Zeolitic imidazolate frameworks for use in electrochemical and optical chemical sensing and biosensing: a review

Synthesis and Application of a pH-Responsive Functional Metal-Organic Framework: In Vitro Investigation for Delivery of Oridonin in Cancer Therapy

Oridonin (Ori) is a naturally existing diterpenoid substance that mainly exists in the Chinese medicinal plant Rabdosia rubescens. It was previously found to possess intriguing biological properties; however, the quick clearance from plasma and limited solubility in water restricts its use as a drug. Several metal-organic frameworks (MOFs), having big surfaces and large pores, have recently been considered promising drug transporters. The zeolitic imidazolate framework-8 (ZIF-8), a form of MOF consisting of 2-methylimidazole with zinc ions, is structurally stable under physiologically neutral conditions, while it can degrade at low pH values such as in tumor cells. Herein, a nanosized drug delivery system, Ori@ZIF-8, was successfully designed for encapsulating and transporting oridonin to the tumor site. The drug loading of the prepared Ori@ZIF-8 was 26.78%, and the particles' mean size was 240.5 nm. In vitro, the release of Ori@ZIF-8 exhibited acid sensitivity, with a slow release under neutral conditions and rapid release of the drug under weakly acidic conditions. According to the in vitro anti-tumor experiments, Ori@ZIF-8 produced higher cytotoxicity than free Ori and induced apoptosis in A549 cancer cells. In conclusion, Ori@ZIF-8 could be a potential pH-responsive carrier to accurately release more oridonins at the tumor site.

Natural Polymer Encapsulated Zeolitic Imidazolate Framework-12 Composite toward Electrochemical Sensing of Antitumor Agent

Encapsulation of natural polymer pectin (Pec) into a zeolitic imidazolate framework-12 (ZIF-12) matrix via a simple chemical method toward anticancer agent gallic acid (GA) detection is reported in this work. GA, a natural phenol found in many food sources, has gained attention by its biological effects on the human body, such as an antioxidant and anti-inflammatory. Therefore, it is crucial to accurately and rapidly determine the GA level in humans. The encapsulation of Pec inside the ZIF-12 has been successfully confirmed from the physiochemical studies such as XRD, Raman, FTIR, and XPS spectroscopy along with morphological FESEM, BET, and HRTEM characterization. Under optimized conditions, the Pec@ZIF-12 composite exhibits wide linear range of 20 nM-250 μM with a detection limit of 2.2 nM; also, it showed excellent selectivity, stability, and reproducibility. Furthermore, the real sample analysis of food samples including tea, coffee, grape, and pomegranate samples shows exceptional recovery percentage in an unspiked manner. So far, there is little literature for encapsulating proteins, enzymes, metals, etc., that have been reported; here, we successfully encapsulated a natural polymer Pec inside the ZIF-12 cage. This encapsulation significantly enhanced the composite electrochemical performance, which could be seen from the overall results. All of these strongly suggest that the proposed Pec@ZIF-12 composite could be used for miniaturized device fabrication for the evaluation of GA in both home and industrial applications.

Portable wireless electrochemical sensing of breviscapine using core-shell ZIFs-derived Co nanoparticles embedded in N-doped carbon nanotube polyhedra-modified electrode

A core-shell ZIF-67@ZIF-8-derived Co nanoparticles embedded in N-doped carbon nanotube polyhedra (Co/C-NCNP) hybrid nanostructure was prepared by a pyrolysis method. The synthesized Co/C-NCNP was modified on the screen-printed carbon electrode and used for the portable wireless sensitive determination of breviscapine (BVC) by differential pulse voltammetry. The Co/C-NCNP had a large surface area and excellent catalytic activity with increasing Co sites to combine with BVC for selective determination, which led to the improvement of the sensitivity of the electrochemical sensor. Under optimized conditions, the constructed sensor had linear ranges from 0.15 to 20.0 µmol/L and 20.0 to 100.0 µmol/L with the limit of detection of 0.014 µmol/L (3S0/S). The sensor was successfully applied to BVC tablet sample analysis with satisfactory results. This work provided the potential applications of zeolitic imidazolate framework-derived nanomaterials in the fabrication of electrochemical sensors for the sensitive detection of drug samples.

Vibrational dynamics as an essential determinant of the thermal stability of zinc zeolitic imidazolate lattices

Thermal stability and kinetics of zeolitic imidazolate frameworks (ZIFs) are crucial for their applications as energetic materials. Here, the effect of microscopic vibrational dynamics on the thermal stability of ZIFs is demonstrated by using simple tools. Specifically, we explored the thermal kinetics based on Flynn-Wall-Ozawa and Kissinger's methods. The study comprises a combination of structure-related effects such as topology, density, and alkyl substitution with respect to vibrational dynamics in ZIFs. The results exhibit a linear correlation between the vibrational dynamics of the linkers and activation energy, I.E. stabilization of ZIFs, in the polymorphic Zn(EtIm)2 series. At the same time, thermal destabilization was observed with the growing alkyl chain and was further probed by IR spectroscopy.

The Impact of ZIF-8 Particle Size Control on Low-Humidity Sensor Performance

An accurate humidity measurement is essential in various industries, including product stability, pharmaceutical and food preservation, environmental control, and precise humidity management in experiments and industrial processes. Crafting effective humidity sensors through precise material selection is crucial for detecting minute humidity levels across various fields, ultimately enhancing productivity and maintaining product quality. Metal-organic frameworks (MOFs), particularly zeolitic imidazolate frameworks (ZIFs), exhibit remarkable properties and offer a wide range of applications in catalysis, sensing, and gas storage due to their structural stability, which resembles zeolites. The previous research on MOF-based humidity sensors have primarily used electrical resistance-based methods. Recently, however, interest has shifted to capacitive-based sensors using MOFs due to the need for humidity sensors at low humidity and the resulting high sensitivity. Nevertheless, further studies are required to optimize particle structure and size. This study analyzes ZIF-8, a stable MOF synthesized in varying particle sizes, to evaluate its performance as a humidity sensor. The structural, chemical, and sensing properties of synthesized ZIF-8 particles ranging from 50 to 200 nanometers were examined through electron microscopy, spectroscopic, and electrochemical analyses. The fabricated copper electrodes combined with these particles demonstrated stable and linear humidity sensing capabilities within the range of 3% to 30% relative humidity (RH).

