Metal-Organic Framework in Situ Post-Encapsulating DNA-Enzyme Composites on a Magnetic Carrier with High Stability and Reusability

Exploring the effects of excipients on complex coacervation

Complex coacervation is an associative liquid-liquid phase separation phenomenon that takes place due to the electrostatic complexation of oppositely-charged polyelectrolytes and the entropic gains associated with the release of bound counterions and rearrangement of solvent. The aqueous nature of coacervation has resulted in its broad use in systems requiring high biocompatibility. The significance of electrostatic interactions in coacervates has meant that studies investigating the phase behaviors of these systems have tended to focus on parameters such as the charge stoichiometry of the polyions, the solution pH, and the ionic strength. However, the equilibrium that exists between the polymer-rich coacervate phase and the polymer-poor supernatant phase represents a balance among attractive electrostatic interactions and excluded volume repulsions as well as osmotic pressure effects. As such, we hypothesize that it should be possible to tune coacervate phase behavior via the addition of non-electrostatic excipients which would partition between the two phases and potentially alter both the solvent quality and the osmotic pressure balance. In particular, our work focuses on small molecule excipients such as sugars, amino acids, and other additives that have a history of use in vaccine formulation. We quantified the ability of these excipients to partition into the coacervate phase, and their potential for destabilizing the phase separation. Furthermore, we demonstrate that these additives can be combined with complex coacervation in the context of a virus formulation.

A New Phosphorylated Protein Analysis Strategy based on Trypsin Encapsulated in Metal-Organic Frameworks with High Efficiency and a Simplified Workflow

Phosphoproteomics research is crucial for clinical diagnosis. However, due to the self-hydrolysis of natural proteases and the complex typical pretreatment protocol, the traditional bottom-up method is not enough to achieve rapid analysis of phosphorylated proteins. In this work, we encapsulate trypsin (Try) in the ZIF-L(Co) to develop a new strategy that simplifies the phosphorylated protein analysis process and achieves rapid analysis. Try is encapsulated in the mesoporous ZIF-L(Co) to allow the proteins to be accessible to the enzymes. The hydrophobic ZIF-L(Co) can cause the unfolding of proteins and accelerates the digestion process. The Co(II) nodes enhance the affinity toward phosphorylated proteins and capture phosphopeptides selectively. Compared to the traditional denaturation, digestion, and enrichment method, which costs 20 h at least, our strategy simplifies the pretreatment workflow and yields phosphopeptides in just 3.4 h. This strategy is further applied in the analysis of phosphorylated proteins in biosamples such as nonfat milk, egg yolk, and human serum. The results show equivalent performance with the traditional method and exhibit great potential in bioanalysis. This new phosphorylated protein analysis strategy provides a powerful tool for proteomics analysis and promotes research in the field of biomedicine.

Fabrication of Compartmentalized Multienzyme Reactor for Colorimetric Biosensing of Glucose and Phenol with High Sensitivity

Enzymatic cascade reactions are widely utilized in food security, environmental monitoring, and disease diagnostics, whereas their practical application was hindered due to their limited catalytic efficiency and intrinsic fragility to environmental influences. Herein, a compartmentalized dual-enzyme cascade nanoreactor was constructed in metal-organic frameworks (ZIF-8) by a shell-by-shell growth method. ZIF-8 provided a good microenvironment to maintain the activity of enzymes and protected them against harsh conditions. Importantly, experimental results revealed that the encapsulation order and enzyme ratio affected the cascade catalytic activity. When the cascade enzyme ratio was 1:1 and horseradish peroxidase (HRP) was encapsulated in the inner layer with glucose oxidase (GOx) in the outer layer (H@ZIF-8@G@ZIF-8), the nanoreactor facilitated the mass transfer process of substrates and showed the highest cascade catalytic efficiency. The maximum reaction rate (Vmax) of H@ZIF-8@G@ZIF-8 was 294.96 nM s-1, which was 1.6 times greater than G@ZIF-8@H@ZIF-8 (182.84 nM s-1). Therefore, H@ZIF-8@G@ZIF-8 was effectively applied in glucose monitoring and phenol sensing. The glucose biosensor showed a low detection limit of 0.76 μM and a broad linear range of 5-300 μM. The phenol biosensor demonstrated a wide linear range (20-300 μM) with a detection limit of 0.60 μM. In addition, the spiked recovery experiments for glucose and phenol were carried out in serum (recovery: 95.26-100.04%) and tap water (recovery: 97.05-106.50%), respectively. The high accuracy demonstrated potential applications of the cascade system in biosensing and environmental detection.

Recent Progress in Enzyme Immobilization to Metal-Organic Frameworks to Enhance the CO2 Conversion Efficiency

Climate change and the energy crisis, driven by excessive CO2 emissions, have emerged as pressing global challenges. The conversion of CO2 into high-value chemicals not only mitigates atmospheric CO2 levels but also optimizes carbon resource utilization. Enzyme-catalyzed carbon technology offers a green and efficient approach to CO2 conversion. However, free enzymes are prone to inactivation and denaturation under reaction conditions, which limit their practical applications. Metal-organic frameworks (MOFs) serve as effective carriers for enzyme immobilization, offering porous crystalline structures that enhance enzyme stability. Moreover, their high specific surface area facilitates strong gas adsorption, making enzyme@MOF composites particularly advantageous for CO2 catalytic conversion. In this paper, we review the synthesis technologies and the application of enzyme@MOFs in CO2 catalytic conversion. Furthermore, the strategies, including the enhancement of CO2 utilization, coenzyme regeneration efficiency, and substrate mass transfer efficiency, are also discussed to further improve the efficiency of enzyme@MOFs in CO2 conversion. The aim of this review is to present innovative ideas for future research and to highlight the potential applications of enzyme@MOFs in achieving efficient CO2 conversion.

Exploring enzyme-immobilized MOFs and their application potential: biosensing, biocatalysis, targeted drug delivery and cancer therapy

Enzymes are indispensable in several applications including biosensing and degradation of pollutants and in the drug industry. However, adverse conditions restrict enzymes' utility in biocatalysis due to their inherent limitations. Metal-organic frameworks (MOFs), with their robust structure, offer an innovative avenue for enzyme immobilization, enhancing their resilience against harsh solvents and temperatures. This advancement is pivotal for application in bio-sensing, bio-catalysis, and specifically, targeted drug delivery in cancer therapy, where enzyme-MOF composites enable precise therapeutic localization, minimizing the side effects of traditional treatment. The adaptable nature of MOFs enhances drug biocompatibility and availability, significantly improving therapeutic outcomes. Moreover, the integration of enzyme-immobilized MOFs into bio-sensing represents a leap forward in the rapid and accurate identification of biomarkers, facilitating early diagnosis and disease monitoring. In bio-catalysis, this synergy promotes efficient and environmentally safe chemical synthesis, enhancing reaction rates and yields and broadening the scope of enzyme application in pharmaceutical and bio-fuel production. This review article explores the immobilization techniques and their biomedical applications, specifically focusing on drug delivery in cancer therapy and bio-sensing. Additionally, it addresses the challenges faced in this expanding field.

