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.

Epitaxial Growth of Guanidyl-Functionalized Magnetic Metal-Organic Frameworks with Multiaffinity Sites for Selective Capture of Global Phosphopeptides

The flexible and controlled synthesis of metal-organic framework (MOF)-derived hybrid nanostructures is of great significance in fine tuning of their enrichment performance in large-scale and in-depth phosphoproteome analysis. Herein, a magnetic guanidyl-functionalized MOF hybrid coating with multiaffinity sites, denoted as Fe₃O₄@G-ZIF-8, was fast fabricated via a one-pot epitaxial growth strategy for the first time and applied for selective and highly efficient enrichment of global phosphopeptides. The intrinsic unsaturated metal sites of ZIF-8 endow the surface-mounted MOF coatings with immobilized metal ion affinity chromatography interaction with multiphosphorylated peptides. The oriented anchoring of bifunctional guanidineacetic acid on the magnetic MOF nanospheres provides additional affinity sites (guanidyl groups) for specific recognition of phosphopeptides by "salt bridge" interaction, as well as active site carboxyl groups for the coordination with the metal ions. The as-prepared Fe₃O₄@G-ZIF-8 exhibits large surface area (382.5 m² g^-1), good superparamagnetic property (41.6 emu g^-1) and stability, and size-exclusion effect (1.73 nm), which can serve as a specific adsorbent for global phosphopeptide analysis with satisfactory selectivity, great detection sensitivity (1 fmol), and rapid magnetic separation. Moreover, the successful application of Fe₃O₄@G-ZIF-8 for selective capture of both multi- and mono-phosphopeptides from human saliva and serum demonstrated the great potential of magnetic surface-mounted MOF coatings in effective identification of low-abundance phosphopeptides by matrix-assisted laser desorption ionization time-of-flight mass spectrometry from complicated biological matrices.

Recent trends on the implementation of reticular materials in column‐centered separations

Advances in the development of column‐based analytical separations are strongly linked to the development of novel materials. Stationary phases for chromatographic separation are usually based on silica and polymer materials. Nevertheless, recent advances have been made using porous crystalline reticular materials, such as metal‐organic frameworks and covalent organic frameworks. However, the direct packing of these materials is often limited due to their small crystal size and nonspherical shape. In this review, recent strategies to incorporate porous crystalline materials as stationary phases for liquid‐phase separations are covered. Moreover, we discuss the potential future directions in their development and integration into suitable supports for analytical applications. Finally, we discuss the main challenges to be solved to take full advantage of these materials as stationary phases for analytical separations.

Metal-Organic Frameworks for Liquid Phase Applications

In the last two decades, metal-organic frameworks (MOFs) have attracted overwhelming attention. With readily tunable structures and functionalities, MOFs offer an unprecedentedly vast degree of design flexibility from enormous number of inorganic and organic building blocks or via postsynthetic modification to produce functional nanoporous materials. A large extent of experimental and computational studies of MOFs have been focused on gas phase applications, particularly the storage of low-carbon footprint energy carriers and the separation of CO2-containing gas mixtures. With progressive success in the synthesis of water- and solvent-resistant MOFs over the past several years, the increasingly active exploration of MOFs has been witnessed for widespread liquid phase applications such as liquid fuel purification, aromatics separation, water treatment, solvent recovery, chemical sensing, chiral separation, drug delivery, biomolecule encapsulation and separation. At this juncture, the recent experimental and computational studies are summarized herein for these multifaceted liquid phase applications to demonstrate the rapid advance in this burgeoning field. The challenges and opportunities moving from laboratory scale towards practical applications are discussed.

