-L-ascorbic acid (AA-2G) by α-Glu produces ascorbic acid (AA), which reduces oxTMB to TMB, leading to the fading of the blue color. However, the presence of α-Glu inhibitors (AGIs) hinders the generation of AA, allowing Ch-PtNPs to re-oxidize colorless TMB back to blue oxTMB. This unique phenomenon enables the colorimetric detection of α-Glu activity and AGIs. The linear range for α-Glu was found to be 0.1-1.0 U mL-1 and the detection limit was 0.026 U mL-1. Additionally, the half-maximal inhibition value (IC50) for acarbose, an α-Glu inhibitor, was calculated to be 0.4769 mM. Excitingly, this sensing platform successfully detected α-Glu activity in human serum samples and effectively screened AGIs. These promising findings highlight the potential application of the proposed strategy in clinical diabetes diagnosis and drug discovery.

Encapsulation of Enzymes into Hydrophilic and Biocompatible Metal Azolate Framework: Improved Functions of Biocatalyst in Cascade Reactions and its Sensing Applications

Multiple enzyme-triggered cascade biocatalytic reactions are vital in vivo or vitro, considering the basic biofunction preservation in living organisms and signals transduction for biosensing platforms. Encapsulation of such enzymes into carrier endows a sheltering effect and can boost catalytic performance, although the selection and preparation of an appropriate carrier is still a concern. Herein, focusing on MAF-7, a category of metal azolate framework (MAF) with superiority against the topologically identical ZIF-8, this enzyme@MAF system can ameliorate the sustainability of encapsulating natural enzymes into carriers. The proposed biocatalyst composite AChE@ChOx@MAF-7/hemin is constructed via one-pot in situ coprecipitation method. Subsequently, MAF-7 is demonstrated to exhibit an excellent capacity of the carrier and protection against external factors in the counterpart of ZIF-8 through encapsulated and free enzymes. In addition, detections for specific substrates or inhibitors with favorable sensitivity are accomplished, indicating that the properties above expectation of different aspects of the established platform are successfully realized. This biofunctional composite based on MAF-7 can definitely provide a potential approach for optimization of cascade reaction and enzyme encapsulation.

Superlarge, Rigidified DNA Tetrahedron with a Y-Shaped Backbone for Organizing Biomolecules Spatially and Maintaining Their Full Bioactivity

A major impediment to the clinical translation of DNA tiling nanostructures is a technical bottleneck for the programmable assembly of DNA architectures with well-defined local geometry due to the inability to achieve both sufficient structural rigidity and a large framework. In this work, a Y-backbone was inserted into each face to construct a superlarge, sufficiently rigidified tetrahedral DNA nanostructure (called RDT) with extremely high efficiency. In RDT, the spatial size increased by 6.86-fold, and the structural rigidity was enhanced at least 4-fold, contributing to an ∼350-fold improvement in the resistance to nucleolytic degradation even without a protective coating. RDT can be mounted onto an artificial lipid-bilayer membrane with molecular-level precision and well-defined spatial orientation that can be validated using the fluorescence resonance energy transfer (FRET) assay. The spatial orientation of Y-shaped backbone-rigidified RDT is unachievable for conventional DNA polyhedrons and ensures a high level of precision in the geometric positioning of diverse biomolecules with an approximately homogeneous environment. In tests of RDT, surface-confined horseradish peroxidase (HRP) exhibited nearly 100% catalytic activity and targeting aptamer-immobilized gold nanoparticles showed 5.3-fold enhanced cellular internalization. Significantly, RDT exhibited a 27.5-fold enhanced structural stability in a bodily environment and did not induce detectable systemic toxicity.

Carboxy-Functionalized Covalent Organic Framework as a Carrier for Lipase Immobilization and Its Application in Inhibitors Screening

Covalent organic frameworks (COFs) with large specific surface areas, high porosity, good stability, and designable structure are promising carriers for immobilized enzymes. It is important to explore lipase inhibitors from natural foods as lipase inhibitors are closely related to the treatment of obesity. In this work, a carboxyl functionalized covalent organic framework (TpBD-3COOH) was prepared by solvothermal method for covalent immobilization of porcine pancreatic lipase (PPL) and obtained the enzyme-decorated COF (PPL@COF). The immobilized lipase showed wider pH and temperature tolerance with the same optimal pH and temperature of 7.5 and 50 ℃ compared to free lipase. After 6 successive reuses, the PPL@COF maintained 53.0% of its original activity. Immobilized lipase also displayed enhanced storage stability (55.4% after 14 days at 4 ℃). When p-nitrophenyl acetate was applied as the substrate, the calculated Michaelis constant was 3.57 mM and the half maximal inhibitory concentration of orlistat was 3.20 μM. Finally, the PPL@COF was used for enzyme inhibitors screening from natural foods combined with UV spectrophotometry, and Hawthorn was screened for excellent lipase inhibitory activity.