Biosilica-coated carbonic anhydrase displayed on Escherichia coli: A novel design approach for efficient and stable biocatalyst for CO2 sequestration

A robust and stable carbonic anhydrase (CA) system is indispensable for effectively sequestering carbon dioxide to mitigate climate change. While microbial surface display technology has been employed to construct an economically promising cell-displayed CO2-capturing biocatalyst, the displayed CA enzymes were prone to inactivation due to their low stability in harsh conditions. Herein, drawing inspiration from biomineralized diatom frustules, we artificially introduced biosilica shell materials to the CA macromolecules displayed on Escherichia coli surfaces. Specifically, we displayed a fusion of CA and the diatom-derived silica-forming Sil3K peptide (CA-Sil3K) on the E. coli surface using the membrane anchor protein Lpp-OmpA linker. The displayed CA-Sil3K (dCA-Sil3K) fusion protein underwent a biosilicification reaction under mild conditions, resulting in nanoscale self-encapsulation of the displayed enzyme in biosilica. The biosilicified dCA-Sil3K (BS-dCA-Sil3K) exhibited improved thermal, pH, and protease stability and retained 63 % of its initial activity after ten reuses. Additionally, the BS-dCA-Sil3K biocatalyst significantly accelerated the CaCO3 precipitation rate, reducing the time required for the onset of CaCO3 formation by 92 % compared to an uncatalyzed reaction. Sedimentation of BS-dCA-Sil3K on a membrane filter demonstrated a reliable CO2 hydration application with superior long-term stability under desiccation conditions. This study may open new avenues for the nanoscale-encapsulation of enzymes with biosilica, offering effective strategies to provide efficient, stable, and economic cell-displayed biocatalysts for practical applications.

Separable Metal-Organic Framework-Based Materials for the Adsorption of Emerging Contaminants

Thousands of chemicals have been released into the environment in recent decades. The presence of emerging contaminants (ECs) in water has emerged as a pressing concern. Adsorption is a viable solution for the removal of ECs. Metal-organic frameworks (MOFs) have shown great potential as efficient adsorbents, but their dispersed powder form limits their practical applications. Recently, researchers have developed various separable MOF-based adsorbents to improve their recyclability. The purpose of this review is to summarize the latest developments in the construction of separable MOF-based adsorbents and their applications in adsorbing ECs. The construction strategies for separable MOFs are classified into four categories: magnetic MOFs, MOF-fiber composites, MOF gels, and binder-assisted shaping. Typical emerging contaminants include pesticides, pharmaceuticals and personal care products, and endocrine-disrupting compounds. The adsorption performance of different materials is evaluated based on the results of static and dynamic adsorption experiments. Additionally, the regeneration methods of MOF-based adsorbents are discussed in detail to facilitate effective recycling and reuse. Finally, challenges and potential future research opportunities are proposed, including reducing performance losses during the shaping process, developing assessment systems based on dynamic purification and real polluted water, optimizing regeneration methods, designing multifunctional MOFs, and low-cost, large-scale synthesis of MOFs.

Integration of multienzyme co-immobilization and biomimetic catalysis in magnetic metal-organic framework nanoflowers for α-amylase detection in fermentation samples

Multiple enzymes induce biological cascade catalysis is essential in nature and industrial production. However, the shortcomings of enzymes, including unsatisfactory stability, reusability, and sensitivity in harsh microenvironment, have restricted their broader use. Here, we report a facile method for fabricating a cascade system by combining the benefits of immobilized enzymes and biomimetic catalysis based on magnetic metal-organic framework nanoflowers (mMOFNFs). mMOFNFs prepared through the layered double hydroxide-derived strategy exhibited remarkable peroxidase-like activity and accessible amino interface, enabling it to serve not only as a reliable carrier for α-glucosidase and glucose oxidase fixation, but also as a nanozyme participating in cascade. On this basis, a colorimetric biosensor of excellent sensitivity and selectivity for α-amylase detection was constructed with a wide range (2-225 U L-1), low detection limit (2.48 U L-1), and rapid operation (30 min). This work provides a versatile strategy for establishing multi-enzyme cascade systems and rapid analysis of α-amylase.

Trypsin Encapsulation in the Zeolitic Imidazolate Framework for Low-Molecular Weight Protein Analysis with High Selectivity and Efficiency

Low-molecular weight proteins (LWPs) are important sources of biological information in biomarkers, signaling molecules, and pathology. However, the separation and analysis of LWPs in complex biological samples are challenging, mainly due to their low abundance and the complex sample pretreatment procedure. Herein, trypsin modified by poly(acrylic acid) (PAA) was encapsulated by a zeolitic imidazolate framework (ZIF-L). Mesopores were formed on the ZIF-L with the introduction of PAA. An alternative strategy for separation and pretreatment of LWPs was developed based on the prepared ZIF-L-encapsulated trypsin with adjustable pore size. The mesoporous structure of the prepared materials selectively excluded high-molecular weight proteins from the reaction system, allowing LWPs to enter the pores and react with the internal trypsin, resulting in an improved separation efficiency. The hydrophobicity of the ZIF-L simplified the digestion process by inducing significant structural changes in substrate proteins. In addition, the enzymatic activity was significantly enhanced by the developed encapsulation method that maintained the enzyme conformation, allowed low mass transfer resistance, and possessed a high enzyme-to-substrate ratio. As a result, the ZIF-L-encapsulated trypsin can achieve highly selective separation, valid denaturation, and efficient digestion of LWPs in a short time by simply mixing with substrate proteins, greatly simplifying the separation and pretreatment process of the traditional hydrolysis method. The prepared materials and the developed strategy demonstrated an excellent size-selective assay performance in model protein mixtures, showing great potential in the application of proteomics analysis.

Detection of acrylamide in food based on MIL-glucose oxidase cascade colorimetric aptasensor

BACKGROUND

Maillard reaction involves the polymerization, condensation, and other reactions between compounds containing free amino groups and reducing sugars or carbonyl compounds during heat processing. This process endows unique flavors and colors to food, while it can also produce numerous hazards. Acrylamide (AAm) is one of Maillard's hazards with neurotoxicity and carcinogenicity, these effects can trigger mutations and alternations in gene expression in human cells and accelerate organ aging. An accurate and reliable acrylamide detection method with high sensitivity and specificity for future regulatory activities is urgently needed.

