Recent advances in enzyme immobilization based on novel porous framework materials and its applications in biosensing

Recent advances in the analytical methods for quantitative determination of antioxidants in food matrices

Antioxidants are crucial in reducing oxidative stress and enhancing health, necessitating precise quantification in food matrices. Advanced techniques such as biosensors and nanosensors offer high sensitivity and specificity, enabling real-time monitoring and accurate antioxidant quantification in complex food systems. These technologies herald a new era in food analysis, improving food quality and safety through sophisticated detection methods. Their application facilitates comprehensive antioxidant profiling, driving innovation in food technology to meet the rising demand for nutritional optimization and food integrity. These are complemented by electrochemical techniques, spectroscopy, and chromatography. Electrochemical methods provide rapid response times, spectroscopy offers versatile chemical composition analysis, and chromatography excels in precise separation and quantification. Collectively, these methodologies establish a comprehensive framework for food analysis, essential for improving food quality, safety, and nutritional value. Future research should aim to refine these analytical methods, promising significant advancements in food and nutritional science.

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.

Molecular modeling of cellulose tosylate immobilized α-amylases: An in silico case study through MD simulation and refinement

The use of enzymes as catalysts in industrial processes has been studied, and they offer more ecologically friendly options for chemical reactions. In the current work, we investigated the potential of molecular modeling to solve the ordinarily difficult problem of identifying the amino acids involved in the covalent mode of immobilization by in silico investigations. The immobilized α-Amylase on Cellulose tosylate (henceforth referred to as Celltos) shows extra peaks of OH and NH2, CN, SO, C-O-C, and CS. Celltos exhibits distinct ether, imine, and CS peaks, indicating the potential contribution of α-Amylase's hydroxyl, amino, and thiol groups towards immobilization with cellulose's tosylate group. The native amylase was processed for Molecular Dynamics simulation. The simulated amylase was found to be the root mean squarely deviated to 1.16 Å. Autodock Vina, GOLD, SwissDock, and iGemdock generate output averages of 6.164, 6.549, 9.313 & 137.811 and 5.903, 7.656, 9.752 & 132.218 for an unrefined and refined dataset, respectively. The catalytic site intactness values for unrefined and refined SAT9, SAT13, and LAT21 were 83.3 %, 100 %, 100 %, and 8.33 %, 0 %, and 0 %, respectively. Our findings were additionally confirmed by bond distance similarity computations.

Unlocking of Hidden Mesopores for Enzyme Encapsulation by Dynamic Linkers in Stable Metal-Organic Frameworks

Mesoporous metal-organic frameworks (MOFs) are promising supports for the immobilization of enzymes, yet their applications are often limited by small pore apertures that constrain the size of encapsulated enzymes to below 5 nm. In this study, we introduced labile linkers (4,4',4''-(2,4,6-boroxintriyl)-tribenzoate, TBTB) with dynamic boroxine bonds into mesoporous PCN-333, resulting in PCN-333-TBTB with enhanced enzyme loading and protection capabilities. The selective breaking of B-O bonds creates defects in PCN-333, which effectively expands both window and cavity sizes, thereby unlocking hidden mesopores for enzyme encapsulation. Consequently, this strategy not only increases the adsorption kinetics of small enzymes (<5 nm) such as cytochrome c (Cyt C) and horseradish peroxidase (HRP), but also enables the immobilization of various large-sized enzymes (>5 nm), such as glycoenzymes. The glycoenzymes@PCN-333-TBTB platform was successfully applied to synthesize thirteen complex oligosaccharides and polysaccharides, demonstrating high activity and enhanced enzyme stability. The dynamic linker-mediated enzyme encapsulation strategy enables the immobilization of enzymes exceeding the inherent pore size of MOFs, thus broadening the scope of enzymatic catalytic reactions achievable with MOF materials.

Evaluation of the immobilized enzymes function in soil remediation following polycyclic aromatic hydrocarbon contamination

The bioremediation of polycyclic aromatic hydrocarbon (PAHs) from soil utilizing microorganisms, enzymes, microbial consortiums, strains, etc. has attracted a lot of interest due to the environmentally friendly, and cost-effective features. Enzymes can efficiently break down PAHs in soil by hydroxylating the benzene ring, breaking the C-C bond, and catalyze the hydroxylation of a variety of benzene ring compounds via single-electron transfer oxidation. However, the practical application is limited by its instability and ease to loss function under harsh environmental conditions such as pH, temperature, and edaphic stress etc. Therefore, this paper focused on the techniques used to immobilize enzymes and remediate PAHs in soil. Moreover, previous research has not adequately covered this topic, despite the employment of several immobilized enzymes in aqueous solution cultures to remediate other types of organic pollutants. Bibliometric analysis further highlighted the research trends from 2000 to 2023 on this field of growing interest and identified important challenges regarding enzyme stability and interaction with soil matrices. The findings indicated that immobilized enzymes may catalyzed PAHs via oxidation of OH groups in benzene rings, and generate benzyl radicals (i.e., •OH and •O2) that undergo further reaction and release water. As a result, the intermediate products of PAHs further catalyze by enzyme and enzyme induced microbes producing carbon dioxide and water. Meanwhile efficiency, activity, lifetime, resilience, and sustainability of immobilized enzyme need to be further improved for the large-scale and field-scale clean-up of PAHs polluted soils. This could be possible by integrating enzyme-based with microbial and plant-based remediation strategies. It can be coupled with another line of research focused on using a new set of support materials that can be derived from natural resources.

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.

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.

Improving the sulfite-detection performance of a fluorescent probe via post-synthetic modification with a metal-organic framework

In this work, a post-synthetic modification strategy was attempted to improve the performance of the probe for sulfite detection. The assembled platform UiO-66-NH-DQA, which was acquired by anchoring the sulfite-response fluorescent probe DQA onto the surface of UiO-66-NH2via amide covalent bonds, exhibited enhanced fluorescence intensity and practical intracellular imaging capability. In spite of the structural similarity, as verified by characterization tests, the conversion rate of post-synthetic modification was calculated as 35%, equaling an approximate assembly ratio of 1 : 2 between UiO-66-NH2 and DQA. Most significantly, conversion into UiO-66-NH-DQA led to a 5.6-fold enhancement in the reporting signal with a red shift of 20 nm. For sulfite detection, the linear range was 0-150 μM, with a limit of detection value of 0.025 μM. UiO-66-NH-DQA retained advantages including high stability (within pH 5.0-9.0), rapid response (within 15 min) and high selectivity. Based on low cytotoxicity and relatively rapid cellular uptake, UiO-66-NH-DQA achieved the imaging of both the exogenous and endogenous sulfite levels in living cells. In particular, its rapid cell-permeating capability was guaranteed during the modification. The post-synthetic modification strategy reported herein has potential for improving the practical properties of fluorescent monitoring materials.

