Phase dependent encapsulation and release profile of ZIF-based biocomposites

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.

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.

A smartphone-based fluorescent biosensor with metal-organic framework biocomposites and cotton swabs for the rapid determination of tetrodotoxin in seafood

BACKGROUND

Tetrodotoxin (TTX) is a potent neurovirulent marine biotoxin that is present in puffer fish and certain marine animals. It is capable of causing severe neurotoxic symptoms and even death when consumed through contaminated seafood. Due to its high toxicity, developing an effective assay for TTX determination in seafood has significant benefits for food safety and human health. Currently, it remains challenging to achieve on-site determination of TTX in seafood. To facilitate mass on-site assays, more affordable technologies utilizing accessible equipment that require no skilled personnel are needed.

RESULTS

A smartphone-based portable fluorescent biosensor is proposed for TTX determination by using metal-organic framework (MOF) biocomposites and cotton swabs. Oriented antibody (Ab)-decorated and fluorescent quantum dot (QD)-loaded MOF biocomposites (QD@MOF*Ab) are rapidly synthesized for binding targets and fluorescent responses by utilizing the tunability of zinc-based MOF. Moreover, facile Ab-immobilized household cotton swabs are utilized as TTX capture tools. TTX forms sandwich immune complexes with QD@MOF*Ab probes, achieving signal amplification. These probes are excited by a portable device to generate bright fluorescent signals, which can be detected by the naked eye, and TTX quantitative results are obtained using a smartphone. When observed with the naked eye, the limit of detection (LOD) is 0.4 ng/mL, while intelligent quantitation presents an LOD of 0.13 ng/mL at logarithmic concentrations of 0.2-400 ng/mL.

SIGNIFICANCE

This biosensor is convenient to use, and an easy-to-operate analysis is completed within 15 min, thus demonstrating excellent performance in terms of detection speed and portability. Furthermore, it successfully determines TTX contents in puffer fish and clam samples, demonstrating its potential for monitoring seafood. Herein, this work provides a favorable rapid sensing platform that is easily portable.

Stereoselective reduction of diarylmethanones via a ketoreductase@metal-organic framework

Mainly owing to their well-defined pore structures and high surface areas, metal-organic frameworks (MOFs) have recently become a versatile class of materials for enzyme immobilization. Nevertheless, most previous studies were focused on model enzymes such as cytochrome c, catalase, and glucose oxidase, with the application of MOF-derived biocomposites for (asymmetric) organic synthesis being rare. In the present work, the immobilization of the ketoreductase KmCR2 onto the zeolitic imidazolate framework (ZIF), a prominent type of MOF, was pursued using the controlled co-precipitation strategy, with a low 2-methylimidazole (2-mIM)/Zn molar ratio of 8 : 1 being employed. Such fabricated biocomposites denoted as KmCR2@ZIF were found to exist mainly in an amorphous phase, as suggested by the scanning electron microscopy (SEM) and powder X-ray diffraction (PXRD) data. Improved thermal and storage stabilities were observed for KmCR2@ZIF compared with the free enzyme. Stereoselective reduction of nine diarylmethanones 1 catalyzed by KmCR2@ZIF was performed, and the corresponding enantioenriched diarylmethanols 2 were afforded in 40-92% conversions with good to excellent optical purities (up to >99% ee). Critically, the current work demonstrated that the unique characteristic of KmCR2, namely the substituent position-controlled stereospecificity (meta versus para or ortho), was not altered upon the enzyme immobilization onto the ZIF.

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.

Organophosphate Detoxification and Acetylcholinesterase Reactivation Triggered by Zeolitic Imidazolate Framework Structural Degradation

Organophosphate (OP) toxicity is related to inhibition of acetylcholinesterase (AChE) activity, which plays a key role in the neurotransmission process. In this work, we report the ability of different zinc zeolitic imidazolate frameworks (ZIFs) to behave as potential antidotes against OP poisoning. The Zn-L coordination bond (L = purine, benzimidazole, imidazole, or 2-methylimidazole) is sensitive to the G-type nerve agent model compounds diisopropylfluorophosphate (DIFP) and diisopropylchlorophosphate, leading to P-X (X = F or Cl) bond breakdown into nontoxic diisopropylphosphate. P-X hydrolysis is accompanied by ZIF structural degradation (Zn-imidazolate bond hydrolysis), with the concomitant release of the imidazolate linkers and zinc ions representing up to 95% of ZIF particle dissolution. The delivered imidazolate nucleophilic attack on the OP@AChE adduct gives rise to the recovery of AChE enzymatic function. P-X bond breakdown, ZIF structural degradation, and AChE reactivation are dependent on imidazolate linker nucleophilicity, framework topology, and particle size. The best performance is obtained for 20 nm nanoparticles (NPs) of Zn(2-methylimidazolate)2 (sod ZIF-8) exhibiting a DIFP degradation half-life of 2.6 min and full recovery of AChE activity within 1 h. 20 nm sod ZIF-8 NPs are not neurotoxic, as proven by in vitro neuroblastoma cell culture viability tests.

Tunable growth of a single high-density ZIF nanoshell on a gold nanoparticle isolated in an optical trap

Here, we demonstrate an all-optical method using an optical tweezer to controllably grow high quality zeolitic imidazolate framework (ZIF) nanoshells on the surface of gold nanoparticles (AuNPs) and monitor the growth via darkfield spectroscopy. Our single particle approach allows us to localize an individual NP within a microscope slide chamber containing ZIF precursors at the focus of an optical microscope and initiate growth through localized heating without affecting the bulk system. Darkfield spectroscopy is used to characterize changes to the localized surface plasmon resonance (LSPR) of the AuNP resulting from refractive index changes as the ZIF crystal grows on the surface. We show that the procedure can be generalized to grow various types of ZIF crystals, such as ZIF-8, ZIF-11, and a previously undocumented ZIF variety. Utilizing both computational models and experimental methods, we identify the thickness of ZIF layers to be self-limiting to ∼50 nm or less, depending on the trapping laser power. Critically, the refractive index of the shells here was found to be above 1.6, indicating the formation of high-density crystals, previously accessible only through slow atomic layer deposition and not through a bulk heating process. The single particle method developed here opens the door for bottom-up controllable growth of custom nanostructures with tunable optical properties.