RESULTS

Herein, we constructed a colorimetric aptasensor with the hybridization of MIL-glucose oxidase (MGzyme)-cDNA and magnetic nanoparticle-aptamer (MNP-Apt) to specifically detect AAm. The incorporation of MB-Apt and AAm released MGzyme-cDNA in the supernatant, took the supernatant out, with the addition of glucose and TMB, MGzyme would oxidize glucose, the resulting •OH facilitated the oxidation of colorless TMB to blue ox-TMB. The absorbance value at 652 nm, which indicates the characteristic absorption peak of ox-TMB, exhibited a proportion to the concentration of AAm. MGzyme avoided the addition of harmful intermediate H2O2 and created an acid microenvironment for the catalytic reaction. MNP-Apt possessed the advantages of high specificity and simplified separation. Under optimal conditions, this method displayed a linear range of 0.01-100 μM with the limit of detection of 1.53 nM. With the spiked analysis data cross-verified by ELISA kit, this aptasensor was proven to specifically detect AAm at low concentrations.

SIGNIFICANCE

This colorimetric aptasensor was the integration of aptamer and the enzyme-cascade system, which could broaden the applicable range of enzyme-cascade system, break the limits of specific detection of substrates, eliminate the need for harmful intermediates, improve the reaction efficiency, implement the specific detection, whilst enabling the accurate detection of AAm. Given these remarkable performances, this method has shown significant potential in the field of food safety inspection.

Enzymatic hydrolysates of κ-carrageenan by κ-carrageenase-CLEA immobilized on amine-modified ZIF-8 confer hypolipidemic activity in HepG2 cells

κ-Carrageenase can degrade κ-carrageenan to produce bioactive κ-carrageenan oligosaccharides (KCOs) that have potential applications in pharmaceutical, food, agricultural, and cosmetics industries. Immobilized enzymes gain their popularity due to their good reusability, enhanced stability, and tunability. In this study, the previously characterized catalytic domain of Pseudoalteromonas purpurea κ-carrageenase was covalently immobilized on the synthesized amine-modified zeolitic imidazolate framework-8 nanoparticles with the formation of cross-linked enzyme aggregates, and the immobilized κ-carrageenase was further characterized. The immobilized κ-carrageenase demonstrated excellent pH stability and good reusability, and exhibited higher optimal reaction temperature, better thermostability, and extended storage stability compared with the free enzyme. The KCOs produced by the immobilized κ-carrageenase could significantly decrease the TC, TG, and LDL-C levels in HepG2 cells, increase the HDL-C level in HepG2 cells, and reduce the free fatty acids level in Caco-2 cells. Biochemical assays showed that the KCOs could activate AMPK activity, increase the ratios of p-AMPK/AMPK and p-ACC/ACC, and downregulate the expression of the lipid metabolism related proteins including SREBP1 and HMGCR in the hyperlipidemic HepG2 cells. This study provides a novel and effective method for immobilization of κ-carrageenase, and the KCOs produced by the immobilized enzyme could be a potential therapeutic agent to prevent hyperlipidemia.

Metal-Organic Framework for the Immobilization of Oxidoreductase Enzymes: Scopes and Perspectives

Oxidoreductases are a wide class of enzymes that can catalyze biological oxidation and reduction reactions. Nowadays, oxidoreductases play a vital part in most bioenergetic metabolic pathways, which have important applications in biodegradation, bioremediation, environmental applications, as well as biosensors. However, free oxidoreductases are not stable and hard to be recycled. In addition, cofactors are needed in most oxidoreductases catalyze reactions, which are so expensive and unstable that it hinders their industrial applications. Enzyme immobilization is a feasible strategy that can overcome these problems. Recently, metal-organic frameworks (MOFs) have shown great potential as support materials for immobilizing enzymes due to their unique properties, such as high surface-area-to-volume ratio, chemical stability, functional designability, and tunable pore size. This review discussed the application of MOFs and their composites as immobilized carriers of oxidoreductase, as well as the application of MOFs as catalysts and immobilized carriers in redox reactions in the perspective of the function of MOFs materials. The paper also focuses on the potential of MOF carrier-based oxidoreductase immobilization for designing an enzyme cascade reaction system.

The screening of lipase inhibitors based on the metal-organic framework Zeolitic Imidazolate Framework-8-immobilized enzyme microreactor

An online capillary electrophoresis method based-lipase immobilized enzyme microreactor was developed for lipase kinetic study and inhibitor screening from compounds from natural products. Zeolitic Imidazolate Framework-8 (ZIF-8) has the advantages of large pore size, mild synthesis conditions and good biocompatibility. Lipase was immobilized on the inner wall of capillary with the help of the metal-organic framework ZIF-8. The results of electron microscopy showed that lipase could be aggregated and fixed on the inner wall of capillary by ZIF-8. After the experimental conditions including electrophoretic separation and enzymatic reaction were optimized, the baseline separation of substrate p-nitrophenyl acetate (pNPA) and product p-nitrophenol (pNP) was achieved within 3 min. The immobilized enzyme microreactor showed good repeatability and stability, and the determined Michaelis-Menten constant (Km) of lipase was 2.75 mM, which was lower than the kinetic constant determined in off-line reaction, indicating that the immobilized enzyme had a high affinity with the substrate. In addition, the IC50 value of the positive control compound orlistat on lipase inhibition was 7.26 nM, which was consistent with the literature. Then the inhibitory activity of 10 compounds from natural products on lipase was evaluated by the ZIF-8-IMER. Among them, 7 compounds including baicalein, luteolin, epicatechin gallic acid, and chlorogenic acid, had a certain inhibitory effect on lipase. The molecular docking technology proved the interaction between the enzyme and the screened inhibitor, which provides a new method for the screening of lipase inhibitors.

Construction of co-immobilized multienzyme systems using DNA-directed immobilization technology and multifunctionalized nanoparticles

The multienzyme co-immobilization systems with high cascade catalytic efficiency and selectivity have attracted considerable attention. In this study, through DNA-directed immobilization (DDI) technology, two model enzymes, glucose oxidase (GOD) and horseradish peroxide (HRP) were co-immobilized on the multifunctional silica nanoparticles (DDI enzyme). In addition to the directional distribution promoted by DNA complementary chains, the multienzyme system allowed the control of the stoichiometric ratio of the enzymes by adjusting the ratio of amino/carboxyl groups. The optimal mole ratio of GOD/HRP was 1:2, while the protein loading amount could reach 8.06 mg·g-1. Compared with the conventional direct adsorption, the catalytic activity of the DDI enzyme was 2.49 times higher. Moreover, with the enhancement of thermal and mechanical stability, the DDI enzyme could still retain at least 50% of its initial activity after 12 cycles. Accompanied by an excellent response and good selectivity, the constructed multienzyme systems simultaneously showed the potential as a glucose detector. Therefore, based on the DDI technology, the highly efficient multienzyme co-immobilization system could be further extended for a wider range of research fields.