Integrated Eu3+ loaded covalent organic framework with smartphone for ratiometric fluorescence detection of tetracycline

Developing rapid tetracycline sensing system is of great significance to monitor the illegal addition to drugs and pollution to food and ecosystem. By loading covalent organic frameworks (COFs) with Eu3+, a new hybridized material (COF@Eu3+) was prepared for tetracycline determination. Based on the Schiff base reaction, the COFs were by synthesized through solvent evaporation in 30 min at room temperature. Thereafter, Eu3+ was modified into COFs to develop the COF@Eu3+ sensing platform by adsorption and coordination. In presence of tetracycline, tetracycline can displace water molecules and coordinate with Eu3+ through the antenna effect. As a result, the red fluorescence of Eu3+ was enhanced by tetracycline with green fluorescence of COF as a reference. The developed ratiometric fluorescence sensor exhibits a linear range of 0.1-20 μM for detecting tetracycline with a detection limit of 30 nM. Integrated with a smartphone, the rapid tetracycline detection can be realized in situ, which is potential for high-throughput screening of tetracycline contaminated samples. Furthermore, the COF@Eu3+ fluorescence sensor has been successfully applied to the detection of tetracycline in traditional Chinese medicine compound preparation with satisfied recoveries. Therefore, a smartphone-assisted device was successfully developed based on Eu3+-functionalized COF, which is an attractive candidate for further applications of fluorescence sensing and visual detection.

Lignin: The green powerhouse for enzyme immobilization in biocatalysis and biosensing

Enzymes play an important role in diverse industries and are critical components of many industrial products, yet, their application is limited due to their sensitivity to environmental conditions, recovery challenges, and susceptibility to inhibition. Immobilizing enzymes onto a suitable support matrix imparts higher resistance and improves operational flexibility, recyclability, and reusability. Lignin, a renewable and abundant biopolymer derived from the paper and pulp industry, has emerged as one of the prominent materials to be incorporated in support matrices. The distinctive characteristics of lignin include high mechanical strength, ease of separation, chemical stability, robust matrix for securing enzyme binding, biocompatibility, and ease of surface functionalization, making it a promising alternative to traditional synthetic materials. Research studies suggest the effectiveness of various lignin-based materials for immobilizing enzymes and significantly improving their stability, reusability, and catalytic activity. This article critically examines the unique properties of lignin and highlights significant contributions made in the development of enzyme immobilization for biocatalysis and biosensing applications. Additionally, the roles of hybrid materials, multienzyme immobilization, and innovative strategies like interfacial activation and enzyme shielding are discussed for overcoming the current challenges and developing sustainable, efficient, and robust biocatalytic and biosensing processes for industrial applications.

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.

In Situ Biomineralization and Citric Acid Etching Strategy for Enhancing Activity of Immobilized Acetylcholinesterase

Enhancing the structural stability of an enzyme and maintaining its catalytic activity are effective ways to improve enzyme utilization and reduce the cost of drug screening. However, immobilized enzyme activity tends to decrease in existing immobilization techniques due to conformational changes and microenvironmental restrictions. In this paper, we present a facile approach to prepare immobilized acetylcholinesterase (AChE) with high activity by a ZIF-8 in situ immobilization and citric acid (CA) etching strategy. CA breaks the coordination bond of ZIF-8 and produces defects, expanding the pore space, improving substrate accessibility, and fully exposing the active site of the enzyme. The enhancement of the catalytic activity of AChE@ZIF-8-CA was about 6.10-fold compared with the free enzyme. In addition, AChE@ZIF-8-CA exhibited an excellent encapsulation efficiency and good tolerance to temperature, pH, and organic solvents. The relative activity remains at the initial 83.77% even in five repeated experiments. The strategy provides a novel and efficient way to quickly construct highly active immobilized enzymes under mild conditions.

Enhancing CRISPR/Cas-mediated electrochemical detection of nucleic acid using nanoparticle-labeled covalent organic frameworks reporters

Molecular detection of nucleic acid plays an important role in early diagnosis and therapy of disease. Herein, a novel and enhanced electrochemical biosensor was exploited based on target-activated CRISPR/Cas12a system coupling with nanoparticle-labeled covalent organic frameworks (COFs) as signal reporters. Hollow spherical COFs (HCOFs) not only served as the nanocarriers of silver nanoparticles (AgNPs)-DNA conjugates for enhanced signal output but also acted as three-dimensional tracks of CRISPR/Cas12a system to improve the cleavage accessibility and efficiency. The presence of target DNA triggered the trans-cleavage activity of the CRISPR/Cas12a system, which rapidly cleaved the AgNPs-DNA conjugates on HCOFs, resulting in a remarkable decrease of the electrochemical signal. As a proof of concept, the fabricated biosensing platform realized highly sensitive and selective detection of human papillomavirus type 16 (HPV-16) DNA ranging from 100 fM to 1 nM with the detection limit of 57.2 fM. Furthermore, the proposed strategy provided a versatile and high-performance biosensor for the detection of different targets by simple modification of the crRNA protospacer, holding promising applications in disease diagnosis.

Enzyme encapsulation in metal-organic frameworks using spray drying for enhanced stability and controlled release: A case study of phytase

Encapsulating enzymes in metal-organic frameworks is a common practice to improve enzyme stability against harsh conditions. However, the synthesis of enzyme@MOFs has been primarily limited to small-scale laboratory settings, hampering their industrial applications. Spray drying is a scalable and cost-effective technology, which has been frequently used in industry for large-scale productions. Despite these advantages, its potential for encapsulating enzymes in MOFs remains largely unexplored, due to challenges such as nozzle clogging from MOF particle formation, utilization of toxic organic solvents, controlled release of encapsulated enzymes, and high temperatures that could compromise enzyme activity. Herein, we present a novel approach for preparing phytase@MIL-88 A using solvent-free spray drying. This involves atomizing two MOF precursor solutions separately using a three-fluid nozzle, with enzyme release controlled by manipulating defects within the MOFs. The physicochemical properties of the spray dried particles are characterized using X-ray diffraction, Fourier-transform infrared spectroscopy, and scanning electron microscopy. Leveraging the efficiency and scalability of spray drying in industrial production, this scalable encapsulation technique holds considerable promise for broad industrial applications.