Degradation Kinetic Studies of BSA@ZIF-8 Nanoparticles with Various Zinc Precursors, Metal-to-Ligand Ratios, and pH Conditions

Nanosized zeolitic imidazolate framework particles (ZIF-8 nanoparticles [NPs]) have strong potential as effective carriers for both in vivo and in vitro protein drug delivery. Synthesis of ZIF-8 and stability of protein encapsulation within ZIF-8 are affected by several factors, notably the metal ion source and molar ratio. To systematically investigate these factors, we investigated such effects using BSA as a model test protein to synthesize BSA@ZIF-8 NPs at various metal-to-ligand (M:L) ratios. SEM, FTIR, XRD, and DLS were applied to characterize the morphology and structure of BSA@ZIF-8 NPs and their effects on protein loading capacity. Degradation kinetics and protein release behavior of BSA@ZIF-8 NPs were evaluated at pH 5.0 (to simulate the tumor environment) and pH 7.4 (to mimic the blood environment). Our objective was to define optimal combinations of the high protein loading rate and rapid release under varying pH conditions, and we found that (i) the yield of BSA@ZIF-8 NPs decreased as the M:L ratio increased, but the protein content increased. This highlights the need to strike a balance between cost-effectiveness and practicality when selecting ZIF-8 NPs with different molar ratios for protein-based drug formulation. (ii) BSA@ZIF-8 NPs exhibited cruciate flower-like shapes when synthesized using Zn(NO3)2 as the zinc precursor at M:L ratios of 1:16 or 1:20. In all other cases, the NPs displayed a regular rhombic dodecahedral structure. Notably, the release behavior of the NPs did not differ significantly between these morphologies. (iii) When Zn(OAc)2 was used as the zinc precursor, the synthesized ZIF-8 NPs exhibited a smaller size compared to the Zn(NO3)2-derived ZIF-8 NPs. (iv) The release rate and amount of BSA protein were higher at pH 5.0 compared to pH 7.4. (v) Among the different formulations, BSA@ZIF-8 with an M:L ratio of 1:16 at pH 5.0 was observed to have a shorter time to reach a plateau (0.5 h) and higher protein release, making it suitable for locally rapid administration in a tumor environment. BSA@ZIF-8 prepared from Zn(OAc)2 at an M:L ratio of 1:140 showed the slower release of BSA protein over a 24-h period, indicating its suitability for sustained release delivery. In conclusion, our findings provide a useful basis for the practical application of ZIF-8 NPs in protein-based drug delivery systems.

A selenoureido-iminoglycolipid transported by zeolitic-imidazolate framework nanoparticles: a novel antioxidant therapeutic approach

A selenium-containing metal-organic framework with remarkable antioxidant capacity and ROS-scavenging activity was constructed by a controlled de novo encapsulation approach of a glycoconjugate mimetic, specifically a sp2-iminoglycolipid bearing a selenoureido fragment (DSeU), within a zeolitic-imidazolate framework exoskeleton. Biocompatible and homogeneous nanosized particles of ∼70 nm (DSeU@ZIF8) were obtained, which could be efficiently internalized in cells, overcoming the poor solubility in biological media and limited bioavailability of glycolipids. The ZIF-particle served as nanocarrier for the intracellular delivery of the selenocompound to cells, promoted by the acidic pH inside endosomes/lysosomes. As demonstrated by in vitro studies, the designed DSeU@ZIF8 nanoparticles displayed a high antioxidant activity at low doses; lower intracellular ROS levels were observed upon the uptake of DSeU@ZIF8 by human endothelial cells. Even more interesting was the finding that these DSeU@ZIF8 particles were able to reverse to a certain level the oxidative stress induced in cells by pre-treatment with an oxidizing agent. This possibility of modulating the oxidative stress in living cells may have important implications in the treatment of diverse pathological complications that are generally accompanied with elevated ROS levels.

Histidine-Rich Protein Accelerates the Biomineralization of Zeolitic Imidazolate Frameworks for In Vivo Protein Delivery

Biomineralization of metal-organic frameworks (MOFs) provides a powerful approach for intracellular protein delivery, enabling the study of biological function and therapeutic potential of proteins. However, the potency of this approach is largely challenged by the low efficiency of current strategies for interfacing proteins with MOFs for biomineralization and intracellular delivery. Here, we report a versatile and convenient biomineralization strategy for the rapid encapsulation and enhanced delivery of proteins using MOFs, accelerated by histidine-rich proteins. We demonstrate that the histidine-rich green fluorescent protein (H39GFP) can accelerate the biomineralization of MOFs by promoting the coordination between proteins and metal ions, leading to enhanced protein delivery efficiency up to 15-fold. Moreover, we show that the delivery of H39GFP-fused cytotoxic ribonuclease and bacterial-derived RAS protease can effectively inhibit tumor cell growth. The strategy of promoting the biomineralization of MOFs via histidine-rich proteins for enhanced intracellular delivery could be expanded to other biomacromolecules, advancing their therapeutic potential and the biomedical scope of MOFs.

Comparison of protein quantification methods for protein encapsulation with ZIF-8 metal-organic frameworks

The use of metal-organic frameworks (MOFs) as delivery systems for biologically functional macromolecules has been explored widely in recent years due to their ability to protect their payload from a wide range of harsh conditions. Given the wide usage and diversity of potential applications, optimising the encapsulation efficiency by MOFs for different biological is of particular importance. Here, several protein quantitation methods and report were compared on the accuracy, practicality, limitations, and sensitivity of these methods to assess the encapsulation efficiency of zeolitic imidazolate frameworks (ZIF)-8 MOFs for two common biologicals commonly used in nanomedicine, bovine serum albumin (BSA), and the enzyme catalase (CAT). Using these methods, ZIF-8 encapsulation of BSA and CAT was confirmed to enrich for high molecular weight and glycosylated protein forms. However, contrary to most reports, a high degree of variance was observed across all methods assessed, with fluorometric quantitation providing the most consistent results with the lowest background and greatest dynamic range. While bicinchoninic acid (BCA) assay has showed greater detection range than the Bradford (Coomassie) assay, BCA and Bradford assays were found to be susceptible to background from the organic "MOF" linker 2-methylimidazole, reducing their overall sensitivity. Finally, while very sensitive and useful for assessing protein quality SDS-PAGE is also susceptible to confounding artifacts and background. Given the increasing use of enzyme delivery using MOFs, and the diversity of potential uses in biomedicine, identifying a rapid and efficient method of assessing biomolecule encapsulation is key to their wider acceptance.

A simple one step synthesis of magnetic-optical dual functional ZIF-8 in a sodalite phase for magnetically guided targeting bioimaging and drug delivery

Functionalized metal-organic frameworks (MOFs) that integrate targeted tumor imaging and drug delivery are expected to significantly enhance the therapeutic efficacy of cancer. However, the complicated synthesis process has greatly limited their utilization in clinical application. Herein, a one-step simple method was used to construct novel multifunctional MOFs by co-loading doxorubicin (DOX) and Fe3O4 into the ZIF-8 with sodalite topology. DOX serves as a fluorescence imaging reagent and an anticancer drug and Fe3O4 is used as a magnetic resonance imaging and magnetic targeting anticancer reagent. The fabricated DOX/Fe3O4@ZIF-8 nanocomposite showed excellent fluorescence and magnetic resonance imaging performances in tumors. Moreover, DOX/Fe3O4@ZIF-8 can be accumulated in tumors via a magnetic targeting effect and tumor growth could be inhibited in vivo due to the release of DOX. Additionally, the apoptosis process of DOX/Fe3O4@ZIF-8 on HepG2 cells is well investigated. Overall, DOX/Fe3O4@ZIF-8 synthesized in simple one step can be used for simultaneous targeted bioimaging and cancer therapy.