Paper-based ligand fishing method for rapid screening and real-time capturing of α-glucosidase inhibitors from the Chinese herbs

Identifying medicinally relevant compounds from natural resources generally involves the tedious work of screening plants for the desired activity before capturing the bioactive molecules from them. In this work, we created a paper-based ligand fishing platform to vastly simplify the discovery process. This paper-based method exploits the enzymatic cascade reaction between α-glucosidase (GAA), glucose oxidase (GOx), and horseradish peroxidase (HRP), to simultaneously screen the plants and capture the GAA inhibitors from them. The designed test strip could capture ligands in tandem with screening the plants, and it features a very simply operation based on direct visual assessment. Multiple acylated flavonol glycosides from the leaves of Quercus variabilis Blume were newly found to possess GAA inhibitory activities, and they may be potential leads for new antidiabetic medications. Our study demonstrates the prospect of the newly discovered GAA ligands as potential bioactive ingredients as well as the utility of the paper-based ligand fishing method.

GAA/(Au-Au/IrO2)@Cu(PABA) reactor with cascade catalytic activity for α-glucosidase inhibitor screening

BACKGROUND

In vitro screening strategies based on the inhibition of α-glucosidase (GAA) activity have been widely used for the discovery of potential antidiabetic drugs, but they still face some challenges, such as poor enzyme stability, non-reusability and narrow range of applicability. To overcome these limitations, an in vitro screening method based on GAA@GOx@Cu-MOF reactor was developed in our previous study. However, the method was still not satisfactory enough in terms of construction cost, pH stability, organic solvent resistance and reusability. Thence, there is still a great need for the development of in vitro screening methods with lower cost and wider applicability.

RESULTS

A colorimetric sensing strategy based on GAA/(Au-Au/IrO2)@Cu(PABA) cascade catalytic reactor, which constructed through simultaneous encapsulating Au-Au/IrO2 nanozyme with glucose oxidase-mimicking and peroxidase-mimicking activities and GAA in Cu(PABA) carrier with peroxidase-mimicking activity, was innovatively developed for in vitro screening of GAA inhibitors in this work. It was found that the reactor not only exhibited excellent thermal stability, pH stability, organic solvent resistance, room temperature storage stability, and reusability, but also possessed cascade catalytic performance, with approximately 12.36-fold increased catalytic activity compared to the free system (GAA + Au-Au/IrO2). Moreover, the in vitro GAA inhibitors screening method based on this reactor demonstrated considerable anti-interference performance and detection sensitivity, with a detection limit of 4.79 nM for acarbose. Meanwhile, the method owned good reliability and accuracy, and has been successfully applied to the in vitro screening of oleanolic acid derivatives as potential GAA inhibitors.

SIGNIFICANCE

This method not only more effectively solved the shortcomings of poor stability, narrow scope of application, and non-reusability of natural enzymes in the classical method compared with our previous work, but also broaden the application scope of Au-Au/IrO2 nanozyme with glucose oxidase and peroxidase mimicking activities, and Cu(PABA) carrier with peroxidase mimicking activity, which was expected to be a new generation candidate method for GAA inhibitor screening.

Fluorometric and colorimetric dual-mode sensing of α-glucosidase based on aggregation-induced emission enhancement of AuNCs

Herein, a fluorometric and colorimetric dual-mode assay platform used for α-glucosidase (α-Glu) activity sensing based on aggregation-induced emission enhancement (AIEE) of AuNCs was developed for the first time. The quantum yield (QY) and fluorescence lifetime of AuNCs were successfully ameliorated by Ce3+-triggered AIEE (Ce@AuNCs). Subsequently, on the basis of the inner filter effect (IFE) and dynamic quenching effect (DQE) between 2,6-dichlorophenolindophenol (DCIP) and Ce@AuNCs as well as the reduction of DCIP by ascorbic acid (AA) generated from α-Glu-catalyzed hydrolysis of L-ascorbic acid-2-O-α-D-glucopyranosyl (AA2G), the marriage of fluorometric and colorimetric modes applied for α-Glu activity monitoring was achieved. Besides, the feasibility of this dual-mode sensing system was confirmed by the assays versus potential interfering substances and in real samples. In particular, this system was further applied to evaluate natural α-Glu inhibitors (AGIs) including luteolin, apigenin, and hesperidin. Overall, the multi-mode optical sensor newly designed here has the potential for the accurate discovery of natural anti-diabetes drugs and the therapy of diabetes.

