Immobilization of MP-11 into a Mesoporous Metal–Organic Framework, MP-11@mesoMOF: A New Platform for Enzymatic Catalysis

Design of Multivariate Biological Metal-Organic Frameworks: Toward Mimicking Active Sites of Enzymes

Mimicking enzymatic processes carried out by natural enzymes, which are highly efficient biocatalysts with key roles in living organisms, attracts much interest but constitutes a synthetic challenge. Biological metal-organic frameworks (bioMOFs) are potential candidates to be enzyme catalysis mimics, as they offer the possibility to combine biometals and biomolecules into open-framework porous structures capable of simulating the catalytic pockets of enzymes. In this work, we first study the catalase activity of a previously reported bioMOF, derived from the amino acid L-serine, with formula {CaIICuII6[(S,S)-serimox]3(OH)2(H2O)} · 39H2O (1) (serimox = bis[(S)-serine]oxalyl diamide), which is indeed capable to mimic catalase enzymes, in charge of preventing cell oxidative damage by decomposing, efficiently, hydrogen peroxide to water and oxygen (2H2O2 → 2 H2O + O2). With these results in hand, we then prepared a new multivariate bioMOF (MTV-bioMOF) that combines two different types of bioligands derived from L-serine and L-histidine amino acids with formula CaIICuII6[(S,S)-serimox]2[(S,S)-hismox]1(OH)2(H2O)}·27H2O (2) (hismox = bis[(S)-histidine]oxalyl diamide ligand). MTV-bioMOF 2 outperforms 1 degrading hydrogen peroxide, confirming the importance of the amino acid residue from the histidine amino acid acting as a nucleophile in the catalase degradation mechanism. Despite displaying a more modest catalytic behavior than other reported MOF composites, in which the catalase enzyme is immobilized inside the MOF, this work represents the first example of a MOF in which an attempt is made to replicate the active center of the catalase enzyme with its constituent elements and is capable of moderate catalytic activity.

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.

Understanding Diffusion in a Single-Metal Organic Framework Crystal Used for Sensing Applications

Metal-organic frameworks (MOFs) stand out as remarkable materials renowned for their exceptionally high surface area and large number of pores, making them invaluable for diverse sensing applications including gas, biomedical, chemical, and optical sensing. Traditional methods of molecule infusion and release often involve a large number of crystals with varying shapes and sizes, leading to averaged outcomes across a heterogeneous crystal population. In this study, we present continuous monitoring of the infusion and release dynamics of model drug molecules, specifically vitamin B12, within individual Tb-mesoMOF crystals. Our findings underscore the critical influence of crystal size and shape on the infusion and diffusion processes and corresponding color change, underscoring the necessity to account for these factors in the design of large-scale systems. Leveraging optical microscopy, we employed a histogram-based algorithm for image processing, enabling automated tracking of diffusion phenomena. This investigation offers crucial insights into the dynamics of these processes, laying the groundwork for optimizing parameters in future sensing systems.

Green solvent systems for material syntheses and chemical reactions

It is of great significance to develop environmentally benign, non-volatile and recyclable green solvents for different applications. This feature article overviews the properties of green solvent systems (e.g., ionic liquids, supercritical carbon dioxide, deep eutectic solvents and mixed green solvent systems) and their applications in (1) framework material syntheses, including metal-organic frameworks, covalent organic frameworks and hydrogen-bonded organic frameworks, and (2) CO2 conversion reactions, including photocatalytic and electrocatalytic reduction reactions. Finally, the future perspective for research on green solvent systems is proposed from different aspects.

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).

Synthesis of novel Cu/Fe based benzene Dicarboxylate (BDC) metal organic frameworks and investigations into their optical and electrochemical properties

In the recent past Metal-organic frameworks (MOFs) based thin films have demonstrated superior performance in various technological applications such as optical and optoelectronic devices, electrochemical energy storage, catalysis, and sensing. Herein we report tuning the optical performance of stable complexes using Cu and Fe metal ions with carboxylate benzene dicarboxylic (BDC), leading toward the formation of novel MOF structures. The formation of Cu-BDC and Fe-BDC were confirmed by XRD and SEM studies. The thermal stability of two MOFs was investigated, indicating that, the Cu-BDC is more stable than Fe-BDC. Further, the optical properties were investigated in the wavelength range 325-1100 nm, and the Fe-BDC exhibited greater optical transmission properties than Cu-BDC by 33 %, as investigated by Wemple-DiDomenico and Tauc models. The dispersion parameters related to optical studies for Cu-BDC were better in comparison to Fe-BDC, which could be attributed to the increase in Cu valence electrons due to an increase in the number of cations. The electrochemical behavior in terms of CV measurements shows the presence of pseudo capacitance in both Fe-BDC and Cu-BDC MOFs. The improved CV performance of Cu-BDC MOF suggests that it could be used as a storage material. This work successfully demonstrates the tailoring of optical properties related to MOF thin films through the formation of stable complexes using BDC as a potential material for the fabrication of OLED's and Solar cells. The improved CV performance suggests that these MOF based materials could be used as anodes in fabrication of batteries or supercapacitors.

