Metal–Organic Framework-Based Enzyme Biocomposites

An ultrasensitive electrochemical aptasensor based on zeolitic imidazolate framework-67 loading gold nanoparticles and horseradish peroxidase for detection of aflatoxin B1

Aflatoxin B1 (AFB1) is one of the most toxic mycotoxins and poses a high risk to human health. Highly sensitive and rapid detection is one of the most effective preventive measures to avoid potential hazards. Herein, an electrochemical aptasensor based on DNA nanotetrahedron and zeolitic imidazolate framework-67 loading gold nanoparticles, horseradish peroxidase, and aptamers was designed for the ultrasensitive detection of AFB1. The high specific surface area and large pore volume of zeolitic imidazolate framework-67 can increase the loading capacity and further improve the detection sensitivity of electrochemical aptasensors. DNA nanotetrahedron can enhance the capture ability of AFB1 with steady immobilization. The developed aptasensor showed good analytical performance for AFB1 detection, with a detection limit of 3.9 pg mL-1 and a wide linear range of 0.01-100 ng mL-1. The aptasensor detected AFB1 in corn samples with recovery rates ranging from 94.19%-105.77% and has potential for use in food safety monitoring.

A novel PEG-mediated approach to entrap hemoglobin (Hb) within ZIF-8 nanoparticles: Balancing crystalline structure, Hb content and functionality

Hemoglobin (Hb)-based oxygen carriers are investigated as a potential alternative or supplement to regular blood transfusions, particularly in critical and life-threatening scenarios. These include situations like severe trauma in remote areas, battlefield conditions, instances where blood transfusion is not feasible due to compatibility concerns, or when patients decline transfusions based on religious beliefs. This study introduces a novel method utilizing poly(ethylene glycol) (PEG) to entrap Hb within ZIF-8 nanoparticles (i.e., Hb@ZIF-8 NPs). Through meticulous screening, we achieved Hb@ZIF-8 NPs with a record-high Hb concentration of 34 mg mL-1. These NPs, sized at 168 nm, displayed exceptional properties: a remarkable 95 % oxyhemoglobin content, excellent encapsulation efficiency of 85 %, and resistance to Hb oxidation into methemoglobin (metHb). The addition of PEG emerged as a crucial factor amplifying Hb entrapment within ZIF-8, especially at higher Hb concentrations, reaching an unprecedented 34 mg mL-1. Importantly, PEG exhibited a protective effect, preventing metHb conversion in Hb@ZIF-8 NPs at elevated Hb concentrations.

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.

Co-immobilization of a bi-enzymatic cascade into hierarchically porous MIL-53 for efficient 6'-sialyllactose production

6'-Sialyllactose (6'-SL), the most abundant sialylated human milk oligosaccharide, has attracted attention for its potential application in supplementary infant formulas. Herein, we report a facile strategy to construct a cascade bioreactor for the enzymatic synthesis of 6'-SL by co-immobilizing an enzymatic module consisting of CMP-sialic acid synthase and α-2,6-sialyltransferase into hierarchically porous MIL-53 (HP-MIL-53). The as-prepared HP-MIL-53 showed high enzyme immobilization capacity, reaching 226 mg g-1. Furthermore, the co-immobilized enzymes exhibited higher initial catalytic efficiency, and thermal, pH and storage stability than the free ones. Finally, the 6'-SL yield remained >80% after 13 cycles of use. We expect that HP-MIL-53 would have potential industrial applications in the enzymatic modular synthesis of 6'-SL and other glycans.

Bionanocomposites comprising mesoporous metal organic framework (ZIF-8) phytofabricated with Allium sativum as alternative nanomaterials to combat antimicrobial drug resistance

Green nanotechnology is one of the most expanding fields that provides numerous novel nanoparticle drug formulations with enhanced bioactivity performance. This study aims to synthesize mesoporous metal organic framework (ZIF-8) phytofabricated with the herb Allium sativum (As) as an indicator system for its antibacterial and antifungal impact. The successful synthesis of ZIF-8 as nanocomposite was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and scanning coupled with energy-dispersive X-ray spectroscopy and transmission electron microscopy (SEM-EDX and TEM) that showed the textural retainment of ZIF-8 on composite formation with A. sativum. The nanocomposite, A. sativum extract, and ZIF-8 were subjected to antimicrobial assays against Shigella flexneri, Candida albicans, and Candida parapsilosis. The comparative results indicated the potential action of nanocomposite against the bacteria and both the Candida sps; however, the antifungal action against the Candida sps was more effective than the bacterium S. flexneri. The findings suggest that plants, being an important component of ecosystems, could be further explored for the novel drug discovery using green nanotechnology to enhance their impact on the drug-resistant pathogens.

Raspberry-shaped ZIF-8/Au nanozymes with excellent peroxidase-like activity for simple and visual detection of glutathione

Artificial enzymes with high stability, adjustable catalytic activity, controllable preparation, and good reproducibility have been widely studied. Noble metal nanozymes, particularly gold nanoparticles (Au NPs), exhibit good catalytic activity, but their stability is poor. In this study, zeolitic imidazolate framework-8 (ZIF-8) was used as a carrier for Au NPs, thus improving the utilization efficiency and conservation stability of the nanozymes. A ZIF-8/Au nanocomposite with peroxidase activity and a raspberry-shaped structure was synthesized. In the assay, ZIF-8/Au catalyzed the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to a blue product oxidized TMB (oxTMB). Glutathione (GSH) selectively inhibited this reaction, with a detection limit of 0.28 µM and linear range of 0.5-60 µM. Using the photo and chromaticity analysis functions, we developed a portable analysis method using a smartphone equipped with a camera module as a detection terminal for a wide range of rapid screening techniques for GSH. Preparation of raspberry-shaped ZIF-8/Au improved the catalytic activity of Au NPs and good results were demonstrated in serum, which suggests their promising application under physiological conditions.