Signal-enhanced electrochemical sensor employing MWCNTs/CMK-3/AuNPs and Au@Pd core-shell structure for sensitive determination of AFB1 in complex matrix

A sandwich electrochemical sensor was fabricated based on multi-walled carbon nanotubes/ordered mesoporous carbon/AuNP (MWCNTs/CMK-3/AuNP) nanocomposites and porous core-shell nanoparticles Au@PdNPs to achieve rapid and sensitive detection of AFB1 in complex matrices. MWCNTs/CMK-3/AuNP nanocomposite, which was prepared by self-assembly method, served as a substrate material to increase the aptamer loading and improve the conductivity and electrocatalytic activity of the electrode for the first signal amplification. Then, Au@PdNPs, which were synthesized by one-pot aqueous phase method, were applied as nanocarriers loaded with plenty of capture probe antibody (Ab) and signal molecule toluidine blue (Tb) to form the Au@PdNPs-Ab-Tb bioconjugates for secondary signal amplification. The sensing system could still significantly improve the signal output intensity even in the presence of ultra-low concentration target compound due to the dual signal amplification of MWCNTs/CMK-3/AuNP nanocomposites and Au@PdNPs-Ab-Tb. The method exhibited high selectivity, low detection limit (9.13 fg/mL), and strong stability to differentiate AFB1 from other mycotoxins. Furthermore, the sensor has been successfully applied to the quantitative determination of AFB1 in corn, malt, and six herbs, which has potential applications in food safety, quality control, and environmental monitoring.

A new method to immobilize urease in silk fibroin membrane by unidirectional nanopore dehydration

The immobilization of free enzymes is crucial for enhancing their stability in different environments, enabling reusability, and expanding their applications. However, the development of a straightforward immobilization method that offers stability, high efficiency, biocompatibility, and modifiability remains a significant challenge. Silk fibroin (SF) is a good carrier for immobilized enzymes and drugs. Here, we employed urease as a model enzyme and utilized our developed technology called unidirectional nanopore dehydration (UND) to efficiently dehydrate a regenerated SF solution containing urease in a single step, resulting in the preparation of a highly functionalized SF membrane immobilizing urease (UI-SFM). The preparation process of UI-SFM is based on an all-water system, which is mild, green and able to efficiently and stably immobilize urease in the membranes, maintaining 92.7% and 82.8% relative enzyme activity after 30 days of storage in dry and hydrated states, respectively. Additionally, we performed additional post-treatments, including stretching and cross-linking with polyethylene glycol diglycidyl ether (PEGDE), to obtain two more robust immobilized urease membranes (UI-SFMs and UI-SFMc). The thermal and storage stability of these two membranes were significantly improved, and the recovery ratio of enzyme activity reached more than 90%. After 10 repetitions of the enzymatic reaction, the activity recovery of UI-SFMs and UI-SFMc remained at 92% and 88%, respectively. The results suggest that both UND-based and post-treatment-developed membranes exhibit excellent urease immobilization capabilities. Furthermore, the enzyme immobilization method offers a straightforward and versatile approach for efficient and stable enzyme immobilization, while its flexible modifiability caters to diverse application requirements.

Enzyme immobilization with nanomaterials for hydrolysis of lignocellulosic biomass: Challenges and future Perspectives

Enzyme immobilization has emerged as a prodigious strategy in the enzymatic hydrolysis of lignocellulosic biomass (LCB) promising enhanced efficacy and stability of the enzymes. Further, enzyme immobilization on magnetic nanoparticles (MNPs) facilitates the easy recovery and reuse of biocatalysts. This results in the development of a nanobiocatalytic system, that serves as an eco-friendly and inexpensive LCB deconstruction approach. This review provides an overview of nanomaterials used for immobilization with special emphasis on the nanomaterial-enzyme interactions and strategies of immobilization. After the succinct outline of the immobilization procedures and supporting materials, a comprehensive assessment of the catalysis enabled by nanomaterial-immobilized biocatalysts for the conversion and degradation of lignocellulosic biomasses is provided by gathering state-of-the-art examples. The challenges and future directions associated with this technique providing a potential solution in the present article. Insight on the recent advancements in the process of nanomaterial-based immobilization for the hydrolysis of lignocellulosic biomass has also been highlighted in the article.

Lewis Acid Regulation Strategy for Constructing D-A-A Covalent Organic Frameworks with Enhanced Photocatalytic Organic Conversion

Owing to their excellent photoelectric properties, donor-acceptor (D-A) type photocatalytic covalent organic frameworks (COFs) have attracted significant research interest in recent years. However, the limited D-A structural units of existing COFs restrict the development of novel and efficient photocatalytic COF materials. To solve this problem, we developed a series of D-A-A-type COFs utilizing a Lewis acid regulation strategy, in which Lewis acids act as the coordination centers, and pyridine and cyano groups act as ligands. Lewis acid sites in COFs serve as electron acceptors, facilitating the separation and transfer of photogenerated electron-hole pairs. This process is crucial for photocatalysis because it significantly increases the efficiency of the catalytic reaction by reducing the recombination rate of charge carriers. The developed Lewis acid-activated D-A-A COFs efficiently catalyzed the hydroxylation of various phenylboronic acid compounds under visible light. The developed catalysts are expected to contribute to increasing the fabrication efficiency of industrially important organic materials.

Conjugated molecularly imprinted polymers based on covalent organic frameworks: Fluorescent sensing platform for specific capture of urea and elimination of ethyl carbamate

This study described the preparation of an azide covalent organic framework-embedded molecularly imprinted polymers (COFs(azide)@MIPs) platform for urea adsorption and indirect ethyl carbamate (EC) removal from Chinese yellow rice wine (Huangjiu). By modifying the pore surface of COFs using the copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction, COFs(azide) with a high fluorescence quantum yield and particular recognition ability were inventively produced. In order to selectively trap urea, the COFs(azide) were encased in an imprinted shell layer via imprinting technology. With a detection limit (LOD) of 0.016 μg L-1 (R2 = 0.9874), the COFs(azides)@MIPs demonstrated a good linear relationship with urea in the linear range of 0-5 μg L-1. Using real Huangjiu samples, the spiking recovery trials showed the viability of this sensing platform with recoveries ranging from 88.44 % to 109.26 % and an RSD of less than 3.40 %. The Huangjiu processing model system achieved 38.93 % EC reduction by COFs(azides)@MIPs. This research will open up new avenues for the treatment of health problems associated with fermented alcoholic beverages, particularly Huangjiu, while also capturing and removing hazards coming from food.

