Magnetic Metal-organic Framework Research Articles

Tailoring the interfacial microenvironment of magnetic metal-organic frameworks using amino–acid-based ionic liquids for lipase immobilization

Modifying the carrier interface is a promising method to improve the microenvironment of immobilized enzymes and enhance their activity and stability. In this work, using proline as amino acid, magnetic metal-organic frameworks (MOFs) were modified with an amino-acid-based ionic liquid (AAIL) with two hydroxyl groups followed by adsorption of porcine pancreatic lipase (PPL). The activity recovery of the prepared immobilized lipase (MMOF-AAIL/PPL) was up to 162 % higher than that of MMOF-PPL (70.8 %). The Michaelis constant of MMOF-AAIL/PPL was 0.0742 mM lower than that of MMOF-PPL, but the catalytic efficiency was 0.0223 min−1 which was higher than MMOF-PPL. Furthermore, MMOF-AAIL/PPL maintained 85.6 % residual activity after stored for 40 days and its residual activity was 71.9 % while that for MMOF-PPL was 58.8 % after incubated in 6 M urea for 2 h. Particularly, after ten consecutive cycles, the residual activity of MMOF-AAIL/PPL still reached 84.4 %. In addition, the magnetic properties of the support facilitate the separation process which improves the utilization efficiency of immobilized enzymes.

A novel magnetic Fe, N co-doped Ce-MOFs derived carbon as a peroxymonosulfate activator for the degradation of tetracycline hydrochloride: Performance and activation mechanism

The activation of peroxymonosulfate (PMS) using metal-organic frameworks (MOFs) has garnered significant interest in the field of wastewater treatment. However, the environmental challenges associated with traditional methods for synthesizing MOFs precursors, such as the requirement for high temperatures and pressures, remain. Furthermore, the catalytic performance and stability of mono-metallic materials are areas needing enhancement. This work successfully synthesized a novel magnetic Fe-Ce bimetallic N-doped porous MOF material (Fe/Ce@5MNC). The optimized Fe/Ce@5MNC exhibited a higher specific surface area and a more extensive pore structure, as verified by various characterization techniques. Moreover, the synthesis process of the precursor is simpler, energy-saving, and relatively environmentally friendly. Notably, the synergistic effect between Fe and Ce, coupled with the presence of multiple active sites such as FeNx and graphite N, enabled Fe/Ce@5MNC to decompose 86.4 % of TCH within 30 min, marking a 31.4 % increase over Ce@NC. After four cycles, the catalyst maintained good surface stability, with the degradation efficiency remaining at 67.7 %. Quenching and electron paramagnetic resonance (EPR) experiments confirmed that the main degradation mechanisms are singlet oxygen (1O2) generation and electron transfer. This study presents a new method for synthesizing efficient Fe, N co-doped magnetic bimetallic PMS activators and designing carbon catalysts for deep oxidation.

Preparation of polyoxometalate modified magnetic metal–organic framework and application to the enrichment of phosphopeptides

Herein, polyoxometalate modified magnetic metal–organic framework (Fe3O4@PDA@MOF-POM) was successfully prepared and then applied to the enrichment of phosphopeptides. Fe3O4@PDA@MOF-POM can bind with phosphopeptides through ZrO clusters provided by the MOF layer and metal oxide originated from Zr-W-POM. The magnetic nanomaterial had high sensitivity (0.1 fmol), good reusability (10 cycles), and high selectivity (α-casein: β-casein: bovine serum albumin = 1: 1: 5000). Coupling with MALDI-TOF MS determination, non-fat milk was selected to preliminarily explore the applicability of Fe3O4@PDA@MOF-POM. Furthermore, 241 phosphopeptides derived from 232 phosphoproteins and 99 phosphopeptides attributed to 89 phosphoproteins were identified in human serum and saliva by nano LC-MS. This work paves a new way for the recognition of phosphopeptides in bio-samples.

