Modulating the Biofunctionality of Metal–Organic‐Framework‐Encapsulated Enzymes through Controllable Embedding Patterns

Embedding an enzyme within a MOF as exoskeleton (enzyme@MOF) offers new opportunities to improve the inherent fragile nature of the enzyme, but also to impart novel biofunctionality to the MOF. Despite the remarkable stability achieved for MOF‐embedded enzymes, embedding patterns and conversion of the enzymatic biofunctionality after entrapment by a MOF have only received limited attention. Herein, we reveal how embedding patterns affect the bioactivity of an enzyme encapsulated in ZIF‐8. The enzyme@MOF can maintain high activity when the encapsulation process is driven by rapid enzyme‐triggered nucleation of ZIF‐8. When the encapsulation is driven by slow coprecipitation and the enzymes are not involved in the nucleation of ZIF‐8, enzyme@MOF tends to be inactive owing to unfolding and competing coordination caused by the ligand, 2‐methyl imidazole. These two embedding patterns can easily be controlled by chemical modification of the amino acids of the enzymes, modulating their biofunctionality.     

Black Gold: Plasmonic Colloidosomes with Broadband Absorption Self‐Assembled from Monodispersed Gold Nanospheres by Using a Reverse Emulsion System

A facile approach for the fabrication of novel black plasmonic colloidosomes assembled from Au nanospheres is developed by an emulsion‐templating strategy. This self‐assembly process is based on a new reverse water‐in‐1‐butanol emulsion system, in which the water emulsion droplets can dissolve into 1‐butanol (oil) phase at an appropriate rate. These Au colloidosomes possess hexagonal close‐packed multilayer shells and show a low reflectivity and intense broadband absorption owing to the strong interparticle plasmonic coupling, which is further investigated by a finite‐difference time‐domain method. This method is universal and is suitable for self‐assembly of different noble‐metal nanoparticles into different colloidosomes. These colloidosomes have important applications in photothermal therapy, biosensors, and drug delivery.     

Controlling Dissolution and Transformation of Zeolitic Imidazolate Frameworks by using Electron‐Beam‐Induced Amorphization

Amorphous zeolitic imidazolate frameworks (ZIFs) offer promising applications as novel functional materials. Herein, amorphization of ZIF‐L through scanning‐electron‐beam exposure is demonstrated, based on amorphization of individual ZIF‐L crystals. The amorphized ZIF product has drastically increased stability against dissolution in water. An electron dose that allows for complete preservation of amorphous particles after immersion in water is established, resulting in new shapes of amorphous ZIF‐L with spatial control at the sub‐micrometer length scale. Changed water stability as a consequence of scanning‐electron‐beam exposure is demonstrated for three additional metal–organic frameworks (ZIF‐8, Zn(BeIm)OAc, MIL‐101), highlighting the potential use of an electron beam for top‐down MOF patterning. Lastly, recrystallization of ZIF‐L in the presence of linker is studied and shows distinct differences for crystalline and amorphized material.     

In situ Growth of a Cobalt‐based Metal‐organic Framework on Multi‐walled Carbon Nanotubes for Simultaneously Detection of Hydroquinone and Catechol.

In the present study, we report a facile method for preparing a porous MWCNTs/ZIF‐67 nanocomposite with the help of a morphology‐maintained ZIF‐67 in situ growth on multi‐walled carbon nanotubes. Interesting, the MWCNTs/ZIF‐67 nanocomposite demonstrated excellent electrochemical activity for hydroquinone (HQ) and catechol (CC) attribute to the effective interconnections ZIF‐67 crystals and MWCNTs. The analytical curves for HQ and CC obtained by differential pulse voltammetry (DPV) were linear in the range from 0.5 to 100 μM. Benefitting from the excellent conductivity of MWCNTs as well as the high surface area and porosity of ZIF‐67, the advanced nanocomposite displayed good reproducibility, high selectivity and excellent stability, and was successfully employed to assay the content of dihydroxybenzene isomers in the lake water samples.     