Three-dimensional ordered magnetic macroporous metal-organic frameworks for enzyme immobilization

Metal-organic frameworks (MOFs) have been emerged as a promising support for immobilizing enzymes owing to the tunable porosity, high surface area, and structural diversity. However, most of these possess nanometer size and small pores, which are difficult to recover them from the reaction medium and present low immobilization efficiency and protein loading capacity, and high substrate diffusion limitations. Herein, a novel magnetic amino-functionalized zeolitic imidazolate framework-8 (ZIF-8) with 3D highly ordered macroporous structure was synthesized using the assembled polystyrene (PS) nanosphere monoliths as a template. Subsequently, catalase (CAT) molecules were immobilized on the surface of macroporous magnetic ZIF-8 and inside the macropores by precipitation, covalent binding and cross-linking. The resultant immobilized CAT showed high immobilization efficiency (58%) and protein loading capacity (29%), leading to 500% higher activity than the immobilized CAT on ZIF-8 (CAT/ZIF-8). Meanwhile, the immobilized CAT could be easily recovered with a magnet without obvious activity loss. The traditional CAT/ZIF-8 lost its activity after 6 cycles, whereas, the immobilized CAT retained 90% activity of its initial activity after reusing for 8 cycles, indicating excellent reusability. In conclusion, this study provides a facile and efficient approach to immobilize enzymes on/in MOFs with enhanced activity and excellent recyclability.

C18-functionalized magnetic nanocomposites fabricated by one-step aqueous coating of tailored oligopeptides for enrichment of low-abundance peptides

Screening and monitoring endogenous peptides from complicated biosamples is still a major challenge in mass spectrometry-based proteomics research, mainly due to their low concentration and the interference of high-abundance proteins and other contaminants in biological samples. Herein, a facile and novel approach was described for rapid fabrication of C₁₈-functionalized magnetic nanocomposites (C₁₈-MNCs) based on one-step aqueous coating of C₁₈-Val-Lys-Val-Lys-Val-Lys (C₁₈-VK-VI) for the highly selective enrichment of low-abundance endogenous peptides from biological samples. C₁₈-VK-VI can readily self-assemble into complete monolayers mainly composed of β-sheets with C₁₈ hydrophobic chains erecting on the surface of GO@Fe₃O₄ MNCs under the physiological conditions. The resulting C₁₈VK-VI-GO@Fe₃O₄ MNCs exhibited good performance for peptides enrichment from digests of standard protein (myoglobin, MYO) and human serum, such as high sensitivity (0.05 fmol μL^-1) and selectivity (mass ratio of MYO digests and MYO = 1:500), rapid separation, and good reproducibility. Such a simple mild and rapid one-step aqueous coating method on the basis of oligopeptides self-assembly showed great potential in surface functionalization of various nanoadsorbents for proteome/peptidome researches.

A new strategy for the preparation of core-shell MOF/Polymer composite material as the mixed-mode stationary phase for hydrophilic interaction/ reversed-phase chromatography

A facile method for efficient synthesis of core-shell composite material was proposed. In this method, the silica microspheres were co-modified with metal organic framework (MOF-235) and polyethylene glycol polymer (PEG) and used as mixed-mode stationary phase (MOF-235@PEG@silica) for high-performance liquid chromatography. Elemental analysis, scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, and Brunauer-Emmett-Teller etc. methods were used to investigate the properties of the core-shell composite material. The MOF-235@PEG@silica stationary phase showed flexible selectivity for the separation of both hydrophilic and hydrophobic compounds especially for the separation of nine alkaloids, which showed superior hydrophilic separation performance than previous MOF-based composite stationary phases. Some factors including the pH of buffer salt, the ratio of organic phase and water phase in the mobile phase have been investigated, suggesting that the chromatographic retention mechanism of the column was a mixed mode of hydrophilic and reversed phase. The composite material also showed excellent chromatographic repeatability with the RSDs of the retention time found to be 0.2%-0.6% (n = 10) and the standard addition test in the actual sample proved that it can be used for practical sample analysis. In short, it provided a general way for preparing MOFs-based composites as mixed-mode chromatographic stationary phases, and changed the current status of MOF-based composite materials as single mode chromatographic stationary phases.