Understanding and controlling the nucleation and growth of metal-organic frameworks

Metal-organic frameworks offer a diverse landscape of building blocks to design high performance materials for implications in almost every major industry. With this diversity stems complex crystallization mechanisms with various pathways and intermediates. Crystallization studies have been key to the advancement of countless biological and synthetic systems, with MOFs being no exception. This review provides an overview of the current theories and fundamental chemistry used to decipher MOF crystallization. We then discuss how intrinsic and extrinsic synthetic parameters can be used as tools to modulate the crystallization pathway to produce MOF crystals with finely tuned physical and chemical properties. Experimental and computational methods are provided to guide the probing of MOF crystal formation on the molecular and bulk scale. Lastly, we summarize the recent major advances in the field and our outlook on the exciting future of MOF crystallization.

Enhanced Bioactivity of Enzyme/MOF Biocomposite via Host Framework Engineering

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

Cellulose/Zeolitic Imidazolate Framework (ZIF-8) Composites with Antibacterial Properties for the Management of Wound Infections

Metal-organic frameworks (MOFs) are a class of crystalline porous materials with outstanding physical and chemical properties that make them suitable candidates in many fields, such as catalysis, sensing, energy production, and drug delivery. By combining MOFs with polymeric substrates, advanced functional materials are devised with excellent potential for biomedical applications. In this research, Zeolitic Imidazolate Framework 8 (ZIF-8), a zinc-based MOF, was selected together with cellulose, an almost inexhaustible polymeric raw material produced by nature, to prepare cellulose/ZIF-8 composite flat sheets via an in-situ growing single-step method in aqueous media. The composite materials were characterized by several techniques (IR, XRD, SEM, TGA, ICP, and BET) and their antibacterial activity as well as their biocompatibility in a mammalian model system were investigated. The cellulose/ZIF-8 samples remarkably inhibited the growth of Gram-positive and Gram-negative reference strains, and, notably, they proved to be effective against clinical isolates of Staphylococcus epidermidis and Pseudomonas aeruginosa presenting different antibiotic resistance profiles. As these pathogens are of primary importance in skin diseases and in the delayed healing of wounds, and the cellulose/ZIF-8 composites met the requirements of biological safety, the herein materials reveal a great potential for use as gauze pads in the management of wound infections.

Oriented Antibody-Assembled Metal-Organic Frameworks for Persistent Wearable Sweat Cortisol Detection

The level of cortisol can reflect people's psychological stress, help diagnose adrenal gland diseases, and is also related to several mental diseases. In this study, we developed a cortisol monoclonal antibody-oriented approach to modify an immunosensor for wearable label-free and persistent sweat cortisol detection. On such an antibody-oriented immunosensor, the fragment crystallizable (Fc) region is partially inserted within the metal-organic framework (MOF), and antibody-binding regions of the cortisol monoclonal antibody (Cmab) were exposed on the MOF surface via selective growth and self-assembly. Such ordered and oriented embedding of antibodies in the MOF resulted in excellent antibody activity and improved stability and antigen-binding capacity. We also engineered the full integrated system for on-body sweat cortisol biosensing performance in several volunteers, and the results indicated that this wearable sensor is suitable for practical cortisol detection with a good linear detection range from 1 pg/mL to 1 μg/mL with a lower limit of detection of 0.26 pg/mL. Moreover, the wearable sensor demonstrated good persistence in detecting cortisol, with only 4.1% decay after 9 days of storage. The present work represents a simple oriented antibody assembling approach to improve the stability of antibodies, providing an important step toward long-term continuous sweat biomarker detection.

Targeting telomerase utilizing zeolitic imidazole frameworks as non-viral gene delivery agents across different cancer cell types

Telomerase, a ribonucleoprotein coded by the hTERT gene, plays an important role in cellular immortalization and carcinogenesis. hTERT is a suitable target for cancer therapeutics as its activity is highly upregulated in most of cancer cells but absent in normal somatic cells. Here, by employing the two Metal-Organic Frameworks (MOFs), viz. ZIF-C and ZIF-8, based biomineralization we encapsulate Clustered Regularly Interspaced Short Palindromic Repeat (CRISPR)/Cas9 plasmid system that targets hTERT gene (CrhTERT) in cancer cells. When comparing the two biocomposites, ZIF-C shows the better loading capacity and cell viability. The loaded plasmid in ZIF-C is highly protected against enzymatic degradation. CrhTERT@ZIF-C is efficiently endocytosed by cancer cells and the subcellular release of CrhTERT leads to telomerase knockdown. The resultant inhibition of hTERT expression decreases cellular proliferation and causing cancer cell death. Furthermore, hTERT knockdown shows a significant reduction in tumour metastasis and alters protein expression. Collectively we show the high potential of ZIF-C-based biocomposites as a promising general tool for gene therapy of different types of cancers.

Interrogating Encapsulated Protein Structure within Metal-Organic Frameworks at Elevated Temperature

Encapsulating biomacromolecules within metal-organic frameworks (MOFs) can confer thermostability to entrapped guests. It has been hypothesized that the confinement of guest molecules within a rigid MOF scaffold results in heightened stability of the guests, but no direct evidence of this mechanism has been shown. Here, we present a novel analytical method using small-angle X-ray scattering (SAXS) to solve the structure of bovine serum albumin (BSA) while encapsulated within two zeolitic imidazolate frameworks (ZIF-67 and ZIF-8). Our approach comprises subtracting the scaled SAXS spectrum of the ZIF from that of the biocomposite BSA@ZIF to determine the radius of gyration of encapsulated BSA through Guinier, Kratky, and pair distance distribution function analyses. While native BSA exposed to 70 °C became denatured, in situ SAXS analysis showed that encapsulated BSA retained its size and folded state at 70 °C when encapsulated within a ZIF scaffold, suggesting that entrapment within MOF cavities inhibited protein unfolding and thus denaturation. This method of SAXS analysis not only provides insight into biomolecular stabilization in MOFs but may also offer a new approach to study the structure of other conformationally labile molecules in rigid matrices.

Porous zeolitic imidazolate frameworks assembled with highly-flattened tetrahedral copper(II) centres and 2-nitroimidazolates

Cu(II)-based zeolitic imidazolates (Cu-ZIFs), Cu-ZIF-gis and -rho, formulated as Cu(nIm)₂ (nIm = 2-nitroimidazolate) have highly-flattened tetrahedral coordination geometry. Cu-ZIF-gis has 2.4 Å cylindrical pores that can adsorb H₂ gas, and Cu-ZIF-rho has 19.8 Å cages with a BET surface area of 1320 m² g^-1.

Using Defect Control To Break the Stability-Activity Trade-Off in Enzyme Immobilization via Competitive Coordination

Immobilization of enzymes within metal-organic frameworks is a powerful strategy to enhance the long-term usability of labile enzymes. However, the thus-confined enzymes suffer from the trade-off between enhanced stability and reduced activity because of the contradiction between the high crystallinity and the low accessibility. Here, by taking laccase and zeolitic imidazolate framework-8 (ZIF-8) as prototypes, we disclosed an observation that the stability-activity trade-off could be solved by controlling the defects via competitive coordination. Owing to the presence of competitive coordination between laccase and the ligand precursor of ZIF-8, there existed a three-stage process in the de novo encapsulation: nucleation-crystallization-recrystallization. Our results show that the biocomposites collected before the occurrence of recrystallization possessed both increased activity and enhanced stability. The findings here shed new light on the control of defects through the subtle use of competitive coordination, which is of great significance for the engineering application of biomacromolecules.