Advances and Applications of Metal-Organic Frameworks (MOFs) in Emerging Technologies: A Comprehensive Review

Metal-organic frameworks (MOFs) that are the wonder material of the 21st century consist of metal ions/clusters coordinated to organic ligands to form one- or more-dimensional porous structures with unprecedented chemical and structural tunability, exceptional thermal stability, ultrahigh porosity, and a large surface area, making them an ideal candidate for numerous potential applications. In this work, the recent progress in the design and synthetic approaches of MOFs and explore their potential applications in the fields of gas storage and separation, catalysis, magnetism, drug delivery, chemical/biosensing, supercapacitors, rechargeable batteries and self-powered wearable sensors based on piezoelectric and triboelectric nanogenerators are summarized. Lastly, this work identifies present challenges and outlines future opportunities in this field, which can provide valuable references.

Trajectory in biological metal-organic frameworks: Biosensing and sustainable strategies-perspectives and challenges

The ligand attribute of biomolecules to form coordination bonds with metal ions led to the discovery of a novel class of materials called biomolecule-associated metal-organic frameworks (Bio-MOFs). These biomolecules coordinate in multiple ways and provide versatile applications. Far-spread bio-ligands include nucleobases, amino acids, peptides, cyclodextrins, saccharides, porphyrins/metalloporphyrin, proteins, etc. Low-toxicity, self-assembly, stability, designable and selectable porous size, the existence of rigid and flexible forms, bio-compatibility, and synergistic interactions between metal ions have led Bio-MOFs to be commercialized in industries such as sensors, food, pharma, and eco-sensing. The rapid growth and commercialization are stunted by absolute bio-compatibility issues, bulk morphology that makes it rigid to alter shape/porosity, longer reaction times, and inadequate research. This review elucidates the structural vitality, biocompatibility issues, and vital sensing applications, including challenges for incorporating bio-ligands into MOF. Critical innovations in Bio-MOFs' applicative spectrum, including sustainable food packaging, biosensing, insulin and phosphoprotein detection, gas sensing, CO2 capture, pesticide carriers, toxicant adsorptions, etc., have been elucidated. Emphasis is placed on biosensing and biomedical applications with biomimetic catalysis and sensitive sensor designing.

Alternative protein encapsulation with MOFs: overcoming the elusive mineralization of HKUST-1 in water

Protein encapsulation by in situ formation of MOFs is a valuable strategy to immobilise and protect these bioentities. However the required biocompatible conditions limits the scope of MOFs under investigation, particularly in the case of hydrolytically unstable MOFs such as HKUST-1. We report alternative synthetic procedures to obtain protein@HKUST-1 biocomposites from related Cu-BTC dense biocomposites. pH dependent dense phase precursors are first obtained and their transformations into HKUST-1 are characterized. Encapsulation efficiency is affected by the protein's nature, and can be modulated by the sequential or simultaneous addition of MOF precursors.

Assembly of an iron-based complex into a metal-organic framework: a space confinement strategy for isolation of mono-iron complexes to protect from dimerization

Non-heme mononuclear iron complexes, especially when supported by tripodal tetradentate ligands, show promising C-H bond activation efficiency in catalytic reactions. Nevertheless, they intrinsically decay readily to their dinuclear form, and the dimerization process is inevitable in homogenous solution, which dramatically hinders their further application. Hence, we demonstrate that the mononuclear iron complex [(TPA)FeII-2L]2+ (L = labile ligands, mainly solvent molecules) was successfully encapsulated in a highly robust metal-organic framework UiO-66 via a two-step "ship-in-a-bottle" strategy. The nearly perfect size matching of the octahedral cages of the host UiO-66 provides ideal space confinement for the guest complex to protect from dimerization and dramatically increases the mono-nuclear complex stability compared to its un-confined state. The successful encapsulation of [(TPA)FeII-2L]2+ in UiO-66 was verified thoroughly by spectroscopy, microscopy, N2 adsorption, and electrochemistry characterization techniques. This work shows that encapsulating an unstable molecular complex in MOFs via a two-step "ship-in-a-bottle" strategy highlights opportunities for extending the heterogenization of homogeneous complexes.

Immobilization of purified enzyme EreB in metalorganic framework (MOF) mesopores for erythromycin degradation

Erythromycin, a commonly used macrolide antibiotic, plays a crucial role in both human medicine and animal husbandry. However, its abuse has led to residual presence in the environment, with problems such as the emergence of resistant bacteria and enrichment of resistance genes. These issues pose significant risks to human health. Thus far, there are no effective, environmentally friendly methods to manage this problem. Enzymes can specifically degrade erythromycin without causing other problems, but their unrecyclability and environmental vulnerability hinder large-scale application. Enzyme immobilization may help to solve these problems. This study used Cu-BTC, a synthetic metal-organic framework, to immobilize the erythromycin-degrading enzyme EreB. The loading temperature and enzyme quantity were optimized. The Cu-BTC and EreB@Cu-BTC were characterized by various methods to confirm the preparation of Cu-BTC and immobilization of EreB. The maximum enzyme loading capacity was 66.5 mg g-1. In terms of enzymatic properties, immobilized EreB had improved heat (25-45 °C) and alkaline (6.5-10) tolerance, along with greater affinity between the enzyme and its substrate; Km decreased from 438.49 to 372.30 mM. Recycling was also achieved; after 10 cycles, 57.12% of the enzyme activity was maintained. After composite degradation, the antibacterial activity of erythromycin-containing wastewater was examined; the results showed that the novel composite could completely inactivate erythromycin. In summary, Cu-BTC was an ideal carrier for immobilization of the enzyme EreB, and the EreB@Cu-BTC composite has good prospects for the treatment of erythromycin-containing wastewater.