Compartmentalized Nano-MOFs as Co-delivery Systems for Enhanced Antitumor Therapy

Therapeutic bioactive macromolecules hold great promise in cancer therapy, but challenges such as low encapsulation efficiency and susceptibility to inactivation during the targeted co-delivery hinder their widespread applications. Compartmentalized nano-metal-organic frameworks (nMOFs) can easily load macromolecules in the innermost layer, protect them from the outside environment, and selectively release them in the target location after stimulation, showing great potential in the co-delivery of biomacromolecules. Herein, the rationally designed (GOx + CAT)/ZIF-8@BSATPZ/ZIF-8 (named GCZ@BTZ) nMOFs with compartmentalized structures are employed to deliver cascaded enzymes and the chemotherapeutic drug tirapazamine (TPZ)-conjugated bovine serum albumin (BSATPZ). Benefiting from the compartmentalized structure and protective shell, the GCZ@BTZ system is stable during blood circulation and preferentially accumulates in the tumor. Furthermore, in response to the acidic tumor environment, GCZ@BTZ effectively released the loading enzymes and BSATPZ. Along with the tumor starvation caused by depletion of glucose, cascaded reactions could also contribute to the enhancement of tumor hypoxia, which further activated BSATPZ-based chemotherapy. Notably, in the mouse tumor models, GCZ@BTZ treatment significantly inhibits tumor survival and metastasis. Such a compartmentalized nMOF delivery system presents a promising avenue for the efficient delivery of bioactive macromolecules.

Review: Synthesis of metal organic framework-based composites for application as immunosensors in food safety

Ensuring food safety continues to be one of the major global challenges. For effective food safety monitoring, fast, sensitive, portable, and efficient food safety detection strategies must be devised. Metal organic frameworks (MOFs) are porous crystalline materials that have attracted attention for use in high-performance sensors for food safety detection owing to their advantages such as high porosity, large specific surface area, adjustable structure, and easy surface functional modification. Immunoassay strategies based on antigen-antibody specific binding are one of the important means for accurate and rapid detection of trace contaminants in food. Emerging MOFs and their composites with excellent properties are being synthesized, providing new ideas for immunoassays. This article summarizes the synthesis strategies of MOFs and MOF-based composites and their applications in the immunoassays of food contaminants. The challenges and prospects of the preparation and immunoassay applications of MOF-based composites are also presented. The findings of this study will contribute to the development and application of novel MOF-based composites with excellent properties and provide insights into advanced and efficient strategies for developing immunoassays.

Self-powered enzyme-linked microneedle patch for scar-prevention healing of diabetic wounds

Diabetic wounds with complex pathological features and a difficult-to-heal nature remain a formidable challenge. To address this challenge, we design and fabricate a self-powered enzyme-linked microneedle (MN) patch composed of anode and cathode MN arrays, which respectively contain glucose oxidase (GOx) and horseradish peroxidase (HRP) encapsulated in ZIF-8 nanoparticles. The enzymatic cascade reaction in the MN patch can effectively reduce local hyperglycemia in diabetic wounds while generating stable microcurrents to promote rapid healing of diabetic wounds. Therefore, the diabetic wounds treated with this MN patch exhibit rapid, complete, and scar-preventative healing, which can be attributed to the synergistic actions of hypoglycemic, antibacterial, anti-inflammatory, and bioelectrical stimulation. In brief, the self-powered MN patch is an effective method to rapidly promote diabetic wound healing and prevent scar formation.

Improved stability and activity of laccase through de novo and post-synthesis immobilization on a hierarchically porous metal-organic framework (ZIF-8)

Porous materials such as metal-organic frameworks (MOFs) are considered to be suitable materials for immobilizing enzymes to improve their stability. However, conventional MOFs reduce the enzymes' catalytic activity due to difficulties with mass transfer and diffusing reactants after their micropores are occupied by enzyme molecules. To address these issues, a novel hierarchically structured zeolitic imidazolate framework-8 (HZIF-8) was prepared to study the effects of different laccase immobilization approaches such as the post-synthesis (LAC@HZIF-8-P) and de novo (LAC@HZIF-8-D) immobilization of catalytic activities for removing 2,4-dichlorophenol (2,4-DCP). The results showed higher catalytic activity for the laccase-immobilized LAC@HZIF-8 prepared using different methods than for the LAC@MZIF-8 sample, with 80% of 2,4-DCP removed under optimal conditions. These results could be attributable to the multistage structure of HZIF-8. The LAC@HZIF-8-D sample was stable and superior to LAC@HZIF-8-P, maintaining a 2,4-DCP removal efficiency of 80% after three recycles and demonstrating superior laccase thermostability and storage stability. Moreover, after loading with copper nanoparticles, the LAC@HZIF-8-D approach exhibited a 2,4-DCP removal efficiency of 95%, a promising finding for its potential use in environmental purification.

Magnetic metal-organic frameworks immobilized enzyme-based nano-biocatalytic systems for sustainable biotechnology

Nanobiocatalysts, in which enzyme molecules are integrated into/onto multifunctional materials, such as metal-organic frameworks (MOFs), have been fascinating and appeared as a new interface of nanobiocatalysis with multi-oriented applications. Among various nano-support matrices, functionalized MOFs with magnetic attributes have gained supreme interest as versatile nano-biocatalytic systems for organic bio-transformations. From the design (fabrication) to deployment (application), magnetic MOFs have manifested notable efficacy in manipulating the enzyme microenvironment for robust biocatalysis and thus assure requisite applications in several areas of enzyme engineering at large and nano-biocatalytic transformations, in particular. Magnetic MOFs-linked enzyme-based nano-biocatalytic systems offer chemo-regio- and stereo-selectivities, specificities, and resistivities under fine-tuned enzyme microenvironments. Considering the current sustainable bioprocesses demands and green chemistry needs, we reviewed synthesis chemistry and application prospects of magnetic MOFs-immobilized enzyme-based nano-biocatalytic systems for exploitability in different industrial and biotechnological sectors. More specifically, following a thorough introductory background, the first half of the review discusses various approaches to effectively developed magnetic MOFs. The second half mainly focuses on MOFs-assisted biocatalytic transformation applications, including biodegradation of phenolic compounds, removal of endocrine disrupting compounds, dye decolorization, green biosynthesis of sweeteners, biodiesel production, detection of herbicides and screening of ligands and inhibitors.