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

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

Advances in Functionalized Biocomposites of Living Cells Combined with Metal-Organic Frameworks

Motivated by the remarkable innate characteristics of cells in living organisms, we have found that hybrid materials that combine bioorganisms with nanomaterials have significantly propelled advancements in industrial applications. However, the practical deployment of unmodified living entities is inherently limited due to their sensitivity to environmental fluctuations. To surmount these challenges, an efficacious strategy for the biomimetic mineralization of living organisms with nanomaterials has emerged, demonstrating extraordinary potential in biotechnology. Among them, innovative composites have been engineered by enveloping bioorganisms with a metal-organic framework (MOF) coating. This review systematically summarizes the latest developments in living cells/MOF-based composites, detailing the methodologies employed in structure fabrication and their diverse applications, such as bioentity preservation, sensing, catalysis, photoluminescence, and drug delivery. Moreover, the synergistic benefits arising from the individual compounds are elucidated. This review aspires to illuminate new prospects for fabricating living cells/MOF composites and concludes with a perspective on the prevailing challenges and impending opportunities for future research in this field.

Enhancing Substrate Channeling with Multi-Enzyme Architectures in Hydrogen-Bonded Organic Frameworks

Hydrogen-bonded organic frameworks (HOF) represent an emerging category of organic structures with high crystallinity and metal-free, which are not commonly observed in alternative porous organic frameworks. These needle-like porous structure can help in stabilizing enzymes and allow transfer of molecules between enzymes participating in cascade reactions for enhanced substrate channelling. Herein, we systematically synthesized and investigated the stability of HOF at extreme conditions followed by one-pot encapsulation of single and bi-enzyme systems. Firstly, we observed HOF to be stable at pH 1 to 14 and at high temperatures (up to 115 °C). Secondly, the encapsulated glucose oxidase enzyme (GOX) showed 80 % and 90 % of its original activity at 70 °C and pH 11, respectively. Thirdly, transient time close to 0 seconds was observed for HOF encapsulated bi-enzyme cascade reaction system demonstrating a 4.25-fold improvement in catalytic activity when compared to free enzymes with enhanced substrate channelling. Our findings showcase a facile system synthesized under ambient conditions to encapsulate and stabilize enzymes at extreme conditions.

Heterogeneous CuxO Nano-Skeletons from Waste Electronics for Enhanced Glucose Detection

Electronic waste (e-waste) and diabetes are global challenges to modern societies. However, solving these two challenges together has been challenging until now. Herein, we propose a laser-induced transfer method to fabricate portable glucose sensors by recycling copper from e-waste. We bring up a laser-induced full-automatic fabrication method for synthesizing continuous heterogeneous CuxO (h-CuxO) nano-skeletons electrode for glucose sensing, offering rapid (< 1 min), clean, air-compatible, and continuous fabrication, applicable to a wide range of Cu-containing substrates. Leveraging this approach, h-CuxO nano-skeletons, with an inner core predominantly composed of Cu2O with lower oxygen content, juxtaposed with an outer layer rich in amorphous CuxO (a-CuxO) with higher oxygen content, are derived from discarded printed circuit boards. When employed in glucose detection, the h-CuxO nano-skeletons undergo a structural evolution process, transitioning into rigid Cu2O@CuO nano-skeletons prompted by electrochemical activation. This transformation yields exceptional glucose-sensing performance (sensitivity: 9.893 mA mM-1 cm-2; detection limit: 0.34 μM), outperforming most previously reported glucose sensors. Density functional theory analysis elucidates that the heterogeneous structure facilitates gluconolactone desorption. This glucose detection device has also been downsized to optimize its scalability and portability for convenient integration into people's everyday lives.

HP35 Protein in the Mesopore of MIL-101(Cr) MOF: A Model to Study Cotranslocational Unfolding

The immobilization of enzymes in metal-organic framework (MOF) cages is important in biotechnology. In this context, the mechanism of translocation of proteins through the cavities of the MOF and the roles played by confinement and MOF chemistry in giving rise to stable protein intermediates that are otherwise transiently populated in the physiological environment are important questions to be addressed. These unexplored aspects are examined with villin headpiece (HP35) as a model protein confined within a mesopore of MIL-101(Cr) using molecular dynamics simulations. At equilibrium, the protein is located farther from the center of the cavity and closer to the MOF surface. Molecular interactions with the MOF partially unfold helix-1 at its N-terminus. Umbrella sampling simulations inform the range of conformations that HP35 undertakes during translocation from one cavity to another and associated changes in free energy. Relative to its equilibrium state within the cavity, the free energy barrier for the unfolded protein at the cage window is estimated to be 16 kcal/mol. This study of MOF-based protein conformation can also be a general approach to observing intermediates in folding-unfolding pathways.

Multivariate Silicification-Assisted Single Enzyme Structure Augmentation for Improved Enzymatic Activity-Stability Trade-Off

The ability to finely tune/balance the structure and rigidity of enzymes to realize both high enzymatic activity and long-term stability is highly desired but highly challenging. Herein, we propose the concept of the "silicazyme", where solid inorganic silica undergoes controlled hybridization with the fragile enzyme under moderate conditions at the single-enzyme level, thus enabling simultaneous structure augmentation, long-term stability, and high enzymatic activity preservation. A multivariate silicification approach was utilized and occurred around individual enzymes to allow conformal coating. To realize a high activity-stability trade-off the structure flexibility/rigidity of the silicazyme was optimized by a component adjustment ternary (CAT) plot method. Moreover, the multivariate organosilica frameworks bring great advantages, including surface microenvironment adjustability, reversible modification capability, and functional extensibility through the rich chemistry of silica. Overall silicazymes represent a new class of enzymes with promise for catalysis, separations, and nanomedicine.

In Situ Measurement of Urea Concentration With an In-Fiber SPR-MZI Sensor

A fiber-optic urea sensor based on surface plasmon resonance (SPR) and Mach-Zehnder interference (MZI) combined principle was designed and implemented. By plating gold film on the single-mode-no-core-thin-core-single-mode fiber structure, we successfully excited both SPR and MZI, and constructed two parallel detection channels for simultaneously measurement of urea concentration and temperature. Urease was immobilized on the gold film by metal-organic zeolite skeleton (ZIF-8), which can not only fix a large number of urease to improve measurement sensitivity of urea, but also protect urease activity to ensure the sensor stability. Experimental results indicate that the designed urea sensor with temperature compensation function can detect urea solution with concentration of 1-9 mM, and the sensitivity is 1.4 nm/mM. The proposed measurement method provides a new choice for monitoring urea concentration in the field of medical diagnosis and human health monitoring.