Bioinspired Framework Catalysts: From Enzyme Immobilization to Biomimetic Catalysis

Enzymatic catalysis has fueled considerable interest from chemists due to its high efficiency and selectivity. However, the structural complexity and vulnerability hamper the application potentials of enzymes. Driven by the practical demand for chemical conversion, there is a long-sought quest for bioinspired catalysts reproducing and even surpassing the functions of natural enzymes. As nanoporous materials with high surface areas and crystallinity, metal-organic frameworks (MOFs) represent an exquisite case of how natural enzymes and their active sites are integrated into porous solids, affording bioinspired heterogeneous catalysts with superior stability and customizable structures. In this review, we comprehensively summarize the advances of bioinspired MOFs for catalysis, discuss the design principle of various MOF-based catalysts, such as MOF-enzyme composites and MOFs embedded with active sites, and explore the utility of these catalysts in different reactions. The advantages of MOFs as enzyme mimetics are also highlighted, including confinement, templating effects, and functionality, in comparison with homogeneous supramolecular catalysts. A perspective is provided to discuss potential solutions addressing current challenges in MOF catalysis.

Immobilized enzyme for screening and identification of anti-diabetic components from natural products by ligand fishing

Diabetes is a chronic metabolic disease caused by insufficient insulin secretion and insulin resistance. Natural product is one of the most important resources for anti-diabetic drug. However, due to the extremely complex composition, this research is facing great challenges. After the advent of ligand fishing technology based on enzyme immobilization, the efficiency of screening anti-diabetic components has been greatly improved. In order to provide critical knowledge for future research in this field, the application progress of immobilized enzyme in screening anti-diabetic components from complex natural extracts in recent years was reviewed comprehensively, including novel preparation technologies and strategies of immobilized enzyme and its outstanding application prospect in many aspects. The basic principles and preparation steps of immobilized enzyme were briefly described, including entrapment, physical adsorption, covalent binding, affinity immobilization, multienzyme system and carrier-free immobilization. New formatted immobilized enzymes with different carriers, hollow fibers, magnetic materials, microreactors, metal organic frameworks, etc., were widely used to screen anti-diabetic compositions from various natural products, such as Ginkgo biloba, Morus alba, lotus leaves, Pueraria lobata, Prunella vulgaris, and Magnolia cortex. Furthermore, the challenges and future prospects in this field were put forward in this review.

Dual-target affinity analysis and separation of α-amylase and α-glucosidase inhibitors from Morus alba leaves using a magnetic bifunctional immobilized enzyme system

Morus alba leaves are a natural product with great antidiabetic potential. However, the therapeutic efficacy of natural products is usually achieved through the interaction of active compounds with specific targets. Among them, active compounds with multi-target therapeutic functions are more effective than single-target enzymes. In this study, a bienzyme system was constructed by co-immobilizing α-amylase and α-glucosidase onto Fe₃ O₄ for affinity screening of dual-target active components in the complex extract from M. alba leaves. As a result, a potential active compound was selectively screened by ligand fishing, separated by high-speed countercurrent chromatography using a solvent system of ethyl acetate-n-butanol-water (3:2:5, v/v), and identified as rutin. In addition, the result of molecular docking showed that rutin could interact with the active center of α-amylase and α-glucosidase through multiple hydrogen bonds, van der Waals forces, etc. to play an inhibitory role. These results demonstrate the effectiveness of the polydopamine magnetically immobilized bienzyme system for dual-target affinity screening of active substances. This study not only reveals the chemical basis of the antidiabetic activity of M. alba leaves from a dual-target perspective, but also promotes the progress of multitarget affinity screening.

One step cascade detection of galactose based on a galactose oxidase-composited peroxidase nanozyme

Abnormal galactose metabolism is the main cause of galactosemia, which makes the accurate and rapid analysis of galactose levels in food and organism the key issue at present. In this study, a novel strategy for one-step galactose determination was proposed based on galactose oxidase and copper-based metal-organic framework complexes (GAOx@MOF) with dual catalytic activities at neutral pH. Typically, GAOx catalyzes the oxidation of the C6 hydroxyl group of D-galactose to generate an aldehyde (D-galactose-hexanedial), and coupled with the reduction of dioxygen to H₂O₂, which was immediately transformed to ˙OH by mimicking peroxidase activity and at the same time oxidized ABTS to a green product with a clear colorimetric signal. The whole process was completed using one buffer, which simplified the procedure and increased the sensitivity. Moreover, the proposed method can also be used for the quantitative analysis of galactose. It showed a good linear relationship at 20-1000 μM, while the LOD was 6.67 μM. Furthermore, the strategy has been successfully utilized for galactose determination in milk samples, which proved its promising applications in clinical analysis and the food industry.

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.

