Metal-Organic Frameworks for Enzyme Immobilization: Beyond Host Matrix Materials

Protein and peptide confinement within metal-organic materials

Metal-organic materials (MOMs), including both discrete metal-organic cages (MOCs) and metal-organic frameworks (MOFs), are emerging as promising materials for peptide and protein immobilisation. In particular, the ease of synthesis of MOMs alongside their well-defined and modular internal void spaces makes them appealing when considering routes to immobilise and stabilise peptides and proteins outside of biological environments whilst retaining their native activity. Here we review recent advances made in understanding the conformation of peptidic materials confined within MOMs and the enzymes@MOF constructs which show the best enzymatic performance. We highlight opportunities for further advancement in each of these areas and proposed that complementary approaches taken by the MOC and MOF communities might be fruitfully combined to advance our understanding and the development of peptide/protein@MOM applications.

Engineering Oxidase-Based Cascade Nanoreactors Design, Catalytic Efficiency, and Applications in Disease Monitoring

Inspired by the advantages of biological cascade catalytic systems, it has been devoted to the discovery of novel oxidase-based cascade catalytic systems for disease monitoring. However, the low stability, easy inactivation, and poor reproducibility of oxidase significantly limit their practical applications. Immobilization of the oxidase can be enabled to protect them from external mediators and improve catalytic efficiency and reproducibility. Notably, the substrate channels and spatial confinement play an essential role in the construction of immobilized cascade nanoreactors to enhance the overall activity. Moreover, nanozymes, a class of enzyme mimics, have not only enzyme-like activity but also high stability and tunable catalytic properties, which bolster the development of cascade nanoreactors. Herein, recent advances in the assembly of cascade reactors involving enzymes/nanozymes are described. The importance of substrate channeling and spatial distribution in regulating the catalytic efficiency of the nanoreactor is highlighted. Then, along with an in-depth discussion of the cascade biosensors for disease monitoring, the design and application of innovative devices based on these sensing principles are also summarized, including microfluidic systems, hydrogel-based platforms, and test paper technologies. Finally, challenges and prospects for cascade nanoreactors are briefly discussed and prospected.

Novel Immobilized Enzyme System Using Hydrophobic Dendritic Mesoporous Silica Nanospheres for Efficient Flavor Ester Production

Enzymatic synthesis of flavor esters is widely used in the food and flavor industries, but challenges remain in improving the catalytic efficiency and stability of biocatalysts. This study evaluates the performance of a novel biocatalyst, CALB@DMSN-C8, formed by immobilizing Candida antarctica lipase B (CALB) on hydrophobic dendritic mesoporous silica nanospheres (DMSN-C8), for synthesizing flavor esters. The CALB@DMSN-C8 catalyst achieves a caproic acid conversion rate of 98.5 ± 0.5% in just 30 min and demonstrates outstanding thermal stability, retaining a high conversion efficiency over 20 reuse cycles. To our knowledge, this study represents the most efficient synthesis of flavor esters, including ethyl valerate, ethyl caproate, ethyl heptanoate, and ethyl caprylate, compared to studies in the existing literature. Analysis of aroma characteristics and molecular docking simulations revealed the typical flavor profiles and synthesis mechanisms of various mellow esters. This study develops an innovative strategy by using self-made immobilized lipases to catalyze the production of flavor esters with potential applications in food and cosmetics.

Study of the biochemical and kinetic properties of Candida antarctica lipase immobilized on magnetized poly(styrene-co-ethylene glycol dimethacrylate) and the development of a mathematical model for emollient ester synthesis

The present study aimed to develop a biocatalyst through the immobilization of Candida antarctica lipase B (CALB) via physical adsorption onto magnetized poly(styrene-co-ethylene glycol dimethacrylate) (STY-EGDMA-M). Biochemical property characterization, apparent kinetic parameter determination, and thermal stability assessment were conducted using a methodology developed based on the hydrolysis of the ester methyl butyrate. The results demonstrated that immobilization expanded the enzyme's optimal pH range, with the best performance observed at pH 7.5 and 8, reaching approximately 730 U g⁻1. Additionally, increasing the temperature to 55°C led to an enhancement in the biocatalyst's hydrolytic activity, achieving a maximum of 916.24 U g⁻1. Kinetic parameter analysis yielded values of 321.38 ± 6.31 mM for Km and 4322.46± 75.73 U g⁻1 for Vmax. Thermal stability tests were conducted at 55°C, revealing that 83% of the biocatalyst's initial activity was retained after 24 h of exposure. Furthermore, the biocatalyst's performance in the synthesis of emollient esters (butyl oleate, 2-ethylhexyl oleate, and octyl oleate) via solvent-free esterification was evaluated. The synthesis of emollient esters demonstrated conversions exceeding 55% for octyl oleate and 2-ethylhexyl oleate at 50 and 55°C, whereas the maximum conversion for butyl oleate was 42% at 55°C. Among the bioprocesses evaluated, the synthesis of octyl oleate was selected for kinetic modeling using the ping-pong bi-bi mechanism, with five different parameter arrangements constructed. The model with the lowest corrected Akaike information criterion (AICC = 129.649) was selected. The findings obtained in this work open new avenues for biotechnological applications, reinforcing the relevance of the biocatalyst as a promising tool for industrial processes and scientific research. Additionally, this study provides an alternative methodology for the biochemical characterization of immobilized lipases and employs mathematical modeling to enhance the kinetic understanding of enzymatic reactions conducted at different temperatures.

Precise modulation of protein refolding by rationally designed covalent organic frameworks

Precisely regulating protein conformation (folding) for biomanufacturing and biomedicine is of great significance but remains challenging. In this work, we innovate a covalent organic framework (COF)-directed protein refolding strategy to modulate protein conformation by rationally designed covalent organic frameworks with adapted pore structures and customizable microenvironments. The conformation of denatured protein can be efficiently recovered through a simple one-step approach using covalent organic framework treatment in aqueous or buffer solutions. This strategy demonstrates high generality that can be applied to various proteins (for example, lysozyme, glucose oxidase, trypsin, nattokinase, and papain) and diverse covalent organic frameworks. An in-depth investigation of the refolding mechanism reveals that pore size and microenvironments such as hydrophobicity, π-π conjugation, and hydrogen bonding are critical to regulating protein conformation. Furthermore, we use this covalent organic framework platform to build up solid-phase columns for continuous protein recovery and achieved a ~ 100% refolding yield and excellent recycling performance (30 cycles), enabling an integrated process for the extracting and refolding denatured proteins (such as the harvest of protein in inclusion bodies). This study creates a highly efficient and customizable covalent organic framework platform for precisely regulating proteins refolding and enhancing their performance, opening up a new avenue for advanced protein manufacturing.

Advancements in lipase immobilization: Enhancing enzyme efficiency with nanomaterials for industrial applications

One of the most widely utilized enzymes, lipase is crucial to many biotechnological and industrial processes, including those in the biodiesel, food, paper, and oleochemical sectors, as well as in applications related to medicine. However, its use is highly costly and challenging due to its instability and aqueous solubility. Immobilization is a commonly employed way to enhance lipase activity, and it has proven to be a successful approach. In comparison to free lipase, immobilized lipase on nanomaterials (NMs) as demonstrated superior properties, including greater pH and temperature stability, a longer stable duration, and the ability to be recycled. However, under specific circumstances, protein loading is comparatively decreased and lipase immobilization on NMs might also occasionally result in activity loss. The processes of immobilization, the kind of NM's being employed, and the physicochemical characteristics of the NMs (such as particle size, aggregation behaviour, NM dimension, and kind of coupling/modifying agents being used) all affect the overall performance of immobilized lipase on NM's. In recent years, innovative nanostructured forms such nanoflowers, carbon nanotubes, nanofibers, and metal-organic frameworks (MOFs) have been researched for numerous applications along with classic nanomaterials like nano silicon, magnetic nanoparticles, and nanometal particles. To use immobilized lipase on/in nanomaterials for large-scale industrial applications, a few issues still need to be resolved. This study addresses the current advancements and the impact of NMs on lipase immobilization and activity based on the unique characteristics of lipase and NM's.