Exploring Enzyme-Mimicking Metal-Organic Frameworks for CO2 Conversion through Vibrational Spectra-Based Machine Learning

In pursuing the benefits of natural enzyme catalysts while overcoming their limitations, we find metal-organic frameworks (MOFs), renowned for their highly tunable functionalities, stand out in biomimetic applications. We used unsupervised machine learning on density functional theory-computed vibrational infrared and Raman spectral features to screen 300 Zn-MOFs for CO2 conversion, similar to carbonic anhydrase (CA). Our findings confirmed that MOFs with spectroscopic attributes closely resembling those of CA hold the potential for replicating CA's electronic and catalytic properties. Unlike previous studies that relied on heuristic or trial-and-error methods and focused on geometric configurations, our research uses vibrational spectral features to explore structure-property relationships, making them more accessible through spectroscopy. Moreover, we highlight vibrational spectral features as efficient carriers for highly dimensional chemical information, enabling the simultaneous optimization of multiple performance parameters. These findings pave the way for pioneering designs of enzyme-mimetic MOFs and concurrently expand the application scope of spectroscopic tools in biomimetic catalysis.

Multifunctional nano-in-micro delivery systems for targeted therapy in fundus neovascularization diseases

Fundus neovascularization diseases are a series of blinding eye diseases that seriously impair vision worldwide. Currently, the means of treating these diseases in clinical practice are continuously evolving and have rapidly revolutionized treatment opinions. However, key issues such as inadequate treatment effectiveness, high rates of recurrence, and poor patient compliance still need to be urgently addressed. Multifunctional nanomedicine can specifically respond to both endogenous and exogenous microenvironments, effectively deliver drugs to specific targets and participate in activities such as biological imaging and the detection of small molecules. Nano-in-micro (NIM) delivery systems such as metal, metal oxide and up-conversion nanoparticles (NPs), quantum dots, and carbon materials, have shown certain advantages in overcoming the presence of physiological barriers within the eyeball and are widely used in the treatment of ophthalmic diseases. Few studies, however, have evaluated the efficacy of NIM delivery systems in treating fundus neovascular diseases (FNDs). The present study describes the main clinical treatment strategies and the adverse events associated with the treatment of FNDs with NIM delivery systems and summarizes the anatomical obstacles that must be overcome. In this review, we wish to highlight the principle of intraocular microenvironment normalization, aiming to provide a more rational approach for designing new NIM delivery systems to treat specific FNDs.

Co-Immobilization of ADH and GDH on Metal-Organic-Framework: An Effective Biocatalyst for Asymmetric Reduction of Ketones

Chiral alcohols are not only important building blocks of various bioactive natural compounds and pharmaceuticals, but can serve as synthetic precursors for other valuable organic chemicals, thus the synthesis of these products is of great importance. Bio-catalysis represents one effective way to obtain these molecules, however, the weak stability and high cost of enzymes often hinder its broad application. In this work, we designed a biological nanoreactor by embedding alcohol dehydrogenase (ADH) and glucose dehydrogenase (GDH) in metal-organic-framework ZIF-8. The biocatalyst ADH&GDH@ZIF-8 could be applied to the asymmetric reduction of a series of ketones to give chiral alcohols in high yields (up to 99 %) and with excellent enantioselectivities (>99 %). In addition, the heterogeneous biocatalyst could be recycled and reused at least four times with slight activity decline. Moreover, E. coli containing ADH and GDH was immobilized by ZIF-8 to form biocatalyst E. coli@ZIF-8, which also exhibits good catalytic behaviours. Finally, the chiral alcohols are further converted to marketed drugs (R)-Fendiline, (S)-Rivastigmine and NPS R-568 respectively.

Artificial cellulosic leaf with adjustable enzymatic CO2 sequestration capability

Developing artificial leaves to address the environmental burden of CO2 is pivotal for advancing our Net Zero Future. In this study, we introduce EcoLeaf, an artificial leaf that closely mimics the characteristics of natural leaves. It harnesses visible light as its sole energy source and orchestrates the controlled expansion and contraction of stomata and the exchange of petiole materials to govern the rate of CO2 sequestration from the atmosphere. Furthermore, EcoLeaf has a cellulose composition and mechanical strength similar to those of natural leaves, allowing it to seamlessly integrate into the ecosystem during use and participate in natural degradation and nutrient cycling processes at the end of its life. We propose that the carbon sequestration pathway within EcoLeaf is adaptable and can serve as a versatile biomimetic platform for diverse biogenic carbon sequestration pathways in the future.

Selective Removal of Denatured Proteins Using MOF Nanopores

Here we present, for the first time, the selective adsorption of denatured proteins using a metal-organic framework (MOF), demonstrating promising potential for protein purification. Typical proteins, such as lysozyme and carbonic anhydrase B, enter the pores of MIL-101 through their narrow apertures when they are denatured to an unfolded state. Selective adsorption is achieved by finely tuning two key features: the sizes of the aperture and cage of the MOF nanopores, which are responsible for sorting unfolded polypeptide chains and inhibiting the translocation of the native form into the pores, respectively. By leveraging this selective adsorption, we successfully purified a mixture of native and denatured proteins by adding MOF to the mixture, achieving a native purity of over 99%.

Enhancing Chymotrypsin Activity and Stability of Capillary Immobilized Enzyme Microreactors Using Zeolitic Imidazolate Frameworks as Encapsulation Materials

Open-tubular immobilized enzyme microreactors (OT-IMERs) are some of the most widely used enzyme reaction devices due to the advantages of simple preparation and fast sample processing. However, the traditional approaches for OT-IMERs preparation had some defects such as limited enzyme loading amount, susceptibility to complex sample interference, and less stability. Here, we report a strategy for the preparation of highly active and stable OT-IMERs, in which the single-stranded DNA-enzyme composites were immobilized in capillaries and then encapsulated in situ in the capillaries via zeolitic imidazolate frameworks (ZIF-L). The phosphate groups of the DNA adjusted the surface potential of the enzyme to negative values, which could attract cations, such as Zn2+, to promote the formation of ZIF-L for enzyme encapsulation. Using chymotrypsin (ChT) as a model enzyme, the prepared ChT@ZIF-L-IMER has higher activity and better affinity than the free enzyme and ChT-IMER. Moreover, the thermal stability, pH stability, and organic solvent stability of ChT@ZIF-L-IMER were much higher than those of free enzyme and ChT-IMER. Furthermore, the activity of ChT@ZIF-L-IMER was much higher than that of ChT-IMER after ten consecutive reactions. To demonstrate the versatility of this preparation method, we replaced ChT with glucose oxidase (GOx). The stability of GOx@ZIF-L-IMER was also experimentally demonstrated to be superior to that of GOx and GOx-IMER. Finally, ChT@ZIF-L-IMER was used for proteolytic digestion analysis. The results showed that ChT@ZIF-L-IMER had a short digestion time and high digestive efficiency compared with the free enzyme. The present study broadened the synthesis method of OT-IMERs, effectively integrating the advantages of metal-organic frameworks and IMER, and the prepared OT-IMERs significantly improved enzyme stability. All of the results indicated that the IMER prepared by this method had a broad application prospect in capillary electrophoresis-based high-performance enzyme analysis.

