Harnessing Self-Repairing and Crystallization Processes for Effective Enzyme Encapsulation in Covalent Organic Frameworks

A new β-amylase detection strategy based on encapsulated enzyme in magnetic layered double hydroxide with high sensitivity and simplified workflow

β-Amylase (BMY) is a linchpin in food production and the pharmaceutical industry because the enzyme efficiently controls the ratio of diverse saccharides in fermentation and the manufacture of high-quality maltose. However, existing BMY detection tactics suffer from inadequate selectivity/sensitivity and cumbersome operation and do not meet the needs of precise quantification. Consequently, there is an urgent need to develop an ultrasensitive sensing platform to achieve precise BMY analysis with a low detection limit and simpler workflow. In this work, we establish an encapsulated-enzyme-based BMY biosensing platform in which α-glucosidase is embedded in magnetic layered double hydroxide using a self-sacrificing template. The encapsulated enzyme has increased activity, robustness, and recyclability and was utilized for BMY detection via a cascade chromatic process. We found a detection limit for the quantification of BMY activity of 2.67 U/L with a broad range (5-400 U/L), fast response speed (10 min), and satisfactory specificity. We applied the biosensing platform to liquor starters to verify the capability of the assay in complicated fermentation samples. The proposed platform holds great promise as an efficient and simple method for enzymatic bioactivity monitoring in food manufacturing, biopharmaceutical processing, and clinical laboratory tests.

Construction of hierarchically porous covalent organic frameworks with enhanced enzyme accessibility for sensitive dopamine detection

Immobilization of fragile enzymes is vital to expanding its application in the extracellular environment. Covalent organic frameworks (COFs), as a class of emerging porous materials, are promising platforms for enzyme immobilization owing to their high porosity and tunable structure. However, the interior pores of COFs often fail to play their roles because of inaccessibility, resulting in decreased performance of immobilized enzymes. Here, we introduce a facile approach to construct hierarchically macro-mesoporous COF (Hm-COF) via a template-assistant strategy. The mesoporous channels of Hm-COF were used to entrap cytochrome c (Cyt c), and the macropores of Hm-COF were adopted as diffusion channels to enhance the mass transfer of guest molecules. The resulting Hm-COF demonstrated an enhanced uptake capacity of Cyt c compared with mesoporous COF (m-COF). Furthermore, the catalytic activity of Cyt c immobilized in Hm-COF (Cyt c@Hm-COF) was remarkably higher than that of Cyt c immobilized in m-COF (Cyt c@m-COF). Taking advantage of the excellent activity, Cyt c@Hm-COF was employed as the sensor for the sensitive detection of dopamine (DA). This study opens a new avenue for the construction of COFs with hierarchical pores and high-performance immobilized enzymes.

Covalent Organic Framework Nanosheets for the Assembly of Efficient Membrane Bioreactors

Immobilizing fragile enzymes in porous materials holds significant potential for biocatalysis but encounters challenges such as mismatched enzyme size and pore structure of host materials, along with harsh assembly conditions that can denature enzymes. Herein, we present a versatile strategy for constructing membrane bioreactors through water-mediated, vacuum-assisted layer-by-layer assembly of covalent organic framework (COF) nanosheets with enzymes. This method effectively addresses pore size limitations, preserves enzyme activity, and promotes convective transport of reactants to active sites, while shielding enzymes from harmful by-products through rapid transport in continuous membrane catalysis. The optimized bioreactor achieves a 1018-fold increase in relative activity compared to free enzymes in batch reactions, completing substrate conversion in just 7.95 s, and demonstrating enhanced stability.

Cascade Reaction Enables Heterointerfaces-Enriched Nanoarrays for Ampere-Level Hydrogen Production

Designing high-performance electrocatalysts with superior catalytic activity and stability is essential for large-scale hydrogen production via water electrolysis. Heterostructure nanoarrays are promising candidates, though achieving both high activity and stability simultaneously, especially under high current densities, remains challenging. To this end, we have developed a cascade reaction process that constructs a series of heterostructure nanoarrays with rich heterointerfaces. This process involves treating nickel foam (NF) with molten KSCN and transition metal salts. Initially, NF reacts with KSCN to form Ni9S8 nanoarrays and S2- ions, which are subsequently captured by transition metal ions to form sulfides that are directly integrated onto the nanoarrays, resulting in abundant heterointerfaces. Both experimental and theoretical results indicate that these rich heterointerfaces significantly enhance the interfacial interaction between Ni9S8 and RuS2 within the nanoarrays (termed RH-Ni9S8/RuS2), markedly improving both the intrinsic activity and stability for the hydrogen evolution reaction (HER). Impressively, the RH-Ni9S8/RuS2 demonstrates exceptional HER performance, achieving a low overpotential of just 180 mV at 1000 mA cm-2 and maintaining stability for up to 500 h under such high-current-density conditions. This innovative approach paves the way for the interfacial design and synthesis of high-performance catalysts for ampere-level hydrogen production.