Mesoporous Metal-Organic Frameworks for Catalytic RNA Deprotection and Activation

A metal-organic framework (MOF) with mespores (2 to 50 nm) allows the inclusion of large biomolecules, such as nucleic acids. However, chemical reaction on the nucleic acids, to further regulate their bioactivity, is yet to be demonstrated within MOF pores. Here, we report the deprotection of carbonate protected RNA molecules (21 to 102 nt) to restore their original activity using a MOF as a heterogeneous catalyst. Two MOFs, MOF-626 and MOF-636 are designed and synthesized, with mesopores of 2.2 and 2.8 nm, respectively, carrying isolated metal sites (Ni, Co, Cu, Pd, Rh and Ru). The pores favor the entrance of RNA, while the metal sites catalyze C-O bond cleavage at the carbonate group. Complete conversion of RNA is achieved by Pd-MOF-626, 90 times more efficiently than Pd(NO3 )2 . MOF crystals are also removable from the aqueous reaction media, leaving a negligible metal footprint, 3.9 ppb, only 1/55 of that using homogeneous Pd catalysts. These features make MOF potentially suited for bioorthogonal chemistry.

Microperoxidase-11 functionalized nanozyme with enhanced peroxidase-mimicking activities for visual detection of cysteine

Various nanomaterials with peroxidase activity (nanozyme) have been designed for bio catalysis and biosensing, however, most of them need further design and modification of probe molecules for the specific binding reaction with targets. This results in a decrease in catalysis activity and hinders them to be perfect alternatives to natural enzyme in biosensing. In this work, an enhanced nanozyme was synthesized by functionalizing natural microperoxidase-11 (MP-11) on a hybrid graphene oxide-gold (GO-Au) material. The designed nanozyme showed an enhanced catalysis activity and realized a robust and efficient colorimetric detection of cysteine based on specific binding reaction between active iron center from MP-11 and thiol in cysteine. The enhanced properties show promising applications of complex nanozyme and provides a great opportunity for developing efficient sensing systems.

Construction of Immobilized Enzymes with Yeast and Metal-Organic Frameworks for Enhanced Biocatalytic Activities

Metal-organic frameworks (MOFs) have become promising host materials for enzyme immobilization and protection. Herein, ZIF-8 nanocubes were successfully self-assembled onto yeast as a biological template to obtain hybrid Y@ZIF-8. The size, morphology, and loading efficiency of ZIF-8 nanoparticles assembled on yeast templates can be well-regulated by adjusting the various synthetic parameters. Particularly, the amount of water significantly affected the particle size of ZIF-8 assembled on yeast. Through using a cross-linking agent, the relative enzyme activity of Y@ZIF-8@t-CAT could be greatly enhanced and remained the highest even after seven consecutive cycles, with improved cycling stability, as compared to that of Y@ZIF-8@CAT. In addition to the effect of the physicochemical properties of Y@ZIF-8 on the loading efficiency, the temperature tolerance, pH tolerance, and storage stability of Y@ZIF-8@t-CAT were also systematically investigated. Importantly, the catalytic activity of free catalase was decreased to 72% by 45 days, while the activity of the immobilized catalase remained above 99%, suggesting good storage stability. The present work demonstrates that yeast-templated ZIF-8 nanoparticles have a high potential to be used as biocompatible immobilization materials and are promising candidates for the preparation of effective biocatalysts in biomedicine applications.

Encapsulating and stabilizing enzymes using hydrogen-bonded organic frameworks

Enzymes are outstanding natural catalysts with exquisite 3D structures, initiating countless life-sustaining biotransformations in living systems. The flexible structure of an enzyme, however, is highly susceptible to non-physiological environments, which greatly limits its large-scale industrial applications. Seeking suitable supports to immobilize fragile enzymes is one of the most efficient routes to ameliorate the stability problem. This protocol imparts a new bottom-up strategy for enzyme encapsulation using a hydrogen-bonded organic framework (HOF-101). In short, the surface residues of the enzyme can trigger the nucleation of HOF-101 around its surface through the hydrogen-bonded biointerface. As a result, a series of enzymes with different surface chemistries are able to be encapsulated within a highly crystalline HOF-101 scaffold, which has long-range ordered mesochannels. The details of experimental procedures are described in this protocol, which involve the encapsulating method, characterizations of materials and biocatalytic performance tests. Compared with other immobilization methods, this enzyme-triggering HOF-101 encapsulation is easy to operate and affords higher loading efficiency. The formed HOF-101 scaffold has an unambiguous structure and well-arranged mesochannels, favoring mass transfer and understanding of the biocatalytic process. It takes ~13.5 h for successful synthesis of enzyme-encapsulated HOF-101, 3-4 d for characterizations of materials and ~4 h for the biocatalytic performance tests. In addition, no specific expertise is necessary for the preparation of this biocomposite, although the high-resolution imaging requires a low-electron-dose microscope technology. This protocol can provide a useful methodology to efficiently encapsulate enzymes and design biocatalytic HOF materials.