Metalation of metal-organic frameworks: fundamentals and applications

Metalation of metal-organic frameworks (MOFs) has been developed as a prominent strategy for materials functionalization for pore chemistry modulation and property optimization. By introducing exotic metal ions/complexes/nanoparticles onto/into the parent framework, many metallized MOFs have exhibited significantly improved performance in a wide range of applications. In this review, we focus on the research progress in the metalation of metal-organic frameworks during the last five years, spanning the design principles, synthetic strategies, and potential applications. Based on the crystal engineering principles, a minor change in the MOF composition through metalation would lead to leveraged variation of properties. This review starts from the general strategies established for the incorporation of metal species within MOFs, followed by the design principles to graft the desired functionality while maintaining the porosity of frameworks. Facile metalation has contributed a great number of bespoke materials with excellent performance, and we summarize their applications in gas adsorption and separation, heterogeneous catalysis, detection and sensing, and energy storage and conversion. The underlying mechanisms are also investigated by state-of-the-art techniques and analyzed for gaining insight into the structure-property relationships, which would in turn facilitate the further development of design principles. Finally, the current challenges and opportunities in MOF metalation have been discussed, and the promising future directions for customizing the next-generation advanced materials have been outlined as well.

Boosted Enzyme Activity via Encapsulation within Metal-Organic Frameworks with Pores Matching Enzyme Size and Shape

A novel and versatile approach called "physical imprinting" is introduced to modulate enzyme conformation using mesoporous materials, addressing challenges in achieving improved enzyme activity and stability. Metal-organic frameworks with tailored mesopores, precisely matching enzyme size and shape, are synthesized. Remarkably, enzymes encapsulated within these customized mesopores exhibit over 1670% relative activity compared to free enzymes, maintaining outstanding efficiency even under harsh conditions such as heat, exposure to organic solvents, wide-ranging pH extremes from acidic to alkaline, and exposure to a digestion cocktail. After 18 consecutive cycles of use, the immobilized enzymes retain 80% of their initial activity. Additionally, the encapsulated enzymes exhibit a substantial increase in catalytic efficiency, with a 14.1-fold enhancement in kcat/KM compared to native enzymes. This enhancement is among the highest reported for immobilized enzymes. The improved enzyme activity and stability are corroborated by solid-state UV-vis, electron paramagnetic resonance, Fourier-transform infrared spectroscopy, and solid-state NMR spectroscopy. The findings not only offer valuable insights into the crucial role of size and shape complementarity within confined microenvironments but also establish a new pathway for developing solid carriers capable of enhancing enzyme activity and stability.

Boosting humoral and cellular immunity with enhanced STING activation by hierarchical mesoporous metal-organic framework adjuvants

Vaccination is essential for preventing and controlling infectious diseases, along with reducing mortality. Developing safe and versatile adjuvants to enhance humoral and cellular immune responses to vaccines remains a key challenge in vaccine development. Here, we designed hierarchical mesoporous MOF-801 (HM801) using a Cocamidopropyl betaine (CAPB) and a Pluronics F127 in an aqueous phase system. Meanwhile, we synthesized a novel SARS-CoV-2 nanovaccine (R@M@HM801) with a high loading capacity for both the STING agonist (MSA-2) and the Delta receptor binding domain (Delta-RBD) antigen. R@M@HM801 enhanced MSA-2 and RBD utilization and effectively co-delivered MSA-2 and RBD antigens to antigen-presenting cells in the draining lymph nodes, thereby promoting the activation of both T and B cells. Lymphocyte single-cell analysis showed that R@M@HM801 stimulated robust CD11b+CD4+ T cells, CXCR5+CD4+ T follicular helper (Tfh), and durable CD4+CD44+CD62L-, CD8+CD44+CD62L- effector memory T cell (TEM) immune responses, and promoted the proliferative activation of CD26+ B cells in vivo. Meanwhile, R@M@HM801 induced stronger specific antibodies and neutralization of pseudovirus against Delta compared to the RBD + MAS-2 and RBD + MAS-2 + Alum vaccines. Our study demonstrated the efficacy of a hierarchical mesoporous HM801 and its potential immune activation mechanism in enhancing adaptive immune responses against viruses and other diseases.

Palmitic acid-capped MIL-101-Al as a nano-adjuvant to amplify immune responses against Pseudomonas aeruginosa

As a highly contagious opportunistic pathogen, Pseudomonas aeruginosa (P. aeruginosa) is one of the main causes of healthcare-associated infections. The drug-resistant nature of P. aeruginosa can render antibiotic treatments ineffective, leading to a high morbidity and mortality. Higher specificity and reduced toxicity are features of immunotherapy, which can generate robust immune responses and preserve long-term immunological memory to completely eradicate infections. In this study, we developed a type of P. aeruginosa vaccine based on a metal-organic framework. Specifically, MIL-101-Al nanoparticles were synthesized to encapsulate antigens derived from the bacterial lysate (BL) of PAO1, a drug-resistant P. aeruginosa, and the adjuvant unmethylated cytosine-phosphate-guanine oligonucleotide (CpG), which were then modified with palmitic acid (PAA) to obtain MIL-BC@PAA. The stability and biocompatibility were significantly increased by capping with PAA. Moreover, MIL-BC@PAA showed significantly enhanced uptake by antigen presenting cells (APCs), and promoted their maturation. Importantly, immunity studies revealed the greatly elicited antigen-specific humoral and cellular responses, and a protection rate of about 70% was observed in P. aeruginosa-challenged mice. Overall, these results demonstrate the promising potential of MIL-BC@PAA as an ideal nanovaccine for P. aeruginosa vaccination.