Research progress of β-xylosidase in green synthesis

β-Xylosidase, an important hydrolase, catalyzes the degradation of xylan and xylosides, demonstrating significant potential for applications in biomass conversion and green synthesis. In recent years, with the rise of green chemistry, research on β-xylosidase in sustainable chemical synthesis has garnered increasing attention. Lignocellulosic biomass, a readily available and sustainable natural resource, requires the involvement of β-xylosidase for the production of biofuels. This enzyme not only efficiently degrades the xylan components of plant cell walls to produce biofuels but also synthesizes high-value glycosides through transglycosylation reactions, providing an eco-friendly catalytic tool for green chemical synthesis. This review summarizes the structural characteristics and catalytic mechanisms of β-xylosidase, along with related techniques to enhance its catalytic performance, such as enzyme immobilization, enzyme fusion technology, genetic engineering, and enzyme synergy. It focuses on recent advancements in its green applications, including the production of active compounds, waste degradation, bioenergy development, pulp bleaching, and deinking of waste paper (as shown in Fig. 1). Additionally, in light of current research trends, this review offers insights into the future prospects and challenges of β-xylosidase in green synthesis, aiming to provide valuable references for related fields.

Hierarchical encapsulation of enzymes with multishell metal-organic frameworks for sensitive detection of α-amylase activity in complex fermentation samples

In natural world, sophisticated cascade reactions occur in compartmentalized organelles. However, simulating cascade processes in living systems remains problematic, and the drawbacks of enzymes, including dissatisfactory stability, reusability, and sensitivity in extreme microenvironments, have hampered further applications. Here, we report a confined multi-enzyme system in which MnFe metal-organic framework (MFM) is applied to encapsulate enzymes through shell-by-shell epitaxial-overgrowth in diverse compartments. MFM possessed excellent peroxidase-mimicking activity and biocompatibility, enabling it to serve not only as a reliable carrier for multiple enzymes, but also as a high-performance nanozyme in cascades. Compared with free enzymes, this system exhibited significantly improved bioactivity and environmental tolerance. On this basis, the confined multi-enzyme system was applied for selective α-amylase analysis in complicated fermentation specimens with a broad linear range (5-500 U·L-1) and low detection limit (2.14 U·L-1). This work sheds new light on the construction of efficient biocatalytic cascades to accelerate applications in food manufacturing.

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.

Crystal Phase Transition-Driven Integration of Enzymes into 2D Metal-Organic Frameworks

In situ encapsulation of enzymes within a metal-organic framework (MOF) represents a promising technique for engineering robust biocatalysts. However, the success of enzyme encapsulation is often constrained by intricate interfacial interactions between enzyme surfaces and MOF precursors, limiting the versatility of this MOF method. Herein, we introduce a phase transition strategy for encapsulating enzymes within a Zn-HHTP framework, demonstrating its effectiveness across a wide range of enzymes irrespective of their surface chemistry. In this approach, enzyme molecules are preloaded in a zinc oxide (ZnO) template through a simple yet efficient coprecipitation process, followed by a ZnO-to-Zn-HHTP MOF crystal phase transition in the presence of ligand precursors, resulting in the formation of a quasi-mesoporous hybrid Zn-HHTP MOF inside, for which the original enzymes are preserved. The long-range ordered quasi-mesopore channels enhance substrate accessibility to the immobilized enzymes, endowing enzyme@Zn-HHTP with higher catalytic activity compared to enzymes immobilized within the well-known MOF, ZIF-8, which has narrow apertures. Additionally, the resultant enzyme@Zn-HHTP exhibits exceptional structural stability across a broad pH range (3-14), and Zn-HHTP can provide robust protection against enzyme denaturation by heat, organic solvents, and proteases. This work offers a facile and reliable phase transition strategy for synthesizing active and robust MOF biocatalysts, advancing biocatalysis across various fields.

Synthesis and Characterisation of Multivariate Metal-Organic Frameworks for Controlled Doxorubicin Absorption and Release

The development of drug carriers with efficient absorption and controlled delivery properties is crucial for advancing medical treatments. Metal-organic frameworks (MOFs) with tunable porosity and a large surface area represent a promising class of materials for this application. Among them, NUIG4 stands out as a biocompatible MOF that exhibits exceptionally high doxorubicin (Dox) absorption (1995 mg dox/g NUIG4) and pH-controlled release properties. In this study, we report the synthesis and characterisation of multivariate MOFs (MV-NUIG4), which are analogues of NUIG4 that maintain the same topology while incorporating different functional groups within their framework. Eight new MV-NUIG4 MOFs have been synthesised through in situ reactions of the corresponding 4-aminobenzoic acid derivative with 4-formylbenzoic acid. The compounds were thoroughly characterised using a range of techniques, including powder X-ray diffraction, infrared spectroscopy, 1H-NMR, and single-crystal X-ray crystallography. The experimental ratio of the reagents and ligand precursors for the synthesis of MV-NUIG4 MOFs matched the ratio of the linkers in the final products. These structures incorporate additional functional groups, such as methyl and hydroxyl, in varying ratios. Computational modelling was used to provide further insight into the crystal structure of the MOFs, revealing a random distribution of the functional groups in the framework. The Dox absorption and release capacity of all analogues were studied, and the results revealed that all analogues displayed high drug absorption in the range of 1234-1995 mg Dox/g MOF. Furthermore, the absorption and release rates of the drug are modulated by the ratio of functional groups, providing a promising approach for controlling drug delivery properties in MOFs.

Enhancing cellulase performance through nanomaterials and MOFs: innovations and applications

Cellulase is widely utilized in industries such as biofuel production, food processing, textiles, and waste management due to its catalytic efficiency in breaking down cellulose. However, its industrial application is limited by instability under harsh conditions. This review examines innovative methodologies for enhancing cellulase performance through immobilization on nanomaterials, including magnetic nanoparticles, carbon-based nanomaterials, and metal-organic frameworks (MOFs). Immobilization techniques, such as adsorption, covalent bonding, and cross-linking, have been shown to significantly improve cellulase stability, activity, and reusability. Key findings include a threefold increase in catalytic efficiency when cellulase is immobilized on magnetic nanoparticles, alongside notable enhancements in thermal stability when employing MOF composites. Despite these advancements, challenges such as enzyme leakage, material costs, and scalability remain. Future opportunities lie in developing more cost-effective, scalable immobilization strategies, with interdisciplinary approaches offering the potential to further enhance enzyme efficiency across diverse application.

The role of metal-organic framework (MOF) in laccase immobilization for advanced biocatalyst formation for use in micropollutants removal

A detailed physicochemical and functional analysis of immobilized laccase on Cu-BDC material was carried out to evaluate its efficiency and stability in the removal of 17α-ethynylestradiol (EE2). Structural and morphological studies of Cu-BDC before and after laccase immobilization were conducted using SEM, CLSM, and AFM microscopy. Before immobilization, the material was characterized by a smooth structure with few defects, numerous free spaces, and open internal channels. After laccase immobilization, the MOF surface was coated with the enzyme, forming agglomerates of irregular shape, confirmed by an increase in particle number and a decrease in surface roughness. The immobilization process achieved an efficiency of more than 80%, with 88% retention of the enzyme's catalytic activity. The kinetic and thermodynamic parameters indicated higher stability of the immobilized laccase compared to the free enzyme, suggesting that MOF provides a suitable support for enzyme immobilization, enhancing its stability and efficiency. The fabricated biocatalytic systems also exhibited greater tolerance to varying pH and temperature conditions as compared to the free enzyme. These biocatalytic systems demonstrated high efficiency in the degradation of 17α-ethynylestradiol from model solutions and real wastewater. The results obtained indicate that the immobilization of laccase on a Cu-BDC carrier can be an effective solution for bioremediation processes of pollutants in wastewater, opening up prospects for the wide application of this technology in the water and wastewater industry.