Recent advances and synergistic effect of bioactive zeolite imidazolate frameworks (ZIFs) for biosensing applications

The rapid developments in the field of zeolitic imidazolate frameworks (ZIFs) in recent years have created unparalleled opportunities for the development of unique bioactive ZIFs for a range of biosensor applications. Integrating bioactive molecules such as DNA, aptamers, and antibodies into ZIFs to create bioactive ZIF composites has attracted great interest. Bioactive ZIF composites have been developed that combine the multiple functions of bioactive molecules with the superior chemical and physical properties of ZIFs. This review thoroughly summarizes the ZIFs as well as the novel strategies for incorporating bioactive molecules into ZIFs. They are used in many different applications, especially in biosensors. Finally, biosensor applications of bioactive ZIFs were investigated in optical (fluorescence and colorimetric) and electrochemical (amperometric, conductometric, and impedance) fields. The surface of ZIFs makes it easier to immobilize bioactive molecules like DNA, enzymes, or antibodies, which in turn enables the construction of cutting-edge, futuristic biosensors.

Thermo-Switchable Enzyme@Metal-Organic Framework for Selective Biocatalysis and Biosensing

The stimulus-responsive regulation of enzyme catalytic activity and selectivity provides a new opportunity to extend the functionality and efficiency of immobilized enzymes. This work aims to design and synthesize a thermo-switchable enzyme@MOF for size-selective biocatalysis and biosensing through the immobilization of Candida rugosa lipase (CRL) within ZIF-8 functionalized with thermally responsive polymer, poly(N-isopropylacrylamide) (PNIPAM) (CRL@ZIF-8-PNIPAM). Unlike free CRL, which does not demonstrate substrate selectivity, we can reversibly tune the pore size of the ZIF-8-PNIPAM nanostructures (open pores or blocked pores) through temperature stimulus and subsequently modulate the substrate selectivity of CRL@ZIF-8-PNIPAM. CRL@ZIF-8-PNIPAM had the highest hydrolytic activity for small molecules (12 mM p-nitrophenol/mg protein/min, 4-nitrophenyl butyrate (p-NP Be)) and the lowest hydrolytic activity for large molecules (0.16 mM p-nitrophenol/mg protein/min, 4-nitrophenyl palmitate (p-NP P)). In addition, CRL@ZIF-8-PNIPAM demonstrated thermo-switchable behavior for large molecules (p-NP P). The p-NP P hydrolytic activity of CRL@ZIF-8-PNIPAM was significantly lower at 40 °C (blocked pores) than at 27 °C (open pores). However, the transition of blocked pores and open pores is a gradual process that resulted in a delay in the "thermo-switchable" catalytic behavior of CRL@ZIF-8-PNIPAM during thermal cycling. CRL@ZIF-8-PNIPAM was also successfully used for the fabrication of electrochemical biosensors for the selective biosensing of pesticides with different molecular sizes.

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.

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

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

Structural Design and Energy and Environmental Applications of Hydrogen-Bonded Organic Frameworks: A Systematic Review

Hydrogen-bonded organic frameworks (HOFs) are emerging porous materials that show high structural flexibility, mild synthetic conditions, good solution processability, easy healing and regeneration, and good recyclability. Although these properties give them many potential multifunctional applications, their frameworks are unstable due to the presence of only weak and reversible hydrogen bonds. In this work, the development history and synthesis methods of HOFs are reviewed, and categorize their structural design concepts and strategies to improve their stability. More importantly, due to the significant potential of the latest HOF-related research for addressing energy and environmental issues, this work discusses the latest advances in the methods of energy storage and conversion, energy substance generation and isolation, environmental detection and isolation, degradation and transformation, and biological applications. Furthermore, a discussion of the coupling orientation of HOF in the cross-cutting fields of energy and environment is presented for the first time. Finally, current challenges, opportunities, and strategies for the development of HOFs to advance their energy and environmental applications are discussed.

When nanozymes meet enzyme: Unlocking the dual-activity potential of integrated biocomposites

Integrating enzymes and nanozymes in various applications is a topic of significant interest. The researchers have explored the encapsulation of enzymes using diverse nanostructures to create nanomaterial-enzyme hybrids. These nanomaterials introduce unique properties that contribute to the additional activity along with the stabilization of enzymes in immobilized form, enabling a cascade of second-order reactions. This review centers on dual-activity nanozymes, providing insights into their applications in biosensors and biocatalysis. These applications leverage the enhanced catalytic activity and stability offered by dual-activity nanozymes. These nanozymes find promising applications in fields like bioremediation, offering eco-friendly solutions for mitigating environmental pollution while showing potential in medical diagnostics. The review delves into various techniques for creating enzyme-nanozyme hybrid catalysts, including adsorption, encapsulation, and incorporation methods. The review also addresses the challenges that must be overcome, such as overlapping catalytic surfaces and disparities in reaction rates in multi-enzyme cascade reactions. It concludes by presenting strategies to tackle these issues and offers insights into the field's promising future, suggesting that machine learning may drive further advancements in enzyme-nanozyme integration. This comprehensive exploration illuminates the present and charts a promising course for future innovations in the seamless integration of enzymes and nanozymes, heralding a new era of catalytic possibilities.

Protein-Integrated Hydrogen-Bonded Organic Frameworks: Chemistry and Biomedical Applications

Hydrogen-bonded organic frameworks (HOFs) are porous nanomaterials that offer exceptional biocompatibility and versatility for integrating proteins for biomedical applications. This minireview concisely discusses recent advancements in the chemistry and functionality of protein-HOF interfaces. It particularly focuses on strategic methodologies, such as the careful selection of building blocks and the genetic engineering of proteins, to facilitate protein-HOF interactions. We examine the role of enzyme encapsulation within HOFs, highlighting its capability to preserve enzyme function, a crucial aspect for applications in biosensing and disease diagnosis. Moreover, we discuss the emerging utility of nanoscale HOFs for intracellular protein delivery, illustrating their applicability as nanoreactors for intracellular catalysis and neuroprotective biorthogonal catalysis within cellular compartments. We highlight the significant advancement of designing biodegradable HOFs tailored for cytosolic protein delivery, underscoring their promising application in targeted cancer therapies. Finally, we provide a perspective viewpoint on the design of biocompatible protein-HOF assemblies, underlining their promising prospects in drug delivery, disease diagnosis, and broader biomedical applications.