Hydrophobic Metal-Organic Frameworks: Assessment, Construction, and Diverse Applications

Tens of thousands of metal-organic frameworks (MOFs) have been developed in the past two decades, and only ≈100 of them have been demonstrated as porous and hydrophobic. These hydrophobic MOFs feature not only a rich structural variety, highly crystalline frameworks, and uniform micropores, but also a low affinity toward water and superior hydrolytic stability, which make them promising adsorbents for diverse applications, including humid CO2 capture, alcohol/water separation, pollutant removal from air or water, substrate-selective catalysis, energy storage, anticorrosion, and self-cleaning. Herein, the recent research advancements in hydrophobic MOFs are presented. The existing techniques for qualitatively or quantitatively assessing the hydrophobicity of MOFs are first introduced. The reported experimental methods for the preparation of hydrophobic MOFs are then categorized. The concept that hydrophobic MOFs normally synthesized from predesigned organic ligands can also be prepared by the postsynthetic modification of the internal pore surface and/or external crystal surface of hydrophilic or less hydrophobic MOFs is highlighted. Finally, an overview of the recent studies on hydrophobic MOFs for various applications is provided and suggests the high versatility of this unique class of materials for practical use as either adsorbents or nanomaterials.

Organic molecule-assisted synthesis of Fe3O4/graphene oxide nanocomposites for selective capture of low-abundance peptides and phosphopeptides

The iron oxide nanoparticles (Fe₃O₄) were prepared by organic molecule-assisted method in aqueous solution. The facile synthetic process of Fe₃O₄ nanoparticles was conducted only by mixing FeCl₂ and 2-methylimidazole (2-MIM) without any additives. A possible growth mechanism of the Fe₃O₄ nanocrystals was proposed for this mild reaction. Then, the Fe₃O₄ nanoparticles were anchored onto graphene oxide (GO) sheets in water by ultrasound-assisted method, forming an affinity probe with strong biocompatibility. Due to the hydroxy and carboxylic groups of GO sheets, Fe₃O₄/GO probe exhibits excellent performance for enriching low-abundance hydrophilic peptides, while the Fe₃O₄ nanoparticles endure the probe with specific affinity to phosphopeptides. The analytical protocol was developed for sequential enrichment of low-abundance peptides and phosphopeptides by the affinity probe. It exhibited the sequence coverage of 26% for capture of 17 low-abundance peptides from bovine serum albumin (BSA), as well as the selectivity of 1:1:100 for phosphopeptides from α-/β-casein/BSA, and low detectable concentration of 2.5 fmol and probe reusability of 5 times for capture of phosphopeptides from α-/β-casein. Consequently, the prepared Fe₃O₄/GO material possesses excellent feature as multifunctional affinity probe for low-abundance peptides including phosphopeptides from complex biological matrices detected by matrix-assisted laser desorption ionization time-of-flight mass spectrometry.

Characterization of starch phosphorylase from the marine green microalga (Chlorophyta) Tetraselmis subcordiformis reveals its potential role in starch biosynthesis

In a marine green starch-producing microalga Tetraselmis subcordiformis, the role of starch phosphorylase (SP) in the starch biosynthesis was disclosed by characterizing the enzyme properties and activity variations during the starch accumulation process. TsSP4, a SP isoform accounting for the major SP activity in T. subcordiformis, was unique to be active in a monomer form with a molecular weight of approximately 110kDa. It resembled one of the chloroplast-located SPs (PhoA) in Chlamydomonas reinhardtii with a similarity of 63.3% in sequence, though it possessed the typical L78/80 domain found in the plastidial SPs (Pho1) of higher plants that was absent in PhoA. TsSP4 exhibited moderate sensitivity to ADP-Glc inhibition and had a high activity for longer-chain linear maltooligosacchride (MOS) and amylopectin against highly branched glycogen as the substrates. TsSP4 had 2-fold higher affinity for Glc-1-P in the synthetic direction than for Pi in the phosphorolytic direction, and the catalytic constant k_cat for Glc-1-P was 2-fold of that for Pi. Collectively, TsSP4 preferred synthetic rather than phosphorolytic direction. TsSP4 could elongate MOSs even initially with Pi alone in the absence of Glc-1-P, which further supported its synthetic role in the starch biosynthesis. TsSP4 displayed increased activities in the developing and mature stage of starch biosynthesis under nitrogen-starvation conditions, indicating its possible contribution to the amylopectin amplification.