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.

Tailored Metal-Organic Framework-Based Nanozymes for Enhanced Enzyme-Like Catalysis

The global crisis of bacterial infections is exacerbated by the escalating threat of microbial antibiotic resistance. Nanozymes promise to provide ingenious solutions. Here, we reported a homogeneous catalytic structure of Pt nanoclusters with finely tuned metal-organic framework (ZIF-8) channel structures for the treatment of infected wounds. Catalytic site normalization showed that the active site of the Pt aggregates structure with fine-tuned pore modifications structure had a catalytic capacity of 14.903×105 min-1, which was 18.7 times higher than that of the Pt particles in monodisperse state in ZIF-8 (0.793×105 min-1). In situ tests revealed that the change from homocleavage to heterocleavage of hydrogen peroxide at the interface of the nanozyme was one of the key reasons for the improvement of nanozyme activity. Density-functional theory and kinetic simulations of the reaction interface jointly determine the role of the catalytic center and the substrate channel together. Metabolomics analysis showed that the developed nanozyme, working in conjunction with reactive oxygen species, could effectively block energy metabolic pathways within bacteria, leading to spontaneous apoptosis and bacterial rupture. This pioneering study elucidates new ideas for the regulation of artificial enzyme activity and provides new perspectives for the development of efficient antibiotic substitutes.

Nanoencapsulation of Living Microbial Cells in Porous Covalent Organic Framework Shells

Encapsulating living cells within nanoshells offers an important approach to enhance their stability against environmental stressors and broaden their application scope. However, this often leads to impaired mass transfer at the cell biointerface. Strengthening the protective shell with well-defined, ordered transport channels is crucial to regulating molecular transport and maintaining cell viability and biofunctionality. Herein, we report the construction of covalent organic framework (COF) mesoporous shells for single-cell nanoencapsulation, providing selective permeability and comprehensive protection for living microbial cells. The COF shells ensure nutrient uptake while blocking large harmful molecules and UV-C radiation, thereby preserving cell viability and metabolic activity. Integration of such crystalline porous shells with genetically modified cell factories for metabolic production is further investigated, revealing no adverse effects, as demonstrated by riboflavin production. Moreover, the COF shell effectively shields cells, ensuring efficient bioproduction even after being treated under harsh conditions. This versatile encapsulation approach is applicable for different cell types, providing a robust platform for cell surface engineering.

Fast Production of Covalent Organic Frameworks for Covalent Enzyme Immobilization with Boosted Enzymatic Catalysis by Solar-Driven Photothermal Effect

Developing new enzyme-immobilization systems to stabilize their dynamic structures and meanwhile enhance their catalytic activity is of great significance but very challenging. Herein, we design and fabricate a class of robust mesoporous covalent organic frameworks (COFs) via Michael addition-elimination reaction. It is found that highly crystalline COFs can be produced in 10 min, which is attributed to the promoting effect of the intramolecular hydrogen bond activation. The COFs rich in hydroxyl groups can be facilely post-modified by epibromohydrin to covalently immobilize enzymes with both high loading and activity. Furthermore, we create a solar-driven photothermal-promoted strategy by introducing photoactive azo groups to COF carriers, which can boost the enzyme catalytic performance (lipase) with much higher conversion of various racemic substrates and chiral resolution upon solar light irradiation. The heterogeneous biocatalysts also demonstrate exceptional reusability and stability. This work provides a green and energy-efficient approach to facilitate the scale application of enzyme-immobilized biocatalysts.