In situ embedding of glucose oxidase in amorphous ZIF-7 with high catalytic activity and stability and mechanism investigation

Glucose oxidase (GOx) has a great application potential in the determination of glucose concentration. However, its sensitivity to the environment and poor recyclability limited its broader application. Herein, with the assistance of DA-PEG-DA, a novel immobilized GOx based on amorphous Zn-MOFs (DA-PEG-DA/GOx@aZIF-7/PDA) was developed to impart excellent properties to the enzyme. SEM, TEM, XRD, and BET analyses confirmed that GOx was embedded in amorphous ZIF-7 with ~5 wt% loading. Compared with free GOx, DA-PEG-DA/GOx@aZIF-7/PDA exhibited enhanced stability, excellent reusability, and promising potential for glucose detection. After 10 repetitions, the catalytic activity of DA-PEG-DA/GOx@aZIF-7/PDA can maintain 95.53 % ± 3.16 %. In understanding the in situ embedding of GOx in ZIF-7, the interaction of zinc ion and benzimidazole with GOx was studied by using molecular docking and multi-spectral methods. Results showed that zinc ions and benzimidazole had multiple binding sites on the enzyme, which induced the accelerated synthesis of ZIF-7 around the enzyme. During binding, the structure of the enzyme changes, but such changes hardly affect the activity of the enzyme. This study provides not only a preparation strategy of immobilized enzyme with high activity, high stability, and low enzyme leakage rate for glucose detection, but also a more comprehensive understanding of the formation of immobilized enzymes using the in situ embedding strategy.

ZIF-8 nanoparticles coated with macrophage-derived microvesicles for sustained, targeted delivery of dexamethasone to arthritic joints

Dexamethasone sodium phosphate (Dex) is widely used in the clinic for the treatment of rheumatoid arthritis. However, it circulates in blood for a short time and it is linked to high risk of severe side effects caused by repeated dosing. Here, we encapsulated Dex onto zeolitic imidazolate framework-8 (ZIF-8) to prepare metal-organic framework nanoparticles with high drug loading efficiency. To prevent clearance by the mononuclear phagocyte system and extend time in circulation, the nanoparticles were also camouflaged with macrophage-derived microvesicles (MV) to obtain the biomimetic drug delivery system MV/Dex/ZIF-8. In vitro and in vivo experiments showed that the nanosystem had high drug loading and encapsulation efficiency, high stability, and long circulation time, and it permitted sustained drug release longer in inflamed joint tissues. Our study provides new insights into designing camouflaged drug carriers to prevent their phagocytosis and prolong their time in circulation.

Template-Free In Situ Encapsulation of Enzymes in Hollow Covalent Organic Framework Capsules for the Electrochemical Analysis of Biomarkers

Although capsule-like materials as host carriers for enzyme encapsulation have been a hot topic in recent years, creating an ideal microenvironment for enhanced enzymatic performance is still a formidable challenge. Herein, we created a template-free method to in situ encapsulate natural enzymes in hollow covalent organic framework (COF) capsules at room temperature. The COF crystallites migrated from the inner core and self-assembled at the outside walls during the inside-out Ostwald ripening process, retaining the enzymes in the cavity. The adjustable hollow structure of the enzyme@COF capsule allowed the basic vibration of the enzyme to maintain a certain degree of freedom, thus significantly enhancing the enzymatic bioactivity. The hollow enzyme@COF capsule has large mesoporous tunnels allowing the efficient transport. In addition, the enzyme encapsulated in the capsule showed superior activity and ultrahigh stability under various extreme conditions that may lead to enzyme inactivation, such as high temperature, organic solvents, chelates, and the denaturing agent. Finally, the prepared hollow GOx@COF capsule was used for electrochemical sensing of glucose in human serum, and the electrochemical sensor exhibited high selectivity and satisfactory test results. This research not only provides a new way for COFs to encapsulate enzymes but also has potential applications in biocatalysis and biosensing, making artificial organelles possible.

Development of dual-enhancer biocatalyst with photothermal property for the degradation of cephalosporin

The abuse of cephalosporins poses a serious threat to human health and the ecological environment. In this work, cephalosporinase (AmpC enzyme) and Prussian blue (PB) crystals were encapsulated into ZIF-8 metal-organic frameworks (MOFs), and a photothermal AmpC/PB@ZIF-8 MOFs (APZ) nanocatalyst was prepared for the catalytic degradation of cephalosporin. The temperature of the APZ catalytic degradation system can be regulated by irradiation with near infrared light due to the photothermal effect of PB, and then, the activity of the APZ biocatalyst is significantly enhanced. Thereby, the degradation efficiency of cefuroxime can reach to 96%, and the degradation kinetic rate of cefuroxime augmented 4.5-fold comparing with that catalyzed by free enzyme. Moreover, encapsulation of the enzyme and PB can increase the affinity and charge transfer efficiency between APZ and substrate molecules, which can also improve the degradation efficiency of cephalosporins. Catalytic degradation pathways for three generations of cephalosporins were proposed based on their degradation products. The dual-enhancer biocatalyst based on the photothermal effect and immobilization of the PB and enzyme can significantly enhance the activity and stability of the enzyme, and it can also be recycled. Therefore, the biocatalyst has potential applications for the effective degradation of cephalosporins in the environment.

Biomineralized Cascade Enzyme-Encapsulated ZIF-8 Nanoparticles Combined with Antisense Oligonucleotides for Drug-Resistant Bacteria Treatment

The unrestrained use of antibiotics accelerates the development of drug-resistant bacteria and leads to an increasing threat to human health. Therefore, there is an urgent need to explore novel and effective strategies for the treatment of bacterial infections. Herein, zeolite imidazole framework-8 (ZIF-8) material was utilized to construct biomineralized nanomaterial (GOx&HRP@ZIF-8/ASO) by encapsulating biological cascade enzymes and combining with antisense oligonucleotides (ASOs), which achieved effective and synergistic antidrug-resistant bacteria therapy. Various in vitro assays confirmed that GOx&HRP@ZIF-8/ASO exhibited excellent antibacterial properties against Escherichia coli, Staphylococcus aureus, methicillin-resistant S. aureus (MRSA) during catalysis of glucose (Glu), especially the minimum inhibitory concentration (MIC) against MRSA was only 16 μg/mL. Compared with simple ZIF-8 (32.85%) and ftsZ ASO (58.65%), GOx&HRP@ZIF-8/ASO+Glu exhibited superb biofilm destruction ability, and the bacteria removal efficiency of the MRSA biofilm could be as high as 88.2%, indicating that the reactive oxygen species (ROS) produced by the cascade enzyme reaction imparted the main synergistic antibacterial capability, and simultaneously, ftsZ ASO significantly enhanced the antibacterial effect by inhibiting the expression of the ftsZ gene. In vivo anti-infection treatment experiments revealed that GOx&HRP@ZIF-8/ASO exhibited the best wound repairing performance and excellent biocompatibility in the presence of Glu. These findings suggested that GOx&HRP@ZIF-8/ASO has favorably realized high-efficiency treatment of MRSA infection and filled the gap in the antibacterial application of biological enzymes.