Recyclable Fe3O4@UiO-66-PDA core–shell nanomaterials for extensive metal ion adsorption: Batch experiments and theoretical analysis

With the ever-increasing challenge of heavy metal pollution, the imperative for developing highly efficient adsorbents has become apparent to remove metal ions from wastewater completely. In this study, we introduce a novel magnetic core–shell adsorbent, Fe3O4@UiO-66-PDA. It features a polydopamine (PDA) modified zirconium-based metal–organic framework (UiO-66) synthesized through a simple solvothermal method. The adsorbent boasts a unique core–shell architecture with a high specific surface area, abundant micropores, and remarkable thermal stability. The adsorption capabilities of six metal ions (Fe3+, Mn2+, Pb2+, Cu2+, Hg2+, and Cd2+) were systematically investigated, guided by the theory of hard and soft acids and bases. Among these, three representative metal ions (Fe3+, Pb2+, and Hg2+) were scrutinized in detail. The activated Fe3O4@UiO-66-PDA exhibited exceptional adsorption capacities for these metal ions, achieving impressive values of 97.99 mg/g, 121.42 mg/g, and 130.72 mg/g, respectively, at pH 5.0. Moreover, the adsorbent demonstrated efficient recovery from aqueous solution using an external magnet, maintaining robust adsorption efficiency (>80%) and stability even after six cycles. To delve deeper into the optimized adsorption of Hg2+, density functional theory (DFT) analysis was employed, revealing an adsorption energy of -2.61 eV for Hg2+. This notable adsorption capacity was primarily attributed to electron interactions and coordination effects. This study offers valuable insights into metal ion adsorption facilitated, by magnetic metal–organic framework (MOF) materials.

A non-targeting magnetic metal-organic framework probe for highly specific peptide-mediated precise disease monitoring

Alzheimer's disease (AD) is a universal neurodegenerative disease in older adults with incurable and progressive properties, urging for precise monitoring to perform timely treatment to delay its progression. Herein, we introduced a non-targeting magnetic metal-organic framework probe coupled with high-throughput mass spectrometry, creating a rapid screening strategy for highly specific peptides associated with AD. Notably, an elution-free extraction process was proposed, significantly reducing sample preprocessing time while simultaneously ensuring the efficient detection of captured peptides. Using this elution-free extraction process, high-quality peptide profiles were rapidly extracted from the hundreds of samples from both diseased and healthy individuals. By integrating machine learning algorithms, LC-MS/MS, and Uniprot database searching, we identified three specific serum endogenous peptides (m/z = 4215.41, 2884.77 and 2704.61) closely associated with AD. Remarkably, with the use of any single specific peptide, the AUC (Area Under the Curve) values can reach approximately 0.9 during monitoring AD. Moreover, integrating three specific biomarkers provides a robust basis for machine learning algorithms to build monitoring models, with AUC value up to 1.000. This work represents a substantial advancement in the development of peptide-specific precise monitoring approaches for complex diseases, serving as a catalyst for increased dedication to the molecular detection field.

Functionalization of Magnetic UiO-66-NH2 with a Chiral Cu(l-proline)2 Complex as a Hybrid Asymmetric Catalyst for CO2 Conversion into Cyclic Carbonates.

In this study, a chiral [Cu(l-proline)2] complex-modified Fe3O4@SiO2@UiO-66-NH2(Zr) metal-organic framework [Fe3O4@SiO2@UiO-66-NH-Cu(l-proline)2] via multifunctionalization strategies was designed and synthesized. One simple approach to chiralize an achiral MOF-structure that cannot be directly chiralized using a chiral secondary agent like 4-hydroxy-l-proline. Therefore, this chiral catalyst was synthesized with a simple and multistep method. Accordingly, Fe3O4@SiO2@UiO-66-NH2 has been synthesized via Fe3O4 modification with tetraethyl orthosilicate and subsequently with ZrCl4 and 2-aminoterephthalic acid. The presence of the silica layer helps to stabilize the Fe3O4 core, while the bonding between Zr4+ and the -OH groups in the silica layer promotes the development of Zr-MOFs on the Fe3O4 surface, and then the surfaces of the synthesized magnetic MOFs composite are functionalized with 1,2-dichloroethane and Cu(II) complex with 4-hydroxy-l-proline, [Cu(l-proline)2] to afford the magnetically chiral nanocatalyst. Multiple techniques were employed to characterize this magnetically chiral nanocatalyst such as Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectrometry (EDX), powder X-ray diffraction (PXRD), circular dichroism (CD), inductively coupled plasma (ICP), thermogravimetric analysis (TGA), vibrating-sample magnetometry (VSM), and Brunauer-Emmett-Teller (BET) analyses. Moreover, a magnetically chiral nanocatalyst shows the asymmetric CO2 fixation reaction under solvent-free conditions at 80 °C and in ethanol under reflux conditions with up to 99 and 98% ee, respectively. Furthermore, the reaction mechanism was illustrated concerning the total energy of the reactant, intermediates and product, and the structural parameters were analyzed.