Recent applications of metal-organic frameworks in sample pretreatment

Metal-organic frameworks are promising materials in diverse analytical applications especially in sample pretreatment by virtue of their diverse structure topology, tunable pore size, permanent nanoscale porosity, high surface area, and good thermostability. According to hydrostability, metal-organic frameworks are divided into moisture-sensitive and water-stable types. In the actual applications, both kinds of metal-organic frameworks are usually engineered into hybrid composites containing magnetite, silicon dioxide, graphene, or directly carbonized to metal-organic frameworks derived carbon. These metal-organic frameworks based materials show good extraction performance to environmental pollutants. This review provides a critical overview of the applications of metal-organic frameworks and their composites in sample pretreatment modes, that is, solid-phase extraction, magnetic solid-phase extraction, micro-solid-phase extraction, solid-phase microextraction, and stir bar solid extraction.

Metal-Organic Frameworks at the Biointerface: Synthetic Strategies and Applications

Many living organisms are capable of producing inorganic materials of precisely controlled structure and morphology. This ubiquitous process is termed biomineralization and is observed in nature from the macroscale (e.g., formation of exoskeletons) down to the nanoscale (e.g., mineral storage and transportation in proteins). Extensive research efforts have pursued replicating this chemistry with the overarching aims of synthesizing new materials of unprecedented physical properties and understanding the complex mechanisms that occur at the biological-inorganic interface. Recently, we demonstrated that a class of porous materials termed metal-organic frameworks (MOFs) can spontaneously form on protein-based hydrogels via a process analogous to natural matrix-mediated biomineralization. Subsequently, this strategy was extended to functional biomacromolecules, including proteins and DNA, which have been shown to seed and accelerate crystallization of MOFs. Alternative strategies exploit co-precipitating agents such as polymers to induce MOF particle formation thus facilitating protein encapsulation within the porous crystals. In these examples the rigid molecular architecture of the MOF was found to form a protective coating around the biomacromolecule offering improved stability to external environments that would normally lead to its degradation. In this way, the MOF shell mimics the protective function of a biomineralized exoskeleton. Other methodologies have also been explored to encapsulate enzymes within MOF structures, including the fabrication of polycrystalline hollow MOF microcapsules that preserve the original enzyme functionality over several batch reaction cycles. The potential to design MOFs of varied pore size and chemical functionality has underpinned studies describing the postsynthesis infiltration of enzymes into MOF pore networks and bioconjugation strategies for the decoration of the MOF outer surface, respectively. These methods and configurations allow for customized biocomposites. MOF biocomposites have been extended from simple proteins to complex biological systems including viruses, living yeast cells, and bacteria. Indeed, a noteworthy result was that cells encapsulated within a crystalline MOF shell remain viable after exposure to a medium containing lytic enzymes. Furthermore, the cells can adsorb nutrients (glucose) through the MOF shell but cease reproducing until the MOF casing is removed, at which point normal cellular activity is fully restored. The field of MOF biocomposites is expansive and rapidly developing toward different applied research fields including protection and delivery of biopharmaceuticals, biosensing, biocatalysis, biobanking, and cell and virus manipulation. This Account describes the current progress of MOFs toward biotechnological applications highlighting the different strategies for the preparation of biocomposites, the developmental milestones, the challenges, and the potential impact of MOFs to the field.