Calcium-based MOFs as scaffolds for shielding immobilized lipase and enhancing its stability

The enzyme immobilization technology has become a key tool in the field of enzyme applications; however, improving the activity recovery and stability of the immobilized enzymes is still challenging. Herein, we employed a magnetic carboxymethyl cellulose (MCMC) nanocomposite modified with ionic liquids (ILs) for covalent immobilization of lipase, and used Ca-based metal-organic frameworks (MOFs) as the support skeleton and protective layer for immobilized enzymes. The ILs contained long side chains (eight CH2 units), which not only enhanced the hydrophobicity of the carrier and its hydrophobic interaction with the enzymes, but also provided a certain buffering effect when the enzyme molecules were subjected to compression. Compared to free lipase, the obtained CaBPDC@PPL-IL-MCMC exhibited higher specific activity and enhanced stability. In addition, the biocatalyst could be easily separated using a magnetic field, which is beneficial for its reusability. After 10 cycles, the residual activity of CaBPDC@PPL-IL-MCMC could reach up to 86.9%. These features highlight the good application prospects of the present immobilization method.

Covalent organic frame based high-performance nanocomposite for construction of ATP sensor

In this work, a novel covalent organic frame (TAPT-TFPB COF) with self-enhanced photoelectric activity was prepared for decorating on conductive single-walled carbon nanotubes (SWCNT) to synthetize a high-performance photoelectric nanocomposite (COF/SWCNT), in which the interfacial charge separation and photogenerated carrier migration rate was significantly improved to obtain desiring photoelectric conversion efficiency for generating an extremely high photocurrent. Accordingly, the synthetic COF/SWCNT was ingeniously applied in the fabrication of ultrasensitive photoelectrochemical (PEC) biosensor for realizing the trace ATP detection by integrating with an Exo III-assisted dual DNA recycling amplification strategy. The recycling amplification could efficiently convert trace target ATP into plentiful output DNA, which ingeniously triggered the hybridization chain reaction (HCR) to generate a long DNA strand with substantial quencher manganese porphyrin (MnPP) loading to depress the photocurrent of COF/SWCNT. The experimental data showed that proposed biosensor had a detection range from 10 fmol L-1 to 10 nmol L-1 with the detection limit as low as 2.75 fmol L-1 (S/N = 3). In addition, this proposed biosensor showed excellent analytical performance in terms of stability, specificity and reproducibility, providing a possibility to accomplish sensitive and accurate in vitro diagnosis.

Design and Advanced Manufacturing of NU-1000 Metal-Organic Frameworks with Future Perspectives for Environmental and Renewable Energy Applications

Metal-organic frameworks (MOFs) represent a relatively new family of materials that attract lots of attention thanks to their unique features such as hierarchical porosity, active metal centers, versatility of linkers/metal nodes, and large surface area. Among the extended list of MOFs, Zr-based-MOFs demonstrate comparably superior chemical and thermal stabilities, making them ideal candidates for energy and environmental applications. As a Zr-MOF, NU-1000 is first synthesized at Northwestern University. A comprehensive review of various approaches to the synthesis of NU-1000 MOFs for obtaining unique surface properties (e.g., diverse surface morphologies, large surface area, and particular pore size distribution) and their applications in the catalysis (electro-, and photo-catalysis), CO2 reduction, batteries, hydrogen storage, gas storage/separation, and other environmental fields are presented. The review further outlines the current challenges in the development of NU-1000 MOFs and their derivatives in practical applications, revealing areas for future investigation.

Artificial oil bodies: A review on composition, properties, biotechnological applications, and improvement methods

In order to simulate the structure of natural oil body, artificial oil bodies (AOBs) are fabricated by the integration of oleosins, triacylglycerols (TAGs) and phospholipids (PLs) in vitro. Recently, AOBs have gained great research interest both in the food and biological fields due to its ability to act as a novel delivery system for bioactive compounds and as a carrier for target proteins. This review aims to summarize the composition and the preparation methods of AOBs, examine the factors influencing their stability. Moreover, this contribution focusses on exploring the application of AOBs to encapsulate functional ingredients that are prone to oxidation as well as improve efficiency involved in protein purification, renaturation and immobilization by reducing the complex steps. In addition, the improvement measures to further enhance the stability and efficacy of AOBs are also discussed. The application of AOBs is expected to be a big step towards replacing existing bioreactors and delivery systems.

Research Progress on the Application of Covalent Organic Framework Nanozymes in Analytical Chemistry

Covalent organic frameworks (COFs) are porous crystals that have high designability and great potential in designing, encapsulating, and immobilizing nanozymes. COF nanozymes have also attracted extensive attention in analyte sensing and detection because of their abundant active sites, high enzyme-carrying capacity, and significantly improved stability. In this paper, we classify COF nanozymes into three types and review their characteristics and advantages. Then, the synthesis methods of these COF nanozymes are introduced, and their performances are compared in a list. Finally, the applications of COF nanozymes in environmental analysis, food analysis, medicine analysis, disease diagnosis, and treatment are reviewed. Furthermore, we also discuss the application prospects of COF nanozymes and the challenges they face.

Boosting Enzyme Activity in Enzyme Metal-Organic Framework Composites

Enzymes, as highly efficient biocatalysts, excel in catalyzing diverse reactions with exceptional activity and selective properties under mild conditions. Nonetheless, their broad applications are hindered by their inherent fragility, including low thermal stability, limited pH tolerance, and sensitivity to organic solvents and denaturants. Encapsulating enzymes within metal-organic frameworks (MOFs) can protect them from denaturation in these harsh environments. However, this often leads to a compromised enzyme activity. In recent years, extensive research efforts have been dedicated to enhancing enzymatic activity within MOFs, leading to the development of new enzyme-MOF composites that not only preserve their catalytic potential but also outperform their free counterparts. This Review provides a comprehensive review on recent developments in enzyme-MOF composites with a specific emphasis on their enhanced enzymatic activity compared to free enzymes.