Amino Functionality Enables Aqueous Synthesis of Carboxylic Acid-Based MOFs at Room Temperature by Biomimetic Crystallization

Enzyme immobilization within metal-organic frameworks (MOFs) is a promising solution to avoid denaturation and thereby utilize the desirable properties of enzymes outside of their native environments. The biomimetic mineralization strategy employs biomacromolecules as nucleation agents to promote the crystallization of MOFs in water at room temperature, thus overcoming pore size limitations presented by traditional postassembly encapsulation. Most biomimetic crystallization studies reported to date have employed zeolitic imidazole frameworks (ZIFs). Herein, we expand the library of MOFs suitable for biomimetic mineralization to include zinc(II) MOFs incorporating functionalized terephthalic acid linkers and study the catalytic performance of the enzyme@MOFs. Amine functionalization of terephthalic acids is shown to accelerate the formation of crystalline MOFs enabling new enzyme@MOFs to be synthesized. The structure and morphology of the enzyme@MOFs were characterized by PXRD, FTIR, and SEM-EDX, and the catalytic potential was evaluated. Increasing the linker length while retaining the amino moiety gave rise to a family of linkers; however, MOFs generated with the 2,2'-aminoterephthalic acid linker displayed the best catalytic performance. Our data also illustrate that the pH of the reaction mixture affects the crystal structure of the MOF and that this structural transformation impacts the catalytic performance of the enzyme@MOF.

Developing Covalent Organic Framework Biocatalysts through Enzyme Encapsulation

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

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.

Metal-Organic Framework-Based Antimicrobial Touch Surfaces to Prevent Cross-Contamination

Infection diseases are a major threat to global public health, with nosocomial infections being of particular concern. In this context, antimicrobial coatings emerge as a promising prophylactic strategy to reduce the transmission of pathogens and control infections. Here, antimicrobial door handle covers to prevent cross-contamination are prepared by incorporating iodine-loaded UiO-66 microparticles into a potentially biodegradable polyurethane polymer (Baycusan eco E 1000). These covers incorporate MOF particles that serve as both storage reservoirs and delivery systems for the biocidal iodine. Under realistic touching conditions, the door handle covers completely inhibit the transmission of Gram-positive bacterial species (Staphylococcus aureus, and Enterococcus faecalis), Gram-negative bacterial species (Escherichia coli, Pseudomonas aeruginosa, and Acinetobacter baumannii), and fungi (Candida albicans). The covers remain effective even after undergoing multiple contamination cycles, after being cleaned, and when tinted to improve discretion and usability. Furthermore, as the release of iodine from the door handle covers follow hindered Fickian diffusion, their antimicrobial lifetime is calculated to be as long as approximately two years. Together, these results demonstrate the potential of these antimicrobial door handle covers to prevent cross-contamination, and underline the efficacy of integrating MOFs into innovative technologies.

Functionalized Ionic Liquids-Modified Metal-Organic Framework Material Boosted the Enzymatic Performance of Lipase

The development of immobilized enzymes with high activity and stability is critical. Metal-organic frameworks (MOFs) have attracted much academic and industrial interest in the field of enzyme immobilization due to their unique properties. In this study, the amino-functionalized ionic liquid (NIL)-modified metal-organic framework (UiO-66-NH2) was prepared to immobilize Candida rugosa lipase (CRL), using dialdehyde starch (DAS) as the cross-linker. The results of the Fourier transform infrared (FT-IR) spectra, X-ray powder diffraction (XRD), and scanning electronic microscopy (SEM) confirmed that the NIL was successfully grafted to UiO-66-NH2. The CRL immobilized on NIL-modified UiO-66-NH2 (UiO-66-NH2-NIL-DAS@CRL) exhibited satisfactory activity recovery (79.33%), stability, reusability, and excellent organic solvent tolerance. The research results indicated that ionic liquid-modified UiO-66-NH2 had practical potential for application in enzyme immobilization.

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

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

Direct Imaging of Protein Clusters in Metal-Organic Frameworks

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

Four birds with one stone: Aggregation-induced emission-type zeolitic imidazolate framework-8 based bionic nanoreactor for portable detection of olaquindox in environmental water and swine urine by smartphone

The abuse of olaquindox (OLA) as both an antimicrobial agent and a growth promoter poses significant threats to the environment and human health. While nanoreactors have proven effective in hazard detection, their widespread adoption has been hindered by tedious chemical processes and limited functionality. In this study, we introduce a novel green self-assembly strategy utilizing invertase, horseradish peroxidase, antibodies, and gold nanoclusters to form an aggregation-induced emission-type zeolitic imidazolate framework-8 nanoreactor. The results demonstrate that the lateral flow immunoassay not only allows for qualitative naked eye detection but also enables optical analysis through the fluorescence generated by aggregated gold nanoclusters and enzyme-catalyzed enhancement of visible colorimetric signals. To accommodate more detection scenarios, the photothermal effects and redox reactions of the nanoreactor can fulfill the requirements of thermal sensing and electrochemical analysis for smartphone applications. Remarkably, the proposed approach achieves a detection limit 17 times lower than conventional methods. Besides, the maximum linear range spans from 0.25 to 5 μg/L with high specificity, and the recovery is 85.2-112.9% in environmental water and swine urine. The application of this high-performance nanoreactor opens up avenues for the construction of multifunctional biosensors with great potential in monitoring hazardous materials.

Catalytic Nanoparticles in Biomedical Applications: Exploiting Advanced Nanozymes for Therapeutics and Diagnostics

Catalytic nanoparticles (CNPs) as heterogeneous catalyst reveals superior activity due to their physio-chemical features, such as high surface-to-volume ratio and unique optical, electric, and magnetic properties. The CNPs, based on their physio-chemical nature, can either increase the reactive oxygen species (ROS) level for tumor and antibacterial therapy or eliminate the ROS for cytoprotection, anti-inflammation, and anti-aging. In addition, the catalytic activity of nanozymes can specifically trigger a specific reaction accompanied by the optical feature change, presenting the feasibility of biosensor and bioimaging applications. Undoubtedly, CNPs play a pivotal role in pushing the evolution of technologies in medical and clinical fields, and advanced strategies and nanomaterials rely on the input of chemical experts to develop. Herein, a systematic and comprehensive review of the challenges and recent development of CNPs for biomedical applications is presented from the viewpoint of advanced nanomaterial with unique catalytic activity and additional functions. Furthermore, the biosafety issue of applying biodegradable and non-biodegradable nanozymes and future perspectives are critically discussed to guide a promising direction in developing span-new nanozymes and more intelligent strategies for overcoming the current clinical limitations.

