Thermo-responsive polymer tethered metal-organic framework core-shell magnetic microspheres for magnetic solid-phase extraction of alkylphenols from environmental water samples

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

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

Highly efficient determination of trace ascorbic acid in vitamin C tablets by boronate affinity-modified magnetic metal-organic frameworks

Ascorbic acid (AA) plays an important role in many life processes. The chronic nutritional deficiency of AA will lead to the symptoms of scurvy. Therefore, the sensitive quantitative detection of AA is most important in the pharmaceutical analysis, food industry and diagnostic application. In this study, a dual-functional magnetic metal-organic frameworks (Fe3O4@SiO2@UiO-PBA) nanoparticles was synthesized by modifying phenylboronic acid to the surface of magnetic UiO-66-NH2 via postsynthetic modification for selectively and sensitively florescent detection of AA. Due to the abundant amino groups and grafted phenylboronic acid, the proposed nanoparticles have the dual properties of hydrophilicity and boronate affinity. Under optimum conditions, the obtained Fe3O4@SiO2@UiO-PBA nanoparticles can detect AA within 30 s, and has a good linear relationship with the concentration of AA in the range of 5.0-60 μM with a detection limit of 2.5 μM (S/N = 3). In addition, the prepared Fe3O4@SiO2@UiO-PBA nanoparticles showed excellent selectivity and great potential application in the highly efficient determination of trace AA in vitamin C tablets. These results indicated that a convenient method was proposed to develop fluorescent probes for rapid and sensitive detection of trace AA in real samples.

Magnetite Metal-Organic Frameworks: Applications in Environmental Remediation of Heavy Metals, Organic Contaminants, and Other Pollutants

Due to the increasing environmental pollution caused by human activities, environmental remediation has become an important subject for humans and environmental safety. The quest for beneficial pathways to remove organic and inorganic contaminants has been the theme of considerable investigations in the past decade. The easy and quick separation made magnetic solid-phase extraction (MSPE) a popular method for the removal of different pollutants from the environment. Metal-organic frameworks (MOFs) are a class of porous materials best known for their ultrahigh porosity. Moreover, these materials can be easily modified with useful ligands and form various composites with varying characteristics, thus rendering them an ideal candidate as adsorbing agents for MSPE. Herein, research on MSPE, encompassing MOFs as sorbents and Fe₃O₄ as a magnetic component, is surveyed for environmental applications. Initially, assorted pollutants and their threats to human and environmental safety are introduced with a brief introduction to MOFs and MSPE. Subsequently, the deployment of magnetic MOFs (MMOFs) as sorbents for the removal of various organic and inorganic pollutants from the environment is deliberated, encompassing the outlooks and perspectives of this field.

On the use of metal-organic frameworks for the extraction of organic compounds from environmental samples

The determination of trace metals and organic contaminants in environmental samples, such as water, air, soil, and sediment, is until today a challenging process for the analytical chemistry. Metal-organic frameworks (MOFs) are novel porous nanomaterials that are composed of metal ions and an organic connector. These materials are gaining more and more attention due to their superior characteristics, such as high surface area, tunable pore size, mechanical and thermal stability, luminosity, and charge transfer ability between metals and ligands. Among the various applications of MOFs are gas storage, separation, catalysis, and drug delivery. Recently, MOFs have been successfully introduced in the field of sample preparation for analytical chemistry and they have been used for sample pretreatment of various matrices. This review focuses on the applications of MOFs as novel adsorbents for the extraction of organic compounds from environmental samples.

A novel approach for the preparation of core-shell MOF/polymer composites as mixed-mode stationary phase

The nickel organic framework capped with polyvinylpyrrolidone was prepared and synergistically immobilized onto porous silica surface as the mixed-mode stationary phase for high-performance liquid chromatography. Here, polyvinylpyrrolidone firstly was chosen as functional molecules to change morphology and size of the metal organic framework. The silica microspheres were then modified by them via a simple bonding method rather than in-situ growth method with the aid of electrostatic interaction commonly used before. The stationary phase showed flexible selectivity for separation of both hydrophilic and hydrophobic compounds, especially for hydrophilic compounds such as carbohydrates, alkaloids and sulfonamides etc. The chromatographic behaviors were evaluated by investigating various factors, and a typical mixed-mode retention feature of the column was observed. The composites could be prepared repetitively, and relative standard deviations of retention time of objective compounds among different batches were less than 1.75%. It also showed excellent chromatographic reproducibility, stability and potentiality for application in real samples. In short, the composites can be used for a feasible option for analysis of multiple compounds as the mixed-mode stationary phase and it provides a general approach for preparing MOFs-based composites by changing morphology and size of MOFs.