Bioinspired Framework Catalysts: From Enzyme Immobilization to Biomimetic Catalysis

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

Multivariate Porous Aromatic Frameworks with High Porosity and Hierarchical Structures for Enzyme Immobilization

As materials with permanently porous structures and readily modifying availability, porous aromatic frameworks (PAFs) are considered as promising porous materials with versatile functionality. Currently the designable synthesis of PAFs with the desired surface area and pore size is still a challenge, and instead kinetically irreversible coupling reactions for PAFs synthesis has resulted in the unpredictable connection of building units. Herein, a series of PAFs with highly porous and hierarchical structures were successfully synthesized through a multivariate inspired strategy, where multiple building units with various topologies and sizes were selected for PAFs synthesis. All the PAFs synthesized through this strategy possessed hierarchical structures and high specific surface areas at the same time. Encouraged by their high surface area and hierarchical structures, we loaded lipase onto one of the multivariate PAFs. The enzyme loading content of the obtained lipase@PAF-147 was as high as 1456 mg g^-1, which surpassed any other currently reported enzyme loading materials. The lipase@PAF-147 also exhibited favorable catalytic activity and stability to a model reaction of p-nitrophenyl caprylate (p-NPC) hydrolysis. This multivariate strategy inspired synthetic method broadens the selection of building units for PAFs design and opens a new avenue for the design of functional porous materials.

Nanoscale MOFs in nanomedicine applications: from drug delivery to therapeutic agents

Metal-organic frameworks (MOFs) hold great promise for widespread applications in biomedicine and nanomedicine. MOFs are one of the most fascinating nanocarriers for drug delivery, benefiting from their high porosity and facile modification. Furthermore, the tailored components of MOFs can be therapeutic agents for various treatments, including drugs as organic ligands of MOFs, active metal as central metal ions of MOFs, and their combinations as carrier-free MOF-based nanodrug. In this review, the advances in delivery systems and applications as therapeutic agents for nanoscale MOF-based materials are summarized. The challenges of MOFs in clinical translation and the future directions in the field of MOFs therapy are also discussed. We hope that more researchers will focus their attention on advancing and translating MOF-based nanodrugs into pre-clinical and clinical applications.

Utilization of Functionalized Metal–Organic Framework Nanoparticle as Targeted Drug Delivery System for Cancer Therapy

Cancer is a multifaceted disease that results from the complex interaction between genetic and environmental factors. Cancer is a mortal disease with the biggest clinical, societal, and economic burden. Research on better methods of the detection, diagnosis, and treatment of cancer is crucial. Recent advancements in material science have led to the development of metal–organic frameworks, also known as MOFs. MOFs have recently been established as promising and adaptable delivery platforms and target vehicles for cancer therapy. These MOFs have been constructed in a fashion that offers them the capability of drug release that is stimuli-responsive. This feature has the potential to be exploited for cancer therapy that is externally led. This review presents an in-depth summary of the research that has been conducted to date in the field of MOF-based nanoplatforms for cancer therapeutics.

Pulmonary Delivery of Recombinant Human Bleomycin Hydrolase Using Mannose-Modified Hierarchically Porous UiO-66 for Preventing Bleomycin-Induced Pulmonary Fibrosis

Bleomycins (BLMs) are widely used in clinics as antitumor agents. However, BLM-based chemotherapies often accompany severe pulmonary fibrosis (PF). Human bleomycin hydrolase is a cysteine protease that can convert BLMs into inactive deamido-BLMs. In this study, mannose-modified hierarchically porous UiO-66 (MHP-UiO-66) nanoparticles (NPs) were used to encapsulate the recombinant human bleomycin hydrolase (rhBLMH). When rhBLMH@MHP-UiO-66 was intratracheally instilled into the lungs, the NPs were transported into the epithelial cells, and rhBLMH prevented the lungs from PF during BLM-based chemotherapies. Encapsulation of rhBLMH in the MHP-UiO-66 NPs protects the enzyme from proteolysis in physiological conditions and enhances cellular uptake. In addition, the MHP-UiO-66 NPs significantly enhance the pulmonary accumulation of intratracheally instilled rhBLMH, thus providing more efficient protection of the lungs against BLMs during the chemotherapies.

Spatially confined protein assembly in hierarchical mesoporous metal-organic framework

Immobilization of biomolecules into porous materials could lead to significantly enhanced performance in terms of stability towards harsh reaction conditions and easier separation for their reuse. Metal-Organic Frameworks (MOFs), offering unique structural features, have emerged as a promising platform for immobilizing large biomolecules. Although many indirect methods have been used to investigate the immobilized biomolecules for diverse applications, understanding their spatial arrangement in the pores of MOFs is still preliminary due to the difficulties in directly monitoring their conformations. To gain insights into the spatial arrangement of biomolecules within the nanopores. We used in situ small-angle neutron scattering (SANS) to probe deuterated green fluorescent protein (d-GFP) entrapped in a mesoporous MOF. Our work revealed that GFP molecules are spatially arranged in adjacent nanosized cavities of MOF-919 to form "assembly" through adsorbate-adsorbate interactions across pore apertures. Our findings, therefore, lay a crucial foundation for the identification of proteins structural basics under confinement environment of MOFs.