Hybrid metal organic frameworks as an Exotic material for the photocatalytic degradation of pollutants present in wastewater: A review

In this world, water is considered as the Elixir for all living creatures. Human life rolls with water, and every activity depends upon water. Worldwide water resources are being contaminated due to the elevation in the population count, industrialization and urbanization. Ejection of chemicals by industries and domestic sewages remains the major reason in the destruction of natural water resources. Contaminated water with harmful microbes, chemical dyes, pesticides, and carcinogens are the root cause of many diseases and deaths of living species. In this scenario, researchers engaged in producing ultra components to remove the contaminants. Metal organic frameworks (MOF) are the desired combination of organic and inorganic materials to achieve the required target. MOFs possess unique characteristics like tunable internal structure, porosity, crystallinity and high surface area which enable them for energy and environmental application. For the past years, MOFs are concentrated more as a photocatalyst in the treatment of polluted water. These research studies discuss the improvement of photocatalytic performance of MOF by the incorporation of metals, metal coupled with nanoparticles like polymers, graphene, etc., into it to achieve the enhanced photocatalytic activity by scavenging entire chemicals and harmful microbes to retain the quality of water. The target of this review article is to focus on the state of the art research work on MOFs in photocatalytic water treatment technique.

Fabricated Metal-Organic Frameworks (MOFs) as luminescent and electrochemical biosensors for cancer biomarkers detection

In the health domain, a major challenge is the detection of diseases using rapid and cost-effective techniques. Most of the existing cancer detection methods show poor sensitivity and selectivity and are time consuming with high cost. To overcome this challenge, we analyzed porous fabricated metal-organic frameworks (MOFs) that have better structures and porosities for enhanced biomarker sensing. Here, we summarize the use of fabricated MOF luminescence and electrochemical sensors in devices for cancer biomarker detection. Various strategies of fabrication and the role of fabricated materials in sensing cancer biomarkers have been studied and described. The structural properties, sensing mechanisms, roles of noncovalent interactions, limits of detection, modeling, advantages, and limitations of MOF sensors have been well-discussed. The study presents an innovative technique to detect the cancer biomarkers by the use of luminescence and electrochemical MOF sensors. In addition, the potential association studies have been opening the way for personalized patient treatments and the development of new cancer-detecting devices.

Multienzyme nanoassemblies: from rational design to biomedical applications

Multienzyme nanoassemblies (MENAs) that combine the functions of several enzymes into one entity have attracted widespread research interest due to their improved enzymatic performance and great potential for multiple applications. Considerable progress has been made to design and fabricate MENAs in recent years. This review begins with an introduction of the up-to-date strategies in designing MENAs, mainly including substrate channeling, compartmentalization and control of enzyme stoichiometry. The desirable properties that endow MENAs with important applications are also discussed in detail. Then, the recent advances in utilizing MENAs in the biomedical field are reviewed, with a particular focus on biosensing, tumor therapy, antioxidant and drug delivery. Finally, the challenges and perspectives for development of versatile MENAs are summarized.

Virus-templated magnetic composite hydrogels for surface immobilization of mimic-free-lipase

Surface immobilization of enzymes on magnetic-recoverable carriers is of great interest and importance for the biocatalysis of relatively large molecules. In this work, the nanosized amino-rich filamentous M13 virus, a versatile biological scaffold, was applied as the unique soft backbone for lipase immobilization. Based on the structure and capsid proteins of M13 phages, the magnetic-recoverable mimic-free-lipases (MFLs) composed of the M13 hydrogels and magnetic particles were developed in two designs. In the first design, nanosized wild M13 phages were crosslinked into a phage hydrogel through the N-terminals of pVIII peptides while NH₂-Fe₃O₄ magnetic nanoparticles (MNPs) were attached to the M13 virus through glutaraldehyde, forming the M13-(NH₂-Fe₃O₄) magnetic phage hydrogel. In the second design, special M13 with Fe₃O₄ affinity pIII-peptide (FAP-M13) was biopanned for strongly binding towards bare Fe₃O₄ with the "hook"-like pIII-peptide (N-LPLSTQH-C). TEM observation confirmed the direct grasp of FAP-M13 on bare Fe₃O₄, forming the magnetic (FAP-M13)-Fe₃O₄ virus hydrogel. Lipases were uniformly anchored on the phage surface of nanoscale by crosslinking with the N-terminals of pVIII peptides, and then lipase@M13-(NH₂-Fe₃O₄) and lipase@(FAP-M13)-Fe₃O₄ MFLs were constructed. For both MFLs, high activity recovery yield (>95%) and efficient magnetic separation were characterized. Significantly reduced MNP-usage-amount and enhanced lipase-loading-amount both by about 40 folds were obtained, compared with the conventional NH₂-Fe₃O₄ carriers. The quantified K_m and V_max/K_m values were almost equal to those of the free lipases, verifying free-enzyme-mimicking features of the MFLs. High pH-tolerance, wide temperature adaptability, enhanced thermal stability and stable magnetic separation capability of both MFLs were also observed. In particular, the (FAP-M13)-Fe₃O₄ magnetic virus hydrogel simply using bare Fe₃O₄ MNPs would be more convenient and economical in the scaled-up biocatalysis.