Adsorptive stripping voltammetric sensor based on Cd zeolitic imidazole framework-67 for electrochemical detection of sarin simulant

A selective and reliable modified glassy carbon sensor, based on a 1.0% Cd zeolitic imidazole framework-67 modified glassy carbon sensor (GCS2), has been developed for ultrasensitive detection of dimethyl methyl phosphonate (DMMP) in human biological fluid. The synthesis of porous nanoparticles of Cd zeolitic imidazole framework-67 (Cd ZIF-67) was carried out via the hydrothermal method. The resulting Cd ZIF-67 powder emerges with good crystallinity, a rhombic dodecahedral morphology with particle size in the range 300 ~ 500 nm, and a specific surface area of 1780 m2·g-1. Furthermore, the fabricated sensor exhibited superior performance in the detection of DMMP with two linearity ranges of 0.02-2.0 nM and 2.0-9.0 nM and a limit of detection (LOD) of 0.06 pM. The fabricated sensor exhibited good reliability, long-term stability, and repeatability, which are favourable attributes for electroanalytical detection. In addition, the fabricated sensor displayed superior performance without significant interference during the assay of DMMP in a biological fluid (human serum sample) within two linearity ranges of 0.1-1.0 nM and 1.0-6.0 nM and a LOD of 0.03 nM.

Highly sensitive electrochemical detection of cholesterol based on Au-Pt NPs/PAMAM-ZIF-67 nanomaterials

A cholesterol biosensor was constructed by bimetallic (Au and Pt) and poly(amidoamine)-zeolite imidazole framework (PAMAM-ZIF-67). First, PAMAM-ZIF-67 nanomaterial was immobilized onto the electrode, and then Au and Pt were modified on the electrode by the electro-deposition method. Subsequently, cholesterol oxidase (ChOx) and cholesterol esterase (ChEt) were fixed on the electrode. The stepwise modification procedures were recorded by impedance spectroscopy and voltammetry. The current response presented a linear relation to the logarithm of cholesterol content when content ranged between 0.00015 and 10.24 mM, and the minimum detection concentration reached 3 nM. The electrode was also used for the cholesterol assay in serum, which hinted at its potentially valuable in clinical diagnostics. An electrochemical biosensor based on gold nanoparticles, platinum nanoparticles, and polyamide-zeolitic imidazolate frameworks was developed for detection of cholesterol. First, polyamide-zeolitic imidazolate frameworks nanomaterial was fixed onto the electrode modified of mercaptopropionic acid by Au-S bond. Then, gold nanoparticles and platinum nanoparticles were electrodeposited on the above electrode. Subsequently, cholesterol oxidase and cholesterol esterase were co-immobilized on the surface of the modified electrode to fabricate the cholesterol biosensor. The biosensor has also been used for the measurement of cholesterol in human serum, which implied potential applications in biotechnology and clinical diagnostics.

Anisotropic Interface Successive Assembly for Bowl-Shaped Metal-Organic Framework Nanoreactors with Precisely Controllable Meso-/Microporous Nanodomains

Colloidal metal-organic framework (MOF) nanoparticles, with tailored asymmetric nanoarchitectures and hierarchical meso-/microporosities, have significant implications in high-performance nanocatalysts, nanoencapsulation carriers, and intricate assembly architectures. However, the methodology that could achieve precise control over the anisotropic growth of asymmetric MOF particles with tailored distributions of meso- and microporous regions has not yet been established. In this study, we introduce a facile anisotropic interface successive assembly approach to synthesize asymmetric core-shell MOF (ZIF-67) nanobowls with worm-like mesopores in the core and intrinsic micropores in the shell. Our synthesis pathway relies on anisotropic nucleation of mesoporous MOF nanohemispheres on emulsion interfaces through the cooperative assembly of surfactants and MOF precursors. This is followed by the growth of microporous MOF layers on both interfaces of mesoporous cores and emulsion droplets, resulting in a hierarchically porous core-shell nanostructure. By utilizing this multi-interface-driven approach, we enable the creation of diverse geometries and distributions of mesopores and micropores in asymmetric MOF nanoarchitectures. The obtained bowl-like meso-/microporous core-shell ZIF-67 particles exhibit enhanced catalytic activity for CO2 cycloaddition, attributed to reactant accumulation within the bowl-like architecture, active site accessibility in the open mesoporous core, and improved structural stability. Overall, our study provides insights and inspiration for exploring the intricate asymmetric nanostructures of hierarchically porous MOFs with diverse potential applications.

Application of Pt@ZIF-8 nanocomposite-based electrochemical biosensor for sensitive diagnosis of tau protein in Alzheimer's disease patients

Alzheimer's disease (AD) is a progressive brain disorder characterized by the ongoing decline of brain functions. Studies have revealed the detrimental effects of hyperphosphorylated tau (p-tau) protein fibrils in AD pathogenesis, highlighting the importance of this factor in the early-stage detection of AD conditions. We designed an electrochemical immunosensor for quantitative detection of the cis conformation of the p-tau protein (cis-p-tau) employing platinum nanoparticles (Pt NPs) supported on zeolitic imidazolate frameworks (ZIF) for modifying the glassy carbon electrode (GCE) surface. Under optimum conditions, the immunosensor selectively and sensitively detected cis-p-tau within the broad linear range of 1 fg mL-1 to 10 ng mL-1 and the low limit of detection (LOD) of 1 fg mL-1 with desired reproducibility and stability. Furthermore, the fabricated immunosensor's performance was examined for the cis-p-tau analysis in the serum of AD patients, indicating its accuracy and feasibility for real-sample analysis. Notably, this is the first application of Pt@ZIF-8 nanocomposite in fabricating a valid immunosensor for selective cis-p-tau detection, even in the presence of trans-p-tau. It is worth mentioning that the enzyme-linked immunosorbent assay (ELISA) reference technique is not able to evaluate pico- or femtomolar concentrations of cis-p-tau, making the fabricated immunosensor superior for early-stage measurement and screening of AD.