Synthesis and Evaluation of Coumarin-Chalcone Derivatives as α-Glucosidase Inhibitors

Coumarin and chalcone, two important kinds of natural product skeletons, both exhibit α-glucosidase inhibitory activity. In this work, coumarin-chalcone derivatives 3 (a∼v) were synthesized, and their α-glucosidase inhibitory activity was screened. The results showed that all synthetic derivatives (IC50: 24.09 ± 2.36 to 125.26 ± 1.18 μM) presented better α-glucosidase inhibitory activity than the parent compounds 3-acetylcoumarin (IC50: 1.5 × 105 μM) and the positive control acarbose (IC50: 259.90 ± 1.06 μM). Among them, compound 3t displayed the highest α-glucosidase inhibitory activity (IC50: 24.09 ± 2.36 μM), which was approximately 10 times stronger than that of acarbose. The kinetic assay of 3t (KI = 18.82 μM, KIS = 59.99 μM) revealed that these compounds inhibited α-glucosidase in a mixed-type manner. Molecular docking was used to simulate the interaction between α-glucosidase and compound 3t.

Synthesis and Biological Evaluation of 5-Fluoro-2-Oxindole Derivatives as Potential α-Glucosidase Inhibitors

α-Glucosidase inhibitors are known to prevent the digestion of carbohydrates and reduce the impact of carbohydrates on blood glucose. To develop novel α-glucosidase inhibitors, a series of 5-fluoro-2-oxindole derivatives (3a ∼ 3v) were synthesized, and their α-glucosidase inhibitory activities were investigated. Biological assessment results showed that most synthesized compounds presented potential inhibition on α-glucosidase. Among them, compounds 3d, 3f, and 3i exhibited much better inhibitory activity with IC50 values of 49.89 ± 1.16 μM, 35.83 ± 0.98 μM, and 56.87 ± 0.42 μM, respectively, which were about 10 ∼ 15 folds higher than acarbose (IC50 = 569.43 ± 43.72 μM). A kinetic mechanism study revealed that compounds 3d, 3f, and 3i inhibited the α-glucosidase in a reversible and mixed manner. Molecular docking was carried out to simulate the affinity between the compound and α-glucosidase.

Rapid Screening of Lipase Inhibitors in Scutellaria baicalensis by Using Porcine Pancreatic Lipase Immobilized on Magnetic Core–Shell Metal–Organic Frameworks

As for ligand fishing, the current immobilization approaches have some potential drawbacks such as the small protein loading capacity and difficult recycle process. The core–shell metal–organic frameworks composite (Fe3O4-COOH@UiO-66-NH2), which exhibited both magnetic characteristics and large specific surface area, was herein fabricated and used as magnetic support for the covalent immobilization of porcine pancreatic lipase (PPL). The resultant composite Fe3O4-COOH@UiO-66-NH2@PPL manifested a high loading capacity (247.8 mg/g) and relative activity recovery (101.5%). In addition, PPL exhibited enhanced tolerance to temperature and pH after immobilization. Then, the composite Fe3O4-COOH@UiO-66-NH2@PPL was incubated with the extract of Scutellaria baicalensis to fish out the ligands. Eight lipase inhibitors were obtained and identified by UPLC-Q-TOF-MS/MS. The feasibility of the method was further confirmed through an in vitro inhibitory assay and molecular docking. The proposed ligand fishing technique based on Fe3O4-COOH@UiO-66-NH2@PPL provided a feasible, selective, and effective platform for discovering enzyme inhibitors from natural products.

MOF-Hosted Enzymes for Continuous Flow Catalysis in Aqueous and Organic Solvents

Fully exploiting the potential of enzymes in cell-free biocatalysis requires stabilization of the catalytically active proteins and their integration into efficient reactor systems. Although in recent years initial steps towards the immobilization of such biomolecules in metal-organic frameworks (MOFs) have been taken, these demonstrations have been limited to batch experiments and to aqueous conditions. Here we demonstrate a MOF-based continuous flow enzyme reactor system, with high productivity and stability, which is also suitable for organic solvents. Under aqueous conditions, the stability of the enzyme was increased 30-fold, and the space-time yield exceeded that obtained with other enzyme immobilization strategies by an order of magnitude. Importantly, the infiltration of the proteins into the MOF did not require additional functionalization, thus allowing for time- and cost-efficient fabrication of the biocatalysts using label-free enzymes.

Biocatalytic Metal-Organic Framework: Promising Materials for Biosensing

The high-efficient and specific catalysis of enzyme allow it to recognize a myriad of substrate that impels the biosensing. Nevertheless, the fragility of natural enzymes severely restricts their practical applications. Metal-organic frameworks (MOFs) with porous network and attractive functions have been intelligently employed as supports to encase enzymes for protecting them against hash environments. More importantly, the customizable construction and composition affords the intrinsic enzyme-like activity of some MOFs (known as nanozymes), which provides an alternative guideline to construct robust enzymes mimics. Herein, this review will introduce the concept of these biocatalytic MOFs, with the special emphasis on how the biocatalytic processes operated in these MOFs materials can reverse the plight of native enzymes-based biosensing. In addition, the present challenges and future outlooks in this research field are briefly put forward.