Cancer‐Cell Imaging Using Copper‐Doped Zeolite Imidazole Framework‐8 Nanocrystals Exhibiting Oxidative Catalytic Activity

Copper‐doped zeolite imidazole framework‐8 (Cu/ZIF‐8) was prepared and its peroxidase‐like oxidative catalytic activity was examined with a demonstration of its applicability for cancer‐cell imaging. Through simple solution chemistry at room temperature, Cu/ZIF‐8 nanocrystals were produced that catalytically oxidized an organic substrate of o‐phenylenediamine in the presence of H₂O₂. In a similar manner to peroxidase, the Cu/ZIF‐8 nanocrystals oxidized the substrate through a ping‐pong mechanism with an activation energy of 59.2 kJ mol⁻¹. The doped Cu atoms functioned as active sites in which the active Cu intermediates were expected to be generated during the catalysis, whereas the undoped ZIF‐8 did not show any oxidative activity. Cu/ZIF‐8 nanocrystals exhibited low cell toxicity and displayed catalytic activity through interaction with H₂O₂ among various reactive oxygen species in a cancer cell. This oxidative activity in vitro allowed cancer‐cell imaging by exploiting the photoluminescence emitted from the oxidized product of o‐phenylenediamine, which was insignificant in the absence of the Cu/ZIF‐8 nanocrystals. The results of this study suggest that the Cu/ZIF‐8 nanocrystal is a promising catalyst for the analysis of the microbiological systems.     

GOx@ZIF‐8(NiPd) Nanoflower: An Artificial Enzyme System for Tandem Catalysis

We report a facile approach to prepare an artificial enzyme system for tandem catalysis. NiPd hollow nanoparticles and glucose oxidase (GOx) were simultaneously immobilized on the zeolitic imidazolate framework 8 (ZIF‐8) via a co‐precipitation method. The as‐prepared GOx@ZIF‐8(NiPd) nanoflower not only exhibited the peroxidase‐like activity of NiPd hollow nanoparticles but also maintained the enzymatic activity of GOx. A colorimetric sensor for rapid detection of glucose was realized through the GOx@ZIF‐8(NiPd) based multi‐enzyme system. Moreover, the GOx@ZIF‐8(NiPd) modified electrode showed good bioactivity of GOx and high electrocatalytic activity for the oxygen reduction reaction (ORR), which could also be used for electrochemical detection of glucose.     

Modulation of Higher‐order Behaviour in Model Protocell Communities by Artificial Phagocytosis

Collective behaviour in mixed populations of synthetic protocells is an unexplored area of bottom‐up synthetic biology. The dynamics of a model protocell community is exploited to modulate the function and higher‐order behaviour of mixed populations of bioinorganic protocells in response to a process of artificial phagocytosis. Enzyme‐loaded silica colloidosomes are spontaneously engulfed by magnetic Pickering emulsion (MPE) droplets containing complementary enzyme substrates to initiate a range of processes within the host/guest protocells. Specifically, catalase, lipase, or alkaline phosphatase‐filled colloidosomes are used to trigger phagocytosis‐induced buoyancy, membrane reconstruction, or hydrogelation, respectively, within the MPE droplets. The results highlight the potential for exploiting surface‐contact interactions between different membrane‐bounded droplets to transfer and co‐locate discrete chemical packages (artificial organelles) in communities of synthetic protocells.     

Fabrication of ZIF‐8@Polyphosphazene core‐shell structure and its efficient synergism with ammonium polyphosphate in flame‐retarding epoxy resin

A novel zeolitic imidazolate framework (ZIF‐8) nanoparticles@polyphosphazene (PZN) core‐shell architecture was synthesized, and then, ZIF‐8@PZN and ammonium polyphosphate (APP) were applied for increasing the flame retardancy and mechanical property of epoxy resin (EP) through a cooperative effect. Herein, ZIF‐8 was used as the core; the shell of PZN was coated to ZIF‐8 nanoparticles via a polycondensation method. The well‐designed ZIF‐8@PZN displayed superior fire retardancy and smoke suppression effect. The synthesized ZIF‐8@PZN observably raised the flame retardancy of EP composites, which could be demonstrated by thermogravimetric analysis (TGA) and a cone calorimeter test (CCT). The chemical structure of ZIF‐8@PZN was characterized by X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). Compared with pure epoxy, with the incorporation of 3 wt% ZIF‐8@PZN and 18 wt% APP into the EP, along with 80.8%, 72.6%, and 64.7% decreased in the peak heat release rate (pHRR), the peak smoke production rate (pSPR), and the peak CO production rate (pCOPR), respectively. These suggested that ZIF‐8@PZN and APP generated an intumescent char layer, and ZIF‐8@PZN can strengthen the char layer, resulting in the enhancement in the flame resistance of EP.     