Metal-Organic Frameworks as Formose Reaction Catalysts with Enhanced Selectivity

The formose reaction is an autocatalytic series of aldol condensations that allows one to obtain monosaccharides from formaldehyde. The formose reaction suffers from a lack of selectivity, which hinders practical applications at the industrial level. Over the years, many attempts have been made to overcome this selectivity issue, with modest results. Heterogeneous porous catalysts with acid-base properties, such as Metal-Organic Frameworks (MOFs), can offer advantages compared to homogeneous strong bases (e.g., calcium hydroxide) for increasing the selectivity of this important reaction. For the very first time, four different Zeolite Imidazolate Frameworks are presented in this work as catalysts for the formose reaction in liquid phase, and their catalytic performances were compared with those of the typical homogeneous catalyst (i.e., calcium hydroxide). The heterogeneous nature of the catalysis, the possible contribution of leached metal or linkers to the solution, and the stability of the materials were investigated. The porous structure of these solids and their mild basicity make them suitable for obtaining enhanced selectivity at 30% formaldehyde conversion. Most of the MOFs tested showed low structural stability under reaction conditions, thereby indicating the need to search for new MOF families with higher robustness. However, this important result opens the path for future research on porous heterogeneous basic catalysts for the formose reaction.

Functional MOF-Based Materials for Environmental and Biomedical Applications: A Critical Review

Over the last ten years, there has been a growing interest in metal-organic frameworks (MOFs), which are a unique category of porous materials that combine organic and inorganic components. MOFs have garnered significant attention due to their highly favorable characteristics, such as environmentally friendly nature, enhanced surface area and pore volume, hierarchical arrangements, and adjustable properties, as well as their versatile applications in fields such as chemical engineering, materials science, and the environmental and biomedical sectors. This article centers on examining the advancements in using MOFs for environmental remediation purposes. Additionally, it discusses the latest developments in employing MOFs as potential tools for disease diagnosis and drug delivery across various ailments, including cancer, diabetes, neurological disorders, and ocular diseases. Firstly, a concise overview of MOF evolution and the synthetic techniques employed for creating MOFs are provided, presenting their advantages and limitations. Subsequently, the challenges, potential avenues, and perspectives for future advancements in the utilization of MOFs in the respective application domains are addressed. Lastly, a comprehensive comparison of the materials presently employed in these applications is conducted.

Self-powered enzyme-linked microneedle patch for scar-prevention healing of diabetic wounds

Diabetic wounds with complex pathological features and a difficult-to-heal nature remain a formidable challenge. To address this challenge, we design and fabricate a self-powered enzyme-linked microneedle (MN) patch composed of anode and cathode MN arrays, which respectively contain glucose oxidase (GOx) and horseradish peroxidase (HRP) encapsulated in ZIF-8 nanoparticles. The enzymatic cascade reaction in the MN patch can effectively reduce local hyperglycemia in diabetic wounds while generating stable microcurrents to promote rapid healing of diabetic wounds. Therefore, the diabetic wounds treated with this MN patch exhibit rapid, complete, and scar-preventative healing, which can be attributed to the synergistic actions of hypoglycemic, antibacterial, anti-inflammatory, and bioelectrical stimulation. In brief, the self-powered MN patch is an effective method to rapidly promote diabetic wound healing and prevent scar formation.

A chiral metal-organic framework synthesized by the mixture of chiral and non-chiral organic ligands for enantioseparation of drugs by open-tubular capillary electrochromatography

A chiral metal-organic framework L-Histidine-Zeolitic imidazolate framework-67 (L-His-ZIF-67) was synthesized by the mixture of chiral organic ligand L-histidine and non-chiral organic ligand 2-methylimidazole directly, and to the author's knowledge, the chiral L-His-ZIF-67 coated capillary column we prepared has still not been reported to date in the field of capillary electrophoresis. This chiral metal-organic frameworks material was used as the chiral stationary phase for enantioseparation of drugs by open-tubular capillary electrochromatography. The separation conditions such as pH value, buffer concentration and proportion of organic modifier were optimized. Under optimal conditions, the established enantioseparation system achieved good separation effect, and the resolution of five chiral drugs: esmolol (7.93), nefopam (3.03), salbutamol (2.42), scopolamine (1.08) and sotalol (0.81). In addition, the chiral recognition mechanism of L-His-ZIF-67 was elucidated by a series of mechanism experiments, and the specific interaction force was preliminarily speculated.

Metal-organic frameworks for food contaminant adsorption and detection

Metal-organic framework materials (MOFs) have been widely used in food contamination adsorption and detection due to their large specific surface area, specific pore structure and flexible post-modification. MOFs with specific pore size can be targeted for selective adsorption of some contaminants and can be used as pretreatment and pre-concentration steps to purify samples and enrich target analytes for food contamination detection to improve the detection efficiency. In addition, MOFs, as a new functional material, play an important role in developing new rapid detection methods that are simple, portable, inexpensive and with high sensitivity and accuracy. The aim of this paper is to summarize the latest and insightful research results on MOFs for the adsorption and detection of food contaminants. By summarizing Zn-based, Cu-based and Zr-based MOFs with low cost, easily available raw materials and convenient synthesis conditions, we describe their principles and discuss their applications in chemical and biological contaminant adsorption and sensing detection in terms of stability, adsorption capacity and sensitivity. Finally, we present the limitations and challenges of MOFs in food detection, hoping to provide some ideas for future development.

Nanoparticles-mediated CRISPR-Cas9 gene therapy in inherited retinal diseases: applications, challenges, and emerging opportunities

Inherited Retinal Diseases (IRDs) are considered one of the leading causes of blindness worldwide. However, the majority of them still lack a safe and effective treatment due to their complexity and genetic heterogeneity. Recently, gene therapy is gaining importance as an efficient strategy to address IRDs which were previously considered incurable. The development of the clustered regularly-interspaced short palindromic repeats (CRISPR)-CRISPR-associated protein 9 (Cas9) system has strongly empowered the field of gene therapy. However, successful gene modifications rely on the efficient delivery of CRISPR-Cas9 components into the complex three-dimensional (3D) architecture of the human retinal tissue. Intriguing findings in the field of nanoparticles (NPs) meet all the criteria required for CRISPR-Cas9 delivery and have made a great contribution toward its therapeutic applications. In addition, exploiting induced pluripotent stem cell (iPSC) technology and in vitro 3D retinal organoids paved the way for prospective clinical trials of the CRISPR-Cas9 system in treating IRDs. This review highlights important advances in NP-based gene therapy, the CRISPR-Cas9 system, and iPSC-derived retinal organoids with a focus on IRDs. Collectively, these studies establish a multidisciplinary approach by integrating nanomedicine and stem cell technologies and demonstrate the utility of retina organoids in developing effective therapies for IRDs.