DNA-Directed Assembly of Hierarchical MOF-Cellulose Nanofiber Microbioreactors with "Branch-Fruit" Structures

Assembling metal-organic frameworks (MOFs) into ordered multidimensional porous superstructures promises the encapsulation of enzymes for heterogeneous biocatalysts. However, the full potential of this approach has been limited by the poor stability of enzymes and the uncontrolled assembly of MOF nanoparticles onto suitable supports. In this study, a novel and exceptionally robust Ni-imidazole-based MOF was synthesized in water at room temperature, enabling in situ enzyme encapsulation. Based on this MOF platform, we developed a DNA-directed assembly strategy to achieve the uniform placement of MOF nanoparticles onto bacterial cellulose nanofibers, resulting in a distinctive "branch-fruit" structure. The resulting hybrid materials demonstrated remarkable versatility across various catalytic systems, accommodating natural enzymes, nanoenzymes, and multienzyme cascades, thus showcasing enormous potential as universal microbioreactors. Furthermore, the hierarchical composites facilitated rapid diffusion of the bulky substrate while maintaining the enzyme stability, with ∼3.5-fold higher relative activity compared to the traditional enzyme@MOF immobilized in bacterial cellulose nanofibers.

Biomimetic Mineralization of Large Enzymes Utilizing a Stable Zirconium-Based Metal-Organic Frameworks

Enzymes are natural catalysts for a wide range of metabolic chemical transformations, including selective hydrolysis, oxidation, and phosphorylation. Herein, we demonstrate a strategy for the encapsulation of enzymes within a highly stable zirconium-based metal-organic framework. UiO-66-F4 was synthesized under mild conditions using an enzyme-compatible amino acid modulator, serine, at a modest temperature in an aqueous solution. Enzyme@UiO-66-F4 biocomposites were then formed by an in situ encapsulation route in which UiO-66-F4 grows around the enzymes and, consequently, provides protection for the enzymes. A range of enzymes, namely, lysozyme, horseradish peroxidase, and amano lipase, were successfully encapsulated within UiO-66-F4. We further demonstrate that the resulting biocomposites are stable under conditions that could denature many enzymes. Horseradish peroxidase encapsulated within UiO-66-F4 maintained its biological activity even after being treated with the proteolytic enzyme pepsin and heated at 60 °C. This strategy expands the toolbox of potential metal-organic frameworks with different topologies or functionalities that can be used as enzyme encapsulation hosts. We also demonstrate that this versatile process of in situ encapsulation of enzymes under mild conditions (i.e., submerged in water and at a modest temperature) can be generalized to encapsulate enzymes of various sizes within UiO-66-F4 while protecting them from harsh conditions (i.e., high temperatures, contact with denaturants or organic solvents).

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.

Enhanced High-Fructose Corn Syrup Production: Immobilizing Serratia marcescens Glucose Isomerase on MOF (Co)-525 Reduces Co2+ Dependency in Glucose Isomerization to Fructose

The escalating demand for processed foods has led to the widespread industrial use of glucose isomerase (GI) for high-fructose corn syrup (HFCS) production. This reliance on GIs necessitates continual Co2+ supplementation to sustain high catalytic activity across multiple reaction cycles. In this study, Serratia marcescens GI (SmGI) was immobilized onto surfaces of the metal-organic framework (MOF) material MOF (Co)-525 to generate MOF (Co)-525-GI for use in catalyzing glucose isomerization to generate fructose. Examination of MOF (Co)-525-GI structural features using scanning electron microscopy-energy dispersive spectroscopy, Fourier-transform infrared spectroscopy, and ultraviolet spectroscopy revealed no structural changes after SmGI immobilization and the addition of Co2+. Notably, MOF (Co)-525-GI exhibited optimal catalytic activity at pH 7.5 and 70 °C, with a maximum reaction rate (Vmax) of 37.24 ± 1.91 μM/min and Km value of 46.25 ± 3.03 mM observed. Remarkably, immobilized SmGI exhibited sustained high catalytic activity over multiple cycles without continuous Co2+ infusion, retaining its molecular structure and 96.38% of its initial activity after six reaction cycles. These results underscore the potential of MOF (Co)-525-GI to serve as a safer and more efficient immobilized enzyme technology compared to traditional GI-based food-processing technologies.

Biosensors for the detection of pathogenic bacteria: current status and future perspectives

Pathogenic microorganisms pose significant threats to human health, food safety and environmental integrity. Rapid and accurate detection of these pathogens is essential to mitigate their impact. Fast, sensitive detection methods such as biosensors also play a critical role in preventing outbreaks and controlling their spread. In recent years, biosensors have emerged as a revolutionary technology for pathogen detection. This review aims to present the current developments in biosensor technology, investigate the methods by which these developments are used in the detection of pathogenic bacteria and highlight future perspectives on the subject.

Hydrogen-Bonded Supramolecular Nanotrap Enabling the Interfacial Activation of Hosted Enzymes

Engineering nanotraps to immobilize fragile enzymes provides new insights into designing stable and sustainable biocatalysts. However, the trade-off between activity and stability remains a long-standing challenge due to the inevitable diffusion barrier set up by nanocarriers. Herein, we report a synergetic interfacial activation strategy by virtue of hydrogen-bonded supramolecular encapsulation. The pore wall of the nanotrap, in which the enzyme is encapsulated, is modified with methyl struts in an atomically precise position. This well-designed supramolecular pore results in a synergism of hydrogen-bonded and hydrophobic interactions with the hosted enzyme, and it can modulate the catalytic center of the enzyme into a favorable configuration with high substrate accessibility and binding capability, which shows up to a 4.4-fold reaction rate and 4.9-fold conversion enhancements compared to free enzymes. This work sheds new light on the interfacial activation of enzymes using supramolecular engineering and also showcases the feasibility of interfacial assembly to access hierarchical biocatalysts featuring high activity and stability simultaneously.

Covalent organic framework in-situ immobilized laccase for the covalent polymerization removal of sulfamethoxazole in the presence of natural phenols: Prominent enzyme stability and activity

In current water treatment processes, pollutants are typically degraded into small molecules and CO2 for detoxification. This study employed laccase-mediated aggregation of new pollutants with natural phenolic compounds to remove pollutants by forming large molecular substances, effectively sequestering carbon. Free laccase is susceptible to environmental influences, causing deactivation. However, immobilizing laccase onto a carrier enhances enzyme stability. In the experiment, laccase was immobilized onto the covalent organic framework TpPa-1 through an in-situ loading process, resulting in immobilized laccase Lac@TpPa-1. Stability studies revealed that immobilized laccase outperformed free laccase in terms of pH, temperature, and recyclability. Moreover, immobilized laccase was employed for catalyzing the removal of emerging pollutants containing natural phenolic compounds, achieving an 80.53% removal rate with the addition of 0.02 g of laccase within 5 h. Analytical techniques like Fourier-transform ion cyclotron resonance mass spectrometry were used to uncover reaction pathways, demonstrating the presence of radical polymerization and 1, 4 nucleophilic addition. This research utilized TpPa-1 as a carrier for laccase immobilization, promoting oxidation-induced polymerization for efficient pollutant removal. It provides a theoretical foundation for understanding the interplay between emerging pollutants and phenolic compounds in natural environments and enhances the practical application of laccase through immobilization.