Recent Advances in Enzymatic Biofuel Cells to Power Up Wearable and Implantable Biosensors

Enzymatic biofuel cells (EBFCs) have emerged as a transformative solution in the quest for sustainable energy, offering a biocatalyst-driven alternative for powering wearable and implantable self-powered biosensors. These systems harness renewable enzyme activity under mild conditions, positioning them as ideal candidates for next-generation biosensing applications. Despite their promise, their practical deployment is limited by challenges such as low power density, restricted operational lifespan, and miniaturization complexities. This review provides an in-depth exploration of the evolving landscape of EBFC technology, beginning with fundamental principles and the latest developments in electron transfer mechanisms. A critical assessment of enzyme immobilization techniques, including physical adsorption, covalent binding, entrapment, and cross-linking, underscores the importance of optimizing enzyme stability and catalytic activity for enhanced bioelectrode performance. Additionally, we examine advanced bioelectrode materials, focusing on the role of nanostructures such as carbon-based nanomaterials, noble metals, conducting polymers, and metal-organic frameworks in improving electron transfer and boosting biosensor efficiency. Also, this review includes case studies of EBFCs in wearable self-powered biosensors, with particular attention to the real-time monitoring of neurotransmitters, glucose, lactate, and ethanol through sweat analysis, as well as their integration into implantable devices for continuous healthcare monitoring. Moreover, a dedicated discussion on challenges and trends highlights key limitations, including durability, power management, and scalability, while presenting innovative approaches to address these barriers. By addressing both technical and biological constraints, EBFCs hold the potential to revolutionize biomedical diagnostics and environmental monitoring, paving the way for highly efficient, autonomous biosensing platforms.

Redefining Metal Organic Frameworks in Biosensors: Where Are We Now?

As a broad class of porous nanomaterials, metal organic frameworks (MOFs) exhibit unique properties, such as broad tunability, high stability, atomically well-defined structure, and ordered uniform porosity. These features facilitate the rational design of MOFs as an outstanding nanomaterial candidate in biosensing, therapeutics delivery, and catalysis applications. Recently, novel modifications of the MOF nanoarchitecture and incorporation of synergistic guest materials have been investigated to achieve well-tailored functional design, gradually bridging the fundamental gap between structure and targeted activity. Specifically, the burgeoning studies of MOF-based high-performance biosensors have aimed to achieve high sensitivity, selectivity, and stability for a large variety of analytes in different sensing matrices. In this review, we elaborate the key roles of MOF nanomaterials in biosensors, including their high stability as a protective framework for biomolecules, their intrinsic sensitivity-enhancing functionalities, and their contribution of catalytic activity as a nanozyme. By examining the main structures of MOFs, we further identify varied structural engineering approaches, such as precursor tuning and guest molecule incorporation, that elucidate the concept of the structure-activity relationship of MOFs. Furthermore, we highlight the unique applications of MOF nanomaterials in electrochemical and optical biosensors for enhanced sensor performances. Finally, the challenges and future perspectives of developing next-generation MOF nanomaterials for biosensor applications are discussed.

Integrating Enzymes with Reticular Frameworks To Govern Biocatalysis

Integrating enzymes with reticular frameworks offers promising avenues for access to functionally tailorable biocatalysis. This Minireview explores recent advances in enzyme-reticular framework hybrid biocomposites, focusing on the utilization of porous reticular frameworks, including metal-organic frameworks, covalent-organic frameworks, and hydrogen-bonded organic frameworks, to regulate the reactivity of an enzyme encapsulated inside mainly by pore infiltration and in situ encapsulation strategies. We highlight how pore engineering and host-guest interfacial interactions within reticular frameworks create tailored microenvironments that substantially impact the mass transfer and enzyme conformation, leading to biocatalytic rate enhancement, or imparting enzymes with non-native biocatalytic functions, including substrate selectivity and new activity. Additionally, the feasibility of leveraging the photothermal effect of a framework to optimize the local reaction temperature and photoelectric effect to elicit diverse photoenzyme-coupled reactions is also summarized in detail, which can expand the functional repertoire of biocatalytic transformations under light irradiation. This Minireview underscores the potential of reticular frameworks as tunable and reliable platforms to govern biocatalysis, offering pathways for engineering sustainable, efficient, and selective biocatalytic reactors in pharmaceutical, environmental, and energy-related applications.

Physical Isolation of Single Protein Molecules within Well-Defined Coordination Cages to Enhance Their Stability

Encapsulation of a single protein within a confined space can lead to distinct properties compared to bulk solutions, but controlling the number of encapsulated proteins and their environment remains challenging. This study demonstrates the encapsulation of single proteins within well-defined, tunable cavities of self-assembled coordination cages, thereby enhancing protein stability. Within uniform cavities of size-tunable coordination cages, 15 different proteins of varying sizes (3-6 nm in diameter) and properties (e.g., isoelectric points and hydrophobicity) were successfully confined. Various analytical techniques confirmed that the proteins maintained their secondary structures and enzymatic activities under denaturing conditions such as exposure to organic solvents, heat, and buffers. These findings suggest that such coordination cages have the potential to serve as synthetic hosts for precisely controlling protein functions within their customizable cavities.

Screening of Aluminum-Based MOFs for Effective In Situ Immobilization of Biomolecules

An effective approach for the immobilization and protection of biological entities is their encapsulation via the in situ synthesis of metal-organic frameworks (MOFs). To ensure the preservation of the bioentities, mild synthetic conditions, including aqueous media and ambient conditions (temperature and pressure), are preferred. In this study, we investigated the synthesis of various aluminum polycarboxylate-based MOFs, including the fumarate, terephthalate, amino-terephthalate, and muconate forms of MIL-53(Al), as well as the MIL-110 and MIL-160 MOF types. The potential as immobilization matrices was then assessed using bovine serum albumin (BSA). Finally, MIL-53(Al)-fum was selected for the encapsulation of a mixture of polysaccharides and more structurally complex bioentities (viruses).

Two-dimensional metal-organic frameworks (2D-MOFs) as a carrier for enzyme immobilization: A review on design and bio-applications

In the realm of carriers for enzyme immobilization, the use of MOFs has accelerated owing to their exceptional porosity and stability. Among these, 2D metal-organic frameworks (2D-MOFs) have emerged as promising supports for enzyme immobilization. This review highlights advancements in their synthesis, structural properties, and functional characteristics, focusing on enhancing catalytic performance and stability. Brief insights into computational approaches for optimizing these nanostructures and their catalytic efficiency are provided. The unique synergy between 2D MOF-based nanozymes and enzymes is discussed, showcasing their potential in diverse applications. Challenges in their practical implementation, prospective solutions, and future research directions are also outlined. This review emphasizes the transformative potential of 2D MOFs, focusing on their design and bioapplications and paving the way for innovative and sustainable strategies.

Increasing the dual-enzyme cascade biocatalysis efficiency and stability of metal-organic frameworks via one-step coimmobilization for visual detection of glucose

In biosensing analysis, the activity of enzyme systems is limited by their fragility, and substrates catalyzed by monoenzymes tend to undergo spontaneous decomposition during ineffective mass transfer processes. In this study, we propose a novel strategy to encapsulate the glucose oxidase and horseradish peroxidase (GOx&HRP) cascade catalytic system within the hydrophilic zeolite imidazole framework ZIF-90. By leveraging the specific pore structure of ZIF-90, we effectively immobilized GOx and HRP molecules in their three-dimensional conformations, which improved the catalytic activity of the encapsulated enzymes compared with that of free GOx and HRP in various harsh environments. Additionally, our strategy reduced the occurrence of ineffective mass transfer and enhanced the sensitivity of the biosensor through an enzyme cascade system. When this biosensor was applied to serum samples containing complex biological matrices, the degradation of GOx&HRP by various proteases and the surface adsorption of diverse biomolecules were effectively prevented, thereby generating stable and reliable signals of glucose levels. The sensor shows remarkable sensitivity and selectivity for determining glucose concentrations ranging from 0 to 2.5 μg ml-1, with a detection limit as low as 0.034 μg ml-1. Furthermore, we developed a paper-based colorimetric sensor utilizing GOx&HRP@ZIF-90 integrated with a smartphone platform for the visual detection of blood glucose.