PVP-assisted in situ immobilizing lipase on covalent organic framework for enhanced catalytic activity and stability in bioconversions

Covalent organic frameworks (COFs) are crystalline, porous organic materials that have significant potential as supports for enzyme immobilization. Nevertheless, the in situ preparation of biocatalysts during the COF formation process remains a considerable challenge. Herein, we developed a one-pot in situ preparation strategy. The immobilized lipase PS@TPB-TFPB COF-I was fabricated by mixing the polyvinylpyrrolidone (PVP)-lipase PS complex with precursors 1,3,5-tris(4-aminophenyl)benzene (TPB) and 1,3,5-tris(4-formylphenyl)benzene (TFPB) in acetonitrile catalyzed by acetic acid at room temperature for 48 h. The formation mechanism was systematically investigated using time-dependent microscopy techniques. PVP acts as a guiding reagent, controlling the morphological changes that occur during this process. Furthermore, the biocatalyst was employed in the kinetic resolution of racemic 1-phenylethanol, resulting in a significant enhancement in the conversion rate, with a range of 2.1 to 10.6 times higher compared to free PS at the same reaction time. The robust biocatalyst maintained high catalytic activity and enantioselectivity even after 10 cycles. The strategy described here is promising for lipase immobilization and expands the range of applications for COFs in biomanufacturing.

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.

Helicene Covalent Organic Frameworks for Robust Light Harvesting and Efficient Energy Transfers

Helicenes represent a class of fascinating π compounds with fused yet folded backbones. Despite their broad structural diversity, harnessing helicenes to develop well-defined materials is still a formidable challenge. Here we report the synthesis of crystalline porous helicene materials by exploring helicenes to synthesize covalent 2D lattices and layered π frameworks. Topology-directed polymerization of [6]helicenes and porphyrin creates 2D covalent networks with alternate helicene-porphyrin alignment along the x and y directions at a 1.5-nm interval and develops [6]helicene frameworks through reversed anti-AA stack along the z direction to form segregated [6]helicene and porphyrin columnar π arrays. Notably, this π configuration enables the frameworks to be highly red luminescent with benchmark quantum yields. The [6]helicene frameworks trigger effieicnt intra-framework singlet-to-singlet state energy transfer from [6]helicene to porphyrin and facilitate intermolecular triplet-to-triplet state energy transfer from frameworks to molecular oxygen to produce reactive oxygen species, harvesting a wide range of photons from ultraviolet to near-infrared regions for light emitting and photo-to-chemical conversion. This study introduces a new family of extended frameworks, laying the groundwork for exploring well-defined helicene materials with unprecedented structures and functions.

Imparting insoluble-soluble property to Cyt c by immobilizing Cyt c in UCST-pH dual responsive polymer for highly sensitive detection of phenol

Immobilization of enzymes in porous organic framework (POF) materials is popular strategy to stabilize enzymes. For such solid enzyme catalysis system, improving the catalytic efficiency is challenging due to the diffusion resistance from solid-liquid interface and inner pores. Here, UCST-pH dual responsive polymeric carrier (PEG-b-PAAm-b-P(GMA-co-AAc)) was synthesized to immobilize cytochrome c (Cyt c), which impart the reversibly insoluble-soluble property to the immobilized Cyt c. The PEG-b-PAAm-b-P(GMA-co-AAc) could serve as an insoluble-soluble matrix to fast and efficiently immobilize Cyt c via covalent attachment, achieving a remarkable 92 % loading efficiency within just 120 min. The obtained insoluble PEG-b-PAAm-b-P(GMA-co-AAc)-Cyt c micelles exhibited an improvement in thermal, pH stability and reusability. The completely soluble PEG-b-PAAm-b-P(GMA-co-AAc)-Cyt c conjugates accelerated substrate diffusion and then enhanced the catalytic efficiency. These excellent advantages led to low detection limit (1.99 μM), lower than the presently reported biosensors based on enzyme mimics in the colorimetric detection of phenol. This UCST-pH dual responsive window presents a new platform to efficiently control the immobilization and release of enzymes, which will achieve excellent stability and catalytic efficiency.

One-pot hydrothermal synthesis of silicon, nitrogen co-doped carbon dots for enhancing enzyme activity of acid phosphatase (ACP) to dopamine and for cell imaging

Developing water-soluble nanomaterials with high photoluminescence emission and high yield for biological analysis and imaging is urgently needed. Herein, water-soluble blue emitting silicon and nitrogen co-doped carbon dots (abbreviated as Si-CDs) of a high photoluminescence quantum yield of 80 % were effectively prepared with high yield rate (59.1 %) via one-step hydrothermal treatment of N-[3-(trimethoxysilyl)propyl]ethylenediamine (DAMO) and trans-aconitic acid. Furthermore, the Si-CDs demonstrate environmental robustness, photo-stability and biocompatibility. Given the importance of the potentially abnormal levels of acid phosphatase (ACP) in cancer diagnosis, developing a reliable and sensitive ACP measurement method is of significance for clinical research. The Si-CDs unexpectedly promote the catalytic oxidation of ACP on dopamine (DA) to polydopamine under acidic conditions through the produced reactive oxygen species (ROS). Correspondingly, a fluorescence response strategy using Si-CDs as the dual functions of probes and promoting enzyme activity of ACP on catalyzing DA was constructed to sensitively determine ACP. The quantitative analysis of ACP displayed a linear range of 0.1-60 U/L with a detection limit of 0.056 U/L. The accurate detection of ACP was successfully achieved in human serum through recovery tests. As a satisfactory fluorescent probe, Si-CDs were successfully applied to fluorescent imaging of A549 cells in cytoplasmic with long-term and safe staining. The Si-CDs have the dual properties of outstanding fluorescent probes and auxiliary oxidase activity, indicating their great potential in multifunctional applications.