Application of zeolites and zeolitic imidazolate frameworks in the biosensor development

Biosensors are advanced devices for analysis of composition of blood, urine, environmental samples, and many other media. Their current development is tightly linked with nanomaterials, such as zeolites and zeolitic imidazolate framework (ZIFs). The present review describes electrochemical (amperometric, conductometric, ISFET) and optical (fluorescent and colorimetric) biosensors that incorporate zeolites and ZIFs in their biorecognition elements. The biosensors are based on immobilized enzymes (such as glucose oxidase, urease, and acetylcholinesterase), antibodies, DNA, and aptamers. The review present reasons for application of these nanomaterials, and discusses advantages of zeolite- and ZIF-containing biosensors over other biosensors. In most cases, the biosensors have improved sensitivity, better limit of detection, wider linear range, and other improved characteristics. It is demonstrated that immobilization of biomolecules such as enzymes or antibodies on the surface of zeolites and ZIFs enables creation of unique advanced biosensors that have a potential for further development and practical applications.

ZIF-X (8, 67) based nanostructures for gas-sensing applications

ZIF-8 and ZIF-67 are the most investigated zeolitic imidazolate frameworks (ZIFs) materials that have aroused enormous scientific interests in numerous areas of application including electrochemistry, gas storage, separation, and sensors by reason of their fascinating structural properties. Recently, there is a rapidly growing demand for chemical gas sensors for the detection of various analytes in widespread applications including environmental pollution monitoring, clinical analysis, wastewater analysis, industrial applications, food quality, consumer products, and automobiles. In general, the key to the development of superior gas sensors is exploring innovative sensing materials. ZIF-X (8, 67) based nanostructures have demonstrated great potential as ideal sensing materials for high-performance sensing applications. In this review, the general properties and applications of ZIF-X (8, 67) including gas storage and gas adsorption are first summarized, and then the recent progress of ZIF-X (8, 67) based nanostructures for gas-sensing applications and the structure-property correlations are summarized and analyzed.

Multilayered Mesoporous Composite Nanostructures for Highly Sensitive Label-Free Quantification of Cardiac Troponin-I

Cardiac troponin-I (cTnI) is a well-known biomarker for the diagnosis and control of acute myocardial infarction in clinical practice. To improve the accuracy and reliability of cTnI electrochemical immunosensors, we propose a multilayer nanostructure consisting of Fe₃O₄-COOH labeled anti-cTnI monoclonal antibody (Fe₃O₄-COOH-Ab₁) and anti-cTnI polyclonal antibody (Ab₂) conjugated on Au-Ag nanoparticles (NPs) decorated on a metal–organic framework (Au-Ag@ZIF-67-Ab₂). In this design, Fe₃O₄-COOH was used for separation of cTnI in specimens and signal amplification, hierarchical porous ZIF-67 extremely enhanced the specific surface area, and Au-Ag NPs synergically promoted the conductivity and sensitivity. They were additionally employed as an immobilization platform to enhance antibody loading. Electron microscopy images indicated that Ag-Au NPs with an average diameter of 1.9 ± 0.5 nm were uniformly decorated on plate-like ZIF-67 particles (with average size of 690 nm) without any agglomeration. Several electrochemical assays were implemented to precisely evaluate the immunosensor performance. The square wave voltammetry technique exhibited the best performance with a sensitivity of 0.98 mA mL cm⁻² ng⁻¹ and a detection limit of 0.047 pg mL⁻¹ in the linear range of 0.04 to 8 ng mL⁻¹.

Synthesis of Carbon Nanoparticles with Cobalt-Rich Shell via Pyrolysis of Zn-ZIF@Co/Zn-ZIF: Relevance of Co(III) Precursors

To the best of our knowledge, this is the first report on the rapid one-pot synthesis of a unique core-shell-structured zeolitic imidazolate framework (ZIF) using Co(III) and Zn(II) precursors. The key to obtaining this unique structure is the use of a Co(III) precursor as the starting material. Transmission electron microscopy (TEM) reveals that Co was present within a 30-nm-thick shell layer of the ZIF material. Thermal decomposition of the ZIF material affords core-shell-structured carbon nanoparticles that have Co on the external surface of the carbon grain. We have previously demonstrated that this carbonaceous material obtained by thermal decomposition exhibited high performance as an adsorbent for nitric oxide, even in the presence of excess oxygen and water vapor, and therefore, it was a suitable material for NO_x elimination at low temperatures. The growth mechanism of the synthesized ZIF particles and the differences between synthesized ZIF and conventional Co(II)-ZIF-67 are discussed. The reactivity of the Co(III) precursor is much lower than that of the Co(II) species, leading to slower precipitation of Co(III) than that of Zn(II), thus forming the core-shell structure.

Mechanochemical Synthesis of Fluorine-Containing Co-Doped Zeolitic Imidazolate Frameworks for Producing Electrocatalysts

Catalysts derived from pyrolysis of metal organic frameworks (MOFs) are promising candidates to replace expensive and scarce platinum-based electrocatalysts commonly used in polymer electrolyte membrane fuel cells. MOFs contain ordered connections between metal centers and organic ligands. They can be pyrolyzed into metal- and nitrogen-doped carbons, which show electrocatalytic activity toward the oxygen reduction reaction (ORR). Furthermore, metal-free heteroatom-doped carbons, such as N-F-Cs, are known for being active as well. Thus, a carbon material with Co-N-F doping could possibly be even more promising as ORR electrocatalyst. Herein, we report the mechanochemical synthesis of two polymorphs of a zeolitic imidazole framework, Co-doped zinc 2-trifluoromethyl-1H-imidazolate (Zn_0.9Co_0.1(CF₃-Im)₂). Time-resolved in situ X-ray diffraction studies of the mechanochemical formation revealed a direct conversion of starting materials to the products. Both polymorphs of Zn_0.9Co_0.1(CF₃-Im)₂ were pyrolyzed, yielding Co-N-F containing carbons, which are active toward electrochemical ORR.