Metal-Organic Frameworks-Based Nanomaterials for Drug Delivery

The composition and topology of metal-organic frameworks (MOFs) are exceptionally tailorable; moreover, they are extremely porous and represent an excellent Brunauer-Emmett-Teller (BET) surface area (≈3000-6000 m2·g-1). Nanoscale MOFs (NMOFs), as cargo nanocarriers, have increasingly attracted the attention of scientists and biotechnologists during the past decade, in parallel with the evolution in the use of porous nanomaterials in biomedicine. Compared to other nanoparticle-based delivery systems, such as porous nanosilica, nanomicelles, and dendrimer-encapsulated nanoparticles, NMOFs are more flexible, have a higher biodegradability potential, and can be more easily functionalized to meet the required level of host-guest interactions, while preserving a larger and fully adjustable pore window in most cases. Due to these unique properties, NMOFs have the potential to carry anticancer cargos. In contrast to almost all porous materials, MOFs can be synthesized in diverse morphologies, including spherical, ellipsoidal, cubic, hexagonal, and octahedral, which facilitates the acceptance of various drugs and genes.

Fabrication of thermoresponsive metal-organic nanotube sponge and its application on the adsorption of endocrine-disrupting compounds and pharmaceuticals/personal care products: Experiment and molecular simulation study

Thermoresponsive metal-organic nanotube modified (MONT-pNIPAM, pNIPAM = poly N-isopropylacrylamide) sponge was synthesized using the dip-coating method and served as an adsorbent for endocrine-disrupting compounds (EDCs) and pharmaceuticals/personal care products (PPCPs) removal. The material was characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction, and N2 sorption-desorption. Nonlinear regression-based equations were derived to optimize pH and ionic strength during process. Though thermoresponsive polymer phase transition between dissolve and aggregate, realizing the adsorption tunnel "ON-OFF" under the temperature control. Adsorption kinetics and isotherms were investigated on the basis of a static experiment. The pseudo-second-order kinetic model and the Langmuir isotherm were fitted well to characterize adsorption. At an initial concentration of 50 mg L-1, maximum adsorption capacity were 128 mg/g, 184 mg/g and partition coefficient were 1.09 mg g-1 μM-1, 1.13 mg g-1 μM-1 for dibutyl phthalate (DBP) and parachlorometaxylenol (PCMX), respectively. The density-functional theory (DFT) was applied to calculate the interaction energy and investigate the possible mechanism. Combining the experimental data with theoretical calculation, results demonstrated that the MONT-pNIPAM sponge was a highly efficient adsorbent material that was suitable for the removal of EDCs/PPCPs from water.

Application of stimuli-responsive materials for extraction purposes

Stimuli-responsive materials, frequently designated as "smart/intelligent materials", can modify their structure or properties by either a biological, physical, or chemical stimulus which, if properly controlled, could be used for specific applications. Such materials have been studied and exploited in several fields, like electronics, photonics, controlled drugs administration, imaging and medical diagnosis, among others, as well as in Analytical Chemistry where they have been used as chromatographic stationary phases, as part of sensors and for extraction purposes. This review article pretends to provide an overview of the most recent applications of these materials (mostly polymeric materials) in sample preparation for extraction purposes, as well as to provide a general vision of the current state-of-the-art of this field, their potential use and future applications.

Headspace solid-phase microextraction sampling of endogenous aldehydes in biological fluids using a magnetic metal-organic framework/polyaniline nanocomposite

Nanoporosity, crystal structure, good thermal and mechanical stability, high surface-to-volume ratio, nanoscale cavities, and uniform pore topology have made metal-organic frameworks one of the best class of sorbents for adsorption/separation purposes. In this research, a metal-organic framework/polyaniline magnetite nanocomposite was synthesized and intercalated by polyaniline by electrophoretic deposition on the surface of a thin steel wire, to prepare a solid-phase microextraction fiber. It was coupled with gas chromatography-flame ionization detection and employed for the extraction and determination of aldehydes in biological samples. The magnetic nanocomposite was characterized using scanning electron microscopy, energy dispersive X-ray analysis, and Fourier transform infrared spectroscopy. Under the optimal experimental conditions, the calibration curves were linear in the range of 0.01-1 and 0.1-1 µg/L for hexanal and heptanal, respectively. The limits of detections for hexanal and heptanal were 0.001 and 0.01 µg/L, respectively. Intrafiber repeatability for six replicate analyses of 0.2 µg/L of the analytes was over the range 3.5-7.1%. Interfiber (fiber-to-fiber) reproducibility, calculated by six replicate analyses of the same concentration using three different fibers, and was found to be 10.4-15.7%. The developed procedure was successfully utilized for the analysis of hexanal and heptanal in human plasma and urine samples.