Plasmonic Colloidosomes as Three‐Dimensional SERS Platforms with Enhanced Surface Area for Multiphase Sub‐Microliter Toxin Sensing

Colloidosomes are robust microcapsules attractive for molecular sensing because of their characteristic micron size, large specific surface area, and dual‐phase stability. However, current colloidosome sensors are limited to qualitative fluorogenic receptor‐based detection, which restrict their applicability to a narrow range of molecules. Here, we introduce plasmonic colloidosome constructed from Ag nanocubes as an emulsion‐based 3D SERS platform. The colloidosomes exhibit excellent mechanical robustness, flexible size tunability, versatility to merge, and ultrasensitivity in SERS quantitation of food/industrial toxins down to sub‐femtomole levels. Using just 0.5 μL of sample volumes, our plasmonic colloidosomes exhibit >3000‐fold higher SERS sensitivity over conventional suspension platform. Notably, we demonstrate the first high‐throughput multiplex molecular sensing across multiple liquid phases.     

(110)‐Oriented ZIF‐8 Thin Films on ITO with Controllable Thickness

(110)‐oriented zeolitic imidazolate framework (ZIF)‐8 thin films with controllable thickness are successfully deposited on indium tin oxide (ITO) electrodes at room temperature. The method applied uses 3‐aminopropyltriethoxysilane (APTES) in the form of self‐assembled monolayers (SAMs), followed by a subsequent adoption of the layer‐by‐layer (LBL) method. The crystallographic preferential orientation (CPO) index shows that the ZIF‐8 thin films are (110)‐oriented. A possible mechanism for the growth of the (110)‐oriented ZIF‐8 thin films on 3‐aminopropyltriethoxysilane modified ITO is proposed. The observed cross‐sectional scanning electron microscopy (SEM) images and photoluminescent (PL) spectra of the ZIF‐8 thin films indicate that the thickness of the ZIF‐8 layers is proportional to the number of growth cycles. The extension of such a SAM method for the fabrication of ZIF‐8 thin films as described herein should be applicable in other ZIF materials, and the as‐prepared ZIF‐8 thin films on ITO may be explored for photoelectrochemical applications.     

Growth of lightly crosslinked PHEMA brushes and capsule formation using pickering emulsion interface‐initiated ATRP

In this work, growth of lightly crosslinked poly(2‐hydroxyethyl methacrylate) (PHEMA) brushes and subsequent capsule formation using Pickering emulsion interface‐initiated atom transfer radical polymerization (PEII‐ATRP) were investigated. Initiator‐immobilized silica nanoparticles (2.5 initiators/nm²) assembled at the interface of paraffin oil‐in‐water emulsions and ultimately stable Pickering emulsions were formed. PEII‐ATRP was conducted in the water phase of Pickering emulsions from the part of the surfaces of initiator‐immobilized silica nanoparticles exposed to water by using copper(I) chloride/bipyridine as catalyst at 35 °C. As PHEMA has a character of lightly crosslinking when the polymerization occurs in water, novel hybrid capsules (“colloidosomes”) can be obtained and were observed by confocal laser scanning microscope (CLSM) and optical microscopy (OM). The semipermeability of the resultant hollow capsules was demonstrated by the diffusion of 1‐phenylazo‐2‐naphthol. Meanwhile, the conformation of PHEMA chains can be varied in different solvents, which affects the semipermeability of these hybrid hollow capsules. We expect these hollow capsules can be further utilized to develop microdevices for drugs or cells delivery. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1354–1367, 2009     

Biomimetic Superhydrophobic/Superoleophilic Highly Fluorinated Graphene Oxide and ZIF‐8 Composites for Oil–Water Separation

Superhydrophobic/superoleophilic composites HFGO@ZIF‐8 have been prepared from highly fluorinated graphene oxide (HFGO) and the nanocrystalline zeolite imidazole framework ZIF‐8. The structure‐directing and coordination‐modulating properties of HFGO allow for the selective nucleation of ZIF‐8 nanoparticles at the graphene surface oxygen functionalities. This results in localized nucleation and size‐controlled ZIF‐8 nanocrystals intercalated in between HFGO layers. The composite microstructure features fluoride groups bonded at the graphene. Self‐assembly of a unique micro‐mesoporous architecture is achieved, where the micropores originate from ZIF‐8 nanocrystals, while the functionalized mesopores arise from randomly organized HFGO layers separated by ZIF‐8 nanopillars. The hybrid material displays an exceptional high water contact angle of 162° and low oil contact angle of 0° and thus reveals very high sorption selectivity, fast kinetics, and good absorbencies for nonpolar/polar organic solvents and oils from water. Accordingly, Sponge@HFGO@ZIF‐8 composites are successfully utilized for oil–water separation.     