Debridement of contaminated implants using air-polishing coupled with pH-responsive maximin H5-embedded metal-organic frameworks

The primary goal of peri-implantitis treatments remains the decontamination of implant surfaces exposed to polymicrobial biofilms and renders biocompatibility. In this study, we reported a synergistic strategy for the debridement and re-osteogenesis of contaminated titanium by using erythritol air abrasion (AA) coupled with an as-synthesized pH-responsive antimicrobial agent. Here, the anionic antibacterial peptide Maximin H5 C-terminally deaminated isoform (MH5C) was introduced into the Zeolitic Imidazolate Frameworks (ZIF-8) via a one-pot synthesis process. The formed MH5C@ZIF-8 nanoparticles (NPs) not only possessed suitable stability, but also guarantee the slow-release effect of MH5C. Antibacterial experiments revealed that MH5C@ZIF-8 NPs exhibited excellent antimicrobial abilities toward pathogenic bacteria of peri-implantitis, confirming ZIF-8 NPs as efficient nanoplatforms for delivering antibacterial peptide. To evaluate the comprehensive debridement efficiency, single-species as well as mixed-species biofilms were successively established on commercially used titanium surfaces and decontaminated with different methods: removed only by erythritol air abrasion, treated merely with MH5C@ZIF-8 NPs, or received both managements. The results demonstrated that only erythritol air abrasion accompanied with MH5C@ZIF-8 NPs at high concentrations eliminated almost all retained bacteria and impeded biofilm rehabilitation, while neither erythritol air abrasion nor MH5C@ZIF-8 NPs alone could achieve this. Subsequently, we evaluated the re-osteogenesis on previously contaminated surfaces which were treated with different debridement methods afterwards. We found that cell growth and osteogenic differentiation of bone marrow-derived mesenchymal stem cells (BMSCs) in the group received both treatments (AA + MH5C@ZIF-8) were higher than those in other groups. Our work emphasized the great potential of the synergistic therapy as a credible alternative for removing microorganisms and rendering re-osseointegration on contaminated implant surfaces, boding well for the comprehensive applications in peri-implantitis treatments.

Targeted in vitro gene silencing of E2 and nsP1 genes of chikungunya virus by biocompatible zeolitic imidazolate framework

Chikungunya fever caused by the mosquito-transmitted chikungunya virus (CHIKV) is a major public health concern in tropical, sub-tropical and temperate climatic regions. The lack of any licensed vaccine or antiviral agents against CHIKV warrants the development of effective antiviral therapies. Small interfering RNA (siRNA) mediated gene silencing of CHIKV structural and non-structural genes serves as a potential antiviral strategy. The therapeutic efficiency of siRNA can be improved by using an efficient delivery system. Metal-organic framework biocomposits have demonstrated an exceptional capability in protecting and efficiently delivering nucleic acids into cells. In the present study, carbonated ZIF called ZIF-C has been utilized to deliver siRNAs targeted against E2 and nsP1 genes of CHIKV to achieve a reduction in viral replication and infectivity. Cellular transfection studies of E2 and nsP1 genes targeting free siRNAs and ZIF-C encapsulated siRNAs in CHIKV infected Vero CCL-81 cells were performed. Our results reveal a significant reduction of infectious virus titre, viral RNA levels and percent of infected cells in cultures transfected with ZIF-C encapsulated siRNA compared to cells transfected with free siRNA. The results suggest that delivery of siRNA through ZIF-C enhances the antiviral activity of CHIKV E2 and nsP1 genes directed siRNAs.

Carrier gas triggered controlled biolistic delivery of DNA and protein therapeutics from metal-organic frameworks

The efficacy and specificity of protein, DNA, and RNA-based drugs make them popular in the clinic; however, these drugs are often delivered via injection, requiring skilled medical personnel, and producing biohazardous waste. Here, we report an approach that allows for their controlled delivery, affording either a burst or slow release without altering the formulation. We show that when encapsulated within zeolitic-imidazolate framework eight (ZIF-8), the biomolecules are stable in powder formulations and can be inoculated with a low-cost, gas-powered "MOF-Jet" into living animal and plant tissues. Additionally, their release profiles can be modulated through judicious selection of the carrier gas used in the MOF-Jet. Our in vitro and in vivo studies reveal that when CO₂ is used, it creates a transient and weakly acidic local environment that causes a near-instantaneous release of the biomolecules through an immediate dissolution of ZIF-8. Conversely, when air is used, ZIF-8 biodegrades slowly, releasing the biomolecules over a week. This is the first example of controlled-biolistic delivery of biomolecules using ZIF-8, which provides a powerful tool for fundamental and applied science research.

App-based quantification of crystal phases and amorphous content in ZIF biocomposites

The performance of zeolitic imidazolate frameworks (ZIFs) as protective hosts for proteins in drug delivery or biocatalysis strongly depends on the type of crystalline phase used for the encapsulation of the biomacromolecule (biomacromolecule@ZIF). Therefore, quantifying the different crystal phases and the amount of amorphous content of ZIFs is becoming increasingly important for a better understanding of the structure-property relationship. Typically, crystalline ZIF phases are qualitatively identified from diffraction patterns. However, accurate phase examinations are time-consuming and require specialized expertise. Here, we propose a calibration procedure (internal standard ZrO2) for the rapid and quantitative analysis of crystalline and amorphous ZIF phases from diffraction patterns. We integrated the procedure into a user-friendly web application, named ZIF Phase Analysis, which facilitates ZIF-based data analysis. As a result, it is now possible to quantify i) the relative amount of various common crystal phases (sodalite, diamondoid, ZIF-CO3-1, ZIF-EC-1, U12 and ZIF-L) in biomacromolecule@ZIF biocomposites based on Zn2+ and 2-methylimidazole (HmIM) and ii) the crystalline-to-amorphous ratio. This new analysis tool will advance the research on ZIF biocomposites for drug delivery and biocatalysis.

Role of Molecular Modification and Protein Folding in the Nucleation and Growth of Protein-Metal-Organic Frameworks

Metal-organic frameworks (MOFs) are a class of porous nanomaterials that have been extensively studied as enzyme immobilization substrates. During in situ immobilization, MOF nucleation is driven by biomolecules with low isoelectric points. Investigation of how biomolecules control MOF self-assembly mechanisms on the molecular level is key to designing nanomaterials with desired physical and chemical properties. Here, we demonstrate how molecular modifications of bovine serum albumin (BSA) with fluorescein isothiocyanate (FITC) can affect MOF crystal size, morphology, and encapsulation efficiency. Final crystal properties are characterized using scanning electron microscopy (SEM), powder X-ray diffraction (PXRD), fluorescent microscopy, and fluorescence spectroscopy. To probe MOF self-assembly, in situ experiments were performed using cryogenic transmission electron microscopy (cryo-TEM) and X-ray diffraction (XRD). Biophysical characterization of BSA and FITC-BSA was performed using ζ potential, mass spectrometry, circular dichroism studies, fluorescence spectroscopy, and Fourier transform infrared (FTIR) spectroscopy. The combined data reveal that protein folding and stability within amorphous precursors are contributing factors in the rate, extent, and mechanism of crystallization. Thus, our results suggest molecular modifications as promising methods for fine-tuning protein@MOFs' nucleation and growth.