A colorimetric detection strategy and micromotor-assisted photo-Fenton like degradation for hydroquinone based on the peroxidase-like activity of Co3O4–CeO2 nanocages

Co3O4–CeO2 micromotors were fabricated and the colorimetric detection and micromotor-assisted photodegradation capability were studied.

Recent Advances in Emerging Metal- and Covalent-Organic Frameworks for Enzyme Encapsulation

Enzyme catalysis enables complex biotransformation to be imitated. This biomimetic approach allows for the application of enzymes in a variety of catalytic processes. Nevertheless, enzymes need to be shielded by a support material under challenging catalytic conditions due to their intricate and delicate structures. Specifically, metal-organic frameworks and covalent-organic frameworks (MOFs and COFs) are increasingly popular for use as enzyme-carrier platforms because of their excellent tunability in structural design as well as remarkable surface modification. These porous organic framework capsules that host enzymes not only protect the enzymes against harsh catalytic conditions but also facilitate the selective diffusion of guest molecules through the carrier. This review summarizes recent progress in MOF-enzyme and COF-enzyme composites and highlights the pore structures tuned for enzyme encapsulation. Furthermore, the critical issues associated with interactions between enzymes and pore apertures on MOF- and COF-enzyme composites are emphasized, and perspectives regarding the development of high-quality MOF and COF capsules are presented.

Cobalt Phosphate Nanocrystals: A Catalase-Like Nanozyme and In Situ Enzyme-Encapsulating Carrier for Efficient Chemoenzymatic Synthesis of α-Keto Acid

Chemoenzymatic catalysis combining the traits of chemical and enzymatic catalysis provides tremendous possibilities for the design of biosynthetic pathways utilizing inorganic catalysts and enzymes. However, the efficiency of chemoenzymatic catalysis is usually governed by the synergy and compatibility of the two catalysts. Here, we report for the first time the catalase-like activity of cobalt phosphate nanocrystals (CoPs). By a one-pot biomimetic mineralization with CoPs and l-amino acid oxidase (LAAO) under a mild condition, we have fabricated a hybrid nanobiocatalyst, LAAO@CoPs, for the chemoenzymatic synthesis of α-keto acid. The as-fabricated nanobiocatalyst with directly contacted catalytic sites of the enzyme and nanozyme maximizes the substrate channeling effects for in situ chemical decomposition of the oxidative intermediate, H₂O₂, during the enzymatic oxidation of l-tryptophan (l-Trp), thus minimizing the H₂O₂ accumulation and byproduct generation. Benefiting from the superiority of LAAO@CoPs, complete conversion (100.0%) of l-Trp to indole pyruvic acid is achieved, over two times higher than the yield of the free LAAO system (47.6%). Meanwhile, LAAO@CoPs show high stabilities against heat and proteolytic treatments. This work offers a new design approach for constructing a high-performance nanobiocatalyst for cascade reactions, especially for those systems with toxic or reactive intermediates.

In vitro and in silico studies of bis (indol-3-yl) methane derivatives as potential α-glucosidase and α-amylase inhibitors

In this paper, bis (indol-3-yl) methanes (BIMs) were synthesised and evaluated for their inhibitory activity against α-glucosidase and α-amylase. All synthesised compounds showed potential α-glucosidase and α-amylase inhibitory activities. Compounds 5 g (IC₅₀: 7.54 ± 1.10 μM), 5e (IC₅₀: 9.00 ± 0.97 μM), and 5 h (IC₅₀: 9.57 ± 0.62 μM) presented strongest inhibitory activities against α-glucosidase, that were ∼ 30 times stronger than acarbose. Compounds 5 g (IC₅₀: 32.18 ± 1.66 µM), 5 h (IC₅₀: 31.47 ± 1.42 µM), and 5 s (IC₅₀: 30.91 ± 0.86 µM) showed strongest inhibitory activities towards α-amylase, ∼ 2.5 times stronger than acarbose. The mechanisms and docking simulation of the compounds were also studied. Compounds 5 g and 5 h exhibited bifunctional inhibitory activity against these two enzymes. Furthermore, compounds showed no toxicity against 3T3-L1 cells and HepG2 cells.

Highlights

A series of bis (indol-3-yl) methanes (BIMs) were synthesised and evaluated inhibitory activities against α-glucosidase and α-amylase.

Compound 5g exhibited promising activity (IC₅₀ = 7.54 ± 1.10 μM) against α-glucosidase.

Compound 5s exhibited promising activity (IC₅₀ = 30.91 ± 0.86 μM) against α-amylase.