Enzyme_Metal-Organic Framework Composites as Novel Approach for Microplastic Degradation

Plastic pollution is one of the main worldwide environmental concerns. Our lifestyle involves persistent plastic consumption, aggravating the low efficiency of wastewater treatment plants in its removal. Nano/microplastics are accumulated in living beings, pushing to identify new water remediation strategies to avoid their harmful effects. Enzymes (e. g., Candida rugosa-CrL) are known natural plastic degraders as catalysts in depolymerization reactions. However, their practical use is limited by their stability, recyclability, and economical concerns. Here, enzyme immobilization in metal-organic frameworks (CrL_MOFs) is originally presented as a new plastic degradation approach to achieve a boosted plastic decomposition in aqueous systems while allowing the catalyst cyclability. Bis-(hydroxyethyl)terephthalate (BHET) was selected as model substrate for decontamination experiments for being the main polyethylene terephthalate (PET) degradation product. Once in contaminated water, CrL_MOFs can eliminate BHET (37 %, 24 h), following two complementary mechanisms: enzymatic degradation (CrL action) and byproducts adsorption (MOF effect). As a proof-of-concept, the capacity of a selected CrL_MOF composite to eliminate the BHET degradation products and its reusability are also investigated. The potential of these systems is envisioned in terms of improving enzyme cyclability, reducing costs along with feasible co-adsorption of plastic byproducts and other harmful contaminants, to successfully remove them in a single step.

Nanocomposites Based on Magnetic Nanoparticles and Metal-Organic Frameworks for Therapy, Diagnosis, and Theragnostics

In the last two decades, metal-organic frameworks (MOFs) with highly tunable structure and porosity, have emerged as drug nanocarriers in the biomedical field. In particular, nanoscaled MOFs (nanoMOFs) have been widely investigated because of their potential biocompatibility, high drug loadings, and progressive release. To enhance their properties, MOFs have been combined with magnetic nanoparticles (MNPs) to form magnetic nanocomposites (MNP@MOF) with additional functionalities. Due to the magnetic properties of the MNPs, their presence in the nanosystems enables potential combinatorial magnetic targeted therapy and diagnosis. In this Review, we analyze the four main synthetic strategies currently employed for the fabrication of MNP@MOF nanocomposites, namely, mixing, in situ formation of MNPs in presynthesized MOF, in situ formation of MOFs in the presence of MNPs, and layer-by-layer methods. Additionally, we discuss the current progress in bioapplications, focusing on drug delivery systems (DDSs), magnetic resonance imaging (MRI), magnetic hyperthermia (MHT), and theragnostic systems. Overall, we provide a comprehensive overview of the recent advances in the development and bioapplications of MNP@MOF nanocomposites, highlighting their potential for future biomedical applications with a critical analysis of the challenges and limitations of these nanocomposites in terms of their synthesis, characterization, biocompatibility, and applicability.

Metal-Organic Framework-Mediated Delivery of Nucleic Acid across Intact Plant Cells

Plant synthetic biology is applied in sustainable agriculture, clean energy, and biopharmaceuticals, addressing crop improvement, pest resistance, and plant-based vaccine production by introducing exogenous genes into plants. This technique faces challenges delivering genes due to plant cell walls and intact cell membranes. Novel approaches are required to address this challenge, such as utilizing nanomaterials known for their efficiency and biocompatibility in gene delivery. This work investigates metal-organic frameworks (MOFs) for gene delivery in intact plant cells by infiltration. Hence, small-sized ZIF-8 nanoparticles (below 20 nm) were synthesized and demonstrated effective DNA/RNA delivery into Nicotiana benthamiana leaves and Arabidopsis thaliana roots, presenting a promising and simplified method for gene delivery in intact plant cells. We further demonstrate that small-sized ZIF-8 nanoparticles protect RNA from RNase degradation and successfully silence an endogenous gene by delivering siRNA in N. benthamiana leaves.

Enzymatic Nanomotors Surviving Harsh Conditions Enabled by Metal Organic Frameworks Encapsulation

Enzyme-driven micro/nanomotors (MNMs) have demonstrated potentials in the biomedical field because of their excellent biocompatibility, versatility, and fuel bioavailability. However, the fragility of enzymes limits their practical application, because of their susceptibility to denaturation and degradation in realistic scenarios. Herein, a simple yet versatile and effective approach is reported to preserve the enzymatic activity and propulsion capability of enzymatic MNMs under various harsh conditions using metal organic frameworks (MOFs) as a protective shell. Urease can be encapsulated within the exoskeleton of zeolitic imidazolate framework-8 (ZIF-8) via biomimetic mineralization to form ZIF-8@urease (ZU-I) nanomotors that exhibit self-propulsion in the presence of urea. When exposed to harsh conditions, including high temperature, presence of proteases, and organic solvents, the ZU-I nanomotors still maintained their activity and mobility, whereas ZIF-8 with externally modified urease (ZU-O) nanomotors with externally modified urease as a control rapidly lost their motion capabilities owing to the inactivation of urease. Furthermore, ZU-I nanomotors exhibit effectively enhanced diffusion within the small intestine fluid, achieving a fourfold higher mucus penetration than the ZU-O nanomotors. The results highlight the effectiveness of using MOFs as protective shells for enzyme nano-engines, which can greatly advance the practical applications of enzymatic MNMs under realistic conditions, especially for biomedical purpose.

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.

The Promise and Potential of Metal-Organic Frameworks and Covalent Organic Frameworks in Vaccine Nanotechnology

The immune system's complexity and ongoing evolutionary struggle against deleterious pathogens underscore the value of vaccination technologies, which have been bolstering human immunity for over two centuries. Despite noteworthy advancements over these 200 years, three areas remain recalcitrant to improvement owing to the environmental instability of the biomolecules used in vaccines─the challenges of formulating them into controlled release systems, their need for constant refrigeration to avoid loss of efficacy, and the requirement that they be delivered via needle owing to gastrointestinal incompatibility. Nanotechnology, particularly metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), has emerged as a promising avenue for confronting these challenges, presenting a new frontier in vaccine development. Although these materials have been widely explored in the context of drug delivery, imaging, and cancer immunotherapy, their role in immunology and vaccine-related applications is a recent yet rapidly developing field. This review seeks to elucidate the prospective use of MOFs and COFs for biomaterial stabilization, eliminating the necessity for cold chains, enhancing antigen potency as adjuvants, and potentializing needle-free delivery of vaccines. It provides an expansive and critical viewpoint on this rapidly evolving field of research and emphasizes the vital contribution of chemists in driving further advancements.