Enzyme-Linked Metal Organic Frameworks for Biocatalytic Degradation of Antibiotics

Metal organic frameworks (MOFs) are multi-dimensional network of crystalline material held together by bonding of metal atoms and organic ligands. Owing to unique structural, chemical, and physical properties, MOFs has been used for enzyme immobilization to be employed in different catalytic process, including catalytic degradation of antibiotics. Immobilization process other than providing large surface provides enzyme with enhanced stability, catalytic activity, reusability, and selectivity. There are various approaches of enzyme immobilization over MOFs including physical adsorption, chemical bonding, diffusion and in situ encapsulation. In situ encapsulation is one the best approach that provides extra stability from unfolding and denaturation in harsh industrial conditions. Presence of antibiotic in environment is highly damaging for human in particular and ecosystem in general. Different methods such as ozonation, oxidation, chlorination and catalysis are available for degradation or removal of antibiotics from environment, however these are associated with several issues. Contrary to these, enzyme immobilized MOFs are novel system to be used in catalytic degradation of antibiotics. Enzyme@MOFs are more stable, reusable and more efficient owing to additional support of MOFs to natural enzymes in well-established process of photocatalysis for degradation of antibiotics aimed at environmental remediation. Prime focus of this review is to present catalytic degradation of antibiotics by enzyme@MOFs while outlining their synthetics approaches, characterization, and mechanism of degradation. Furthermore, this review highlights the significance of enzyme@MOFs system for antibiotics degradation in particular and environmental remediation in general. Current challenges and future perspective of research in this field are also outlined along with concluding comments.

Graphical Abstract

A comprehensive review on bio-mimicked multimolecular frameworks and supramolecules as scaffolds for enzyme immobilization

Immobilization depicts a propitious route to optimize the catalytic performances, efficient recovery, minimizing autocatalysis, and also augment the stabilities of enzymes, particularly in unnatural environments. In this opinion, supramolecules and multimolecular frameworks have captivated immense attention to achieve profound controllable interactions between enzyme molecules and well-defined natural or synthetic architectures to yield protein bioconjugates with high accessibility for substrate binding and enhanced enantioselectivities. This scholastic review emphasizes the possibilities of associating multimolecular complexes with biological entities via several types of interactions, namely covalent interactions, host-guest complexation, π - π ${\rm{\pi }}-{\rm{\pi }}$ interactions, intra/inter hydrogen bondings, electrostatic interactions, and so forth offers remarkable applications for the modulations of enzymes. The potential synergies between artificial supramolecular structures and biological systems are the primary concern of this pedagogical review. The majority of the research primarily focused on the dynamic biomolecule-responsive supramolecular assemblages and multimolecular architectures as ideal platforms for the recognition and modulation of proteins and cells. Embracing sustainable green demeanors of enzyme immobilizations in a quest to reinforce site-selectivity, catalytic efficiency, and structural integrality of enzymes are the contemporary requirements of the biotechnological sectors that instigate the development of novel biocatalytic systems.

Biodiesel Production from Transesterification with Lipase from Pseudomonas cepacia Immobilized on Modified Structured Metal Organic Materials

This research presents the modification of MOF-199 and ZIF-8 using furfuryl alcohol (FA) as a carbon source to subsequently fix lipase from Pseudomonas cepacia and use these biocatalysts in the transesterification of African palm oil (APO). The need to overcome the disadvantages of free lipases in the biodiesel production process led to the use of metal organic framework (MOF)-type supports because they provide greater thermal stability and separation of the catalytic phase, thus improving the activity and efficiency in relation to the use of free lipase, disadvantages that could not be overcome with the use of other types of catalysts used in transesterification/esterification reactions for the production of biodiesel. The modification of MOFs ZIF-8 and MOF-199 with FA increases the pore volume which allows better immobilization of Pseudomonas cepacia lipase (PCL). The results show that these biocatalysts undergo transesterification with biodiesel yields above 90%. Additionally, studies were carried out on the effect of (1) enzyme loading, 2) enzyme immobilization time, (3) enzyme immobilization temperature, and (4) pH on the % immobilization of the enzyme and the specific activity. The results show that the highest immobilization efficiency for the FA@ZIF-8 support has a value of 91.2% when the load of this support was 3.5 mg/mg and has a specific activity of 142.5 U/g protein. The FA@MOF-199 support presented 80.3% enzyme immobilization and 125% U/g specific activity protein. We established that the specific activity increases in the period from 0.5 to 5.0 h for the systems under investigation. After this time, both the specific activity and the % efficiency of enzyme immobilization decrease. Therefore, 5.0 h (immobilization efficiency of 95 and 85% for FA@MOF-199, respectively) was chosen as the most appropriate time for PCL immobilization. Methods of adding methanol, with three and four steps, were tested, where biodiesel yields greater than 90% were obtained for the biocatalysts synthesized in this work (FA@ZIF-8-PCL and FA@MOF-199-PCL) and above 70% for free PCL, and the maximum yield was reached at a molar ratio between methanol and APO of 4:1 when using the one-step method under the same reaction conditions (as mentioned above). Only the results of FA@ZIF-8-PCL are presented here; however, it should be noted that the results for biocatalyst FA@MOF-199-PCL and lipase-free PCL presented the same behavior. The order of biocatalyst performance was FA@ZIF-8-PCL > FA@MOF-199-PCL > PCL-Free, which demonstrates that the use of FA as a modifier is a novel aspect in the conversion of palm oil into biodiesel components.