Visual naked-eye detection of SARS-CoV-2 RNA based on covalent organic framework capsules

The ongoing outbreak of coronavirus disease 2019 (COVID-19) caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has highlighted that new diagnosis technologies are crucial for controlling the spread of the disease. Especially in the resources-limit region, conveniently operated detection methods such as "naked-eye" detection are urgently required that no instrument is needed. Herein, we have designed a novel and facile strategy to fabricate covalent organic framework (COF) capsules, which can be utilized to establish a new colorimetric assay for naked-eye detection of SARS-CoV-2 RNA. Specifically, we employ the digestible ZIF-90 as the sacrificial template to prepare the hollow COF capsules for horseradish peroxidase (HRP) encapsulation. The fabricated COF capsules can provide an appropriate microenvironment for the enzyme molecules, which may improve the conformational freedom of enzymes, enhance the mass transfer, and endow the enzyme with high environmental resistance. With such design, the proposed assay exhibits outstanding analytical performance for the detection of SARS-CoV-2 RNA in the linear range from 5 pM to 50 nM with a detection limit of 0.28 pM which can go parallel to qTR-PCR analysis. Our method also possesses excellent selectivity and reproducibility. Moreover, this method can also be served to analyze the clinical samples, and can successfully differentiate COVID-19 patients from healthy people, suggesting the promising potential in clinical diagnosis.

Metal Organic Framework Nanomaterial-Based Extraction and Proteome Analysis of Membrane and Membrane-Associated Proteins

Membrane proteins (MPs) play a key role in various biological processes, while difficulties still exist in the extraction because of their inherent low abundance and poor solubility caused by high hydrophobicity. Metal organic framework (MOF) materials with good hydrophobic properties have the ability to absorb MPs, especially zeolitic imidazolate framework (ZIF) materials. Here, two MOF materials (ZIF-8 and ZIF-67) were compared for MP extraction, and our results revealed that higher yield was obtained with ZIF-67. After method development, the optimal enrichment effect was obtained when the mass ratio of proteins and ZIF-67 reached 1:20 with 100 mM NaCl in 20% ethanol at 4 °C and pH 9.0. When compared with a commercial kit, the extraction yield increased by 88.11% and the average number of identified MPs elevated by 29.17% with the developed ZIF method. Normal lung cell MRC5 was employed to verify the effectiveness of the ZIF method. Results showed 45.13% increase in yield and 22.88% increase in average number of identified MPs by the ZIF method. Our method was further applied to the enrichment of MPs for high-metastatic (95D) and low-metastatic (95C) human lung cancer cells. A total of 1732 (95D) and 1711 (95C) MPs were identified, among which 710 MPs were dysregulated significantly; 441 upregulated MPs in 95D cells were found to be closely related to the growth, proliferation, and migration of lung cancer cells. Our results collectively demonstrated that ZIF-67 was an ideal material for MP extraction, which might be helpful for analysis of cancer proteomics and discovery of cancer migration associated MPs.

A facile fabrication of a hierarchical ZIF-8/MWCNT nanocomposite for the sensitive determination of rutin

In this paper, a novel type of zeolitic imidazolate framework-8 (ZIF-8) polyhedron/multi-walled carbon nanotube (MWCNT) modified electrode was successfully prepared for effective on-site detection of rutin. The morphology and microstructure of the ZIF-8/MWCNT nanocomposite were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The electrochemical performance of the ZIF-8/MWCNT based electrode for the determination of rutin was studied by cyclic voltammetry (CV) and differential pulse stripping voltammetry (DPV). The as-prepared sensor illustrates better electrocatalytic activity and lower background current than the MWCNT modified electrode for the oxidation of rutin. Besides, the ZIF-8/MWCNTs sensor offers a remarkable linear response for rutin concentrations from 0.1 to 15 μM. The detection limit (LOD) was calculated to be 0.26 nM (S/N = 3). Also, the ZIF-8/MWCNT electrode showed high anti-interference ability towards common interfering species. More importantly, the fabricated electrode was quickly evaluated for determination of rutin in medicine tablets with satisfactory recoveries and the obtained results successfully achieved good consistency with the data from high performance liquid chromatography (HPLC). Finally, the method shows an enhanced electrocatalytic property and sensitivity for the analysis of rutin, which may provide an economical and promising electrochemical sensor for practical on-site detection of rutin.

A Cd(II) Luminescent Coordination Grid as a Multiresponsive Fluorescence Sensor for Cr(VI) Oxyanions and Cr(III), Fe(III), and Al(III) in Aqueous Medium

Hydro(solvo)thermal reactions of Cd(NO₃)₂, N-(pyridin-3-ylmethyl)-4-(pyridin-4-yl)-1,8-naphthalimide (NI-mbpy-34), and 5-bromobenzene-1,3-dicarboxylic acid (Br-1,3-H₂bdc) afforded a luminescent coordination polymer, {[Cd(Br-1,3-bdc)(NI-mbpy-34)(H₂O)]∙2H₂O}_n (1). Single-crystal X-ray diffraction analysis showed that 1 features a two-dimensional (2-D) gridlike sql layer with the point symbol of (4⁴·6²), where the Cd(II) center adopts a {CdO₅N₂} pentagonal bipyramidal geometry. Thermogravimetric (TG) analysis confirmed the thermal stability of 1 up to about 340 °C, whereas XRPD patterns proved the maintenance of crystallinity and framework integrity of 1 in CH₂Cl₂, H₂O, CH₃OH, and toluene. Photoluminescence studies indicated that 1 displayed intense blue fluorescence emissions in both solid-state and H₂O suspension-phase. Owing to the good fluorescent properties, 1 could serve as an excellent turn-off fluorescence sensor for selective and sensitive Cr(VI) detection in water, with LOD = 15.15 μM for CrO₄^2- and 14.91 μM for Cr₂O₇^2-, through energy competition absorption mechanism. In addition, 1 could also sensitively detect Cr³⁺, Fe³⁺, and Al³⁺ ions in aqueous medium via fluorescence-enhancement responses, with LOD = 2.81 μM for Cr³⁺, 3.82 μM for Fe³⁺, and 3.37 μM for Al³⁺, mainly through an absorbance-caused enhancement (ACE) mechanism.