Fabrication of magnetic dual-hydrophilic metal organic framework for highly efficient glycopeptide enrichment

Highly selective glycopeptide enrichment is important before mass spectrometry analysis because of the ultra-low abundance of glycopeptides in the peptide mixtures. Herein, a UiO-66-NH₂-based magnetic composite was prepared and used for the hydrophilic enrichment of glycopeptides. The composite was modified with phytic acid (PA) molecules by partially replacing 2-aminoterephthalic acid ligands in UiO-66-NH₂, with electrostatic interactions also promoting this modification process. Based on the hydrophilicity of both the PA molecules and the UiO-66-NH₂ skeleton, the resulting material, denoted as MUiO-66-NH₂/PA, showed excellent dual hydrophilicity towards glycopeptide enrichment. Compared with pure UiO-66-NH₂, the specific surface area and hydrophilicity of the prepared material were increased, and MUiO-66-NH₂/PA exhibited good magnetic responsiveness to facilitate a convenient enrichment procedure. HRP and IgG were used as standard proteins to evaluate the glycopeptide enrichment properties, with 21 and 34 glycopeptides enriched from their tryptic digests. Furthermore, MUiO-66-NH₂/PA showed outstanding sensitivity (1 fmol/μL) and selectivity (HRP/BSA = 1:1000), and achieved remarkable glycopeptide enrichment performance for practical human serum samples. Notably, MUiO-66-NH₂/PA showed perfect reusability and stability, achieving enrichment performance after five cycles similar to that of the first use. This material can be used for glycopeptide enrichment to obtain further glycosylation information, providing the possibility for cancer treatment.

Tailor-made shape memory stents for therapeutic enzymes: A novel approach to enhance enzyme performance

Herein, our suggestion is to immobilize enzymes in-situ on absorbable shape-memory stents instead of injecting therapeutic enzymes into the blood. Chitosan (CHI)-based stents were tailored as novel support and the enzyme-immobilizing ability was elucidated using L-asparaginase (L-ASNase). For developing shape-memory stents, CHI-glycerol (GLY) solution was prepared and further blended with different ratios of polyethylene glycol (PEG), and polyvinyl alcohol (PVA). Afterward, the blends were modified by ionic crosslinking with sodium tripolyphosphate to obtain a shape-memory character. L-ASNase was included in the blends by using in-situ method before ionic crosslinking. The prepared stents, with or without L-ASNase, were comprehensively characterized by using several techniques. Collectively, immobilized L-ASNase exhibited much better performance in immobilization parameters than free one, thanks to its improved stability and reusability. For instance, CHI/GLY/PEG-3@L-ASNase retained about 70% of the initial activity after storage at 30 °C for 2 weeks, whereas the free form lost half of its initial activity. Besides, it retained 73.4% residual activity after 15 consecutive cycles. Most importantly, stent formulations exhibited ~60% activity in the bioreactor system after 4 weeks of incubation. Given the above results, shape-memory stents can be a promising candidate as a new platform for immobilization, especially in the blood circulation system.

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.

α-glucosidase immobilization on magnetic core-shell metal-organic frameworks for inhibitor screening from traditional Chinese medicines

In this work, a simple and rapid screening strategy was developed combining capillary electrophoresis analysis with enzymatic assay based on immobilized α-glucosidase. For α-glucosidase immobilization, magnetic core-shell metal-organic frameworks composite (Fe₃O₄@CS@ZIF-8) was fabricated by a step-by-step assembly method, and α-glucosidase was in situ encapsulated in crystal lattice of ZIF-8. The composite was characterized by transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction and vibrating sample magnetometer. After immobilization, α-glucosidase exhibited enhanced tolerance to temperature and pH, and its reusability was greatly improved with 74 % of initial enzyme activity after being recycled 10 times. The Michaelis-Menten constant of immobilized enzyme was calculated to be 0.47 mM and its inhibition constant and IC₅₀ for acarbose were 0.57 μM and 0.18 μM, respectively. The immobilized enzyme was subsequently applied to inhibitor screening from 14 TCMs, and Rhei Radix et Rhizoma was screened out. Among the commercially available 10 components presented in Rhei Radix et Rhizoma, gallic acid, (+)-catechin and epicatechin exhibited the strongest inhibitory effect on α-glucosidase. Their binding sites and modes with α-glucosidase were simulated via molecular docking to further verify the inhibition screening assay results. The positive results indicated that the Fe₃O₄@CS@ZIF-8-based screening strategy may provide a new avenue for discovering enzyme inhibitors from TCMs.

Oligonucleotide-Functionalized Enzymes Chemisorbing on Magnetic Layered Double Hydroxides: A Multimodal Catalytic Platform with Boosted Activity for Ultrasensitive Glucose Detection

A reasonable design of multifarious chemo- and biocatalytic functions within individual nano/microunits is urgently desired for high-performance cascade reactions but has heretofore remained elusive. Herein, glucose oxidase was functionalized with oligonucleotides and steadily chemisorbed on magnetic layered double hydroxides (mLDHs) to construct a multimodal catalytic platform for realizing divergent reactions with heterogeneous and biocatalytic steps. The flowerlike mLDHs served both as an enzyme support and a peroxidase mimic cooperating with enzymes for tandem catalysis. Oligo-DNA connected the enzymes to mLDHs like a bridge, and a stepwise ligand-exchange-assisted coordination mechanism was proposed to explain the robust interaction between DNA and mLDHs. More importantly, DNA significantly improved the bioactivity of the whole system. The acceleration mechanism was attributed to the diffusion tunnels for the substrate/product and enhanced substrates binding on mLDHs. The multimodal catalytic platform was applied for colorimetric and electrochemical sensing of glucose with a low limit of detection and high selectivity. The practical analysis capability of the ultrasensitive sensor was evaluated by detecting glucose in human serum and sweat, showing reliable results, satisfactory recovery, and excellent stability. The strategy of combining mLDHs and enzymes for cascade catalysis provides a universal approach to prepare chemo-enzyme hybrids with high performance, which holds great promise for applications in biosensors and industrial catalysis.

Calix[4]arene tetracarboxylic acid-treated lipase immobilized onto metal-organic framework: Biocatalyst for ester hydrolysis and kinetic resolution

Metal organic frameworks (MOFs) are hybrid organic inorganic materials with unique properties such as well-defined pore structure, extremely high surface area, excellent chemical-thermal stability. MOFs-based constructs have been extensively engineered and used for applications, such as enzyme immobilization for bio-catalysis. To obtained a zeolitic imidazole framework-8 (ZIF-8) for enzyme immobilization, Candida rugosa lipase (CRL) was pretreated with calix [4]arene tetracarboxylic acid (Calix) and reacted with Zn and imidazole by co-precipitation method. The prepared biocomposite was characterized by SEM, EDX, FT-IR, and XRD. The prepared CRL@Calix-ZIF-8 with high encapsulation efficiency showed improved resistance to alkali and thermal conditions. The CRL@Calix-ZIF-8 with the biocatalytic activity was 2-folds higher than that of the CRL@ZIF-8 (without Calix). The free lipase lost its catalytic activity completely at 60 °C after 100 min, while the CRL@Calix-ZIF-8 and CRL@ZIF-8 retained about 84% and 73%. It was found that CRL@Calix-ZIF-8 and CRL@ZIF-8 still retained ~83 and 67% of catalytic activity after its 6th use, respectively. The kinetic resolution of the immobilized lipases was examined for enantioselective hydrolysis of racemic naproxen methyl ester. CRL@Calix-ZIF-8 showed enantioselectivity against the racemic naproxen methyl ester, with E = 183 and 131 compared to the CRL@ZIF-8.