Optimizing selectivity via membrane molecular packing manipulation for simultaneous cation and anion screening

Advancing membranes with enhanced solute-solute selectivity is essential for expanding membrane technology applications, yet it presents a notable challenge. Drawing inspiration from the unparalleled selectivity of biological systems, which benefit from the sophisticated spatial organization of functionalities, we posit that manipulating the arrangement of the membrane's building blocks, an aspect previously given limited attention, can address this challenge. We demonstrate that optimizing the face-to-face orientation of building blocks during the assembly of covalent-organic-framework (COF) membranes improves ion-π interactions with multivalent ions. This optimization leads to extraordinary selectivity in differentiating between monovalent cations and anions from their multivalent counterparts, achieving selectivity factors of 214 for K+/Al3+ and 451 for NO3-/PO43-. Leveraging this attribute, the COF membrane facilitates the direct extraction of NaCl from seawater with a purity of 99.57%. These findings offer an alternative approach for designing highly selective membrane materials, offering promising prospects for advancing membrane-based technologies.

Facile and scale-up syntheses of high-performance enzyme@meso-HOF biocatalysts

Facile immobilization is essential for the wide application of enzymes in large-scale catalytic processes. However, exploration of suitable enzyme supports poses an unmet challenge, particularly in the context of scale-up biocatalyst fabrication. In this study, we present facile and scale-up syntheses of high-performance enzyme biocatalysts via in situ encapsulation of cytochrome c (Cyt-c) as mono-enzyme and glucose oxidase (GOx)-horseradish peroxidase (HRP) as dual-enzyme cascade (GOx&HRP) systems, respectively, into a stable mesoporous hydrogen-bonded organic framework (meso-HOF) matrix. In situ encapsulation reactions occur under ambient conditions, and facilitate scale up (∼3 g per reaction) of enzyme@meso-HOF within a very short period (5-10 min). The resultant biocatalysts not only exhibit high enzyme loading (37.9 wt% for mono-enzyme and 22.8 wt% for dual-enzyme) with minimal leaching, but also demonstrate high catalytic activity, superior reusability, and durability. This study represents an example of scale-up fabrication of enzyme@meso-HOF biocatalysts on the gram level and highlights superior meso-HOFs as suitable host matrices for biomolecular entities.

Fabricating Polymeric Micelles with Enrichment and Cavity Effect for In Situ Enzyme Imobilization from Natural Biosystems

Metal-organic frameworks and hydrogen-organic frameworks (MOFs and HOFs) are attractive hosts for enzyme immobilization, but they are limited to immobilizing the purified enzymes, making industrial upscaling unattractive. Herein, aptamer-modified dual thermoresponsive polymeric micelles with switchable self-assembly and core-shell structure are constructed, which enable selective immobilization of trypsin directly from complex biological systems through a cascade operation of separation and immobilization. Their steric self-assembly provides a large amount of adsorption sites on the soluble micellar shell, resulting in high adsorption capacity and excellent selectivity. Meanwhile, their aptamer affinity ligand and cavity maintain the native conformations of trypsin and offer protective effects even in harsh conditions. The maximum adsorption capacity of the polymeric micelles for trypsin was determined to be 197 mg/g at 60 min, superior to those of MOFs and HOFs. 67.2 and 86.6% of its original activity was retained for trypsin immobilized in the cavity under strong alkaline and acidic conditions, respectively.

Developing Covalent Organic Framework Biocatalysts through Enzyme Encapsulation

Utilizing covalent organic frameworks (COFs) as porous supports to encapsulate enzyme represents an advanced strategy for constructing COFs biocatalysts, which has inspired numerous interests across various applications. As the structural advantages including ultrastable covalent-bonded linkage, tailorable pore structure, and metal-free biocompatibility, the resultant enzyme-COFs biocatalysts showcase functional enhancement in catalytic activity, chemical stability, long-term durability, and recyclability. This Concept describes the recent advances in the methodological strategies for engineering the COFs biocatalysts, with specific emphasis on the pore entrapment and in situ encapsulation strategies. The structural advantages of the COFs hybrid biocatalysts for organic synthesis, environment- and energy-associated applications are also canvassed. Additionally, the remaining challenges and the forward-looking directions in this field are also discussed. We believe that this Concept can offer useful methodological guidance for developing active and robust COFs biocatalysts.