In silico studies were performed to confirm the binding interactions of synthetic compounds with the enzyme active site.

Reusable Fluorescent Nanobiosensor Integrated in a Multiwell Plate for Screening and Quantification of Antidiabetic Drugs

A highly stable and reusable fluorescent multisample nanobiosensor for the detection of α-glucosidase inhibitors has been developed by coupling fluorescent liposomal nanoparticles based on conjugated polymers (L-CPNs) to the enzyme α-glucosidase, one of the main target enzymes in the treatment of type 2 diabetes. The mechanism of sensing is based on the fluorescence "turn-on" of L-CPNs by p-nitrophenol (PNP), the end product of the enzymatic hydrolysis of p-nitrophenyl-α-d-glucopyranoside. L-CPNs, composed of lipid vesicles coated with a blue-emitting cationic polyfluorene, were designed and characterized to obtain a good response to PNP. Two nanobiosensor configurations were developed in this study. In the first step, a single-sample nanobiosensor composed of L-CPNs and α-glucosidase entrapped in a sol-gel glass was developed in order to characterize and optimize the device. In the second part, the nanobiosensor was integrated and adapted to a multiwell microplate and the possibility of reusing it and performing multiple measurements simultaneously with samples containing different α-glucosidase inhibitors was investigated. Using super-resolution confocal microscopy, L-CPNs could be visualized within the sol-gel matrix, and the quenching of their fluorescence, induced by the substrate, was directly observed in situ. The device was also shown to be useful not only as a platform for screening of antidiabetic drugs but also for quantifying their presence. The latter application was successfully tested with the currently available drug, acarbose.

Metal-Organic Frameworks Enhance Biomimetic Cascade Catalysis for Biosensing

Multiple enzymes-induced biological cascade catalysis guides efficient and selective substrate transformations in vivo. The biomimetic cascade systems, as ingenious strategies for signal transduction and amplification, have a wide range of applications in biosensing. However, the fragile nature of enzymes greatly limits their wide applications. In this regard, metal-organic frameworks (MOFs) with porous structures, unique nano/microenvironments, and good biocompatibility have been skillfully used as carriers to immobilize enzymes for shielding them against hash surroundings and improving the catalytic efficiency. For another, nanomaterials with enzyme-like properties and brilliant stabilities (nanozymes), have been widely applied to ameliorate the low stability of the enzymes. Inheriting the abovementioned merits of MOFs, the performances of MOFs-immboilized nanozymes could be significantly enhanced. Furthermore, in addition to carriers, some MOFs can also serve as nanozymes, expanding their applications in cascade systems. Herein, recent advances in the fabrication of efficient MOFs-involving enzymes/nanozymes cascade systems and biosensing applications are highlighted. Integrating diversified signal output modes, including colorimetry, electrochemistry, fluorescence, chemiluminescence, and surface-enhanced Raman scattering, sensitive detection of various targets (including biological molecules, environmental pollutants, enzyme activities, and so on) are realized. Finally, challenges and opportunities about further constructions and applications of MOFs-involving cascade reaction systems are briefly put forward.

The preparation of bifunctional hybrid nano-flowers and their application in the enzyme-linked immunosorbent assay for Helicobacter pylori detection

As the infection by Helicobacter pylori (H. pylori, HP) remains for a lifetime and may induce diseases such as gastric cancer, it is vital to detect and diagnose it. A new non-invasive indirect enzyme-linked immunosorbent assay (iELISA) method based on nano-flowers (NFs) is very advantageous for the sensitive detection of HP. Furthermore, the established iELISA method based on the organic-inorganic bifunctional hybrid nano-flowers including rabbit polyclonal antibody of HP labeled with peroxidase from horseradish (R-HP-Ab-HRP@Cu2+ NFs) showed linearity with HP at a concentration of 0-105 CFU mL-1 (R2 = 0.9997). Moreover, the limit of detection (LOD) reached 50 CFU mL-1, and not only was the detection sensitivity 20 times higher than that based on rabbit polyclonal antibody of HP labeled with peroxidase from horseradish (R-HP-Ab-HRP) but also the stability of R-HP-Ab-HRP in NFs was improved. In addition, the OD450 nm value was still linearly related to the concentration of HP at a range of 0-105 CFU mL-1 (R2 = 0.9952) with a LOD of 50 CFU mL-1 in an artificial saliva system. This study provided a sensitive, low-cost and convenient method for the non-invasive detection of HP.