ResponZIF Structures: Zeolitic Imidazolate Frameworks as Stimuli-Responsive Materials

Zeolitic imidazolate frameworks (ZIFs) have long been recognized as a prominent subset of the metal-organic framework (MOF) family, in part because of their ease of synthesis and good thermal and chemical stability, alongside attractive properties for diverse potential applications. Prototypical ZIFs like ZIF-8 have become embodiments of the significant promise held by porous coordination polymers as next-generation designer materials. At the same time, their intriguing property of experiencing significant structural changes upon the application of external stimuli such as temperature, mechanical pressure, guest adsorption, or electromagnetic fields, among others, has placed this family of MOFs squarely under the umbrella of stimuli-responsive materials. In this review, we provide an overview of the current understanding of the triggered structural and electronic responses observed in ZIFs (linker and bond dynamics, crystalline and amorphous phase changes, luminescence, etc.). We then describe the state-of-the-art experimental and computational methodology capable of shedding light on these complex phenomena, followed by a comprehensive summary of the stimuli-responsive nature of four prototypical ZIFs: ZIF-8, ZIF-7, ZIF-4, and ZIF-zni. We further expose the relevant challenges for the characterization and fundamental understanding of responsive ZIFs, including how to take advantage of their flexible properties for new application avenues.

Simultaneous electrochemical determination of DNA nucleobases using AgNPs embedded covalent organic framework

An efficient electrochemical biosensor has been developed for the simultaneous evaluation of DNA bases using AgNPs-embedded covalent organic framework (COF). The COF (p-Phenylenediamine and terephthalaldehyde) was synthesized by reflux (DMF; 150 °C; 12 h) and the nanoparticles were embedded from the aqueous solutions of AgNO3 and NaBH4. The nanocomposite-modified COF was confirmed by spectral, microscopic, and electrochemical techniques. The nanocomposite material was deposited on a glassy carbon electrode (GCE) and the redox behavior of AgNPs was confirmed by cyclic voltammetry. The electrocatalytic activities of DNA bases were analyzed by differential pulse voltammetry (DPV) in a physiological environment (PBS; pH = 7.0) based on simple and easy-to-use electrocatalyst. The AgNPs-COF/GCE showed well-defined anodic peak currents for the bases guanine (+ 0.63 V vs. Ag/AgCl), adenine (+ 0.89 V vs. Ag/AgCl), thymine (+ 1.10 V vs. Ag/AgCl), and cytosine (+ 1.26 V vs. Ag/AgCl) in a mixture as well as individuals with respect to the conventional, COF, and AgNPs/GCEs. The AgNPs-COF/GCE showed linear concentration range of DNA bases from 0.2-1000 µM (guanine; (G)), 0.1-500 µM (adenine (A)), 0.25-250 µM (thymine (T)) and 0.15-500 µM (cytosine (C)) and LOD of 0.043, 0.056, 0.062, and 0.051 µM (S/N = 3), respectively. The developed sensor showed reasonable selectivity, reproducibility (RSD = 1.53 ± 0.04%-2.58 ± 0.02% (n = 3)), and stability (RSD = 1.22 ± 0.06%-2.15 ± 0.04%; n = 3) over 5 days of storage) for DNA bases. Finally, AgNPs-COF/GCE was used for the determination of DNA bases in human blood serum, urine and saliva samples with good recoveries (98.60-99.11%, 97.80-99.21%, and 98.69-99.74%, respectively).

Tunable resistance of MOFs films via an anion exchange strategy for advanced gas sensing

Because of their ultra-high surface area, large porosity and excellent structural tailorability, metal-organic frameworks (MOFs) are considered as outstanding candidates among sensing materials for hazardous gas detection. However, most of MOFs-based sensing films show weak film adhesion and low conductivity due to the poor formation ability of MOFs films by traditional sensor fabrication methods as well as the intrinsic insulating character of these MOFs. In this work, we propose a novel strategy to directly grow robust gas-sensing films based on pristine MOFs arrays (ZIF-67 nanosheets) in-situ on the surface of ceramic substrates. To improve the conductivity of MOFs arrays, anion-exchange method is applied to couple Prussian blue analogue (PBA) on the surface of ZIF-67 arrays. Structural characterization revealed that this permutation reaction can significantly improve the conductivity of the MOF films while their sheet-like structures can be mainly remained. Benefiting from the robust structure and improved conductivity, the as-designed ZIF-67/PBA films exhibited superior sensing performances such as good reproducibility, high response value (R_g/R_a=11.7), and fast response/recovery speed (5/182 s) towards triethylamine. This work provides a new strategy to fabricate MOFs gas sensors and paves a new way to modulate the conductivity of MOF films.

An Update on Mesoporous Silica Nanoparticle Applications in Nanomedicine

The efficient and safe delivery of therapeutic drugs, proteins, and nucleic acids are essential for meaningful therapeutic benefits. The field of nanomedicine shows promising implications in the development of therapeutics by delivering diagnostic and therapeutic compounds. Nanomedicine development has led to significant advances in the design and engineering of nanocarrier systems with supra-molecular structures. Smart mesoporous silica nanoparticles (MSNs), with excellent biocompatibility, tunable physicochemical properties, and site-specific functionalization, offer efficient and high loading capacity as well as robust and targeted delivery of a variety of payloads in a controlled fashion. Such unique nanocarriers should have great potential for challenging biomedical applications, such as tissue engineering, bioimaging techniques, stem cell research, and cancer therapies. However, in vivo applications of these nanocarriers should be further validated before clinical translation. To this end, this review begins with a brief introduction of MSNs properties, targeted drug delivery, and controlled release with a particular emphasis on their most recent diagnostic and therapeutic applications.