Pros and Cons in Various Immobilization Techniques and Carriers for Enzymes

In recent years, enzyme immobilization technology has been developed, and studies on immobilized enzyme materials have become very prominent. With the immobilization technique, enzymes and compatible carrier materials are combined or enzyme crystals/aggregates are used in a carrier-free fashion, by physical, chemical, or biochemical methods. As a kind of biocatalyst, immobilized enzymes can catalyze certain chemical reactions with high selectivity and high efficiency under relatively mild reaction conditions and eliminate pollution to the environment. Considering the current status and applications of immobilized enzyme technology and materials emerging in the last 5 years, this mini-review introduces the advantages and disadvantages of various enzyme immobilization techniques with carriers as well as the pros and cons of different materials for immobilization. The future prospects of immobilization technology and carrier materials are outlined, aiming to provide a reference for further research and applications of sustainable technology.

Machine Learning Optimizing Enzyme/ZIF Biocomposites for Enhanced Encapsulation Efficiency and Bioactivity

In this study, we present the first example of using a machine learning (ML)-assisted design strategy to optimize the synthesis formulation of enzyme/ZIFs (zeolitic imidazolate framework) for enhanced performance. Glucose oxidase (GOx) and horseradish peroxidase (HRP) were chosen as model enzymes, while Zn(eIM)2 (eIM = 2-ethylimidazolate) was selected as the model ZIF to test our ML-assisted workflow paradigm. Through an iterative ML-driven training-design-synthesis-measurement workflow, we efficiently discovered GOx/ZIF (G151) and HRP/ZIF (H150) with their overall performance index (OPI) values (OPI represents the product of encapsulation efficiency (E in %), retained enzymatic activity (A in %), and thermal stability (T in %)) at least 1.3 times higher than those in systematic seed data studies. Furthermore, advanced statistical methods derived from the trained random forest model qualitatively and quantitatively reveal the relationship among synthesis, structure, and performance in the enzyme/ZIF system, offering valuable guidance for future studies on enzyme/ZIFs. Overall, our proposed ML-assisted design strategy holds promise for accelerating the development of enzyme/ZIFs and other enzyme immobilization systems for biocatalysis applications and beyond, including drug delivery and sensing, among others.

Enzyme Immobilization using Covalent Organic Frameworks: From Synthetic Strategy to COFs Functional Role

Enzymes, a class of biocatalysts, exhibit remarkable catalytic efficiency, specificity, and selectivity, governing many reactions that are essential for various cascades within living cells. The immobilization of structurally flexible enzymes on appropriate supports holds significant importance in facilitating biomimetic transformations in extracellular environments. Covalent organic frameworks (COFs) have emerged as ideal candidates for enzyme immobilization due to high surface tunability, diverse chemical/structural designs, exceptional stability, and metal-free nature. Various immobilization techniques have been proposed to fabricate COF-enzyme biocomposites, offering significant enhancements in activity and reusability for COF-immobilized enzymes as well as new insights into developing advanced enzyme-based applications. In this review, we provide a comprehensive overview of state-of-the-art strategies for immobilizing enzymes within COFs by focusing on their applicability and versatility. These strategies are systematically summarized and compared by categorizing them into postsynthesis immobilization and in situ immobilization, where their respective strengths and limitations are thoroughly discussed. Combined with an overview of critical emerging applications, we further elucidate the multifaceted roles of COFs in enzyme immobilization and subsequent applications, highlighting the advanced biofunctionality achievable through COFs.