Artificial Bioaugmentation of Biomacromolecules and Living Organisms for Biomedical Applications

The synergistic union of nanomaterials with biomaterials has revolutionized synthetic chemistry, enabling the creation of nanomaterial-based biohybrids with distinct properties for biomedical applications. This class of materials has drawn significant scientific interest from the perspective of functional extension via controllable coupling of synthetic and biomaterial components, resulting in enhancement of the chemical, physical, and biological properties of the obtained biohybrids. In this review, we highlight the forefront materials for the combination with biomacromolecules and living organisms and their advantageous properties as well as recent advances in the rational design and synthesis of artificial biohybrids. We further illustrate the incredible diversity of biomedical applications stemming from artificially bioaugmented characteristics of the nanomaterial-based biohybrids. Eventually, we aim to inspire scientists with the application horizons of the exciting field of synthetic augmented biohybrids.

Carbon nitride nanoparticles as ultrasensitive fluorescent probes for the detection of α-glucosidase activity and inhibitor screening

In recent years, α-glucosidase inhibitors (AGIs) have played a significant role in the treatment of type II diabetes (T2D), so it is necessary to develop a reliable and sensitive method to find new AGIs. Herein, we establish a novel method based on fluorescent carbon nitride nanoparticles (CNNPs) for the sensitive detection of the activity of α-glucosidase (α-glu) and the screening of its inhibitors. A CNNP-based fluorescent probe is synthesized from green raw materials, urea and lysine, by a one-pot method. In the presence of α-glu, the substrate 4-nitrophenyl-α-d-glucopyranoside (pNPG) is hydrolyzed to generate 4-nitrophenol (pNP), leading to the fluorescence (FL) quenching of CNNPs due to the inner filter effect (IFE). On the other hand, the activity of α-glu is inhibited after the addition of AGIs, which turns on the FL of CNNPs. In this way, the detection of α-glu activity and the screening of AGIs are achieved. The linear range is 1.25-10.00 U L^-1 with a limit of detection as low as 0.17 U L^-1 and the IC₅₀ values of two typical inhibitors (gallic acid and acarbose) are 813 μM and 465 μM, respectively. The CNNP probe is further applied for the determination of α-glu activity in human serum samples with satisfactory results.

Cascade amplified colorimetric immunoassay based on an integrated multifunctional composite with catalytic coordination polymers for prostate specific antigen detection

Coordination polymers (CPs) have been extensively investigated for a variety of applications because of their tunable structures and properties. In this work, we demonstrated the potential of catalytic CPs in the fabrication of an integrated multifunctional composite for establishing a cascade amplified immunoassay. For this purpose, an Fe(iii)-based CP (FeCP) with peroxidase-like activity was employed as a model of catalytic CPs to simultaneously integrate glucose oxidase (GOx) and the anti-prostate specific antigen (anti-PSA) antibody through a self-adaptive inclusion process. This leads to the formation of a dual-functional anti-PSA/GOx@FeCP composite with cascade catalytic activity and capture ability to target the antigen. Benefiting from the shielding effect of FeCPs as a host, a significantly improved stability against harsh environments can be achieved for the loaded GOx and anti-PSA antibody in the composite. On this basis, by utilizing anti-PSA/GOx@FeCPs as a detection antibody, a colorimetric immunoassay based on the cascade catalysis of GOx and FeCPs as a signal amplified enhancer was developed for the detection of PSA. Under optimal conditions, satisfactory detection results have been achieved in both buffered aqueous solutions and serum samples. We believe that this study will open up a new avenue for the rational design and fabrication of multifunctional composites while offering a new cascade amplification strategy for PSA detection.

A colorimetric sensing strategy based on enzyme@metal-organic framework and oxidase-like IrO2/MnO2 nanocomposite for α-glucosidase inhibitor screening

A highly sensitive colorimetric sensing strategy based on enzyme@metal-organic framework (GAA@Cu-MOF) and IrO₂/MnO₂ nanocomposite was exploited innovatively for screening of α-glucosidase (GAA) inhibitors. IrO₂/MnO₂ nanocomposite exhibits excellent oxidase-mimicking activity which can directly catalyze the oxidation of 3,3^,5,5^,-tetramethylbenzidine (TMB) into a blue product with an absorption maximum at 652 nm. And GAA@Cu-MOF can decompose L-ascorbic acid-2-O-α-D-glucopyranosyl (AAG) to ascorbic acid (AA). The produced AA can destroy the IrO₂/MnO₂ nanocomposite and reduce its oxidase-like activity. However, the generation of AA is restricted when GAA inhibitors are added to the system, which allows the oxidase-like activity of the IrO₂/MnO₂ nanocomposite to be maintained. In view of this, a method for screening of GAA inhibitors was developed. In addition to enhancing the stability of GAA, the method can also effectively avoid the potential interference of H₂O₂ in the screening process of GAA inhibitors, which helps to improve the sensitivity of the method. Therefore, highly sensitive determination for acarbose and ascorbic acid are achieved with detection limits of 6.27 nM and 1.23 μM, respectively. The proposed method was successfully applied to screen potential GAA inhibitors from oleanolic acid derivatives. Graphical abstract.