Magnetic Multienzyme@Metal-Organic Material for Sustainable Biodegradation of Insoluble Biomass.

Biodegradation of insoluble biomass such as cellulose via carbohydrase enzymes is an effective approach to break down plant cell walls and extract valuable materials therein. Yet, the high cost and poor reusability of enzymes are practical concerns. We recently proved that immobilizing multiple digestive enzymes on metal-organic materials (MOMs) allows enzymes to be reused via gravimetric separation, improving the cost efficiency of cereal biomass degradation [ACS Appl. Mater. Interfaces 2021, 13, 36, 43085-43093]. However, this strategy cannot be adapted for enzymes whose substrates or products are insoluble (e.g., cellulose crystals). Recently, we described an alternative approach based on magnetic metal-organic frameworks (MOFs) using model enzymes/substrates [ACS Appl. Mater. Interfaces 2020, 12, 37, 41794-41801]. Here, we aim to prove the effectiveness of combining these two strategies in cellulose degradation. We immobilized multiple carbohydrase enzymes that cooperate in cellulose degradation via cocrystallization with Ca2+, a carboxylate ligand (BDC) in the absence and presence of magnetic nanoparticles (MNPs). We then compared the separation efficiency and enzyme reusability of the resultant multienzyme@Ca-BDC and multienzyme@MNP-Ca-BDC composites via gravimetric and magnetic separation, respectively, and found that, although both composites were effective in cellulose degradation in the first round, the multienzyme@MNP-Ca-BDC composites displayed significantly enhanced reusability. This work provides the first experimental demonstration of using magnetic solid supports to immobilize multiple carbohydrase enzymes simultaneously and degrade cellulose and promotes green/sustainable chemistry in three ways: (1) reusing the enzymes saves energy/sources to prepare them, (2) the synthetic conditions are "green" without generating unwanted wastes, and (3) using our composites to degrade cellulose is the first step of extracting valuable materials from sustainable biomasses such as plants whose growth does not rely on nonregeneratable resources.

Structurally ordered core-shell MOFs in mixed matrix membrane as magnetic sieves for O2/N2 separation

Membrane separation technology has broad application prospects in O2/N2 separation, and improving the permselectivity of membranes remains a key problem to be solved. O2 and N2 have different magnetic properties and can be separated by magnetism. In addition, coupling magnetic separation with the use of a molecular sieve supported by metal-organic frameworks (MOFs) could further enhance the separation ability. In this work, a magnetic core-shell MOF (Fe3O4@ZIF-8) was prepared as a filler, and the impacts of the Fe3O4@ZIF-8 morphology, loading, channel magnetic properties and ordered arrangement on membrane O2/N2 selectivity were evaluated. To establish a magnetic-sieving O2 permeation channel, the preparation process was carried out in a magnetic field so that the fillers in the membrane were arranged orderly. Due to the synergistic impact of the structurally ordered MOF channel and magnetism, the gas transport performance of the resulting magnetic mixed matrix membranes (MMMs) was substantially improved. Therefore, the O2 permeability and O2/N2 selectivity of the 15 wt%Fe3O4@ZIF-8-8/Pebax MMMs reached 194 Barrer and 11.97, respectively. This study not only presents a novel approach for creating high-performance O2/N2 membranes but also plays a leading role in the development of magnetism-controlled multiscale (magnetic core-shell and filler-ordered) membrane structural engineering.