Exploring Emergent Properties in Enzymatic Reaction Networks: Design and Control of Dynamic Functional Systems

The intricate and complex features of enzymatic reaction networks (ERNs) play a key role in the emergence and sustenance of life. Constructing such networks in vitro enables stepwise build up in complexity and introduces the opportunity to control enzymatic activity using physicochemical stimuli. Rational design and modulation of network motifs enable the engineering of artificial systems with emergent functionalities. Such functional systems are useful for a variety of reasons such as creating new-to-nature dynamic materials, producing value-added chemicals, constructing metabolic modules for synthetic cells, and even enabling molecular computation. In this review, we offer insights into the chemical characteristics of ERNs while also delving into their potential applications and associated challenges.

Hydrogel-encapsulated medium chain lipid-modified zeolite imidazole framework-90 as a promising platform for oral delivery of proteins

The administration of protein therapeutics through oral means is seen as a convenient and painless experience for patients, making it a significant consideration in the field of drug delivery. Nevertheless, the challenging conditions within the gastrointestinal tract, along with the obstacles to absorption, impede the efficient transportation of proteins. Here, we successfully implemented post-synthetic modifications to attach medium-chain lipids (C10) onto the surface of zeolitic imidazole framework-90 (ZIF-90), then encapsulated the nanoparticles with sodium alginate, resulting in a potential platform for the oral administration of proteins. By means of biomimetic mineralization, ZIF-90 achieves a simple and efficient encapsulation of proteins of varying sizes, while shielding them against degradation by digestive enzymes. Sodium alginate hydrogel protects proteins against gastric acid and helps the cargo to rapidly penetrate the mucus layer. Through a mixed mechanism dominated by micropinocytosis, the C10-conjugated ZIF-90 (ZIF-90-C10) can be uptake by Caco-2 cells with a 200-400% increase and transported through the Golgi apparatus after escaping from lysosomes, exhibiting enhanced uptake in the overall gastrointestinal tract. Furthermore, ZIF-90-C10 retains its adenosine triphosphate-responsive release, which drastically lowers the likelihood of accumulation in vivo and allows targeted delivery for disease cells. Our work highlights mid-chain lipid conjugation as a potent approach to enhancing nanoparticle delivery efficiency and a potential strategy for oral delivery of biomacromolecules when combined with pH-responsive gels.

Biomolecules meet organic frameworks: from synthesis strategies to diverse applications

Biomolecules are essential in pharmaceuticals, biocatalysts, biomaterials, etc., but unfortunately they are extremely susceptible to extraneous conditions. When biomolecules meet porous organic frameworks, significantly improved thermal, chemical, and mechanical stabilities are not only acquired for raw biomolecules, but also molecule sieving, substrate enrichment, chirality property, and other functionalities are additionally introduced for application expansions. In addition, the intriguing synergistic effect stemming from elaborate and concerted interactions between biomolecules and frameworks can further enhance application performances. In this paper, the synthesis strategies of the so-called bio-organic frameworks (BOFs) in recent years are systematically reviewed and classified. Additionally, their broad applications in biomedicine, catalysis, separation, sensing, and imaging are introduced and discussed. Before ending, the current challenges and prospects in the future for this infancy-stage but significant research field are also provided. We hope that this review will offer a concise but comprehensive vision of designing and constructing multifunctional BOF materials as well as their full explorations in various fields.

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

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

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).

Co-immobilizing laccase-mediator system by in-situ synthesis of MOF in PVA hydrogels for enhanced laccase stability and dye decolorization efficiency

The laccase mediator system (LMS) with a broad substrate range has attracted much attention as an efficient approach for water remediation. However, the practical application of LMS is limited due to their high solubility, poor stability and low reusability. Herein, the bimetallic Cu/ZIFs encapsulated laccase was in-situ grown in poly(vinyl alcohol) (PVA) polymer matrix. The PVA-Lac@Cu/ZIFs hydrogel was formed via one freeze-thawing cycle, and its catalytic stability was significantly improved. The mediator was further co-immobilized on the hydrogel, and this hierarchically co-immobilized ABTS/PVA-Lac@Cu/ZIFs hydrogel could avoid the continuous oxidation reaction between laccase and redox mediators. The co-immobilized LMS biocatalyst was used to degrade malachite green (MG), and the degradation rate was up to 100 % within 4 h. More importantly, the LMS could be recycled synchronously from the dye solutions and reused to degrade MG multiple times. The degradation rate remained above 69.4 % after five cycles. Furthermore, the intermediate products were detected via liquid chromatography-mass spectrometry, and the potential degradation pathways were proposed. This study demonstrated the significant potential of utilizing the MOF nanocrystals and hydrogel as a carrier for co-immobilized LMS, and the effective reuse of both laccase and mediator was promising for laccase application in wastewater treatment.

A scalable synthesis of adjuvanting antigen depots based on metal-organic frameworks

Vaccines have saved countless lives by preventing and even irradicating infectious diseases. Commonly used subunit vaccines comprising one or multiple recombinant proteins isolated from a pathogen demonstrate a better safety profile than live or attenuated vaccines. However, the immunogenicity of these vaccines is weak, and therefore, subunit vaccines require a series of doses to achieve sufficient immunity against the pathogen. Here, we show that the biomimetic mineralization of the inert model antigen, ovalbumin (OVA), in zeolitic imidazolate framework-8 (ZIF-8) significantly improves the humoral immune response over three bolus doses of OVA (OVA 3×). Encapsulation of OVA in ZIF-8 (OVA@ZIF) demonstrated higher serum antibody titers against OVA than OVA 3×. OVA@ZIF vaccinated mice displayed higher populations of germinal center (GC) B cells and IgG1+ GC B cells as opposed to OVA 3×, indicative of class-switching recombination. We show that the mechanism of this phenomenon is at least partly owed to the metalloimmunological effects of the zinc metal as well as the sustained release of OVA from the ZIF-8 composite. The system acts as an antigen reservoir for antigen-presenting cells to traffic into the draining lymph node, enhancing the humoral response. Lastly, our model system OVA@ZIF is produced quickly at the gram scale in a laboratory setting, sufficient for up to 20 000 vaccine doses.