Simple preparation of magnetic metal-organic frameworks composite as a "bait" for phosphoproteome research

Phosphospecific enrichment techniques and mass spectrometry (MS) are primary tools for comprehending the cellular phosphoproteome. In this work, a rational and extremely facile route to synthesize the magnetic metal-organic frameworks (mMOFs) was employed and the prepared composite was first utilized as a "bait" for selective enrichment of phosphopeptides. Typically, the mMOFs was synthesized via electrostatic self-assembly between the negatively charged Fe₃O₄ magnetic nanoparticles (MNPs) and positively charged MIL-101(Fe). The obtained Fe₃O₄/MIL-101(Fe) composite possessed well-defined structures, rough surface, highly specific surface area and excellent magnetic property. To demonstrate their ability for enrichment of phosphopeptides, we applied Fe₃O₄/MIL-101(Fe) as a "bait" to capture the phosphopeptides from standard protein digestion and practical samples. The enriched phosphopeptides were analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). The MS results show that the Fe₃O₄/MIL-101(Fe) exhibits superior enrichment performance for phosphopeptides with low detectable concentration assessed to be 8 fmol, selectivity investigated to be 1:1000 using β-casein/bovine serum albumin mixture and enrichment recovery evaluated to be 89.8%. Based on these excellent properties, the prepared composite was used to enrich the phosphopeptides from tilapia eggs biological samples for the first time. A total number of 51 phosphorylation sites were identified from the digest of tilapia eggs proteins, suggesting the excellent potential of Fe₃O₄/MIL-101(Fe) composite in the practical application.

Theranostic metal-organic framework core-shell composites for magnetic resonance imaging and drug delivery

Metal-organic frameworks (MOFs) have shown great potential in designing theranostic probes for cancer diagnosis and therapy due to their unique properties, including versatile structures and composition, tunable particle and pore size, enormous porosity, high surface area, and intrinsic biodegradability. In this study, we demonstrate novel MOF-based theranostic Fe3O4@UiO-66 core-shell composites constructed by in situ growth of a UiO-66 MOF shell on a Fe3O4 core for simultaneous drug delivery and magnetic resonance (MR) imaging. In the composites, the UiO-66 shell is devoted for encapsulating the drug, whereas the Fe3O4 core serves as a MR contrast agent. The Fe3O4@UiO-66 core-shell composites show good biocompatibility, high drug loading capacity, sustained drug release, and outstanding MR imaging capability, as well as effective chemotherapeutic efficacy, demonstrating the feasibility of designing theranostic Fe3O4@UiO-66 core-shell composites for cancer diagnosis and therapy.

Graphene-Templated Synthesis of Magnetic Metal Organic Framework Nanocomposites for Selective Enrichment of Biomolecules

Successful control of homogeneous and complete coating of graphene or graphene-based composites with well-defined metal organic framework (MOF) layers is a great challenge. Herein, novel magnetic graphene MOF composites were constructed via a simple strategy for self-assembly of well-distributed, dense, and highly porous MOFs on both sides of graphene nanosheets. Graphene functionalized with magnetic nanoparticles and carboxylic groups on both sides was explored as the backbone and template to direct the controllable self-assembly of MOFs. The prepared composite materials have a relatively high specific surface area (345.4 m(2) g(-1)), and their average pore size is measured to be 3.2 nm. Their relatively high saturation magnetization (23.8 emu g(-1)) indicates their strong magnetism at room temperature. Moreover, the multifunctional composite was demonstrated to be a highly effective affinity material in selective extraction and separation of low-concentration biomolecules from biological samples, in virtue of the size-selection property of the unique porous structure and the excellent affinity of the composite materials. Besides providing a solution for the construction of well-defined functional graphene-based MOFs, this work could also contribute to selective extraction of biomolecules, in virtue of the universal affinity between immobilized metal ions and biomolecules.

Magnetic nanoporous hybrid carbon from core–shell metal–organic frameworks for glycan extraction

Magnetic nanoporous carbon (NPC) materials, which can be thoroughly separated from an aqueous solution easily, are very promising adsorbents.

Facile method for the synthesis of Fe3O4@HCP core–shell porous magnetic microspheres for fast separation of organic dyes from aqueous solution

A novel type of porous magnetic microsphere (Fe3O4@HCP) was firstly synthesized and possesses a high Brunauer–Emmett–Teller specific surface area and excellent adsorption capacity for organic dyes.