Conformation-Stabilized Amorphous Nanocoating for Rational Design of Long-Term Thermostable Viral Vaccines

Despite the great potency of vaccines to combat infectious diseases, their global use is hindered by a lack of thermostability, which leads to a constant need for cold-chain storage. Here, aiming at long-term thermostability and eliminating cold-chain requirements of bioactive vaccines, we propose that efforts should focus on tailoring the conformational stability of vaccines. Accordingly, we design a nanocoating composed of histidine (His)-coordinated amorphous Zn and 2-methylimidazolate complex (His-aZn-mIM) on single nanoparticles of viral vaccines to introduce intramolecular coordinated linkage between viruses and the nanocoatings. The coordinated nanocoating enhances the rigidity of proteins and preserves the vaccine's activity. Importantly, integrating His into the original Zn-N coordinative environment symbiotically reinforces its tolerance to biological and hydrothermal solutions, resulting in the augmented thermostability following the Hofmeister effect. Thus, even after storage of His-aZn-mIM encapsulated Human adenovirus type 5 (Ad5@His-aZn-mIM) at 25 °C for 90 d, the potency loss of the coated Ad5 is less than 10%, while the native Ad5 becomes 100% ineffective within one month. Such a nanocoating gains thermostability by forming an ultrastable hydration shell, which prevents viral proteins from unfolding under the attack of hydration ions, providing a conformational stabilizer upon heat exposure. Our findings represent an easy-access biomimetic platform to address the long-term vaccine storage without the requirement of a cold chain.

Laminar flow-assisted synthesis of amorphous ZIF-8-based nano-motor with enhanced transmigration for photothermal cancer therapy

Because of their biocompatibility, there are promising applications in various fields for enzyme-powered nano-motors. However, enzymes can undergo denaturation under harsh conditions. Here, we report the flow-assisted synthesis of an enzyme-based amorphous ZIF-8 nano-motor (A-motor; Pdop@urease@aZIF-8) for enhanced movement and protection of polydopamine and enzymes. Multiple laminar flow types with varied input ratios effectively entrapped enzymes into amorphous ZIF-8 shells in a serial flow with a momentary difference. The obtained A-motor exhibited superior enzymatic activity and photothermal ablation properties with excellent durability due to the protection the amorphous shell offers from the external environment. Furthermore, in the bio-mimic 2D membrane model, the enhanced mobility of the A-motor afforded high transmigration (>80%), which had a powerful effect on bladder cancer cell ablation via photothermal therapy. This work envisages that the rapid flow approach will facilitate scalable manufacturing of the nano-motors under low stress to vulnerable biomolecules, which would be extended to nano-biomedical applications in various body environments.

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.

Development of dual-enhancer biocatalyst with photothermal property for the degradation of cephalosporin

The abuse of cephalosporins poses a serious threat to human health and the ecological environment. In this work, cephalosporinase (AmpC enzyme) and Prussian blue (PB) crystals were encapsulated into ZIF-8 metal-organic frameworks (MOFs), and a photothermal AmpC/PB@ZIF-8 MOFs (APZ) nanocatalyst was prepared for the catalytic degradation of cephalosporin. The temperature of the APZ catalytic degradation system can be regulated by irradiation with near infrared light due to the photothermal effect of PB, and then, the activity of the APZ biocatalyst is significantly enhanced. Thereby, the degradation efficiency of cefuroxime can reach to 96%, and the degradation kinetic rate of cefuroxime augmented 4.5-fold comparing with that catalyzed by free enzyme. Moreover, encapsulation of the enzyme and PB can increase the affinity and charge transfer efficiency between APZ and substrate molecules, which can also improve the degradation efficiency of cephalosporins. Catalytic degradation pathways for three generations of cephalosporins were proposed based on their degradation products. The dual-enhancer biocatalyst based on the photothermal effect and immobilization of the PB and enzyme can significantly enhance the activity and stability of the enzyme, and it can also be recycled. Therefore, the biocatalyst has potential applications for the effective degradation of cephalosporins in the environment.

Self-Assembly of Oriented Antibody-Decorated Metal-Organic Framework Nanocrystals for Active-Targeting Applications

Antibody (Ab)-targeted nanoparticles are becoming increasingly important for precision medicine. By controlling the Ab orientation, targeting properties can be enhanced; however, to afford such an ordered configuration, cumbersome chemical functionalization protocols are usually required. This aspect limits the progress of Abs-nanoparticles toward nanomedicine translation. Herein, a novel one-step synthesis of oriented monoclonal Ab-decorated metal-organic framework (MOF) nanocrystals is presented. The crystallization of a zinc-based MOF, Zn₂ (mIM)₂ (CO₃ ), from a solution of Zn²⁺ and 2-methylimidazole (mIM), is triggered by the fragment crystallizable (Fc) region of the Ab. This selective growth yields biocomposites with oriented Abs on the MOF nanocrystals (MOF*Ab): the Fc regions are partially inserted within the MOF surface and the antibody-binding regions protrude from the MOF surface toward the target. This ordered configuration imparts antibody-antigen recognition properties to the biocomposite and shows preserved target binding when compared to the parental antibodies. Next, the biosensing performance of the system is tested by loading MOF*Ab with luminescent quantum dots (QD). The targeting efficiency of the QD-containing MOF*Ab is again, fully preserved. The present work represents a simple self-assembly approach for the fabrication of antibody-decorated MOF nanocrystals with broad potential for sensing, diagnostic imaging, and targeted drug delivery.

Biomimetic metal-organic frameworks as protective scaffolds for live-virus encapsulation and vaccine stabilization