The Road Ahead for Metal-Organic Frameworks: Current Landscape, Challenges and Future Prospects

This perspective highlights the transformative potential of Metal-Organic Frameworks (MOFs) in environmental and healthcare sectors. It discusses work that has advanced beyond technology readiness levels of >4 including applications in capture, storage, and conversion of gases to value added products. This work showcases efforts in the most salient applications of MOFs which have been performed at a great cadence, enabled by the federal government, large companies, and startups to commercialize these technologies despite facing significant challenges. This article also forecasts the role of nanoscale MOFs in healthcare, including strides toward personalized medicine, advocating for their use in custom-tailored drug delivery systems. Finally we underscore the potential acceleration in MOF research and development through the integration of machine learning and AI, positioning MOFs as versatile tools poised to address global sustainability and health challenges.

Metal-Organic Framework-Based Cascade Catalysis-Enabled Fluorescent ELISA with Higher Enzymatic Stability for Zearalenone Detection in Maize

The enzyme-linked immunosorbent assay (ELISA) stands as one of the most frequently employed rapid detection techniques for both chemical and biological contaminants. Horseradish peroxidase (HRP) and hydrogen peroxide (H2O2), serving as signal generators, play indispensable roles throughout the entire ELISA process. However, HRP and H2O2 exhibit high sensitivity to elevated temperatures, hindering the broader utilization and transportation of ELISA. Hereby, being inspired by the cascade catalysis of glucose by glucose oxidase (GOx) and HRP as well as the advantageous properties of metal-organic frameworks (MOFs), we developed a cascade catalysis-based competitive fluorescent ELISA (CCF-ELISA) for mycotoxin detection in maize using zearalenone (ZEN) as a model. The results revealed the remarkable protective effects of MOFs on enzymatic activities. Based on upon characteristics, the built CCF-ELISA enabled the detection of ZEN with a half-maximal inhibitory concentration of 0.54 ng/mL and allowed a detection range from 0.19 to 1.51 ng/mL. When applied to naturally contaminated maize samples, the outcomes obtained from the CCF-ELISA showed a high level of comparability with high-performance liquid chromatography-tandem mass spectrometry, demonstrating the promising potential of the developed CCF-ELISA in the rapid detection for food security.

Hyper-Expandable Cross-Linked Protein Crystals as Scaffolds for Catalytic Reactions

Scaffolding catalytic reactions within porous materials is a powerful strategy to enhance the reaction rates of multicatalytic systems. However, it remains challenging to develop materials with high porosity, high diversity of functional groups within the pores, and guest-adaptive tunability. Furthermore, it is challenging to capture large catalysts such as enzymes within porous materials. Protein-based materials are promising candidates to overcome these limitations, owing to their large pore sizes and potential for stimuli-responsive adaptability. In this work, hydrogel beads were generated from cross-linked lysozyme crystals. These swellable lysozyme cross-linked crystals (SLCCs) expand more than 10 mL per gram of crystal following a simple treatment in ethanol, followed by the addition of water. SLCCs are sensitive to the solution environment and change their extent of swelling from adjusting the concentration and identity of the ions in the solution, or by changing the flexibility of the protein backbone, such as adding dithiothreitol to reduce the protein disulfide bonds. SLCCs can adsorb a wide range of catalysts ranging from transition metal complexes to large biomacromolecules, such as the 160 kDa enzyme glucose oxidase (GOx). Transition metal catalysts and enzymes captured within SLCCs maintained their catalytic activity and exhibited minimal leaching. We performed a cascade reaction by adsorbing GOx and the transition metal catalyst Fe-TAML into SLCCs, resulting in enhanced activity compared to a free-floating reaction. SLCCs offer a promising combination of attributes as scaffolds for multicatalytic reactions, including gram-scale batch preparation, tunable expansion to greater than 20-fold in volume, guest-responsive adaptable behavior, and facile capture of a wide array of small molecule and enzyme-catalysts.

Coimmobilized Dual Enzymes in a Continuous Flow Reactor for the Efficient Synthesis of Optically Pure γ/δ-Lactones

Enzyme catalysis is a promising method for producing chiral chemicals with high stereoselectivity under mild conditions. However, the traditional batch reaction suffers from low enzyme stability, low cofactor recycling, and poor enzyme reusability. Here, we present a continuous-flow method using coimmobilized dual enzymes for the synthesis of chiral γ-/δ-lactones, which are widely used in fragrances and flavors. Typically, a carbonyl reductase mutant SmCRM5 from Serratia marcescens, was coimmobilized by covalent binding with BmGDH, a glucose dehydrogenase capable of recovering and recycling the cofactor NADPH. After immobilization, SmCRM5 and BmGDH exhibited a 8.9-/8.7-fold increase in catalytic efficiency (kcat/Km) and a 57-/15-fold increase in half-life at 30 °C, respectively. We demonstrated that coimmobilized dual enzymes used in a continuous flow reactor showed a higher reaction rate and a higher space-time yield (1586 g·L-1 d-1) than free enzymes and immobilized enzymes in a batch reaction for the production of (R)-δ-decalactone. This continuous flow reactor can run continuously for more than 650 h with 99% ee and 80% conversion, and the total volume exceeds 1500 reactor volumes. The robustness of this continuous-flow immobilized enzyme system provides a green and efficient method for the synthesis of high value-added chiral chemicals.

A Multifunctional Tb(III)-Based Metal-Organic Framework for Chemical Conversion of CO2, Fluorescence Sensing of Trace Water and Metamitron

The utilization of metal-organic frameworks (MOFs) as fluorescent sensors for the detection of environmental and chemical reagent pollutants as well as heterogeneous catalysis for CO2 conversion represents a crucial avenue of research with significant implications for the protection of human health. In this work, a Tb(III)-based three-dimensional metal-organic framework, [Tb(L)·4DMF]n (Tb-MOF) (H3L = 5'-(4-carboxy-3-hydroxyphenyl)-3,3″-dihydroxy-[1,1':3',1″-terphenyl]-4,4″-dicarboxylic acid), has been structurally conformed by single-crystal X-ray crystallography. It possesses a 1D rhombus channel along the [010] direction, featuring a pore size of 6.02 × 9.13 Å. Tb-MOF was proved to be a multifunctional material for a fluorescent sensor and CO2 cycloaddition heterogeneous catalyst material. Fluorescence sensing studies revealed that Tb-MOF demonstrates high sensitivity, selectivity, and favorable regeneration properties, making it an effective chemosensor for detecting the metamitron (MMT) pesticide and trace water in organic solvents. The mechanism of fluorescence quenching by MMT and water was elucidated by a combination of XRD, UV-vis absorption spectra, IR spectra, theoretical calculations, and fluorescence lifetimes. The material was also utilized for the sensing of MMT and water in paper strips. Additionally, the open Tb3+ site as Lewis acidic centers makes Tb-MOF achieve efficiently catalytic conversion for CO2 and epoxides to cyclic carbonates. Moreover, a possible catalytic mechanism for the conversion of carbon dioxide to cyclic carbonates was proposed by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) experiments. It also exhibited recyclability for up to five cycles without noticing an appreciable loss in sensing or catalytic efficiency.