Covalent Organic Frameworks: Opportunities for Rational Materials Design in Cancer Therapy

Nanomedicines are extensively used in cancer therapy. Covalent organic frameworks (COFs) are crystalline organic porous materials with several benefits for cancer therapy, including porosity, design flexibility, functionalizability, and biocompatibility. This review examines the use of COFs in cancer therapy from the perspective of reticular chemistry and function-oriented materials design. First, the modification sites and functionalization methods of COFs are discussed, followed by their potential as multifunctional nanoplatforms for tumor targeting, imaging, and therapy by integrating functional components. Finally, some challenges in the clinical translation of COFs are presented with the hope of promoting the development of COF-based anticancer nanomedicines and bringing COFs closer to clinical trials.

Confinement of p-Xylene in the Pores of a Bilanthanide Metal-Organic Framework for Highly Selective Recognition

The rapid and accurate sensing of p-xylene, an essential raw material with a multi-billion-dollar market, in xylene mixture is of great significance in industry; however, the highly similar molecular structures, energy levels, and spectral characteristics of xylene isomers make the selective recognition extremely challenging. Metal-organic frameworks (MOFs) exhibiting tailorable pores and potential binding sites provide prospects for xylene sensing but a comprehensive understanding of the pore effect is still elusive, primarily due to the intricacies involved in the sensing process. Herein, we reported a robust bilanthanide MOF NKU-999-EuTb with precisely engineered pores to accommodate p-xylene, of which the binding sites were confirmed by single crystal X-ray diffraction and dynamic magnetic susceptibilities. NKU-999-EuTb exhibits high-performance in selective recognition for p-xylene towards its isomers. Through a systematical study, it was revealed that absorbing p-xylene into the pores governs the sensing performance. This work provides insights for developing advanced sensing materials for complex isomers.

Metal-pyrimidine nanocubes immobilized enzymes with pH-switchable multienzyme-like activity for broad-pH-responsive sensing assay for organophosphorus pesticides

Peroxidase (POD)-like can only function in acidic environments and the pH mismatch restricts the application of enzyme-nanozyme cascade catalytic sensing platforms in the broad-pH-responsive assay for organophosphorus pesticides (OPs). Herein, the metal-pyrimidine nanocubes (MPNCs) with intrinsic pH-switchable POD-like and catalase (CAT)-like properties were synthesized via the coordination of pyrimidin-2-ol with Cu2+. Meanwhile, acetylcholinesterase (AChE) and choline oxidase (CHO) were simultaneously encapsulated in MPNCs to construct an enzyme-nanozyme cascade catalytic platform (AChE/CHO@MPNCs). AChE/CHO@MPNCs could catalyze the hydrolysis of acetylcholine to choline, which was subsequently converted to H2O2. The POD-like activity of MPNCs was dominant under acidic conditions, while the CAT-like activity prevailed under neutral and alkaline conditions, which could catalyze H2O2 to •OH and O2, respectively, then oxidizing dopamine (DA) to polydopamine quantum dots (PDA QDs) with different fluorescence characteristics. Consequently, OPs could be detected in a linear range from 0.05 to 1000 nM with a LOD of 0.015 nM in acidic environments and a linear range from 0.05 to 500 nM with a LOD of 0.023 nM in alkaline environments. Overall, our work expands the horizon of constructing enzyme@MOFs composites with high catalytic activity. Meanwhile, the intrinsic pH-switchable multienzyme-like property opens avenues to construct sensing platforms with broad-pH-responsive for OPs and other analytes detection.

Synthetic Biohybrids of Red Blood Cells and Cascaded-Enzymes@ Metal-Organic Frameworks for Hyperuricemia Treatment

Hyperuricemia, caused by an imbalance between the rates of production and excretion of uric acid (UA), may greatly increase the mortality rates in patients with cardiovascular and cerebrovascular diseases. Herein, for fast-acting and long-lasting hyperuricemia treatment, armored red blood cell (RBC) biohybrids, integrated RBCs with proximal, cascaded-enzymes of urate oxidase (UOX) and catalase (CAT) encapsulated within ZIF-8 framework-based nanoparticles, have been fabricated based on a super-assembly approach. Each component is crucial for hyperuricemia treatment: 1) RBCs significantly increase the circulation time of nanoparticles; 2) ZIF-8 nanoparticles-based superstructure greatly enhances RBCs resistance against external stressors while preserving native RBC properties (such as oxygen carrying capability); 3) the ZIF-8 scaffold protects the encapsulated enzymes from enzymatic degradation; 4) no physical barrier exists for urate diffusion, and thus allow fast degradation of UA in blood and neutralizes the toxic by-product H2 O2 . In vivo results demonstrate that the biohybrids can effectively normalize the UA level of an acute hyperuricemia mouse model within 2 h and possess a longer elimination half-life (49.7 ± 4.9 h). They anticipate that their simple and general method that combines functional nanomaterials with living cell carriers will be a starting point for the development of innovative drug delivery systems.

Exosome-tuned MOF signal amplifier boosting tumor exosome phenotyping with high-affinity nanostars

The natural phospholipid structure imparts exosomes with not only cargo protection, but rich sites for coordination with metal-organic frameworks (MOFs) to assemble functional nanocomplexes, such as signal amplifiers. Here, we exploit exosomes to tune MOF signal amplifiers (Exo-MOF) for ultrasensitive phenotyping of tumor-derived exosomes (tExo) based on self-driven coordination assembly and high-affinity nanostars. Exo-MOF leverages the specific coordination interaction between exosome and MOF that cages abundant redox molecules to assemble a super-redox signal amplifier. Moreover, the dispersed immuno-magnetic nanostars, which are assembled with antibodies on the surface of Au nanostars-coated magnetic nanoparticles, allow for rapid capturing of target tExo, addressing the limited mass transfer on electrode surface. Both Exo-MOF and high-affinity nanostars orchestrate the ultrahigh sensitivity (1 particle per 100 μL, higher than that no Exo-MOF by at least 10-fold), specificity and speed of the sensor in tExo detection. Such a sensitive strategy allows profiling tExo across seven cancer types, and revealing the distinct exosomal surface expression patterns. Further, the Exo-MOF sensor accurately distinguishes cancer patients from healthy individuals in a clinical cohort, and provides new opportunities for functional materials assembly and precision diagnostics.