The invaluable health, economic and social impacts of vaccination are hard to exaggerate. The ability to stabilize vaccines is urgently required for their equitable distribution without the dependence on the 'cold-chain' logistics. Herein, for the first time we report biomimetic-mineralization of live-viral vaccines using metal-organic frameworks (MOFs) to enhance their storage stability from days to months. Applying ZIF-8 and aluminium fumarate (Alfum), the Newcastle Disease Virus (NDV) V4 strain and Influenza A WSN strain were encapsulated with remarkable retention of their viral titre. The ZIF-8@NDV, ZIF-8@WSN and Alfum@WSN composites were validated for live-virus recovery using a tissue culture infectious dose (TCID₅₀) assay. With the objective of long-term stabilization, we developed a novel, trehalose (T) and skim milk (SM) stabilized, freeze-dried MOF@Vaccine composite, ZIF-8@NDV+T/SM. The thermal stability of this composite was investigated and compared with the control NDV and non-encapsulated, freeze-dried NDV+T/SM composite at 4 °C, RT, and 37 °C over a period of 12 weeks. We demonstrate the fragility of the control NDV vaccine which lost all viability at RT and 37°C by 12 and 4 weeks, respectively. Comparing the freeze-dried counterparts, the MOF encapsulated ZIF-8@NDV+T/SM demonstrated significant enhancement in stability of the NDV+T/SM composite especially at RT and 37 °C upto 12 weeks. STATEMENT OF SIGNIFICANCE: Vaccination is undoubtedly one of the most effective medical interventions, saving millions of lives each year. However, the requirement of 'cold-chain' logistics is a major impediment to widespread immunization. Live viral vaccines (LVVs) are widely used vaccine types with proven efficacy and low cost. Nonetheless, their complex composition increases their susceptability to thermal stress. Several LVV thermostabilization approaches have been investigated, including their complex engineering and the facile addition of stabilizers. Still, the lack of a universal approach urgently requires finding a stabilization technique especially when additives alone may not be sufficient. Herein, we demonstrate MOF biomimetic-mineralization technology to encapsulate LVVs developing an optimised composite which significantly preserves vaccines without refrigeration for extended periods of time.

Microfluidic Synthesis of a Bioactive Metal-Organic Framework for Glucose-Responsive Insulin Delivery

In the current study, we report the microfluidic synthesis of a metal-organic framework (MOF) for insulin delivery based on the stimulus response of glucose. Insulin- and gold nanoparticle (AuNP)-encapsulated zeolitic imidazolate framework-8 (ZIF-8) was synthesized using a continuous-flow, microfluidic mixing system via a single-step process. Glucose oxidase mimicking the activity of AuNPs was utilized for oxidizing glucose molecules that entered the porous ZIF-8. The AuNPs oxidized glucose into gluconic acid and hydrogen peroxide inside the MOF (Ins-AuNP-ZIF-8). The resulting acidic pH led to the disruption of ZIF-8 and released insulin. Thus, the presence of glucose molecules provided a stimulus for insulin release. The bioactive MOFs were characterized for the presence of functional groups, morphology, crystallinity, size, and elemental confirmation. The presence of fluorescein-5-isothiocyanate-labeled insulin in the composite was confirmed using confocal laser scanning microscopy. The loading of insulin per unit weight of the MOF, determined by size-exclusion-high-performance liquid chromatography, was 77 and 88% in the batch and microfluidic processes, respectively. Drug release studies confirmed the response of the MOFs to glucose, which triggered insulin release. The synthesis process did not affect the characteristics and application of ZIF-8 and Ins-AuNP-ZIF-8. This study involving the facile synthesis of bioactive MOFs offers a sustainable strategy to design stimulus-responsive drug delivery systems and could be exploited for biosensing applications.

Multi-layered ZIF-coated cells for the release of bioactive molecules in hostile environments

Metal-organic framework (MOF) coatings on cells enhance viability in cytotoxic environments. Here, we show how protective multi-layered MOF bio-composite shells on a model cell system (yeast) enhance the proliferation of...

Prospects of Exploring the Metal-Organic Framework for Combating Antimicrobial Resistance

Infectious diseases are a major public health concern globally. Infections caused by pathogens with resistance against commonly used antimicrobial drugs or antibiotics (known as antimicrobial resistance, AMR) are becoming extremely difficult to control. AMR has thus been declared as one of the top 10 global public health threats, as it has very limited solutions. The drying pipeline of effective antibiotics has further worsened the situation. There is no absolute treatment, and the limitations of existing methods warrant further development in antimicrobials. Recent developments in the nanomaterial field present them as promising therapeutics and effective alternative to conventional antibiotics and synthetic drugs. The metal-organic framework (MOF) is a recent addition to the antimicrobial category with superior properties. The MOF exerts antimicrobial action on a wide range of species and is highly biocompatible. Additionally, their porous structures allow the incorporation of biomolecules and drugs for synergistic antimicrobial action. This review provides an inclusive summary of the molecular events responsible for resistance development and current trends in antimicrobials to combat antibiotic resistance and explores the potential role of the MOF in tackling the drug-resistant microbial species.

Degradation kinetic study of ZIF-8 microcrystals with and without the presence of lactic acid

The zeolitic imidazolate framework ZIF-8 (Zn(mim)₂, mim = 2-methylimidazolate) has recently been proposed as a drug delivery platform for anticancer therapy based on its capability of decomposing in acidic media. The concept presumes a targeted release of encapsulated drug molecules in the vicinity of tumor tissues that typically produce secretions with elevated acidity. Due to challenges of in vivo and in vitro examination, many studies have addressed the kinetics of ZIF-8 decomposition and subsequent drug release in phosphate buffered saline (PBS) with adjusted acidity. However, the presence of hydrogen phosphate anions [HPO₄]²⁻ in PBS may also affect the stability of ZIF-8. As yet, no separate analysis has been performed comparing the dissolving capabilities of PBS and various acidification agents used for regulating pH. Here, we provide a systematic study addressing the effects of phosphate anions with and without lactic acid on the degradation rate of ZIF-8 microcrystals. Lactic acid has been chosen as an experimental acidification agent, since it is particularly secreted by tumor cells. Interestingly, the effect of a lactic acid solution with pH 5.0 on ZIF-8 degradation is shown to be weaker compared to a PBS solution with pH 7.4. However, as an additive, lactic acid is able to enhance the decomposition efficacy of other solutions by 10 to 40 percent at the initial stage, depending on the presence of other ions. Additionally, we report mild toxicity of ZIF-8 and its decomposition products, as examined on HDF and A549 cell lines.

ZIF-8 microcrystals demonstrate different degradation kinetics in water, PBS (pH 7.4), and PBS with lactic acid (pH 5.0).

Influence of the Synthesis and Storage Conditions on the Activity of Candida antarctica Lipase B ZIF-8 Biocomposites

The biomimetic mineralization of zeolitic imidazolate framework-8 (ZIF-8) has been reported as a strategy for enzyme immobilization, enabling the heterogenization and protection of biomacromolecules. Here, we report the preparation of different Candida antarctica lipase B biocomposites (CALB@ZIF-8) formed by altering the concentrations of Zn2+ and 2-methylimidazole (2-mIM). The influence of synthetic conditions on the catalytic activity of the lipase CALB was examined by hydrolysis and transesterification assays in aqueous and organic media, respectively. We demonstrated that for both reactions, activity was retained for the biocomposites formed at low Zn2+/2-mIM ratios but notably almost entirely lost when the ligand concentration used to form the biocomposites was increased. Additionally, phosphate buffer could regenerate the activity of larger particles by degrading the crystal surfaces and releasing encapsulated CALB into solution. Transesterification reactions using CALB@ZIF-8 biocomposites were undertaken in 100% hexane, giving rise to enhanced CALB activity relative to the free enzyme. These observations highlight the fundamental importance of synthetic protocols and operating parameters for developing enzyme@MOF biocomposites with improved activity in challenging conditions.