Facile access to amino-substituted cyclopentafullerenes: novel reaction of [60]fullerene with β-substituted propionaldehydes and secondary amines in the absence/presence of magnesium perchlorate

A series of scarce amino-substituted cyclopentafullerenes instead of the expected N-alkyl-2,5-disubstituted fulleropyrrolidines were synthesized in moderate to excellent yields via the simple one-step reaction of [60]fullerene with cheap and easily available β-substituted propionaldehydes and secondary amines in the absence/presence of magnesium perchlorate. The in situ generation of allylic amines from β-substituted propionaldehydes and secondary amines played a crucial role in the successful preparation of amino-substituted cyclopentafullerenes without additional carbons. With the addition of magnesium perchlorate, secondary amines containing ethyl group(s) could produce novel amino-substituted cyclopentafullerenes with two additional carbons. All the obtained cyclopentafullerenes displayed high stereoselectivity with cis isomers as the exclusive or major products. Plausible reaction mechanisms are proposed to elucidate the above-mentioned reaction process.

Review of the Biomolecular Modification of the Metal-Organ-Framework

Metal-organ frameworks (MOFs), as a kind of novel artificial material, have been widely studied in the field of chemistry. MOFs are capable of high loading capacities, controlled release, plasticity, and biosafety because of their porous structure and have been gradually functionalized as a drug carrier. Recently, a completely new strategy of combining biomolecules, such as oligonucleotides, polypeptides, and nucleic acids, with MOF nanoparticles was proposed. The synthetic bio-MOFs conferred strong protection and endowed the MOFs with particular biological functions. Biomolecular modification of MOFs to form bridges for communication between different subjects has received increased attention. This review will focus on bio-MOFs modification methods and discuss the advantages, applications, prospects, and challenges of using MOFs in the field of biomolecule delivery.

Gold nanozyme as an excellent co-catalyst for enhancing the performance of a colorimetric and photothermal bioassay

Advanced oxidation processes (AOPs) have recently proposed for advancing colorimetric sensing applications, owing to their excellent performance of sensitive color readout that generated from the oxidation of chromogenic substrates like 3,3',5,5'-tetramethylbenzidine (TMB) by reactive oxygen species (ROS) of AOPs such as ·OH and ·O₂^- radicals. However, the efficiency of ROS generation and the related H₂O₂ decomposition in most AOPs is quite low especially at neutral pH, which greatly hampered the practical sensing applications of the AOPs. We herein communicated that β-cyclodextrin (β-CD)-capped gold nanoparticles (β-CD@AuNPs) can promote catalysis at neutral pH for AOP as an excellent co-catalyst. In this strategy, inorganic pyrophosphate (PPi) ions was first used to coordinate with Cu²⁺ and form Cu²⁺-PPi complex. In the presence of hydrogen peroxide, target inorganic pyrophosphatase (PPase) can hydrolyze PPi into inorganic phosphate (Pi) and release free Cu²⁺ simultaneously, resulting in a Cu²⁺-triggered Fenton-like AOP reaction. The introduced β-CD@AuNPs acts as a co-catalyst, analogous to mediators in the most co-catalyzed system, to enhance the rate-limiting step of Cu²⁺/Cu⁺ conversion in Cu²⁺/H₂O₂ Fenton-like AOP and resulting in an efficient generation of ·OH and ·O₂^- radicals, which further producing an intense blue color by oxidizing TMB into its oxidation product (TMBox) within a short time. Finally, this reaction system was used to simply detecting target PPase with the colorimetric and photothermal readout based on the in-situ generated TMBox indicator. More significantly, we successfully demonstrated nanozyme can serve as a co-catalyst to promote the AOP catalysis at neutral pH, and inspire other strategies to overcome the pH limitation in the AOP catalysis and expand its colorimetric and photothermometric application.

Applications of Functional Metal-Organic Frameworks in Biosensors

In recent decades, fast advancements in the fields of metal-organic frameworks (MOFs) are providing unprecedented opportunities for the development of novel functional MOFs for various biosensing applications. Exciting progress is achieved due to the combination of MOFs with various functional components, which introduces novel structures and new features to the MOFs-based biosensing applications, such as higher stability, higher sensitivity, higher flexibility, and higher specificity. This review aims to be a comprehensive summary of the most recent advances in the development of functional MOFs for various biosensing applications, placing special attention on important contributions in recent 3 years. In this review, the most recent developments in design and synthesis of functional MOFs for biosensing applications are summarized. MOFs-based biosensing applications are outlined according to the central roles of MOFs in biosensors, which include carriers of sensitive elements, enzyme-mimic elements, electrochemical signaling, optical signaling, and gas sensing. Finally, the current challenges and future development trends of functional MOFs for biosensing applications are proposed and discussed.