Enzyme-Immobilized Porous Crystals for Environmental Applications

Developing efficient technologies to eliminate or degrade contaminants is paramount for environmental protection. Biocatalytic decontamination offers distinct advantages in terms of selectivity and efficiency; however, it still remains challenging when applied in complex environmental matrices. The main challenge originates from the instability and difficult-to-separate attributes of fragile enzymes, which also results in issues of compromised activity, poor reusability, low cost-effectiveness, etc. One viable solution to harness biocatalysis in complex environments is known as enzyme immobilization, where a flexible enzyme is tightly fixed in a solid carrier. In the case where a reticular crystal is utilized as the support, it is feasible to engineer next-generation biohybrid catalysts functional in complicated environmental media. This can be interpreted by three aspects: (1) the highly crystalline skeleton can shield the immobilized enzyme against external stressors. (2) The porous network ensures the high accessibility of the interior enzyme for catalytic decontamination. And (3) the adjustable and unambiguous structure of the reticular framework favors in-depth understanding of the interfacial interaction between the framework and enzyme, which can in turn guide us in designing highly active biocomposites. This Review aims to introduce this emerging biocatalysis technology for environmental decontamination involving pollutant degradation and greenhouse gas (carbon dioxide) conversion, with emphasis on the enzyme immobilization protocols and diverse catalysis principles including single enzyme catalysis, catalysis involving enzyme cascades, and photoenzyme-coupled catalysis. Additionally, the remaining challenges and forward-looking directions in this field are discussed. We believe that this Review may offer a useful biocatalytic technology to contribute to environmental decontamination in a green and sustainable manner and will inspire more researchers at the intersection of the environment science, biochemistry, and materials science communities to co-solve environmental problems.

Direct Imaging of Protein Clusters in Metal-Organic Frameworks

Protein@metal-organic frameworks (P@MOFs) prepared by coprecipitation of protein, metal ions, and organic ligands represent an effective method for protein stabilization with a wide spectrum of applications. However, the formation mechanism of P@MOFs via the coprecipitation process and the reason why proteins can retain their biological activity in the frameworks with highly concentrated metal ions remain unsettled. Here, by a combined methodology of single molecule localization microscopy and clustering analysis, we discovered that in this process enzyme molecules form clusters with metal ions and organic ligands, contributing to both the nucleation and subsequent crystal growth. We proposed that the clusters played an important role in the retention of overall enzymatic activity by sacrificing protein molecules on the cluster surface. This work offers fresh perspectives on protein behaviors in the formation of P@MOFs, inspiring future endeavors in the design and development of artificial bionanocomposites with high biological activities.

Covalent Organic Frameworks Based Photoenzymatic Nano-reactor for Asymmetric Dynamic Kinetic Resolution of Secondary Amines

Bio-catalysis represents a highly efficient and stereoselective method for the synthesis of valuable chiral compounds, however, the poor stability and limited reaction types of free enzymes restrict their wide application in industrial production. In this work, to overcome these problems, a multifunctional photoenzymatic nanoreactor CALB@COF-Ir was developed through the encapsulation of Candida antarctica lipase B (CALB) in a photosensitive covalent organic framework COF-Ir. This bio-nanocluster serves as efficient catalysts in asymmetric dynamic kinetic resolution (DKR) of secondary amines to give a series of chiral amines in high yields (up to 99 %) and enantioselectivities (up to 99 % ee). The well-designed COF-Ir not only acts as safety cover to prevent CALB from deactivation but promotes racemization of secondary amines via photo-induced hydrogen atom transfer (HAT) process. Photoelectric characterization and TDDFT calculation revealed that (ppy)2Ir units in COF-Ir play crucial role in this photocatalytic system which enhance its photo-redox properties through facilitating the separation between photoelectrons (e-) and holes (h+). Furthermore, the heterogeneous photoenzymatic nanoreactor could be recycled for five rounds with slight decline of catalytic reactivity.

Strategies for utilizing covalent organic frameworks as host materials for the integration and delivery of bioactives

Covalent organic frameworks (COFs), a new and developing class of porous framework materials, are considered a type of promising carrier for the integration and delivery of bioactives, which have diverse fascinating merits, such as a large specific surface area, designable and specific porosity, stable and orderly framework structure, and various active sites. However, owing to the significant differences among bioactives (including drugs, proteins, nucleic acid, and exosomes), such as size, structure, and physicochemical properties, the interaction between COFs and bioactives also varies. In this review, we firstly summarize three strategies for the construction of single or hybrid COF-based matrices for the delivery of cargos, including encapsulation, covalent binding, and coordination bonding. Besides, their smart response release behaviors are also categorized. Subsequently, the applications of cargo@COF biocomposites in biomedicine are comprehensively summarized, including tumor therapy, central nervous system (CNS) modulation, biomarker analysis, bioimaging, and anti-bacterial therapy. Finally, the challenges and opportunities in this field are briefly discussed.