Probing Molecular Motions in Metal-Organic Frameworks by Three-Dimensional Electron Diffraction

Flexible metal-organic frameworks (MOFs) are known for their vast functional diversities and variable pore architectures. Dynamic motions or perturbations are among the highly desired flexibilities, which are key to guest diffusion processes. Therefore, probing such motions, especially at an atomic level, is crucial for revealing the unique properties and identifying the applications of MOFs. Nuclear magnetic resonance (NMR) and single-crystal X-ray diffraction (SCXRD) are the most important techniques to characterize molecular motions but require pure samples or large single crystals (>5 × 5 × 5 μm3), which are often inaccessible for MOF synthesis. Recent developments of three-dimensional electron diffraction (3D ED) have pushed the limits of single-crystal structural analysis. Accurate atomic information can be obtained by 3D ED from nanometer- and submicrometer-sized crystals and samples containing multiple phases. Here, we report the study of molecular motions by using the 3D ED method in MIL-140C and UiO-67, which are obtained as nanosized crystals coexisting in a mixture. In addition to an ab initio determination of their framework structures, we discovered that motions of the linker molecules could be revealed by observing the thermal ellipsoid models and analyzing the atomic anisotropic displacement parameters (ADPs) at room temperature (298 K) and cryogenic temperature (98 K). Interestingly, despite the same type of linker molecule occupying two symmetry-independent positions in MIL-140C, we observed significantly larger motions for the isolated linkers in comparison to those reinforced by π-π stacking. With an accuracy comparable to that of SCXRD, we show for the first time that 3D ED can be a powerful tool to investigate dynamics at an atomic level, which is particularly beneficial for nanocrystalline materials and/or phase mixtures.

Sustainable One-Pot Immobilization of Enzymes in/on Metal-Organic Framework Materials

The industrial use of enzymes generally necessitates their immobilization onto solid supports. The well-known high affinity of enzymes for metal-organic framework (MOF) materials, together with the great versatility of MOFs in terms of structure, composition, functionalization and synthetic approaches, has led the scientific community to develop very different strategies for the immobilization of enzymes in/on MOFs. This review focuses on one of these strategies, namely, the one-pot enzyme immobilization within sustainable MOFs, which is particularly enticing as the resultant biocomposite Enzyme@MOFs have the potential to be: (i) prepared in situ, that is, in just one step; (ii) may be synthesized under sustainable conditions: with water as the sole solvent at room temperature with moderate pHs, etc.; (iii) are able to retain high enzyme loading; (iv) have negligible protein leaching; and (v) give enzymatic activities approaching that given by the corresponding free enzymes. Moreover, this methodology seems to be near-universal, as success has been achieved with different MOFs, with different enzymes and for different applications. So far, the metal ions forming the MOF materials have been chosen according to their low price, low toxicity and, of course, their possibility for generating MOFs at room temperature in water, in order to close the cycle of economic, environmental and energy sustainability in the synthesis, application and disposal life cycle.

Biodegradation pathway of penicillins by β-lactamase encapsulated in metal-organic frameworks

The pollution caused by the abuse of antibiotics has posed a serious threat to the ecological environment and human health, so development of effective strategies for degradation and disposal of antibiotic residues is urgently needed. In this work, penicillinase, a kind of β-lactamase, was immobilized into zeolitic imidazolate framework-8 (ZIF-8) by self-assembly method and the catalytic performance of the β-lactamase@ZIF-8 porous materials for degradation of penicillins has been investigated by high performance liquid chromatography coupled with mass spectrometry. The results illustrated that the catalytic activity of the encapsulated enzyme was significantly enhanced comparing with that of free enzyme. Meanwhile, the β-lactamase@ZIF-8 exhibited excellent stability under denaturing conditions including high temperature, organic solvent and the enzyme inhibitor. The catalytic degradation mechanism of the β-lactamase@ZIF-8 for penicillins has been probed and verified, and it has been found that the Zn (II) ion on ZIF-8 frameworks could form the complex with the target molecule, which weakened the bond of the four-membered β-lactam ring in the penicillin molecule, and thus enhanced the degradation efficiency of the enzyme. This work provided a promising strategy for eliminating the penicillin residues in water environment.

On the completeness of three-dimensional electron diffraction data for structural analysis of metal-organic frameworks

Three-dimensional electron diffraction (3DED) has been proven as an effective and accurate method for structure determination of nano-sized crystals. In the past decade, the crystal structures of various new complex metal-organic frameworks (MOFs) have been revealed by 3DED, which has been the key to understand their properties. However, due to the design of transmission electron microscopes (TEMs), one drawback of 3DED experiments is the limited tilt range of goniometers, which often leads to incomplete 3DED data, particularly when the crystal symmetry is low. This drawback can be overcome by high throughput data collection using continuous rotation electron diffraction (cRED), where data from a large number of crystals can be collected and merged. Here, we investigate the effects of improving completeness on structural analysis of MOFs. We use ZIF-EC1, a zeolitic imidazolate framework (ZIF), as an example. ZIF-EC1 crystallizes in a monoclinic system with a plate-like morphology. cRED data of ZIF-EC1 with different completeness and resolution were analyzed. The data completeness increased to 92.0% by merging ten datasets. Although the structures could be solved from individual datasets with a completeness as low as 44.5% and refined to a high precision (better than 0.04 Å), we demonstrate that a high data completeness could improve the structural model, especially on the electrostatic potential map. We further discuss the strategy adopted during data merging. We also show that ZIF-EC1 doped with cobalt can act as an efficient electrocatalyst for oxygen reduction reactions.

Expanding the ZIFs Repertoire for Biological Applications with the Targeted Synthesis of ZIF-20 Nanoparticles

Owing to their facile synthesis, tailorable porosity, diverse compositions, and low toxicity, zeolitic imidazolate framework (ZIF) nanoparticles (NPs) have emerged as attractive platforms for a variety of biologically relevant applications. To date, a small subset of ZIFs representing only two topologies and very few linker chemistries have been studied in this realm. We seek to expand the bio-design space for ZIF NPs through the targeted synthesis of a hierarchically complex ZIF based on two types of cages, ZIF-20, with lta topology. This study demonstrates the rapid synthesis and size tunability of ZIF-20 particles across the micro and nanoregimes via microwave heating and the use of a modulating agent. To evaluate the utility of ZIF particles for biological applications, we examine their stability in biologically relevant media and demonstrate biocompatibility with A549 human epithelial cells. Further, the ability to encapsulate and release methylene blue, a therapeutic and bioimaging agent, is validated. Importantly, ZIF-20 NPs display a unique behavior relative to previously studied ZIFs based on their specific structural and chemical features. This finding highlights the need to expand the design space across the broader ZIFs family, to exploit a wider range of relevant properties for biological applications and beyond.