Three-dimensional ordered magnetic macroporous metal-organic frameworks for enzyme immobilization

Metal-organic frameworks (MOFs) have been emerged as a promising support for immobilizing enzymes owing to the tunable porosity, high surface area, and structural diversity. However, most of these possess nanometer size and small pores, which are difficult to recover them from the reaction medium and present low immobilization efficiency and protein loading capacity, and high substrate diffusion limitations. Herein, a novel magnetic amino-functionalized zeolitic imidazolate framework-8 (ZIF-8) with 3D highly ordered macroporous structure was synthesized using the assembled polystyrene (PS) nanosphere monoliths as a template. Subsequently, catalase (CAT) molecules were immobilized on the surface of macroporous magnetic ZIF-8 and inside the macropores by precipitation, covalent binding and cross-linking. The resultant immobilized CAT showed high immobilization efficiency (58%) and protein loading capacity (29%), leading to 500% higher activity than the immobilized CAT on ZIF-8 (CAT/ZIF-8). Meanwhile, the immobilized CAT could be easily recovered with a magnet without obvious activity loss. The traditional CAT/ZIF-8 lost its activity after 6 cycles, whereas, the immobilized CAT retained 90% activity of its initial activity after reusing for 8 cycles, indicating excellent reusability. In conclusion, this study provides a facile and efficient approach to immobilize enzymes on/in MOFs with enhanced activity and excellent recyclability.

Zr-based acid-stable nucleotide coordination polymers: An excellent platform for acidophilic enzymes immobilization

Acidophilic enzymes play an important role in special industrial catalytic reactions. In this work, we reported Zr-based acid-stable nucleotide coordination polymers (CPs) for efficiently improving acidophilic enzymes immobilization. Among all tested metal ions, the Zr⁴⁺/AMP CPs exhibited the highest acid stability and enzyme affinity. As a typical acidophilic enzyme, the immobilized Chloroperoxidase by Zr⁴⁺/AMP CPs displayed robust reusability in the asymmetric synthesis of modafinil, remained 95.7% of conversion rate and 99.1% enantiomeric excess (e.e.) value. This work displayed a novel acid-stable bioorganic and inorganic hybrid nanomaterial for acidophilic enzymes immobilization.

Charge-oriented strategies of tunable substrate affinity based on cellulase and biomass for improving in situ saccharification: A review

The intrinsic recalcitrance of lignocellulosic biomass makes it resistant to enzymatic hydrolysis. The electron-rich surface of the lignin and cellulose-alike structure of hemicellulose competitively absorb the cellulase. Thus, modifying the surface charge on biomass components to alter cellulase affinity is an urgent requisite. Developing charge tunable cellulase will alter substrate affinity. Also, charge-based immobilization generates controllable substrate affinity. Within immobilized cellulase involved in situ biomass saccharification, charge effects made a crucial contribution. In addition to affecting the interaction between immobilized cellulase and biomass, charge exerts an impact on cellulase to immobilize the materials, further investigation is essential. This study aims to review the charge effects on the cellulase affinity in biomass saccharification, strategies of charge tunable cellulase, and immobilized cellulase, thereby explaining the role of electrostatic interaction. In terms of electrostatic behavior, the pathways and plans to improve in situ biomass saccharification seem to be promising.

Synthesis of Magnetic Metal-Organic Frame Material and Its Application in Food Sample Preparation

A variety of contaminants in food is an important aspect affecting food safety. Due to the presence of its trace amounts and the complexity of food matrix, it is very difficult to effectively separate and accurately detect them. The magnetic metal-organic framework (MMOF) composites with different structures and functions provide a new choice for the purification of food matrix and enrichment of trace targets, thus providing a new direction for the development of new technologies in food safety detection with high sensitivity and efficiency. The MOF materials composed of inorganic subunits and organic ligands have the advantages of regular pore structure, large specific surface area and good stability, which have been thoroughly studied in the pretreatment of complex food samples. MMOF materials combined different MOF materials with various magnetic nanoparticles, adding magnetic characteristics to the advantages of MOF materials, which are in terms of material selectivity, biocompatibility, easy operation and repeatability. Combined with solid phase extraction (SPE) technique, MMOF materials have been widely used in the food pretreatment. This article introduced the new preparation strategies of different MMOF materials, systematically summarizes their applications as SPE adsorbents in the pretreatment of food contaminants and analyzes and prospects their future application prospects and development directions.

Size-Tunable Metal-Organic Framework-Coated Magnetic Nanoparticles for Enzyme Encapsulation and Large-Substrate Biocatalysis

Immobilizing enzymes on nanoparticles (NPs) enhances the cost-efficiency of biocatalysis; however, when the substrates are large, it becomes difficult to separate the enzyme@NP from the products while avoiding leaching or damage of enzymes in the reaction medium. Metal-organic framework (MOF)-coated magnetic NPs (MNPs) offer efficient magnetic separation and enhanced enzyme protection; however, the involved enzymes/substrates have to be smaller than the MOF apertures. A potential solution to these challenges is coprecipitating metal/ligand with enzymes on the MNP surface, which can partially bury (protect) the enzyme below the composite surface while exposing the rest of the enzyme to the reaction medium for catalysis of larger substrates. Here, to prove this concept, we show that using Ca²⁺ and terephthalic acid (BDC), large-substrate enzymes can be encapsulated in CaBDC-MOF layers coated on MNPs via an enzyme-friendly, aqueous-phase one-pot synthesis. Interestingly, we found that using MNPs as the nuclei of crystallization, the composite size can be tuned so that nanoscale composites were formed under low Ca²⁺/BDC concentrations, while microscale composites were formed under high Ca²⁺/BDC concentrations. While the microscale composites showed significantly enhanced reusability against a non-structured large substrate, the nanoscale composites displayed enhanced catalytic efficiency against a rigid, crystalline-like large substrate, starch, likely due to the improved diffusivity of the nanoscale composites. To our best knowledge, this is the first report on aqueous-phase one-pot synthesis of size-tunable enzyme@MOF/MNP composites for large-substrate biocatalysis. Our platform can be applied to immobilize other large-substrate enzymes with enhanced reusability and tunable sizes.