Enhancing Biocatalysis: Metal-Organic Frameworks as Multifunctional Enzyme Hosts

Enzymes are highly efficient and selective catalysts that operate under mild conditions, making them invaluable for various chemical transformations. However, their limitations, such as instability and high cost, call for advancements in enzyme immobilization and the development of suitable host materials. Metal-organic frameworks (MOFs), characterized by high porosity, crystallinity, and tunability, are promising candidates for enzyme encapsulation. Among these, zirconium-based MOFs (Zr-MOFs) stand out due to their exceptional structural diversity and chemical stability. The physical and chemical properties of Zr-MOFs can be tuned and characterized with atomic precision, and their interactions with enzymes can be analyzed through a range of techniques spanning from chemistry and materials science to biochemistry. This tunable platform provides opportunities to systematically investigate the impact of encapsulation on the stability and activity of enzymes in order to develop design rules for enzyme hosts. In this Account, we discuss experimentally validated concepts for designing MOF hosts based on their structural properties and enzyme encapsulation mechanisms. We present methods to enhance enzyme catalytic performance through encapsulation and strategies for creating multifunctional enzyme@MOF systems via host modifications. We start by highlighting the importance of host structural design that maximizes substrate diffusion and enzyme availability, with particular focus on MOFs containing hierarchical mesoporous structures such as those in the csq topology. We then delve into the encapsulation process and host-guest interactions examined through techniques such as microscopy, calorimetry, and computational methods, which provide guidelines to fine-tune the local pore chemical environment to enhance enzyme stability and catalytic activity. Techniques found in biochemistry, such as isothermal titration calorimetry (ITC) and confocal laser scanning microscopy (CLSM), were developed to investigate enzyme encapsulation mechanisms, revealing high-entropy-driven host-guest affinity. Additionally, we discuss cases in which enzyme@MOF systems demonstrated enhanced catalytic activities and multifunctional capabilities. Encapsulated enzymes have demonstrated improved thermal and chemical stabilities compared to their free counterparts, maintaining activity under conditions that typically lead to denaturation. Additionally, the highly tunable nature of the MOF platforms allows them to support more complex systems such as tandem reactions, enabling applications in biophotocatalysis, bioelectrocatalysis, and targeted therapeutic protein delivery. The versatility of enzyme@MOFs promises extensive applications in both research and industrial processes across fields including biotechnology, pharmaceutical development, and environmental science. We provide an outlook for promising directions for enzyme@MOF research, with the aim of continuing innovation and exploration. We hope that this Account can benefit chemists, biologists, and material scientists toward designing efficient and adaptable next-generation biocatalytic composite materials.

Engineering Thermoresponsive Enzyme-Polymer Conjugates via Glycan-Selective In Situ Polymerization for Recyclable Homogeneous Biocatalysis

Enzymes are crucial for various technological applications, but their inherent instability and short lifespan pose challenges. This study presents facile immobilized enzyme technology with the development of thermoresponsive enzyme-polymer conjugates (EPCs), using glucose oxidase (GOx) as a model enzyme, to address these limitations. By conjugating heteropolymers to the glycan moieties of GOx through a precise in situ polymerization process, we could modulate the lower critical solution temperature of the EPCs, enhancing enzyme performance without compromising its active site. The EPCs demonstrate a switchable behavior that facilitates efficient homogeneous catalysis and easy heterogeneous separation, reducing costs and environmental impact in industrial applications. Our strategy presents a versatile platform for creating efficient biocatalysts with tunable properties, marking a step forward in sustainable and cost-effective bioprocessing.

Encapsulation of Candida antarctica lipase B in metal-organic framework under ultrasound and using it to one-pot synthesis of 1,3,4,5-tetrasubstituted pyrazoles

Encapsulating the enzyme in metal-organic frameworks (MOFs) is a convenient method to prepare MOF-enzyme biocomposite. In this study, Candida antarctica lipase B (CAL-B) was chosen to immobilize in Cu-BTC MOF under ultrasound irradiation. CAL-B was immobilized in Cu-BTC under ultrasound at 21 kHz and 11.4 W/cm2 and incubation. 98% of CAL-B was immobilized in Cu-BTC with 99 U/mg activity (threefold more active than the free CAL-B). The prepared biocomposite was characterized using FT-IR, XRD, TGA, SEM, EDX, and BET. The thermal and solvent stability of CAL-B@Cu-BTC was investigated. It was found that at a temperature of 55 ℃, CAL-B@Cu-BTC maintains its activity even after 2 h of incubation. Furthermore, in the presence of 20% and 50% concentrations of MeCN, THF, and DMF, CAL-B@Cu-BTC was found to have an activity of over 80%. A prepared biocatalyst was used to synthesize 1,3,4,5-tetrasubstituted pyrazole derivatives (50-75%) in a one-pot vessel, by adding phenyl hydrazine hydrochlorides, benzaldehydes, and dimethyl acetylenedicarboxylate.

Engineering enzyme conformation within liquid-solid hybrid microreactors for enhanced continuous-flow biocatalysis

The artificial engineering of an enzyme's structural conformation and dynamic properties to promote its catalytic activity and stability outside cellular environments is highly pursued in industrial biotechnology. Here, we describe an elegant strategy of combining the rationally designed liquid-solid hybrid microreactor with a tailor-made polyethylene glycol functional ionic liquid (PEG-IL) microenvironment to exercise a high level of control over the configuration of enzymes for practical continuous-flow biocatalysis. As exemplified by a lipase driven kinetic resolution reaction, the obtained system exhibits a 2.70 to 30.35-fold activity enhancement compared to their batch or traditional IL-based counterparts. Also, our results demonstrate that the thermal stability of encapsulated lipase can be significantly strengthened in the presence of PEG groups, showcasing a long-term continuous-flow stability even up to 1000 h at evaluated temperature of 60 oC. Through systematic experiment and molecular dynamics simulation studies, the conformational changes of the active site cavity in the modified lipases are correlated with enzymatic properties alteration, and the pronounced effects of PEG-groups in stabilizing enzyme's secondary structures by delaying unfolding at elevated temperatures are identified. We believe that this study will guide the design of high-performance enzymatic systems, promoting their utilization in real-world biocatalysis applications.

Immobilization of snailase on glutamate modified MIL-88B(Fe) to efficiently convert the rare ginsenoside CK with high enzyme recyclability and stability

The carboxyl groups on MIL-88B(Fe) are crucial for the covalent immobilization of snailase, and the enzyme can convert common ginsenoside Rb1 into the rare ginsenoside compound K (CK) with higher bioavailability. The present study proposed glutamate-modified MIL-88B(Fe) for the immobilization of snailase to improve enzymatic activity and loading capacity. The surface topography characterized by SEM and CLSM indicated snailase was successfully encapsulated and uniformly distributed in the Sna@MIL-88B(Fe). The maximum immobilized capacities of snailase by MIL-88B(Fe)-Glu and MIL-88B(Fe) were 185 mg/g and 140 mg/g, respectively. Moreover, covalently immobilized snailase on MIL-88B(Fe)-Glu showed better pH, thermal, solvent, and storage stabilities than those immobilized on MIL-88B(Fe) and resolvase. Meanwhile, the reaction kinetics exhibited that the Km value of Sna@MIL-88B(Fe)-Glu (1.6 mM) was significantly lower than that of free snailase (2.1 mM), indicating a higher substrate affinity. Besides, more ginsenoside CK with higher conversion (60.71 %) was generated by Sna@MIL-88B(Fe)-Glu, even after five cycles. The glutamate modified covalent grafting method provides a highly efficient strategy for biocatalysis and a reference for the immobilized snailase-catalyzed transformation of rare ginsenosides CK.