Just Soaping Them: The Simplest Method for Converting Metal Organic Frameworks into Superhydrophobic Materials.

The incorporation of superhydrophobic properties into metal organic framework (MOF) materials is highly desirable to enhance their hydrolytic stability, gas capture selectivity in the presence of humidity and efficiency in oil-water separations, among others. The existing strategies for inducing superhydrophobicity into MOFs have several weaknesses, such as increased cost, utilization of toxic reagents and solvents, applicability for limited MOFs, etc. Here, we report the simplest, most eco-friendly, and cost-effective process to impart superhydrophobicity to MOFs, involving a rapid (90 min) treatment of MOF materials with solutions of sodium oleate, a main component of soap. The method can be applied to both hydrolytically stable and unstable MOFs, with the porosity of modified MOFs approaching, in most cases, that of the pristine materials. Interestingly, this approach was used to isolate superhydrophobic magnetic MOF composites, and one of these materials formed stable liquid marbles, whose motion could be easily guided using an external magnetic field. We also successfully fabricated superhydrophobic MOF-coated cotton fabric and fiber composites. These composites exhibited exceptional oil sorption properties achieving rapid removal of floating crude oil from water, as well as efficient purification of oil-in-water emulsions. They are also regenerable and reusable for multiple sorption processes. Overall, the results described here pave the way for an unprecedented expansion of the family of MOF-based superhydrophobic materials, as virtually any MOF could be converted into a superhydrophobic compound by applying the new synthetic approach.

Orientation Growth of N-Doped and Iron-Based Metal-Organic Framework and Its Application for Removal of Cr(VI) in Wastewater.

A series of NH2-functionalized nano-sized magnetic metal-organic frameworks (MOFs) were prepared in this study for Cr(VI) removal from wastewater. It was observed that not only the morphological, i.e., orientation growth of N-doped and iron-based metal-organic frameworks, but also the adsorption of magnetic MOFs is largely related to the used amount of ammonium hydroxide in preparation. For example, with increasing amounts of ammonium hydroxide used in preparation, the morphology of magnetic MOFs changed from spherical to cube and triangular cone. Moreover, the maximum adsorption capacity of spherical-magnetic MOFs, cubic-magnetic MOFs and triangular cone-magnetic MOFs could be up to 204.08 mg/g, 232.56 mg/g and 270.27 mg/g, respectively. Under optimal conditions, the adsorption process of magnetic MOFs for Cr(VI) was consistent with the pseudo-second-order rate equation (R2 = 1) and Langmuir isotherm model (R2 > 0.99). Therefore, magnetic MOFs developed in this work offered a viable option for the removal of Cr(VI) from wastewater.

Enzymatic Synthesis of Indole-Based Imidazopyridine using α-Amylase.

The imidazo[1,2-a]pyridine scaffold has gained significant attention due to its presence as a lead structure in several commercially available pharmaceuticals like zolimidine, zolpidem, olprinone, soraprazan, etc. Further, indole-based imidazo[1,2-a]pyridine derivatives have been found interesting due to their anticancer and antibacterial activities. However, limited methods have been reported for the synthesis of indole-based imidazo[1,2-a]pyridines. In this study, we have successfully developed a biocatalytic process for synthesizing indole-based imidazo[1,2-a]pyridine derivatives using the α-amylase enzyme catalyzed Groebke-Blackburn-Bienayme (GBB) multicomponent reaction of 2-aminopyridine, indole-3-carboxaldehyde, and isocyanide. The generality and robustness of this protocol were shown by synthesizing differently substituted indole-based imidazo[1,2-a]pyridines in good isolated yields. Furthermore, to make α-amylase a reusable catalyst for GBB multicomponent reaction, it was immobilized onto magnetic metal-organic framework (MOF) materials [Fe3 O4 @MIL-100(Fe)] and found reusable up to four consecutive catalytic cycles without the significant loss in catalytic activity.