Fabrication of poly(ethylene glycol)‐based hydrogels entrapping enzyme‐immobilized silica nanoparticles

In this study, we immobilized enzymes by combining covalent surface immobilization and hydrogel entrapment. A model enzyme, glucose oxidase (GOX), was first covalently immobilized on the surface of silica nanoparticles (SNPs) via 3‐aminopropyltriethoxysilane (APTES), and the resultant SNP‐immobilized enzyme was physically entrapped within photopolymerized hydrogels prepared from two different molecular weights (MWs) (575 and 8000 Da) of poly(ethylene glycol)(PEG). The hydrogel entrapment resulted in a decrease in reaction rate and an increase in apparent K_m of SNP‐immobilized GOX, but these negative effects could be minimized by using hydrogel with a higher MW PEG, which provides higher water content and larger mesh size. The catalytic rate of the PEG 8000 hydrogel was about ten times faster than that of the PEG 575 hydrogel because of enhanced mass transfer. Long‐term stability test demonstrated that SNP‐immobilized GOX entrapped within hydrogel maintained more than 60% of its initial activity after a week, whereas non‐entrapped SNP‐immobilized GOX and entrapped GOX without SNP immobilization maintained less than 20% of their initial activity. Incorporation of SNPs into hydrogel enhanced the mechanical strength of the hydrogel six‐fold relative to bare hydrogels. Finally, a hydrogel microarray entrapping SNP‐immobilized GOX was fabricated using photolithography and successfully used for quantitative glucose detection. Copyright © 2009 John Wiley & Sons, Ltd.     

Fabrication of ZIF‐8@SiO2 Core–Shell Microspheres as the Stationary Phase for High‐Performance Liquid Chromatography

The unique features of high porosity, shape selectivity, and multiple active sites make metal–organic frameworks (MOFs) promising as novel stationary phases for high‐performance liquid chromatography (HPLC). However, the wide particle size distribution and irregular shape of conventional MOFs lead to lower column efficiency of such MOF‐packed columns. Herein, the fabrication of monodisperse MOF@SiO₂ core–shell microspheres as the stationary phase for HPLC to overcome the above‐mentioned problems is reported. Zeolitic imidazolate framework 8 (ZIF‐8) was used as an example of MOFs due to its permanent porosity, uniform pore size, and exceptional chemical stability. Unique carboxyl‐modified silica spheres were used as the support to grow the ZIF‐8 shell. The fabricated monodisperse ZIF‐8@SiO₂ packed columns (5 cm long × 4.6 mm i.d.) show high column efficiency (23 000 plates m^?1 for bisphenol A) for the HPLC separation of endocrine‐disrupting chemicals (bisphenol A, β‐estradiol, and p‐(tert‐octyl)phenol) and pesticides (thiamethoxam, hexaflumuron, chlorantraniliprole, and pymetrozine) within 7 min with good relative standard deviations for 11 replicate separations of the analytes (0.01–0.39, 0.65–1.7, 0.70–1.3, and 0.17–0.91 % for retention time, peak area, peak height, and half peak width, respectively). The ZIF‐8@SiO₂ microspheres combine the advantages of the good column packing properties of the uniform monodisperse silica microspheres and the separation ability of the ZIF‐8 crystals.     

Hollow Zn/Co ZIF Particles Derived from Core–Shell ZIF‐67@ZIF‐8 as Selective Catalyst for the Semi‐Hydrogenation of Acetylene

The rational design of metal–organic frameworks (MOFs) with hollow features and tunable porosity at the nanoscale can enhance their intrinsic properties and stimulates increasing attentions. In this Communication, we demonstrate that methanol can affect the coordination mode of ZIF‐67 in the presence of Co²⁺ and induces a mild phase transformation under solvothermal conditions. By applying this transformation process to the ZIF‐67@ZIF‐8 core–shell structures, a well‐defined hollow Zn/Co ZIF rhombic dodecahedron can be obtained. The manufacturing of hollow MOFs enables us to prepare a noble metal@MOF yolk‐shell composite with controlled spatial distribution and morphology. The enhanced gas storage and porous confinement that originate from the hollow interior and coating of ZIF‐8 confers this unique catalyst with superior activity and selectivity toward the semi‐hydrogenation of acetylene.     