Study of the reusability and stability of nylon nanofibres as an antibody immobilisation surface

In the case of a biological threat, early, rapid, and specific detection is critical. In addition, ease of handling, use in the field, and low-cost production are important considerations. Immunological devices are able to respond to these needs. In the design of these immunological devices, surface antibody immobilisation is crucial. Nylon nanofibres have been described as a very good option because they allow for an increase in the surface-to-volume ratio, leading to an increase in immunocapture efficiency. In this paper, we want to deepen the study of other key points, such as the reuse and stability of these nanofibres, in order to assess their profitability. On the one hand, the reusability of nanofibres has been studied using different stripping treatments at different pH values on the nylon nanofibres with well-oriented antibodies anchored by protein A/G. Our study shows that stripping with glycine buffer pH 2.5 allows the nanofibres to be reused as long as protein A/G has been previously anchored, leaving both nanofibre and protein A/G unchanged. On the other hand, we investigated the stability of the nylon nanofibres. To achieve this, we analysed any loss of immunocapture ability of well-oriented antibodies anchored both to the nylon nanofibres and to a specialised surface with high protein binding capacity. The nanofibre immunocapture system maintained an unchanged immunocapture ability for a longer time than the specialised planar surface. In conclusion, nylon nanofibres seem to be a very good choice as an antibody immobilisation surface, offering not only higher immunocapture efficiency, but also more cost efficiency as they are reusable and stable.

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.

Construction and Application of a Pepsin-Functionalized Covalent Organic Framework with Prominent Chiral Recognition Ability

The stable Pepsin@covalent organic framework (Pepsin@COF) were constructed base on matching COF pore diameter to pepsin dimension. It exhibits excellent chiral recognition capabilities (e. e. % up to 62.63 %) and potential for enantioseparation. Furthermore, a positive correlation between the immobilized enzyme activity and chiral recognition was revealed, offering insights for the design of biocatalytic nanosystems in chiral separation.

Hofmeister Effect Promoted the Introduction of Tunable Large Mesopores in MOFs at Low Temperature for Femtomolar ALP Detection

In addressing the demand for hierarchically mesoporous metal-organic frameworks (HMMOFs) with adjustable large mesopores, a method based on the synergistic effects of low-temperature microemulsions and Hofmeister ions is developed. Low temperature dramatically enhanced the solubility of hydrophobic solvent in the microemulsion core, enlarging the mesopores in HMMOFs replica. Meanwhile, Hofmeister salt-in ions continuously controlled mesopore expansion by modulating the permeability of swelling agent into the microemulsion core. The large mesopores up to 33 nm provided sufficient space for the alkaline phosphatase (ALP) enrichment, and retained the remaining channel to facilitate the free mass diffusion. Leveraging these advantages, a colorimetric sensor is successfully developed using large-mesopore HMMOFs for femtomolar ALP detection based on the enrichment and cycling amplification principles. The sensor exhibited a linear detection range of 100 to 7500 fm and a limit of detection of 42 fm, presenting over 4000 times higher sensitivity than classic para-nitrophenyl phosphate colorimetric methods. Such high sensitivity highlights the importance of adjustable mesoporous structures of HMMOFs in advanced sensing applications, and prefigures their potential for detecting large biomolecules in diagnostics and biomedical research.

Metal-organic frameworks for enzyme immobilization and nanozymes: A laccase-focused review

Laccases are natural catalysts with remarkable catalytic activity. However, their application is limited by their lack of stability. Metal-organic frameworks (MOFs) have emerged as a promising alternative for enzyme immobilization. Enzymes can be immobilized in MOFs via two approaches: postsynthetic immobilization and in situ immobilization. In postsynthetic immobilization, an enzyme is embedded after MOF formation by covalent interactions or adsorption. In contrast, in in situ immobilization, a MOF is formed in the presence of an enzyme. Additionally, MOFs have exhibited intrinsic enzyme-like activity. These materials, known as nanozymes when they have the ability to replace enzymes in certain catalytic processes, have multiple key advantages, such as low cost, easy preparation, and large surface areas. This review presents a general overview of the most recent advances in both enzyme@MOF biocatalysts and MOF-based nanozymes in different applications, with a focus on laccase, which is one of the most widely investigated enzymes with excellent industrial potential.

Microfluidic based continuous enzyme immobilization: A comprehensive review

Conventional techniques for enzyme immobilization suffer from suboptimal activity recovery due to insufficient enzyme loading and inadequate stability. Furthermore, these techniques are time-consuming and involve multiple steps which limit the applicability of immobilized enzymes. In contrast, the use of microfluidic devices for enzyme immobilization has garnered significant attention due to its ability to precisely control immobilization parameters, resulting in highly active immobilized enzymes. This approach offers several advantages, including reduced time and energy consumption, enhanced mass-heat transfer, and improved control over the mixing process. It maintains the superior structural configuration in immobilized form which ultimately affects the overall efficiency. The present review article comprehensively explains the design, construction, and various methods employed for enzyme immobilization using microfluidic devices. The immobilized enzymes prepared using these techniques demonstrated excellent catalytic activity, remarkable stability, and outstanding recyclability. Moreover, they have found applications in diverse areas such as biosensors, biotransformation, and bioremediation. The review article also discusses potential future developments and foresees significant challenges associated with enzyme immobilization using microfluidics, along with potential remedies. The development of this advanced technology not only paves the way for novel and innovative approaches to enzyme immobilization but also allows for the straightforward scalability of microfluidic-based techniques from an industrial standpoint.