Small Peptides in the Detection of Mycotoxins and Their Potential Applications in Mycotoxin Removal

Mycotoxins pose significant risks to humans and livestock. In addition, contaminated food- and feedstuffs can only be discarded, leading to increased economic losses and potential ecological pollution. Mycotoxin removal and real-time toxin level monitoring are effective approaches to solve this problem. As a hot research hotspot, small peptides derived from phage display peptide libraries, combinatorial peptide libraries, and rational design approaches can act as coating antigens, competitive antigens, and anti-immune complexes in immunoassays for the detection of mycotoxins. Furthermore, as a potential approach to mycotoxin degradation, small peptides can mimic the natural enzyme catalytic site to construct artificial enzymes containing oxidoreductases, hydrolase, and lyase activities. In summary, with the advantages of mature synthesis protocols, diverse structures, and excellent biocompatibility, also sharing their chemical structure with natural proteins, small peptides are widely used for mycotoxin detection and artificial enzyme construction, which have promising applications in mycotoxin degradation. This paper mainly reviews the advances of small peptides in the detection of mycotoxins, the construction of peptide-based artificial enzymes, and their potential applications in mycotoxin control.

Towards Solving the PFAS Problem: The Potential Role of Metal-Organic Frameworks

Per- and polyfluoroalkyl substances (PFAS) are a group of recalcitrant molecules that have been used since the 1940s in a variety of applications. They are now linked to a host of negative health outcomes and are extremely resistant to degradation under environmental conditions. Currently, membrane technologies or adsorbents are used to remediate contaminated water. These techniques are either inefficient at capturing smaller PFAS molecules, have high energy demands, or result in concentrated waste that must be incinerated at high temperatures. This Review focuses on what role metal-organic frameworks (MOFs) may play in addressing the PFAS problem. Specifically, how the unique properties of MOFs such as their well-defined pore sizes, ultra-high internal surface area, and tunable surface chemistry may be a sustainable solution for PFAS contamination.

Boosting Protein Encapsulation through Lewis-Acid-Mediated Metal-Organic Framework Mineralization: Toward Effective Intracellular Delivery

Encapsulation of biomolecules using metal-organic frameworks (MOFs) to form stable biocomposites has been demonstrated to be a valuable strategy for their preservation and controlled release, which has been however restricted to specific electrostatic surface conditions. We present a Lewis-acid-mediated general in situ strategy that promotes the spontaneous MOF growth on a broad variety of proteins, for the first time, regardless of their surface nature. We demonstrate that MOFs based on cations exhibiting considerable inherent acidity such as MIL-100(Fe) enable efficient biomolecule encapsulation, including elusive alkaline proteins previously inaccessible by the well-developed in situ azolate-based MOF encapsulation. Specifically, we prove the MIL-100(Fe) scaffold for the encapsulation of a group of proteins exhibiting very different isoelectric points (5 < pI < 11), allowing triggered release under biocompatible conditions and retaining their activity after exposure to denaturing environments. Finally, we demonstrate the potential of the myoglobin-carrying biocomposite to facilitate the delivery of O₂ into hypoxic human lung carcinoma A549 cells, overcoming hypoxia-associated chemoresistance.

Applications of metal-organic framework-based bioelectrodes

Metal-organic frameworks (MOFs) are an emerging class of porous nanomaterials that have opened new research possibilities. The inherent characteristics of MOFs such as their large surface area, high porosity, tunable pore size, stability, facile synthetic strategies and catalytic nature have made them promising materials for enormous number of applications, including fuel storage, energy conversion, separation, and gas purification. Recently, their high potential as ideal platforms for biomolecule immobilization has been discovered. MOF-enzyme-based materials have attracted the attention of researchers from all fields with the expansion of MOFs development, paving way for the fabrication of bioelectrochemical devices with unique characteristics. MOFs-based bioelectrodes have steadily gained interest, wherein MOFs can be utilized for improved biomolecule immobilization, electrolyte membranes, fuel storage, biocatalysis and biosensing. Likewise, applications of MOFs in point-of-care diagnostics, including self-powered biosensors, are exponentially increasing. This paper reviews the current trends in the fabrication of MOFs-based bioelectrodes with emphasis on their applications in biosensors and biofuel cells.

Two-Dimensional Metal-Organic Framework-Based Cellular Scaffolds with High Protein Adsorption, Retention, and Replenishment Capabilities

Metal-organic frameworks (MOFs) are porous materials with adsorption, storage, and separation capabilities due to their high specific surface areas and large pore volumes. MOFs are thus used in biomedical applications, and MOF nanoparticles have been widely studied as nanocarriers for drug delivery systems. Several research groups recently reported that specific MOF nanoparticles can adsorb and retain proteins, suggesting to us that MOF nanoparticles may have advantages as novel cell culture scaffolds. However, MOF nanoparticles cannot be used as two-dimensional scaffolds for cells. We therefore established a bottom-up technique to construct two-dimensional MOFs [MIL-53 (Al)] on polymer films. The developed two-dimensional MIL-53 (Al) film [fMIL-53 (Al)] exhibited high serum protein adsorption, retention, and replenishment capabilities as compared to conventional cell culture scaffolds. β-Galactosidase, used as a model protein, adsorbed on fMIL-53 (Al) exhibited original enzymatic activity, indicating that proteins are not denatured during the adsorption process. The viability of mouse myoblast cells (C2C12) cultured on fMIL-53 (Al) was 100%, indicating the cell compatibility of fMIL-53 (Al). Importantly, C2C12 cells cultured on serum protein-preadsorbed fMIL-53 (Al) exhibited excellent long-term adhesion, morphology, and proliferation even in a medium lacking serum proteins, demonstrating an important advantage of fMIL-53 (Al) as a cell culture scaffold, given that conventional cell culture scaffolds typically require a serum-containing medium to support stable cell adhesion and proliferation. To our knowledge, this is the first report regarding the application of MOFs as cell culture scaffolds and will serve as a starting point for studying two- and three-dimensional MOF-based cellular scaffolds for cell culture systems and for in vitro and in vivo tissue engineering.