Zeolitic imidazolate frameworks as intrinsic light harvesting and charge separation materials for photocatalysis

Zeolitic imidazolate frameworks (ZIFs) are a subclass of metal organic frameworks that have attracted considerable attention in the past years and have found many applications including heterogeneous catalysis due to their highly ordered porous structure, large surface area, and structural flexibility. However, ZIFs are largely utilized as simple hosts or passive media for dispersing other catalytically active species, resembling the roles of zeolites in catalysis. In contrast, our recent findings show that ZIFs not only have broad absorption across the UV-visible and near IR spectral region but also have an exceptionally long-lived excited charge separated state, suggesting that ZIFs may be used as intrinsic light harvesting and photocatalytic materials rather than as inert hosts. This Perspective will focus on the recent progress on the fundamental studies of the intrinsic light absorption, charge separation, and photocatalytic properties of ZIFs and will discuss the outlook for future development.

Highly selective gas sensing enabled by filters

Portable and inexpensive gas sensors are essential for the next generation of non-invasive medical diagnostics, smart air quality monitoring & control, human search & rescue and food quality assessment to name a few of their immediate applications. Therein, analyte selectivity in complex gas mixtures like breath or indoor air remains the major challenge. Filters are an effective and versatile, though often unrecognized, route to overcome selectivity issues by exploiting additional properties of target analytes (e.g., molecular size and surface affinity) besides reactivity with the sensing material. This review provides a tutorial for the material engineering of sorption, size-selective and catalytic filters. Of specific interest are high surface area sorbents (e.g., activated carbon, silica gels and porous polymers) with tunable properties, microporous materials (e.g., zeolites and metal-organic frameworks) and heterogeneous catalysts, respectively. Emphasis is placed on material design for targeted gas separation, portable device integration and performance. Finally, research frontiers and opportunities for low-cost gas sensing systems in emerging applications are highlighted.

Simultaneous electrochemical determination of nuc and mecA genes for identification of methicillin-resistant Staphylococcus aureus using N-doped porous carbon and DNA-modified MOF

The detection of Staphylococcus aureus specific gene in combination with the mecA gene is vitally important for accurate identification of methicillin-resistant Staphylococcus aureus (MRSA). A homogeneous electrochemical DNA sensor was fabricated for simultaneous detection of mecA and nuc gene in MRSA. Metal-organic framework (type UiO-66-NH₂) was applied as nanocarrier. Two electroactive dyes, methylene blue (MB) and epirubicin (EP), were encapsulated in UiO-66-NH₂, respectively, and were locked by the hybrid double-stranded DNA. Based on the target-response electroactive dye release strategy, once target DNA exists, it completely hybridizes with displacement DNA (D_EP and D_MB). So D_EP and D_MB is displaced from the MOF surface, causing the release of electroactive dyes. Co-Zn bimetallic zeolitic imidazolate framework-derived N-doped porous carbon serves for electrode modification to improve electrocatalytic performance and sensitivity. The differential pulse voltammetry peak currents of MB and EP were accurately detected at - 0.14 V and - 0.53 V versus the Ag/AgCl reference electrode, respectively. Under the optimal conditions, the detection limits of mecA gene and nuc gene were 3.7 fM and 1.6 fM, respectively. Combining the effective application of MOFs and the homogeneous detection strategy, the sensor exhibited satisfactory performance for MRSA identification in real samples. The recovery was 92.6-103%, and the relative standard deviation was less than 5%. Besides, MRSA and SA can also be distinguished. This sensor has great potential in practical applications.

Recent progress and perspectives on the structural design on metal-organic zeolite (MOZ) frameworks

As a typical group of coordination polymers, metal-organic zeolite (MOZs) frameworks inherit the topological and structural advantages of inorganic zeolites and display great application potential in many areas, including gas adsorption/separation, catalysis, luminescence and chemical sensing. In this review, we outline the recent progress in the synthesis, functionalization and application of metal-organic zeolite frameworks, mainly focusing on the basic structural design principle and synthesis strategy on 4-connect inorganic nodes and 2-connect organic linkers. Employing different valent metals, small inorganic TO₄^2- units and high-nuclear clusters as 4-connect nodes, we derived multi-types of MOZs with a modified framework charge, improved stability and enhanced photo-/eletrocatalytic activity. Besides, the selection, functionalization and defect-engineering on the 2-connect ligands generated different topological and functional MOZs. Finally, the future trends and some perspectives in this area are outlined.

Fluorescence determination of quercetin in food samples using polyhedron-shaped MOF@MOF(NUZ-8) based on NH2-UiO-66 and ZIF-8

A new metal-organic framework compound (MOF@MOF, NUZ-8) comprised of NH₂-UiO-66 and ZIF-8 under the polyvinylpyrrolidone (PVP) as the structure modifier was synthesized through an internal extended growth method (IEGM). The resulting NUZ-8 emerged the unreported unique polyhedron shape and showed considerable specific surface area (1466.1862 m²/g), excellent adsorption capacity, and fluorescence. NUZ-8 was used as a probe for the rapid optical detection of natural antioxidant quercetin (QCT). Its outstanding selectivity and sensitivity to QCT are derived from the fact that NH₂-UiO-66 acted as an optical tentacle to perceive QCT in virtue of its luminescence advantages, and ZIF-8 realized the selective enrichment of the QCT through its electron-rich framework structure. The experiments were carried out at an excitation wavelength of 335 nm and an emission wavelength range of 370-530 nm. Under conditions of the investigation, this probe realized the rapid detection of QCT and considerable adsorption capacity with wide linearity (0.3-80 μM), a low detection limit (0.14 μM), and acceptable recoveries (84.0-97.0%) in red wine samples, properties which were superior to many other detection platforms. The synthesis and the use of the above polyhedral composite provide guidance for the application of the IEGM in enhancing chemical sensing and instant determination of drugs.Graphical abstract Flow chart of this paper.