Highly Enantioselective Catalysis by Enzyme Encapsulated in Metal Azolate Frameworks with Micelle-Controlled Pore Sizes

Encapsulating enzymes within metal-organic frameworks has enhanced their structural stability and interface tunability for catalysis. However, the small apertures of the frameworks restrict their effectiveness to small organic molecules. Herein, we present a green strategy directed by visible linker micelles for the aqueous synthesis of MAF-6 that enables enzymes for the catalytic asymmetric synthesis of chiral molecules. Due to the large pore aperture (7.6 Å), double the aperture size of benchmark ZIF-8 (3.4 Å), MAF-6 allows encapsulated enzyme BCL to access larger substrates and do so faster. Through the optimization of surfactants' effect during synthesis, BCL@MAF-6-SDS (SDS = sodium dodecyl sulfate) displayed a catalytic efficiency (Kcat/Km) that was 420 times greater than that of BCL@ZIF-8. This biocomposite efficiently catalyzed the synthesis of drug precursor molecules with 94-99% enantioselectivity and nearly quantitative yields. These findings represent a deeper understanding of de novo synthetic encapsulation of enzyme in MOFs, thereby unfolding the great potential of enzyme@MAF catalysts for asymmetric synthesis of organics and pharmaceuticals.

Ionic Liquid-Mediated Dynamic Polymerization for Facile Aqueous-Phase Synthesis of Enzyme-Covalent Organic Framework Biocatalysts

Utilizing covalent organic framework (COF) as a hypotoxic and porous scaffold to encapsulate enzyme (enzyme@COF) has inspired numerous interests at the intersection of chemistry, materials, and biological science. In this study, we report a convenient scheme for one-step, aqueous-phase synthesis of highly crystalline enzyme@COF biocatalysts. This facile approach relies on an ionic liquid (2 μL of imidazolium ionic liquid)-mediated dynamic polymerization mechanism, which can facilitate the in situ assembly of enzyme@COF under mild conditions. This green strategy is adaptive to synthesize different biocatalysts with highly crystalline COF "exoskeleton", as well evidenced by the low-dose cryo-EM and other characterizations. Attributing to the rigorous sieving effect of crystalline COF pore, the hosted lipase shows non-native selectivity for aliphatic acid hydrolysis. In addition, the highly crystalline linkage affords COF "exoskeleton" with higher photocatalytic activity for in situ production of H2 O2 , enabling us to construct a self-cascading photo-enzyme coupled reactor for pollutants degradation, with a 2.63-fold degradation rate as the poorly crystalline photo-enzyme reactor. This work showcases the great potentials of employing green and trace amounts of ionic liquid for one-step synthesis of crystalline enzyme@COF biocatalysts, and emphasizes the feasibility of diversifying enzyme functions by integrating the reticular chemistry of a COF.

Covalent Organic Frameworks for the Purification of Recombinant Enzymes and Heterogeneous Biocatalysis

Recombinant enzymes have gained prominence due to their diverse functionalities and specificity and are often a greener alternative in biocatalysis. This context makes purifying recombinant enzymes from host cells and other impurities crucial. The primary goal is to isolate the pure enzyme of interest and ensure its stability under ambient conditions. Covalent organic frameworks (COFs), renowned for their well-ordered structure and permeability, offer a promising approach for purifying histidine-tagged (His-tagged) enzymes. Furthermore, immobilizing enzymes within COFs represents a growing field in heterogeneous biocatalysis. In this study, we have developed a flow-based technology utilizing a nickel-infused covalent organic framework (Ni-TpBpy COF) to combine two distinct processes: the purification of His-tagged enzymes and the immobilization of enzymes simultaneously. Our work primarily focuses on the purification of three His-tagged enzymes β-glucosidase, cellobiohydrolase, and endoglucanase as well as two proteins with varying molecular weights, namely, green fluorescent protein (27 kDa) and BG Rho (88 kDa). We employed Ni-TpBpy as a column matrix to showcase the versatility of our system. Additionally, we successfully obtained a Ni-TpBpy COF immobilized with enzymes, which can serve as a heterogeneous catalyst for the hydrolysis of p-nitrophenyl-β-d-glucopyranoside and carboxymethylcellulose. These immobilized enzymes demonstrated catalytic activity comparable to that of their free counterparts, with the added advantages of recyclability and enhanced stability under ambient conditions for an extended period, ranging from 60 to 90 days. This contrasts with the free enzymes, which do not maintain their activity as effectively over time.