Nanobiohybrid Extracellular Vesicle Nanoreactor with Improving Metabolical Activity for Biocatalytic Therapy

Extracellular vesicles (EVs) hosting enzymatic activities that function as independent metabolic units are attractive natural biocatalytic platforms. However, directly using these metabolically active nanoreactors for effective biocatalytic applications remains challenging, mainly due to their constrained catalytic capabilities. Here, we construct an EV-templated nanobiohybrid system by engineering an EV surface with a photoresponsive zeolitic imidazolate framework (ZIF). The deposition of ZIF nanostructures on EVs not only contributes to improved biocatalytic stability but also enables interfacial coupling between photoexcited electrons from the ZIF and the enzymatic reaction of metabolically active EVs. Nearly 300% of biomass conversion efficiency increment could be achieved by EVs derived from macrophages. This enhanced biocatalysis, high catalytic stability, and low cytotoxicity endowed the EV@ZIF nanosystem with robust biosynthesis and antimicrobial activity. When evaluated in a mouse periodontitis model, we show that the autologous biocatalytic EV@ZIF demonstrated efficient therapeutic capability by killing bacteria and inhibiting inflammation. This nanoengineering strategy will benefit the future optimization of metabolically active EV nanoreactors as biocatalysts for a broad range of therapeutics.

Reticular Chemistry for Enhancing Bioentity Stability and Functional Performance

Addressing the fragility of bioentities that results in instability and compromised performance during storage and applications, reticular chemistry, specifically through metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), offers versatile platforms for stabilization and enhancement of bioentities. These highly porous frameworks facilitate efficient loading and mass transfer, offer confined environments and selective permeability for stabilization and protection, and enable finely tunable biointerfacial interactions and microenvironments for function optimization, significantly broadening the applications of various bioentities, including enzymes, nucleic acids, cells, etc. This Perspective outlines strategies for integrating bioentities with reticular frameworks, highlighting new design ideas for existing issues within these strategies. It emphasizes the crucial roles of these frameworks for bioentities in enhancing stability, boosting activity, imparting non-native functions, and synergizing bioentity systems. Concluding with a discussion of the challenges and prospects in the design, characterization, and practical applications of these biocomposites, this Perspective aims to inspire further development of high-performance biocomposites in this promising field.

A Strep-Tag Imprinted Polymer Platform for Heterogenous Bio(electro)catalysis

Molecularly imprinted polymers (MIPs) are artificial receptors equipped with selective recognition sites for target molecules. One of the most promising strategies for protein MIPs relies on the exploitation of short surface-exposed protein fragments, termed epitopes, as templates to imprint binding sites in a polymer scaffold for a desired protein. However, the lack of high-resolution structural data of flexible surface-exposed regions challenges the selection of suitable epitopes. Here, we addressed this drawback by developing a polyscopoletin-based MIP that recognizes recombinant proteins via imprinting of the widely used Strep-tag II affinity peptide (Strep-MIP). Electrochemistry, surface-sensitive IR spectroscopy, and molecular dynamics simulations were employed to ensure an utmost control of the Strep-MIP electrosynthesis. The functionality of this novel platform was verified with two Strep-tagged enzymes: an O2-tolerant [NiFe]-hydrogenase, and an alkaline phosphatase. The enzymes preserved their biocatalytic activities after multiple utilization confirming the efficiency of Strep-MIP as a general biocompatible platform to confine recombinant proteins for exploitation in biotechnology.

Advances in metal-organic frameworks for optically selective alkaline phosphatase activity monitoring: a perspective

The study of Metal-Organic Frameworks (MOFs) has gained significant momentum due to their remarkable properties, including adjustable pore sizes, extensive surface area, and customizable compositions, which have urged scientists to investigate their applicability in pertinent societal issues such as water absorption, environmental remediation, and sensor technology. MOFs have the ability to transport and detect specific biomolecules, including proteins. One such biomolecule is alkaline phosphatase (ALP) that can be influenced by various diseases and can lead to severe consequences when its regulation is disrupted. The porous nature of MOFs and their tunable nature allows them to selectively adsorb, interact directly or indirectly with ALP. This ultimately influences the electronic and optical properties of the MOF, leading to measurable changes. Early detection and continuous monitoring of ALP play a crucial role in the use of an effective treatment, and recent studies have shown that MOFs are effective in detecting alkaline phosphatases. This manuscript offers a thorough examination of the potential biomedical applications of MOFs for monitoring alkaline phosphatase and envisions possible future trends in this field.

An explore method for quick screening biomarkers based on effective enrichment capacity and data mining

Protein glycosylation acts as a crucial role in regulating protein function and maintaining cellular homeostasis. Efficient peptide enrichment can be utilized to effectively solve the inherent challenges of protein glycosylation analysis to search unknown cancer biomarkers. In this research, a low dimensional porous hydrophilic nanosheets with a multi-level porous structure (Co-MOF-SiO2@HA) was synthetized via an easy one-pot method for the efficient enrichment of the N-glycopeptides in the digests of complex biosamples. The synthetized nanosheets Co-MOF-SiO2@HA demonstrated excellent enriching performances including a high enrichment capacity (300 mg g-1 calculated), a spectacular selectivity (IgG digests and BSA digests at the molar ratio of 1/1200), and an excellent spatial confinement ability (IgG digests, IgG and BSA at the molar ratio of 1/1000/1000). As an explore result, after the enrichment of human colorectal cancer tissue and human healthy tissue by the nanosheets, several proteins related to cancers and one protein directly related to well-known human colorectal cancer were identified by detecting the corresponding glycopeptides. It presented the potential value of the feasibility of this analysis mode by nanosheets Co-MOF-SiO2@HA in proteomic analysis.

Incorporation of enzyme-mimic species in porous materials for the construction of porous biomimetic catalysts

The unique catalytic properties of natural enzymes have inspired chemists to develop biomimetic catalyst platforms for the intention of retaining the unique functions and solving the application limitations of enzymes, such as high costs, instability and unrecyclable ability. Porous materials possess unique advantages for the construction of biomimetic catalysts, such as high surface areas, thermal stability, permanent porosity and tunability. These characteristics make them ideal porous matrices for the construction of biomimetic catalysts by immobilizing enzyme-mimic active sites inside porous materials. The developed porous biomimetic catalysts demonstrate high activity, selectivity and stability. In this feature article, we categorize and discuss the recently developed strategies for introducing enzyme-mimic active species inside porous materials, which are based on the type of employed porous materials, including metal-organic frameworks (MOFs), covalent organic frameworks (COFs), molecular sieves, porous metal silicate (PMS) materials and porous carbon materials. The advantages and limitations of these porous materials-based biomimetic catalysts are discussed, and the challenges and future directions in this field are also highlighted.

Integrating Biocatalysts into Metal-Organic Frameworks: Disentangling the Roles of Affinity, Molecular Weight, and Size

The integration of biocatalysts within metal-organic frameworks (MOFs) is attracting growing interest due to its potential to both enhance biocatalyst stability and sustain biocatalyst activity in organic solvents. However, the factors that facilitate the post-synthetic infiltration of such large molecules into MOF pores remain unclear. This systematic study enabled the identification of the influence of biocatalyst molecular size, molecular weight and affinity on the uptake by an archetypal MOF, NU-1000. We analyzed a range of six biocatalysts with molecular weights from 1.9 kDa to 44.4 kDa, respectively. By employing a combination of fluorescence tagging and 3D-STED confocal laser scanning microscopy, we distinguished between biocatalysts that were internalized within the MOF pores and those sterically excluded. The catalytic functions of the biocatalysts hosted within the MOF were investigated and found to show strong variations relative to the solvated case, ranging from a two-fold increase to a strong decrease.

Rapid screening of xanthine oxidase inhibitors from Ligusticum wallichii by using xanthine oxidase functionalized magnetic metal-organic framework

In this study, xanthine oxidase was immobilized for the first time using a novel magnetic metal-organic framework material (Fe3O4-SiO2-NH2@MnO2@ZIF-8-NH2). A ligand fishing method was established to rapidly screen XOD inhibitors from Ligusticum wallichii based on the immobilized XOD. Characterization and properties of the immobilized enzyme revealed its excellent stability and reusability. A ligand was screened from Ligusticum wallichii and identified as ligustilide by ultra-high performance liquid chromatography tandem mass spectrometry. The IC50 value of ligustilide was determined to be 27.70 ± 0.13 μM through in vitro inhibition testing. Furthermore, molecular docking verified that ligustilide could bind to amino acid residues at the active site of XOD. This study provides a rapid and effective method for the preliminary screening of XOD inhibitors from complex natural products and has great potential for further discovery of anti-hyperuricemic compounds.