Simple magnetization of Fe3 O4 /MIL-53(Al)-NH2 for a rapid vortex-assisted dispersive magnetic solid-phase extraction of phenol residues in water samples

The present work describes a simple route to magnetize MIL-53(Al)-NH₂ sorbent for rapid extraction of phenol residues from environmental samples. To extend the applications and performances of the metal-organic frameworks in the field of adsorption materials, we combined the properties of metal-organic frameworks and magnetite to decrease the extraction time and simplify the extraction process as well. In this study, a simple and quick vortex-assisted dispersive magnetic solid phase extraction method for the extraction of ten United States Environmental Protection Agency's priority phenols from water samples prior to analysis by high-performance liquid chromatography with photodiode array detection was proposed. The developed method exhibits a rapid enrichment of the target analytes within 10 s for extraction and 10 s for desorption. Low detection limits of 1.8-41.7 µg/L and quantitation limits of 6.0-139.0 µg/L with the relative standard deviations for intra- and interday analyses less than 12% were achieved. Satisfactory recoveries in the range of 80-111% with the relative standard deviations less than 11% demonstrated that Fe₃ O₄ /MIL-53(Al)-NH₂ is promising sorbent in the field of magnetic solid-phase extraction for environmental samples.

Thermoregulated extraction of luteolin under neutral conditions using oligo(ethylene glycol)-based magnetic nanoparticles with Wulff-type boronate affinity

Oligo(ethylene glycol)-based thermoresponsive polymers with Wulff-type boronate affinity were anchored on magnetic nanoparticles. The resultant magnetic nanoparticles were used as sorbents for extracting luteolin, a cis-diol-containing model analyte. By exploiting the thermoresponsive properties and Wulff-type boronate affinity of the sorbents, target adsorption at room temperature (25 °C) and target release at high temperature (40 °C) were achieved under neutral conditions without pH alteration. The proposed thermoregulated extraction method was favorable for automated boronate affinity extraction, preventing degradation of the target and avoiding acidic elution for breaking Wulff-type boronate sites. Compared to reported sorbents for extracting luteolin, the sorbents possessed higher maximum adsorption capacity (98.7 mg g^-1) with acceptable sensitivity, simplified operation procedure, and mild extraction condition. Furthermore, the sorbents were applied in thermoregulated extraction of luteolin from honey samples. Satisfactory recoveries in the range of 83.2% - 89.1% with RSD ranging from 2.2% to 4.6% were achieved. The results demonstrated that this work provided a new research direction to design and synthesize efficient thermoresponsive materials for recognition and release of cis-diol compounds under neutral conditions.

Preparation of titanium ion functionalized polydopamine coated ferroferric oxide core-shell magnetic particles for selective extraction of nucleotides from Cordyceps and Lentinus edodes

In this study, a titanium ion (Ti⁴⁺) functionalized polydopamine coated ferroferric oxide (Fe₃O₄@PDA@Ti⁴⁺) core-shell magnetic particle was prepared for the selective extraction of nucleotides. Firstly, different metal ions including Ti⁴⁺, Zr⁴⁺, Fe³⁺, Al³⁺, Cu²⁺, Zn²⁺, Ni²⁺ and Mg²⁺ were respectively immobilized onto Fe₃O₄@PDA particles and their extraction efficiency for five nucleotides [cytidine-5'-monophosphate (CMP), uridine-5'-monophosphate (UMP), guanosine-5'-monophosphate (GMP), thymidine-5'-monophosphate (TMP) and adenosine-5'-monophosphate (AMP)] were compared. Among these prepared materials, Fe₃O₄@PDA@Ti⁴⁺, which exhibited the highest extraction efficiency for nucleotides, was further characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray spectroscopy. After being optimized of the extraction parameters including adsorbent amounts, extraction time, extraction temperature, type and concentration of the eluent, the prepared Fe₃O₄@PDA@Ti⁴⁺ magnetic particles were successfully applied for the selective extraction and determination of CMP, UMP, GMP, TMP and AMP in Cordyceps and Lentinus edodes. Good linearity (varying from 0.063 to 19.000 μg/mL, R² > 0.999) and low limit of detection (LODs) (ranging between 0.0047 and 0.0141 μg/mL) for target analytes were achieved. These results demonstrated that the synthesized material in this study had potential for selective extraction of phosphorylated small molecular compounds in complicated matrix.