Efficient enrichment of glycopeptides using metal-organic frameworks by hydrophilic interaction chromatography

Selective enrichment of glycopeptides from complicated biological samples is critical for glycoproteomics to obtain the structure and glycosylation information of glycoproteins using mass spectrometry (MS), which still remains a great challenge. Hydrophilic interaction chromatography (HILIC)-based strategies have been proposed for selective isolation of glycopeptides via the interactions between the glycan of glycopeptides and the matrices. However, the application of these methods is limited by the medium selectivity of HILIC matrices. In this study, hydrophilic metal-organic frameworks (MOFs) were fabricated and used as a HILIC matrix. The cross-linked CD-MOFs (LCD-MOFs) were facilely prepared with γ-cyclodextrin as ligand and possessed nano-sized cubic structure, superior hydrophilicity, and bio-compatibility. The LCD-MOFs performance for the selective enrichment of glycopeptides from the complex biological samples were investigated with a digested mixture of human immunoglobulin G (IgG) that was used as standard samples. In the selectivity assessment, the non-glycopeptides causing ion suppression to the glycopeptides were effectively removed, the signal of glycopeptides were enhanced significantly by LCD-MOFs, and twenty glycopeptides were identified with 67 fmol of IgG digest. In addition, the resulting LCD-MOFs demonstrated the lower detection limit (3.3 fmol) with a satisfactory recovery yield (84-103%) for glycopeptide enrichment from a digest of IgG. Furthermore, a promising protocol was developed for the selective enrichment of glycopeptides from mouse liver, and 344 unique N-glycosylation sites that mapped to 290 different glycoproteins were identified in a single MS run. The results clearly demonstrated that when used in a HILIC matrix, LCD-MOFs have great potential for identifying and enriching low-abundant glycopeptides in complex biological samples.

Facile Preparation of Core-Shell Magnetic Metal-Organic Framework Nanoparticles for the Selective Capture of Phosphopeptides

In regard to the phosphoproteome, highly specific and efficient capture of heteroideous kinds of phosphopeptides from intricate biological sample attaches great significance to comprehensive and in-depth phosphorylated proteomics research. However, until now, it has been a challenge. In this study, a new-fashioned porous immobilized metal ion affinity chromatography (IMAC) material was designed and fabricated to promote the selectivity and detection limit for phosphopeptides by covering a metal-organic frameworks (MOFs) shell onto Fe3O4 nanoparticles, taking advantage of layer-by-layer method (the synthesized nanoparticle denoted as Fe3O4@MIL-100 (Fe)). The thick layer renders the nanoparticles with perfect hydrophilic character, super large surface area, large immobilization of the Fe(3+) ions and the special porous structure. Specifically, the as-synthesized MOF-decorated magnetic nanoparticles own an ultra large surface area which is up to 168.66 m(2) g(-1) as well as two appropriate pore sizes of 1.93 and 3.91 nm with a narrow grain-size distribution and rapid separation under the magnetic circumstance. The unique features vested the synthesized nanoparticles an excellent ability for phosphopeptides enrichment with high selectivity for β-casein (molar ratio of β-casein/BSA, 1:500), large enrichment capacity (60 mg g(-1)), low detection limit (0.5 fmol), excellent phosphopeptides recovery (above 84.47%), fine size-exclusion of high molecular weight proteins, good reusability, and desirable batch-to-batch repeatability. Furthermore, encouraged by the experimental results, we successfully performed the as-prepared porous IMAC nanoparticle in the specific capture of phosphopeptides from the human serum (both the healthy and unhealthy) and nonfat milk, which proves itself to be a good candidate for the enrichment and detection of the low-abundant phosphopeptides from complicated biological samples.