High-Efficiency Enzyme Assay and Screening of Enzyme-Inhibiting Nanomaterials Using Capillary Electrophoresis with Hierarchically Porous Metal-Organic Framework-Based Immobilized Enzyme Microreactor

Enzyme-inhibiting nanomaterials have significant potential for regulating enzyme activity. However, a universal and efficient method for systematically screening and evaluating the inhibitory effects of various nanomaterials on drug target enzymes has not been established. While the integrated technique of immobilized enzyme microreactor (IMER) with capillary electrophoresis (CE) serves as an effective tool for enzyme analysis, it still faces challenges such as low enzyme loadability, unsatisfactory stability, and limited applicability. Herein, hierarchical porous metal-organic frameworks (HP-MOFs) were explored as high-performance enzyme immobilization carriers and stationary phases to develop a novel HP-MOFs-based IMER-CE microanalysis system for efficient online enzyme assay and systematic screening of enzyme-inhibiting nanomaterials. As a proof-of-concept demonstration, the model enzyme xanthine oxidase (XOD) was immobilized on a HP-UiO-66-NH2 coated capillary, serving as an efficient and durable IMER for screening potential XOD-inhibiting nanomaterials. The hierarchically micro- and mesoporous structure and superior enzyme loadability of as-prepared HP-UiO-66-NH2-IMER was intensively characterized, followed by systematic evaluation of the separation performance of HP-UiO-66-NH2 coated column and the enzyme kinetics of the immobilized XOD. Compared to the microporous UiO-66-NH2-IMER, the HP-UiO-66-NH2-IMER-CE system showed significant improvements in enzyme loading, maximum reaction rate, repeatability, and long-term stability. Furthermore, the established method was effectively employed to screen the XOD inhibitory activity of various nanomaterials, revealing that graphene oxide, single wall carbon nanotube and three other nanomaterials exhibited inhibitory potentials. The HP-MOFs-based microanalysis system can be easily expanded by modifying the types of immobilized enzymes and holds the potential to accelerate the identification and rational design of effective enzyme-inhibiting nanomaterials.

Recyclable Enzymatic Hydrolysis with Metal-Organic Framework Stabilized Humicola insolens Cutinase (HiC) for Potential PET Upcycling

The degradation and recycling of plastics, such as poly(ethylene terephthalate) (PET), often require energy-intensive processes with significant waste generation. Moreover, prevalent methods primarily entail physical recycling, yielding subpar materials. In contrast, upcycling involves breaking down polymers into monomers, generating valuable chemicals and materials for alternative products. Enzyme-catalyzed depolymerization presents a promising approach to break down PET without the need for extreme conditions and unstable or toxic metal catalysts, which are typical of traditional recycling methods. However, the practical application of enzymes has been hindered by their high cost and low stability. In this study, we stabilized the enzyme Humicola insolens cutinase (HiC) by encapsulating it within a mesoporous zirconium-based metal-organic framework, NU-1000. HiC@NU-1000 exhibited a quantitative degradation of the PET surrogate, ethylene glycol dibenzoate (EGDB), with greater selectivity than native HiC in producing the fully hydrolyzed product benzoic acid in partial organic solvent. Additionally, the heterogeneous catalyst is also active toward the hydrolysis of PET and has demonstrated recyclability for at least four catalytic cycles. The HiC@NU-1000 model system represents a promising approach to stabilize industrially relevant enzymes under conditions involving elevated temperatures and organic solvents, offering a potential solution for relevant protein-related applications.

Chitosan-Based Charge-Controllable Supramolecular Carrier for Universal Immobilization of Enzymes with Different Isoelectric Points

Electrostatic adsorption is an enzyme immobilization method that effectively maintains enzyme activity and exhibits considerable binding efficiency. However, enzymes carry different charges at their respective reaction pH levels, which prevents the use of the same carrier to immobilize enzymes with different charges. In this study, we employed a template-mediated polysaccharide-enzyme coupling self-assembly strategy to develop a charge-controllable supramolecular immobilization carrier by regulating the charge properties of carboxymethyl chitosan, enabling the universal immobilization of enzymes with different charge levels across a range of reaction pH values. By using silica nanoparticles of certain sizes as templates, the size of the carrier can be precisely controlled and the hollow network structure formed after removing the template can effectively reduce mass transfer resistance. Trypsin and papain are used as model enzymes, and the experimental results show that the supramolecular self-assembly immobilization strategy does not disrupt the secondary structure of the enzyme molecules. After 2 h of reaction, the enzyme activities of immobilized papain and immobilized trypsin are 13.2% and 7.7% higher than those of the free enzymes, respectively. After 10 consecutive reactions, the enzyme activities of immobilized papain and immobilized trypsin retained 56.3% and 64.3% of their initial values, respectively.

Domingues N, Pougin MJ, Smit B, Hosta-Rigau L, Oostenbrink C. Stability Assessment in Aqueous and Organic Solvents of Metal-Organic Framework PCN 333 Nanoparticles through a Combination of Physicochemical Characterization and Computational Simulations

Mesoporous metal-organic frameworks (MOFs) have been recognized as powerful platforms for drug delivery, especially for biomolecules. Unfortunately, the application of MOFs is restricted due to their relatively poor stability in aqueous media, which is crucial for drug delivery applications. An exception is the porous coordination network (PCN)-series (e.g., PCN-333 and PCN-332), a series of MOFs with outstanding stability in aqueous media at the pH range from 3 to 9. In this study, we fabricate PCN-333 nanoparticles (nPCN) and investigate their stability in different solvents, including water, ethanol, and methanol. Surprisingly, the experimental characterizations in terms of X-ray diffraction, Brunauer-Emmett-Teller (BET), and scanning electron microscopy demonstrated that nPCN is not as stable in water as previously reported. Specifically, the crystalline structure of nPCN lost its typical octahedral shape and even decomposed into an irregular amorphous form when exposed to water for only 2 h, but not when ethanol and methanol were used. Meanwhile, the porosity of nPCN substantially diminished while being exposed to water, as demonstrated by the BET measurement. With the assistance of computational simulations, the mechanism behind the collapse of PCN-333 is illuminated. By molecular dynamics simulation and umbrella sampling, we elucidate that the degradation of PCN-333 occurs by hydrolysis, wherein polar solvent molecules initiate the attack and subsequent breakage of the metal-ligand reversible coordination bonds.

The Exploration of Nanozymes for Biosensing of Pathological States Tailored to Clinical Theranostics

The nanozymes (NZs) are the artificial catalyst deployed for biosensing with their uniqueness (high robustness, surface tenability, inexpensive, and stability) for obtaining a better response/miniaturization of the varied sensors than their traditional ancestors. Nowadays, nanomaterials with their broadened scale such as metal-organic frameworks (MOFs), and metals/metal oxides are widely engaged in generating NZ-based biosensors (BS). Diverse strategies like fluorescent, colorimetric, surface-enhanced Raman scattering (SERS), and electrochemical sensing principles were implemented for signal transduction of NZs. Despite broad advantages, numerous encounters (like specificity, feasibility, stability, and issues in scale-up) are affecting the potentialities of NZs-based BS, and thus need prior attention for a promising exploration for a revolutionary outcome in advanced theranostics. This review includes different types of NZs, and the progress of numerous NZs tailored bio-sensing techniques in detecting abundant bio analytes for theranostic purposes. Further, the discussion highlighted some recent challenges along with their progressive way of possibly overcoming followed by commercial outbreaks.