Highly Efficient Separation of Glycoprotein by Dual-Functional Magnetic Metal-Organic Framework with Hydrophilicity and Boronic Acid Affinity

Protein glycosylation plays a critical role in post-translational modifications of proteins in the organism and is involved in many diseases. However, the huge challenge for glycoproteins to be highly specific isolated and adsorbed from complicated biological samples results from their low abundance and interference. In this work, a novel dual-functionalized magnetic metal-organic frameworks nanoparticle for selective enrichment of glycoproteins was synthesized for the first time. Due to the abundant amino groups and grafted phenylboronic acid, the proposed nanoparticles have the dual properties of hydrophilicity and boronic acid affinity. The obtained nanoparticles show high binding capacities toward glycoproteins under physiological state (pH 7.4) such as ovalbumin (327.28 mg/g), transferrin (241.17 mg/g), horseradish peroxidase (530.79 mg/g). Furthermore, the nanoparticles still have excellent enrichment performance after being used six times repeatedly. More importantly, the prepared nanoparticles also have great potential applications in the adsorption of glycoproteins from complex biological specimens.

Reduced Magnetism in Core-Shell Magnetite@MOF Composites

The magnetic susceptibility of synthesized magnetite (Fe₃O₄) microspheres was found to decline after the growth of a metal-organic framework (MOF) shell on the magnetite core. Detailed structural analysis of the core-shell particles using scanning electron microscopy, transmission electron microscopy, atom probe tomography, and⁵⁷Fe-Mössbauer spectroscopy suggests that the distribution of MOF precursors inside the magnetic core resulted in the oxidation of the iron oxide core.

Recent advances in metal-organic frameworks and covalent organic frameworks for sample preparation and chromatographic analysis

In the field of analytical chemistry, sample preparation and chromatographic separation are two core procedures. The means by which to improve the sensitivity, selectivity and detection limit of a method have become a topic of great interest. Recently, porous organic frameworks, such as metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), have been widely used in this research area because of their special features, and different methods have been developed. This review summarizes the applications of MOFs and COFs in sample preparation and chromatographic stationary phases. The MOF- or COF-based solid-phase extraction (SPE), solid-phase microextraction (SPME), gas chromatography (GC), high-performance liquid chromatography (HPLC) and capillary electrochromatography (CEC) methods are described. The excellent properties of MOFs and COFs have resulted in intense interest in exploring their performance and mechanisms for sample preparation and chromatographic separation.

Rapid magnetic solid-phase extraction of Congo Red and Basic Red 2 from aqueous solution by ZIF-8@CoFe2 O4 hybrid composites

Core-shell metal-organic framework materials have attracted considerable attention mainly due to their enhanced or new physicochemical properties compared with their single-component counterparts. In this work, a core-shell heterostructure of CoFe2 O4 -Zeolitic Imidazolate Framework-8 (ZIF-8@CoFe2 O4 ) is successfully fabricated and used as an solid-phase extraction adsorbent to efficiently extract Congo Red and Basic Red 2 dyes from contaminated aqueous solution. Vibrating sample magnetometry indicates that the saturated magnetization of ZIF-8@CoFe2 O4 is 3.3 emu/g, which is large enough for magnetic separation. The obtained hybrid magnetic metal-organic framework based material ZIF-8@CoFe2 O4 can remove the investigated dyes very fast within 1 min of the contact time. The adsorbent ZIF-8@CoFe2 O4 also shows a good reusability. After regeneration, the adsorbent can still exhibit high removal efficiency (∼97%) toward Congo Red for five cycles of desorption-adsorption. This work reveals the great potential of core-shell ZIF-8@CoFe2 O4 sorbents for the fast separation and preconcentration of organic pollutants in aqueous solution before high-performance liquid chromatography analysis.