Synthesis of magnetic metal-organic framework (MOF) for efficient removal of organic dyes from water

A novel, simple and efficient strategy for fabricating a magnetic metal-organic framework (MOF) as sorbent to remove organic compounds from simulated water samples is presented and tested for removal of methylene blue (MB) as an example. The novel adsorbents combine advantages of MOFs and magnetic nanoparticles and possess large capacity, low cost, rapid removal and easy separation of the solid phase, which makes it an excellent sorbent for treatment of wastewaters. The resulting magnetic MOFs composites (also known as MFCs) have large surface areas (79.52 m² g⁻¹), excellent magnetic response (14.89 emu g⁻¹), and large mesopore volume (0.09 cm³ g⁻¹), as well as good chemical inertness and mechanical stability. Adsorption was not drastically affected by pH, suggesting π–π stacking interaction and/or hydrophobic interactions between MB and MFCs. Kinetic parameters followed pseudo-second-order kinetics and adsorption was described by the Freundlich isotherm. Adsorption capacity was 84 mg MB g⁻¹ at an initial MB concentration of 30 mg L⁻¹, which increased to 245 mg g⁻¹ when the initial MB concentration was 300 mg L⁻¹. This capacity was much greater than most other adsorbents reported in the literature. In addition, MFC adsorbents possess excellent reusability, being effective after at least five consecutive cycles.

Facile synthesis of zwitterionic polymer-coated core-shell magnetic nanoparticles for highly specific capture of N-linked glycopeptides

Highly selective and efficient capture of glycosylated proteins and peptides from complex biological samples is of profound significance for the discovery of disease biomarkers in biological systems. Recently, hydrophilic interaction liquid chromatography (HILIC)-based functional materials have been extensively utilized for glycopeptide enrichment. However, the low amount of immobilized hydrophilic groups on the affinity material has limited its specificity, detection sensitivity and binding capacity in the capture of glycopeptides. Herein, a novel affinity material was synthesized to improve the binding capacity and detection sensitivity for glycopeptides by coating a poly(2-(methacryloyloxy)ethyl)-dimethyl-(3-sulfopropyl) ammonium hydroxide (PMSA) shell onto Fe3O4@SiO2 nanoparticles, taking advantage of reflux-precipitation polymerization for the first time (denoted as Fe3O4@SiO2@PMSA). The thick polymer shell endows the nanoparticles with excellent hydrophilic property and several functional groups on the polymer chains. The resulting Fe3O4@SiO2@PMSA demonstrated an outstanding ability for glycopeptide enrichment with high selectivity, extremely high detection sensitivity (0.1 fmol), large binding capacity (100 mg g(-1)), high enrichment recovery (above 73.6%) and rapid magnetic separation. Furthermore, in the analysis of real complicated biological samples, 905 unique N-glycosylation sites from 458 N-glycosylated proteins were reliably identified in three replicate analyses of a 65 μg protein sample extracted from mouse liver, showing the great potential of Fe3O4@SiO2@PMSA in the detection and identification of low-abundance N-linked glycopeptides in biological samples.

Synthesis of magnetic framework composites for the discrimination of Escherichia coli at the strain level

Rapid and efficient characterization and identification of pathogens at the strain level is of key importance for epidemiologic investigations, which still remains a challenge. In this work, solvothermically Fe3O4-COOH@MIL-101 composites were fabricated by in situ crystallization approach. The composites combine the excellent properties of both chromium (III) terephthalate (MIL-101) and carboxylic-functionalized magnetite (Fe3O4-COOH) particles and possess the efficient peptides/proteins enrichment properties and magnetic responsiveness. Fe3O4-COOH@MIL-101 composites as magnetic solid phase extraction materials were used to increase the discriminatory power of MALDI-TOF MS profiles. BSA tryptic peptides at a low concentration of 0.25 fmol μL(-1) could be detected by MALDI-TOF MS. In addition, Fe3O4-COOH@MIL-101 composites were successfully applied in the selective enrichment of the protein biomarkers from bacterial cell lysates and discrimination of Escherichia coli at the strain level. This work provides the possibility for wide applications of magnetic MOFs to discriminate pathogens below the species level.