Organic and Metal-Organic Polymer-Based Catalysts-Enfant Terrible Companions or Good Assistants?

This overview provides insights into organic and metal-organic polymer (OMOP) catalysts aimed at processes carried out in the liquid phase. Various types of polymers are discussed, including vinyl (various functional poly(styrene-co-divinylbenzene) and perfluorinated functionalized hydrocarbons, e.g., Nafion), condensation (polyesters, -amides, -anilines, -imides), and additional (polyurethanes, and polyureas, polybenzimidazoles, polyporphyrins), prepared from organometal monomers. Covalent organic frameworks (COFs), metal-organic frameworks (MOFs), and their composites represent a significant class of OMOP catalysts. Following this, the preparation, characterization, and application of dispersed metal catalysts are discussed. Key catalytic processes such as alkylation-used in large-scale applications like the production of alkyl-tert-butyl ether and bisphenol A-as well as reduction, oxidation, and other reactions, are highlighted. The versatile properties of COFs and MOFs, including well-defined nanometer-scale pores, large surface areas, and excellent chemisorption capabilities, make them highly promising for chemical, electrochemical, and photocatalytic applications. Particular emphasis is placed on their potential for CO2 treatment. However, a notable drawback of COF- and MOF-based catalysts is their relatively low stability in both alkaline and acidic environments, as well as their high cost. A special part is devoted to deactivation and the disposal of the used/deactivated catalysts, emphasizing the importance of separating heavy metals from catalysts. The conclusion provides guidance on selecting and developing OMOP-based catalysts.

Advanced materials for micro/nanorobotics

Autonomous micro/nanorobots capable of performing programmed missions are at the forefront of next-generation micromachinery. These small robotic systems are predominantly constructed using functional components sourced from micro- and nanoscale materials; therefore, combining them with various advanced materials represents a pivotal direction toward achieving a higher level of intelligence and multifunctionality. This review provides a comprehensive overview of advanced materials for innovative micro/nanorobotics, focusing on the five families of materials that have witnessed the most rapid advancements over the last decade: two-dimensional materials, metal-organic frameworks, semiconductors, polymers, and biological cells. Their unique physicochemical, mechanical, optical, and biological properties have been integrated into micro/nanorobots to achieve greater maneuverability, programmability, intelligence, and multifunctionality in collective behaviors. The design and fabrication methods for hybrid robotic systems are discussed based on the material categories. In addition, their promising potential for powering motion and/or (multi-)functionality is described and the fundamental principles underlying them are explained. Finally, their extensive use in a variety of applications, including environmental remediation, (bio)sensing, therapeutics, etc., and remaining challenges and perspectives for future research are discussed.

Enzyme-mediated green synthesis of glycosaminoglycans and catalytic process intensification

Glycosaminoglycans (GAGs) are a family of structurally complex heteropolysaccharides that play pivotal roles in biological functions, including the regulation of cell proliferation, enzyme inhibition, and activation of growth factor receptors. Therefore, the synthesis of GAGs is a hot research topic in drug development. The enzymatic synthesis of GAGs has received widespread attention due to their eco-friendly nature, high regioselectivity, and stereoselectivity. The enhancement of the enzymatic synthesis process is the key to its industrial applications. In this review, we overviewed the construction of more efficient in vitro biomimetic synthesis systems of glycosaminoglycans and presented the different strategies to improve enzyme catalysis, including the combination of chemical and enzymatic methods, solid-phase synthesis, and protein engineering to solve the problems of enzyme stability, separation and purification of the product, preparation of structurally defined sugar chains, etc., and discussed the challenges and opportunities in large-scale green synthesis of GAGs.

Disposable electrochemical biosensors for the detection of bacteria in the light of antimicrobial resistance

Persistent and inappropriate use of antibiotics is causing rife antimicrobial resistance (AMR) worldwide. Common bacterial infections are thus becoming increasingly difficult to treat without the use of last resort antibiotics. This has necessitated a situation where it is imperative to confirm the infection to be bacterial, before treating it with antimicrobial speculatively. Conventional methods of bacteria detection are either culture based which take anywhere between 24 and 96 hor require sophisticated molecular analysis equipment with libraries and trained operators. These are difficult propositions for resource limited community healthcare setups of developing or less developed countries. Customized, inexpensive, point-of-care (PoC) biosensors are thus being researched and developed for rapid detection of bacterial pathogens. The development and optimization of disposable sensor substrates is the first and crucial step in development of such PoC systems. The substrates should facilitate easy charge transfer, a high surface to volume ratio, be tailorable by the various bio-conjugation chemistries, preserve the integrity of the biorecognition element, yet be inexpensive. Such sensor substrates thus need to be thoroughly investigated. Further, if such systems were made disposable, they would attain immunity to biofouling. This article discusses a few potential disposable electrochemical sensor substrates deployed for detection of bacteria for environmental and healthcare applications. The technologies have significant potential in helping reduce bacterial infections and checking AMR. This could help save lives of people succumbing to bacterial infections, as well as improve the overall quality of lives of people in low- and middle-income countries.

A green approach to encapsulate proteins and enzymes within crystalline lanthanide-based Tb and Gd MOFs

In this work, bovine serum albumin (BSA) and Aspergillus sp. laccase (LC) were encapsulated in situ within two lanthanide-based MOFs (TbBTC and GdBTC) through a green one-pot synthesis (almost neutral aqueous solution, T = 25 °C, and atmospheric pressure) in about 1 h. Pristine MOFs and protein-encapsulated MOFs were characterized through wide angle X-ray scattering, scanning electron microscopy, thermogravimetric analysis, Fourier transform infrared and Raman spectroscopies. The location of immobilized BSA molecules, used as a model protein, was investigated through small angle X-ray scattering. BSA occurs both on the inner and on the outer surface of the MOFs. LC@TbBTC, and LC@GdBTC samples were also characterized in terms of specific activity, kinetic parameters, and storage stability both in water and acetate buffer. The specific activity of LC@TbBTC was almost twice that of LC@GdBTC (10.8 μmol min-1 mg-1vs. 6.6 μmol min-1 mg-1). Both biocatalysts showed similar storage stabilities retaining ∼60% of their initial activity after 7 days and ∼20% after 21 days. LC@TbBTC dispersed in acetate buffer exhibited a higher storage stability than LC@GdBTC. Additionally, terbium-based MOFs showed interesting luminescent properties. Together, these findings suggest that TbBTC and GdBTC are promising supports for the in situ immobilization of proteins and enzymes.

The resistance of hydrogenotrophic methanogenic microorganisms to ofloxacin in sludge anaerobic digestion process

Ofloxacin (OFL) is a commonly used antibiotic that can enter wastewater treatment plants and be adsorbed by the sludge, resulting in a high OFL concentration in sludge and affecting the subsequent sludge anaerobic digestion process. However, the micro mechanisms involved in this process have not been thoroughly studied. Therefore, this study focuses on the effect of OFL on the sludge anaerobic digestion of sludge to provide such support. The experimental results showed that the maximal methane yield decreased from 277.7 to 164.7 mL/g VSS with the OFL concentration increased from 0 to 300 mg/L. Additionally, OFL hindered the intermediate biochemical processes of hydrolysis, acidogenesis, acetogenesis, and acetoclastic methanogenesis. However, it promoted hydrogenotrophic methanogenesis process, using H2 as substrate, with the concentration of 300 mg/L OFL was 5.54 fold methane production of that in the control. Further investigation revealed that the negative effect of OFL was likely due to the induction of reactive oxygen species, which led to a decrease in cell activity and interference with the activity of key enzymes. Microbiological analysis revealed that OFL reduced the relative abundance of hydrolysis and acidogenesis bacteria, and Methanosaeta archaea, while increasing the relative abundance of hydrogenotrophic methanogenesis microorganism from 36.54% to 51.48% as the OFL concentration increase from 0 to 300 mg/L.

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.