Flexible electrochemical sensor for highly sensitive and selective non-enzymatic detection of creatinine via electrodeposited copper over polymelamine formaldehyde

A non-enzymatic electrochemical biosensor was developed for highly sensitive detection of creatinine using copper nanoparticles supported over polymelamine formaldehyde. The synergy between the electrodeposited copper nanoparticles over the highly porous polymer (eCu-PMF) provided a greener platform to boost up the electron transport at the electrode electrolyte interface by eliminating the role of redox species as well as interference of major interferents like glucose, dopamine, and ascorbic acid in physiological media 0.1 M PBS (pH 7.4). The proposed sensor exhibited a wide detection range of 100 fM-60 mM with high sensitivities of 0.320 mA nM-1 cm-2 and 3.8 mA nM-1 cm-2. Moreover, the sensor was applied to real samples of serum creatinine and recoveries of 97 to 114% were found. Additionally, a paper-based flexible screen-printed electrode was fabricated which displayed an excellent activity with the same detection range of 100 fM-60 mM and long-term storage stability of 15 days.

In Situ Encapsulation of Cytochrome c within Covalent Organic Frames Using Deep Eutectic Solvents under Ambient Conditions

In situ integration of enzymes with covalent organic frameworks (COFs) to form hybrid biocatalysts is both significant and challenging. In this study, we present an innovative strategy employing deep eutectic solvents (DESs) to synergistically synthesize COFs and shield cytochrome c (Cyt c). By utilizing DESs as reaction solvents in combination with water, we successfully achieved rapid and in situ encapsulation of Cyt c within COFs (specifically COF-TAPT-TFB) under ambient conditions. The resulting Cyt c@COF-TAPT-TFB composite demonstrates a remarkable preservation of enzymatic activity. This encapsulation strategy also imparts exceptional resistance to organic solvents and exhibits impressive recycling stability. Additionally, the enhanced catalytic efficiency of Cyt c@COF-TAPT-TFB in a photoenzymatic cascade reaction is also showcased.

In-situ encapsulation and construction of Lac@HOFs/hydrogel composite for enhancing laccase stability and azo dyes decolorization efficiency

Enzymes with high catalytic activity and stability have been used for the sustainable development of green chemical applications, such as water remediation. Immobilized laccase can be used to construct a synergistic system for adsorption and degradation, which has great potential for water remediation. Herein, a hydrogen-bonded organic framework was installed onto laccase in-situ to form a net-carboxylate-arranged defective cage, which enhanced its catalytic stability. Thereafter, the CMC/PVA/Lac@HOF-101 hydrogel was fabricated by freeze-thaw cycles using sodium carboxymethylcellulose and polyvinyl alcohol as carriers and copper (II) as a cross-linker. Notably, the MOFs/hydrogel as a protective carrier of laccase maintain long-term recyclability and catalytic stability. After the fifth catalytic cycle, approximately 66.7 % activity of the CP-Lac@HOF-101 was retained. When both free laccase and CP-Lac@HOF-101 were used for decolorization of Acid Orange 7 (AO), the removal rates were 10.9 % and 82.5 % after 5 h, respectively. Furthermore, even in the presence of metal cations, almost 60.0 % of the AO removal efficiency was achieved. The relationship between the structure of the azo dyes and decolorization efficiency of the synergistic system was further investigated. This study offers a method for constructing enzyme@HOF-based composite hydrogels and provides a promising water remediation strategy.

Sustainable Immobilization of β-Glucosidase onto Silver Ions and AgNPs-Loaded Acrylic Fabric with Enhanced Stability and Reusability

Modified polymer design has attracted significant attention for enzyme immobilization, offering promising applications. In this study, amine-terminated polymers were synthesized by incorporating functional groups into polyacrylonitrile using hexamethylenediamine. This work highlights the successful enzyme immobilization strategy using modified polymers, offering improved stability and expanded operational conditions for potential biotechnological applications. The resulting amino groups were utilized to capture silver ions, which were subsequently converted to silver nanoparticles (AgNPs). The obtained materials, AgNPs@TA-HMDA (acrylic textiles coated silver nanoparticles AgNPs) and Ag(I)@TA-HMDA (acrylic textiles coated with Ag ion) were employed as supports for β-glucosidase enzyme immobilization. The highest immobilization yields (IY%) were achieved with AgNPs@TA-HMDA at 92%, followed by Ag(I)@TA-HMDA at 79.8%, resulting in activity yields (AY%) of 81% and 73%, respectively. Characterization techniques such as FTIR, FE-SEM, EDX, TG/DTG, DSC, and zeta potential were employed to investigate the structural composition, surface morphologies, elemental composition, thermal properties, and surface charge of the support materials. After 15 reuses, the preservation percentages decreased to 76% for AgNPs@TA-HMDA/β-Glu and 65% for Ag(I)@TA-HMDA/β-Glu. Storage stability revealed that the decrease in activity for the immobilized enzymes was smaller than the free enzyme. The optimal pH for the immobilized enzymes was broader (pH 5.5 to 6.5) compared to the free enzyme (pH 5.0), and the optimal temperature for the immobilized enzymes was 60 °C, slightly higher than the free enzyme's optimal temperature of 50 °C. The kinetic analysis showed a slight increase in Michaelis constant (Km) values for the immobilized enzymes and a decrease in maximum velocity (Vmax), turnover number (Kcat), and specificity constant (Kcat/Km) values compared to the free enzyme. Through extensive characterization, we gained valuable insights into the structural composition and properties of the modified polymer supports. This research significantly contributes to the development of efficient biotechnological processes by advancing the field of enzyme immobilization and offering valuable knowledge for its potential applications.

Co-encapsulating Cofactor and Enzymes in Hydrogen-Bonded Organic Frameworks for Multienzyme Cascade Reactions with Cofactor Recycling

Use of hydrogen-bonded organic frameworks (HOFs) for enzyme immobilization faces challenges in the improvement of enzyme activity recovery and the assembly of cofactor-dependent multienzyme systems. Herein, we report a polyelectrolyte-assisted encapsulation approach (PAEA) that enables two cascades with four oxidoreductases and two nicotinamide adenine dinucleotide (phosphate) (NAD(P)H) cofactors co-encapsulated in BioHOF-1 with excellent cargo loading and over 100 % cascade activity. The key role of the polyelectrolyte is to coat enzymes and tether NAD(P)H, thus interacting with HOF monomers in place of enzymes, avoiding the destruction of enzymes by HOF monomers. The versatility and efficiency of PAEA are further illustrated by an HOF-101-based bio-nanoreactor. Moreover, the immobilization by PAEA makes enzymes and NAD(P)H display excellent stability and recyclability. This study has demonstrated a facile and versatile PAEA for fabricating cofactor-dependent multienzyme cascade nanoreactors with HOFs.