High-Throughput Electron Diffraction Reveals a Hidden Novel Metal-Organic Framework for Electrocatalysis

Metal-organic frameworks (MOFs) are known for their versatile combination of inorganic building units and organic linkers, which offers immense opportunities in a wide range of applications. However, many MOFs are typically synthesized as multiphasic polycrystalline powders, which are challenging for studies by X-ray diffraction. Therefore, developing new structural characterization techniques is highly desired in order to accelerate discoveries of new materials. Here, we report a high-throughput approach for structural analysis of MOF nano- and sub-microcrystals by three-dimensional electron diffraction (3DED). A new zeolitic-imidazolate framework (ZIF), denoted ZIF-EC1, was first discovered in a trace amount during the study of a known ZIF-CO3 -1 material by 3DED. The structures of both ZIFs were solved and refined using 3DED data. ZIF-EC1 has a dense 3D framework structure, which is built by linking mono- and bi-nuclear Zn clusters and 2-methylimidazolates (mIm- ). With a composition of Zn3 (mIm)5 (OH), ZIF-EC1 exhibits high N and Zn densities. We show that the N-doped carbon material derived from ZIF-EC1 is a promising electrocatalyst for oxygen reduction reaction (ORR). The discovery of this new MOF and its conversion to an efficient electrocatalyst highlights the power of 3DED in developing new materials and their applications.

Interwoven MOF-Coated Janus Cells as a Novel Carrier of Toxic Proteins

Two major issues in cell-mediated drug delivery systems (c-DDS) are the availability of free cell surfaces for the binding of the cells to the target or to their microenvironment and internalization of the cytotoxic drug. In this study, the Janus structure, MOF nanoparticles, and tannic acid (TA) are utilized to address these issues. Janus carrier cells coated with metal-organic frameworks (MOFs) are produced by asymmetrically immobilizing the nanoparticles of a MOF based on zinc with cytotoxic enzymes that are internally encapsulated on the surface of carrier cells. By maintaining the biological and structural features of regular living cells, the MOF-coated Janus cells developed in the present study preserve the intrinsic binding capacity of the cells to their microenvironment. Interconnected MOFs loaded onto the other face of the Janus cells cannot penetrate the cell. Therefore, the carrier cells are protected from the cytotoxic drug contained in MOFs. These MOF-Janus carrier cells are demonstrated to successfully eliminate three-dimensional (3D) tumor spheroids when a chemotherapeutic protein of proteinase K is released from the MOF nanoparticles in an acid environment. The ease with which the MOF-Janus carrier cells are prepared (in 15 min), and the ability to carry a variety of enzymes and even multiple ones should make the developed system attractive as a general platform for drug delivery in various applications, including combination therapy.

Stabilization of supramolecular membrane protein-lipid bilayer assemblies through immobilization in a crystalline exoskeleton

Artificial native-like lipid bilayer systems constructed from phospholipids assembling into unilamellar liposomes allow the reconstitution of detergent-solubilized transmembrane proteins into supramolecular lipid-protein assemblies called proteoliposomes, which mimic cellular membranes. Stabilization of these complexes remains challenging because of their chemical composition, the hydrophobicity and structural instability of membrane proteins, and the lability of interactions between protein, detergent, and lipids within micelles and lipid bilayers. In this work we demonstrate that metastable lipid, protein-detergent, and protein-lipid supramolecular complexes can be successfully generated and immobilized within zeolitic-imidazole framework (ZIF) to enhance their stability against chemical and physical stressors. Upon immobilization in ZIF bio-composites, blank liposomes, and model transmembrane metal transporters in detergent micelles or embedded in proteoliposomes resist elevated temperatures, exposure to chemical denaturants, aging, and mechanical stresses. Extensive morphological and functional characterization of the assemblies upon exfoliation reveal that all these complexes encapsulated within the framework maintain their native morphology, structure, and activity, which is otherwise lost rapidly without immobilization.

Three-Dimensional Electron Diffraction for Structural Analysis of Beam-Sensitive Metal-Organic Frameworks

Electrons interact strongly with matter, which makes it possible to obtain high-resolution electron diffraction data from nano- and submicron-sized crystals. Using electron beam as a radiation source in a transmission electron microscope (TEM), ab initio structure determination can be conducted from crystals that are 6–7 orders of magnitude smaller than using X-rays. The rapid development of three-dimensional electron diffraction (3DED) techniques has attracted increasing interests in the field of metal-organic frameworks (MOFs), where it is often difficult to obtain large and high-quality crystals for single-crystal X-ray diffraction. Nowadays, a 3DED dataset can be acquired in 15–250 s by applying continuous crystal rotation, and the required electron dose rate can be very low (<0.1 e s−1 Å−2). In this review, we describe the evolution of 3DED data collection techniques and how the recent development of continuous rotation electron diffraction techniques improves data quality. We further describe the structure elucidation of MOFs using 3DED techniques, showing examples of using both low- and high-resolution 3DED data. With an improved data quality, 3DED can achieve a high accuracy, and reveal more structural details of MOFs. Because the physical and chemical properties of MOFs are closely associated with their crystal structures, we believe 3DED will only increase its importance in developing MOF materials.

Stimuli-responsive metal-organic framework nanoparticles for controlled drug delivery and medical applications

Stimuli-responsive metal-organic framework nanoparticles, NMOFs, provide a versatile platform for the controlled release of drugs and biomedical applications. The porous structure of NMOFs, their biocompatibility, low toxicity, and efficient permeability turn the NMOFs into ideal carriers for therapeutic applications. Two general methods to gate the drug-loaded NMOFs and to release the loads were developed: by one method, the loaded NMOFs are coated or surface-modified with stimuli-responsive gates being unlocked in the presence of appropriate chemical (e.g., ions or reducing agents), physical (e.g., light or heat), or biomarker (e.g., miRNA or ATP) triggers. By a second approach, the drug-loaded NMOFs include encoded structural information or co-added agents to induce the structural distortion or stimulate the degradation of the NMOFs. Different chemical triggers such as pH changes, ions, ATP, or redox agents, and physical stimuli such as light or heat are applied to degrade the NMOFs, resulting in the release of the loads. In addition, enzymes, DNAzymes, and disease-specific biomarkers are used to unlock the gated NMOFs. The triggered release of drugs for cancer therapy, anti-blood clotting, and the design of autonomous insulin-delivery systems ("artificial pancreas") are discussed. Specifically, multi-drug carrier systems and functional NMOFs exhibiting dual and cooperative therapeutic functions are introduced. The future perspectives and applications of stimuli-responsive particles are addressed.

Coordination-based self-assembled capsules (SACs) for protein, CRISPR-Cas9, DNA and RNA delivery

Biologics, such as functional proteins and nucleic acids, have recently dominated the drug market and comprise seven out of the top 10 best-selling drugs. Biologics are usually polar, heat sensitive, membrane impermeable and subject to enzymatic degradation and thus require systemic routes of administration and delivery. Coordination-based delivery vehicles, which include nanosized extended metal-organic frameworks (nMOFs) and discrete coordination cages, have gained a lot of attention because of their remarkable biocompatibility, in vivo stability, on-demand biodegradability, high encapsulation efficiency, easy surface modification and moderate synthetic conditions. Consequently, these systems have been extensively utilized as carriers of biomacromolecules for biomedical applications. This review summarizes the recent applications of nMOFs and coordination cages for protein, CRISPR-Cas9, DNA and RNA delivery. We also highlight the progress and challenges of coordination-based platforms as a promising approach towards clinical biomacromolecule delivery and discuss integral future research directions and applications.