Electrochemical sensing platform for naphthol isomers based on in situ growth of ZIF-8 on reduced graphene oxide by a reaction-diffusion technique

Enhancing the dispersibility and conductivity is an effective solution to develop the application zeolitic imidazole frameworks (ZIF) in the electrochemical field. This work thus employs a novel reaction-diffusion framework (RDF) technique for the in situ growth of ZIF-8 crystals on graphene oxide (GO@ZIF-8) matrixes. In detail, the outer electrolyte of 2-methyl imidazole naturally diffuses into the inner agar gel matrix containing Zn²⁺ cations and GO nanosheets. The long reaction-diffusion makes the growth of ZIF-8 crystals controllable in a vertical gradient. After thermal treatment, the title product of ZIF-8 in situ grown on reduced graphene oxide (rGO@ZIF-8) is obtained and thus exhibits good dispersibility, high conductivity, large surface area, and more catalytic sites. The glassy carbon electrode (GCE) was modified by casting the rGO@ZIF-8 suspension. The obtained rGO@ZIF-8/GCE displays excellent catalytic activity toward naphthol (NAP) isomers. Under the optimal conditions, the amperometric currents of 1-NAP and 2-NAP demonstrate the good linear relationship in wide ranges of 0.05-12 μM and 0.02-15 μM, respectively. Their limits of detection are as low as 15 and 17 nM, respectively. The fabricated modified electrode exhibits excellent selectivity, stability, and reproducibility. The sensor is also utilized to detect NAP molecules in real water samples and indicates good accuracy and reliability.

Magnetic hollow bimetallic zinc/cobalt zeolitic imidazolate framework as sorbent for efficiently enriching aflatoxins combined with UHPLC-IT-MSn determination

A novel magnetic hollow bimetallic zinc/cobalt-based zeolitic imidazolate framework (MHB-Zn/Co-ZIF-8) was prepared via a microwave-assisted chemical etching in methanol. The structure, morphology, and specific surface area were characterized by X-ray diffraction and FTIR spectroscopy, scanning and transmission electron microscopy, and N₂ adsorption. The hollow nanostructures with high internal specific surface area, abundant active sites, and reduced aggregation of nanoparticles endow the hollow zeolitic imidazolate framework (ZIF) nanoparticle with high chemical stability, desirable durability, and excellent adsorption abilities. The MHB-Zn/Co-ZIF-8 nanoparticle was used as an effective sorbent for magnetic solid-phase extraction (MSPE) of trace aflatoxins B₁, B₂, G₁, and G₂ from fruit juice and fruit samples. The main parameters affecting the efficiency of MSPE procedures were investigated and optimized. The results show that, under optimized conditions, enrichment factors ranging from 67- to 355-fold are obtained for the target analytes. The method is linear in the range 1.0 to 100.0 ng mL^-1 with correlation coefficients (R²) from 0.9960 to 0.9992. The limits of detection of four aflatoxins are in the range 0.18 to 1.50 ng mL^-1 and the average recoveries range from 75.1 to 102.4%, with relative standard deviations (RSDs) less than 13.6%. This work presents the excellent extraction performance of aflatoxins B₁, B₂, G₁, and G₂ on MHB-Zn/Co-ZIF-8. In addition, the applicability of the MSPE coupling with ultrahigh-performance liquid chromatography-ion trap tandem mass spectrometry (UHPLC-IT-MSⁿ) for trace analysis in complex matrices is shown. Graphical abstract Schematic presentation of magnetic hollow bimetallic zinc/cobalt zeolitic imidazolate framework as sorbent for efficiently enriching aflatoxins B₁, B₂, G₁, and G₂ from fruit juice samples prior to ultrahigh-performance liquid chromatography-ion trap tandem mass spectrometry (UHPLC-IT-MSⁿ) determination.

Coordination Polymers Based on Highly Emissive Ligands: Synthesis and Functional Properties

Coordination polymers are constructed from metal ions and bridging ligands, linking them into solid-state structures extending in one (1D), two (2D) or three dimensions (3D). Two- and three-dimensional coordination polymers with potential voids are often referred to as metal-organic frameworks (MOFs) or porous coordination polymers. Luminescence is an important property of coordination polymers, often playing a key role in their applications. Photophysical properties of the coordination polymers can be associated with intraligand, metal-centered, guest-centered, metal-to-ligand and ligand-to-metal electron transitions. In recent years, a rapid growth of publications devoted to luminescent or fluorescent coordination polymers can be observed. In this review the use of fluorescent ligands, namely, 4,4'-stilbenedicarboxylic acid, 1,3,4-oxadiazole, thiazole, 2,1,3-benzothiadiazole, terpyridine and carbazole derivatives, naphthalene diimides, 4,4',4''-nitrilotribenzoic acid, ruthenium(II) and iridium(III) complexes, boron-dipyrromethene (BODIPY) derivatives, porphyrins, for the construction of coordination polymers are surveyed. Applications of such coordination polymers based on their photophysical properties will be discussed. The review covers the literature published before April 2020.

In situ encapsulation of horseradish peroxidase in zeolitic imidazolate framework-8 enables catalyzing luminol reaction under near-neutral conditions for sensitive chemiluminescence determination of cholesterol

HRP@ZIF-8 nanocomposite was prepared by in situ encapsulation of horseradish peroxidase (HRP) in the frame of zeolitic imidazolate framework-8 (ZIF-8) with a simple one-pot method. The HRP@ZIF-8 nanocomposite displays outstanding thermal stability and efficiently catalyzes the chemiluminescence (CL) reaction of luminol with hydrogen peroxide (H₂O₂) under near-neutral pH condition (pH 7-8). This CL system has a good response to H₂O₂ with a linear range of 0.1-100.0 μmol L^-1. The limit of detection (LOD) is 0.06 μmol L^-1 H₂O₂. By marriage with cholesterol oxidase, cholesterol is determined with a linear range from 0.1 to 100.0 μmol L^-1 and a LOD of 0.04 μmol L^-1. The relative standard deviations (RSD) are 1.7% and 2.5%, respectively, in 11 repeated measurements of 50.0 μmol L^-1 solutions of H₂O₂ and cholesterol, indicating excellent precision of the method. The method shows good selectivity and has been applied to the determination of total cholesterol in real serum samples. No significant difference has been observed between the results obtained by this method and the cholesterol oxidase-peroxidase coupling method. Graphical abstract Schematic presentation of in situ one-pot synthesis of horseradish peroxidase@zeolitic imidazolate framework-8 (HRP@ZIF-8) nanocomposite and chemiluminescence determination of cholesterol with HRP@ZIF-8 catalyzing luminol-H₂O₂ system.