Confining enzymes in porous organic frameworks: from synthetic strategy and characterization to healthcare applications

Enzymes are a class of natural catalysts with high efficiency, specificity, and selectivity unmatched by their synthetic counterparts and dictate a myriad of reactions that constitute various cascades in living cells. The development of suitable supports is significant for the immobilization of structurally flexible enzymes, enabling biomimetic transformation in the extracellular environment. Accordingly, porous organic frameworks, including metal organic frameworks (MOFs), covalent organic frameworks (COFs) and hydrogen-bonded organic frameworks (HOFs), have emerged as ideal supports for the immobilization of enzymes because of their structural features including ultrahigh surface area, tailorable porosity, and versatile framework compositions. Specially, organic framework-encased enzymes have shown significant enhancement in stability and reusability, and their tailorable pore opening provides a gatekeeper-like effect for guest sieving, which is beneficial for mimicking intracellular biocatalysis processes. This immobilization technique brings new insight into the development of next-generation enzyme materials and shows huge potential in healthcare applications, such as biomarker diagnosis, biostorage, and cancer and antibacterial therapies. In this review, we describe the state-of-the-art strategies for the structural immobilization of enzymes using the well-explored MOFs and burgeoning COFs and HOFs as scaffolds, with special emphasis on how these porous framework-confined technologies can provide a favorable microenvironment for mimicking natural biocatalysis. Subsequently, advanced characterization techniques for enzyme conformation, the effect of the confined microenvironment on the activity of enzymes, and the emerging healthcare applications will be surveyed.

Selective detection of sulfasalazine antibiotic and its controllable photodegradation into 5-aminosalicylic acid by visible-light-responsive metal-organic framework

The extensive use of sulfasalazine (SSZ) antibiotics has brought potential threats to aquatic ecosystems and human health. Thus, necessary measures for the removal of SSZ must be taken to prevent arbitrary antibiotic exposure to the aquatic environment. However, not all the recent photocatalysts that have been used for the degradation of SSZ could not achieve the controlled release of SSZ and hence are losing their medicinal values. Herein, by utilizing an Eosin Y moiety as an efficient light-harvesting and emission site, an Eosin Y-based visible-light-responsive metal-organic framework has been synthesized and characterized, which exhibits high selectivity for detecting the antibiotic SSZ in water and simulated physiological conditions, with a detection limit of below 1 μM (0.4 μg mL^-1). It also represents the first example of a MOF-based photocatalyst for the controllable degradation of SSZ into 5-aminosalicylic acid with excellent catalytic activity and recyclability.

The Chemistry and Applications of Metal-Organic Frameworks (MOFs) as Industrial Enzyme Immobilization Systems

Enzymatic biocatalysis is a sustainable technology. Enzymes are versatile and highly efficient biocatalysts, and have been widely employed due to their biodegradable nature. However, because the three-dimensional structure of these enzymes is predominantly maintained by weaker non-covalent interactions, external conditions, such as temperature and pH variations, as well as the presence of chemical compounds, can modify or even neutralize their biological activity. The enablement of this category of processes is the result of the several advances in the areas of molecular biology and biotechnology achieved over the past two decades. In this scenario, metal–organic frameworks (MOFs) are highlighted as efficient supports for enzyme immobilization. They can be used to ‘house’ a specific enzyme, providing it with protection from environmental influences. This review discusses MOFs as structures; emphasizes their synthesis strategies, properties, and applications; explores the existing methods of using immobilization processes of various enzymes; and lists their possible chemical modifications and combinations with other compounds to formulate the ideal supports for a given application.

Modulating the Activity of Enzyme in Metal-Organic Frameworks Using the Photothermal Effect of Ti3C2 Nanosheets

Enzymes are versatile catalysts with high potential in various applications, and much attention has been paid to the stability improvement of native enzymes and activity modulation. Encapsulation in metal-organic frameworks (MOFs) as an efficient strategy for protecting fragile native enzymes while modulating the activity of enzymes remotely, which is practically demanded, has rarely been explored in MOF-encapsulated enzymes. Herein, Ti₃C₂ nanosheets exhibiting photothermal effect and biocompatibility were encapsulated in Cyt c-embedded ZIF-8 to tailor the enzymatic activity remotely by near-infrared (NIR) irradiation for the first time. By exposure to NIR light, the temperature of an aqueous solution containing Ti₃C₂/Cyt c@ZIF-8 increases obviously (up to 15 °C), while that of Cyt c@ZIF-8 shows no change. The enzymatic activity in the composites with a certain amount of nanosheets increases, which is attributed to the created defect and transformed microenvironment caused by the introduction of nanosheets. Importantly, the enzymatic activity in ZIF-8 can be further enhanced up to 150% under NIR light irradiation, and this enhancement can be modulated flexibly by varying laser power density. Our investigations indicate that Ti₃C₂ nanosheets are promising candidates for modulating the activity of encapsulated enzymes remotely.