Function-Led Design of Covalent-Organic-Framework Membranes for Precise Ion Separation

Insufficient access to clean water and resources has emerged as one of the most pressing issues affecting people globally. Membrane-based ion separation has become a focal point of research for the generation of fresh water and the extraction of energy elements. This Review encapsulates recent advancements in the selective ion transport of covalent organic framework (COF) membranes, accomplished by strategically pairing diverse monomers to create membranes with various pore sizes and environments for specific purposes. We first discuss the merits of using COF materials as a basis for fabricating membranes for ion separation. We then explore the development of COF membranes in areas such as desalination, acid recovery, and energy element extraction, with a particular emphasis on the fundamental principles of membrane design. Lastly, we address both theoretical and practical challenges, as well as potential opportunities in the targeted design of ion-selective membranes. The goal of this Review is to stimulate future investigative efforts in this field, which is of significant scientific and strategic importance.

Enzyme-immobilized hierarchically porous covalent organic framework biocomposite for catalytic degradation of broad-range emerging pollutants in water

Efficient enzyme immobilization is crucial for the successful commercialization of large-scale enzymatic water treatment. However, issues such as lack of high enzyme loading coupled with enzyme leaching present challenges for the widespread adoption of immobilized enzyme systems. The present study describes the development and bioremediation application of an enzyme biocomposite employing a cationic macrocycle-based covalent organic framework (COF) with hierarchical porosity for the immobilization of horseradish peroxidase (HRP). The intrinsic hierarchical porous features of the azacalix[4]arene-based COF (ACA-COF) allowed for a maximum HRP loading capacity of 0.76 mg/mg COF with low enzyme leaching (<5.0 %). The biocomposite, HRP@ACA-COF, exhibited exceptional thermal stability (∼200 % higher relative activity than the free enzyme), and maintained ∼60 % enzyme activity after five cycles. LCMSMS analyses confirmed that the HRP@ACA-COF system was able to achieve > 99 % degradation of seven diverse types of emerging pollutants (2-mercaptobenzothiazole, paracetamol, caffeic acid, methylparaben, furosemide, sulfamethoxazole, and salicylic acid)in under an hour. The described enzyme-COF system offers promise for efficient wastewater bioremediation applications.

Enhanced Bioactivity of Enzyme/MOF Biocomposite via Host Framework Engineering

This study reports the successful development of a sustainable synthesis protocol for a phase-pure metal azolate framework (MAF-6) and its application in enzyme immobilization. An esterase@MAF-6 biocomposite was synthesized, and its catalytic performance was compared with that of esterase@ZIF-8 and esterase@ZIF-90 in transesterification reactions. Esterase@MAF-6, with its large pore aperture, showed superior enzymatic performance compared to esterase@ZIF-8 and esterase@ZIF-90 in catalyzing transesterification reactions using both n-propanol and benzyl alcohol as reactants. The hydrophobic nature of the MAF-6 platform was shown to activate the immobilized esterase into its open-lid conformation, which exhibited a 1.5- and 4-times enzymatic activity as compared to free esterase in catalyzing transesterification reaction using n-propanol and benzyl alcohol, respectively. The present work offers insights into the potential of MAF-6 as a promising matrix for enzyme immobilization and highlights the need to explore MOF matrices with expanded pore apertures to broaden their practical applications in biocatalysis.

Antioxidant Cascade Modulated Electrochemiluminescence by a Biomimetic Metal-Organic Framework with Dual Enzymatic Activity for Disease Marker Immunoassays

High-performance electrochemiluminescence is a significant approach for the examination of disease biomarkers, and the utilization of innovative electrochemiluminescence detection systems represents a viable strategy to enhance the efficacy of ECL analysis. In this work, the biomimetic engineering metal-organic framework (MOF-818) has realized the ultrasensitive ECL immunoassay of disease markers based on the guidance of the free radical scavenging strategy provided by the antioxidant cascade. Initially, we synthesized a hydrogen-bonded organic framework (HOF) consisting of luminol and three active ligands based on simple room-temperature self-assembly. The luminol-HOF (L-HOF) showed more stable and brighter ECL luminescence activity than the monomer due to the nano-confinement enhancement of the coordinated luminol units. Subsequently, MOF-818 with biomimetic superoxide dismutase (SOD) and catalase (CAT) activities were recruited for the first time as quenching agents for sandwich immunoassay mode. The enzyme activity leads to the reverse transformation of superoxide anion radicals (O2-) and further antioxidant decomposition, decreasing in the responsiveness of luminol ECL signals. Using carcinoembryonic antigen (CEA) as an analytical model, a detection limit of 0.457 pg/mL was obtained within a detection range of 0.001-50 ng/mL. We believe that this novel sandwich sensing model based on enzyme activity provides a meaningful potential tool for precise detection, expanding the broader application of nanoenzymes in analysis.