Detection of Hydrogen Peroxide and Glucose Based on Immobilized C60‐Catalase Enzyme

The interaction between fullerene C60 and catalase enzyme was studied with a fullerene C60‐coated piezoelectric (PZ) quartz crystal sensor. The partially irreversible response of the C60‐coated PZ crystal sensor for catalase was observed by the desorption study, which implied that C60 could chemically react with catalase. Thus, immobilized fullerene C60‐catalase enzyme was synthesized and applied in determining hydrogen peroxide in aqueous solutions. An oxygen electrode detector with the immobilized C60‐catalase was also employed to detect oxygen, a product of the hydrolysis of hydrogen peroxide which was catalyzed by the C60‐catalase. The oxygen electrode/C60‐catalase detection system exhibited linear responses to the concentration of hydrogen peroxide and amount of immobilized C60‐catalase enzyme that was used. The effects of pH and temperature on the activity of the immobilized C60‐catalase enzyme were also investigated. Optimum pH at 7.0 and optimum temperature at 25 °C for activity of the insoluble immobilized C60‐catalase enzyme were found. The immobilized C60‐catalase enzyme could be reused with good repeatability of the activity. The lifetime of the immobilized C60‐catalase enzyme was long enough with an activity of 93% after 95 days. The immobilized C60‐catalase enzyme was also applied in determining glucose which was oxidized with glucose oxidase resulting in producing hydrogen peroxide, followed by detecting hydrogen peroxide with the oxygen electrode/C60‐catalase detection system.     

Chiral Metal–Organic Framework Hollow Nanospheres for High‐Efficiency Enantiomer Separation

Chiral ZIF‐8 hollow nanospheres with d ‐histidine as part of chiral ligands (denoted as H‐d ‐his‐ZIF‐8) were prepared for separation of (±)‐amine acids. Compared to bulk d ‐his‐ZIF‐8 without a hollow cavity, the prepared H‐d ‐his‐ZIF‐8 showed 15 times higher separation capacity and higher ee values of 90.5 % for alanine, 95.2 % for glutamic acid and 92.6 % for lysine, respectively.     

Poly(p‐vinylbenzoic acid)‐block‐polystyrene Self‐assembled Structures as Templates in the Synthesis of ZIF‐8

Hybrid nanocrystals of PVBA‐b ‐PS/ZIF‐8 were prepared by the growth of ZIF‐8 on the surface of the self‐assembled structures from poly(p ‐vinylbenzoic acid)‐block‐polystyrene. Two different morphologies—micelles and vesicles—were obtained in selective solvents owing to the different ratios of PVBA to PS blocks. The structure and morphology of the PVBA‐b ‐PS/ZIF‐8 composites were characterized by Fourier transform IR spectroscopy, thermogravimetric analysis, X‐ray diffraction, transmission electron microscopy and scanning electron microscopy. PVBA‐b ‐PS/ZIF‐8 showed high catalytic performance in Knoevenagel condensation reactions at room temperature, which were attributed to the more exposed active sites of the small ZIF‐8 nanocrystals grown in a confined space and a high concentration of reactants in the polymeric aggregates.     

Mechanically fabricated Metal–organic framework/resin composite nanoparticles for efficient basic catalysis

Zeolitic imidazolate framework‐8 (ZIF‐8) was successfully composited with an anionic basic resin 201 × 7 (717‐resin) to provide a novel ZIF‐8/717‐resin composite. Its catalytic activity toward the Knoevenagel condensation reaction was evaluated. Results showed that ZIF‐8/717‐resin composite could efficiently catalyze this reaction, affording the corresponding products in good to excellent yields. Good functional group tolerance, mild reaction conditions, good stability and reusability of the catalyst are the major features of present protocol.     

Simultaneous Spray Self‐Assembly of Highly Loaded ZIF‐8–PDMS Nanohybrid Membranes Exhibiting Exceptionally High Biobutanol‐Permselective Pervaporation

The ability to obtain a maximum loading of inorganic nanoparticles while maintaining uniform dispersion in the polymer is the key to the fabrication of mixed‐matrix membranes with high pervaporation performance in bioalcohol recovery from aqueous solution. Herein, we report the simultaneous spray self‐assembly of a zeolitic imidazolate framework (ZIF)–polymer suspension and a cross‐linker/catalyst solution as a method for the fabrication of a well‐dispersed ZIF‐8–PDMS nanohybrid membrane with an extremely high loading. The ZIF‐8–PDMS membrane showed excellent biobutanol‐permselective pervaporation performance. When the ZIF‐8 loading was increased to 40 wt %, the total flux and separation factor could reach 4846.2 g m⁻² h⁻¹ and 81.6, respectively, in the recovery of n‐butanol from 1.0 wt % aqueous solution (80 °C). This new method is expected to have serious implications for the preparation of defect‐free mixed‐matrix membranes for many applications.