Advances in Nano-Sized Metal-Organic Frameworks and Biomedical Applications: A Review

Metal-organic frameworks (MOFs) have attracted much attention since their discovery and have potential applications in many fields, including gas storage, separation, catalysis, and thermal energy conversion, due to their unique high porosity structure, tunable pore size, and functionalizability. Nano-sized MOFs (NMOFs) possessed both the properties of conventional bulk MOFs and additional physical/chemical properties because of their nanometer size, and thus can exhibit even better performance than related conventional bulk MOFs. In this paper, we introduced the development of NMOFs and presented several classical NMOFs structures and their applications. It also focused on the preparation methods and applications of some important NMOFs in recent years, and provided an outlook on the applications of NMOFs in novel material fields and their development perspective.

Molecularly Imprinted Polymers with Enzymatic Properties Reduce Cytokine Release Syndrome

A core-shell molecularly imprinted polymer nanoparticle with biological enzyme functional characteristics was developed by oxidative polymerization of template protein and polydopamine on the surface of protease-copper phosphate hybrid nanoflowers by molecular imprinting technology and enzyme immobilization technology. The obtained molecularly imprinted polymer showed specific binding characteristics with the template protein. It recognized and enriched the target molecules through the surface molecularly imprinted sites of the shell structure. In addition, the bound target molecules were further degraded into fragments by nanozymes with biological enzyme characteristics in the core. In this study, molecular imprinting technology and biotechnology were combined to obtain bifunctional molecularly imprinted polymer nanoparticles that can not only enrich template molecules but also degrade them into fragments. Herein, we selected interleukin 6 (IL-6), the target molecule of cytokine release syndrome (CRS), as a template molecule, and reported a molecularly imprinted polymer with degrading enzyme properties that can rapidly reduce IL-6 levels in vivo, including a molecularly imprinted layer that can recognize and bind IL-6 and nanozymes that can degrade IL-6 and deactivate it. It is used to clear the excessive secretion of IL-6 in CRS and reduce the level of IL-6 in the body to achieve the purpose of adjuvant treatment of CRS.

Disposable biosensor based on novel ternary Ru-PEI@PCN-333(Al) self-enhanced electrochemiluminescence system for on-site determination of caspase-3 activity

The number of death due to cancer-related diseases each year is at the alarming level and is constantly growing. Tools that can effectively and conveniently detect cancer cell apoptosis can play a significant role in cancer research, cancer therapy, and other related industries. Herein, we fabricated, for the first time, an ultrasensitive, disposable, self-enhanced off-on electrochemiluminescence (ECL) biosensor based on ternary Ru-PEI@PCN-333(Al) system to determine caspase-3 activity, the biomarker of apoptosis. The biosensor had a low detection limit of 0.017 pg/mL and was able to enhance the ECL emission and stability. A solid-state (SS) ECL strategy was adopted to overcome the relatively weak ECL emission due to the long distance between electrochemiluminophore and electrode surface. The analysis requires only one incubation step, which can significantly reduce the operational complexity and time. The biosensor had higher sensitivity, and the off-on ECL mode was achieved using caspase-3 as a switch. The on-site and rapid detection capability of the biosensor was achieved by the introduction of disposable screen-printed electrodes (SPEs). This study lays a foundation for the development of more advanced, ingenious, portable and reliable ECL devices for biosensing not only caspase-3, but also other bioanalytes.

Polyoxometalate-Based Metal-Organic Frameworks as the Solid Support to Immobilize MP-11 Enzyme for Enhancing Thermal and Recyclable Stability

The immobilization of enzymes has received much attention. Metal-organic framework (MOF) as the adsorbent for enzyme encapsulation provides an effective strategy. However, the encapsulation efficacy is not dependent solely on the specific surface area. Though leading into appropriate substrate with negative charge would enhance the encapsulation efficacy. Polyoxometalates (POMs) as the electron sponge would donate electrons without any structural change. In this study, Keggin-type phosphotungstic acid (PW₁₂) was encapsulated in Zirconium metal-organic framework (PW₁₂@UiO-67) as a heterogeneous adsorbent for the encapsulation of enzyme. Our following data proved that this composite cluster could enhance the adsorption of enzyme and the stability of MP-11 was then significantly improved after immobilization.

A Comprehensive Review on the Use of Metal–Organic Frameworks (MOFs) Coupled with Enzymes as Biosensors

Several studies have shown the development of electrochemical biosensors based on enzymes immobilized in metal–organic frameworks (MOFs). Although enzymes have unique properties, such as efficiency, selectivity, and environmental sustainability, when immobilized, these properties are improved, presenting significant potential for several biotechnological applications. Using MOFs as matrices for enzyme immobilization has been considered a promising strategy due to their many advantages compared to other supporting materials, such as larger surface areas, higher porosity rates, and better stability. Biosensors are analytical tools that use a bioactive element and a transducer for the detection/quantification of biochemical substances in the most varied applications and areas, in particular, food, agriculture, pharmaceutical, and medical. This review will present novel insights on the construction of biosensors with materials based on MOFs. Herein, we have been highlighted the use of MOF for biosensing for biomedical, food safety, and environmental monitoring areas. Additionally, different methods by which immobilizations are performed in MOFs and their main advantages and disadvantages are presented.