Integration of multienzyme co-immobilization and biomimetic catalysis in magnetic metal–organic framework nanoflowers for α-amylase detection in fermentation samples

Multiple enzymes induce biological cascade catalysis is essential in nature and industrial production. However, the shortcomings of enzymes, including unsatisfactory stability, reusability, and sensitivity in harsh microenvironment, have restricted their broader use. Here, we report a facile method for fabricating a cascade system by combining the benefits of immobilized enzymes and biomimetic catalysis based on magnetic metal–organic framework nanoflowers (mMOFNFs). mMOFNFs prepared through the layered double hydroxide-derived strategy exhibited remarkable peroxidase-like activity and accessible amino interface, enabling it to serve not only as a reliable carrier for α-glucosidase and glucose oxidase fixation, but also as a nanozyme participating in cascade. On this basis, a colorimetric biosensor of excellent sensitivity and selectivity for α-amylase detection was constructed with a wide range (2–225 U L−1), low detection limit (2.48 U L−1), and rapid operation (30 min). This work provides a versatile strategy for establishing multi-enzyme cascade systems and rapid analysis of α-amylase.

Development and application of a new deep eutectic solvent based magnetic metal–organic framework adsorbent for the detection of fluorotelomer alcohols in edible oils

The enrichment of per- and polyfluoroalkyl substances (PFASs) poses significant challenges for environmental and food safety monitoring, given their toxic and persistent nature, highly fluorinated character, and low concentration. This study focuses on the construction of a new deep eutectic solvent (DES)-functionalized magnetic metal–organic framework (MOF) adsorbent for fluorotelomer alcohols (FTOHs) analysis in foods. The DES, composed of levulinic acid and trifluoromethoxylbenzene, was modified onto the surface of magnetic UiO-66-NH2 to enable the specific adsorption of FTOHs during the pretreatment process, which was then followed by GC–MS analysis. The method exhibited a limit of detection (LOD) ranging from 31.51 to 185.76 pg g – 1 with satisfactory recoveries (73.83 %-128.55 %), and was successfully used in detecting FTOHs in 12 edible oils samples with the concentrations ranging from 401.89 to 8006.18 pg g − 1. The proposed adsorbent exhibited significantly improved enrichment performance for PFASs, primarily attributed to the cooperative enhancement of double hydrogen-bonding interactions and fluorine affinity via the elucidation of 1H nuclear magnetic resonance (1H NMR), 19F NMR, and quantum chemical calculations. This study provided new insights and directions for the design and fabrication of selective materials to pretreatment ultra-trace emerging contaminants in complex matrices.

Speciation analysis of inorganic selenium in food and water samples utilizing a 2,3-diaminonaphthalene post-synthetic modified magnetic metal–organic framework

In this work, a 2,3-diaminonaphthalene post-synthetic modified magnetic metal–organic framework was fabricated for fast and selective determination of inorganic selenium in real food and water samples. The results exhibited that selenium (IV) is adsorbed by the nano-material at a pH of 2.5, and in this way, selenium (IV) can be quantified selectively. After identifying the nanosorbent with FT-IR, CHNS, XRD, SEM, TEM, VSM, and BET surface analysis, parameters affecting the retention and desorption were optimized. Under optimal conditions, the detection limit of 8 ng/L was achieved for selenium (IV), and the method's precisions were less than 12.5 % intra-day RSD% and < 14.4 % for inter-day RSD%. The highest adsorption capacity was obtained as 264 mg/g. Finally, the desired adsorbent was used to extract and determine selenium species in water samples and total selenium in food samples. One of the most important advantages of the present method is its speed, ease, time-saving, and high accuracy.

A magnetic pore-confined catalyst with ionic liquids supported on MOFs for the synthesis of aryl-oxazolidinones: design, performance, and recyclability

Various methods have been explored for preparing heterogeneous catalysts using metal-organic framework (MOF) supported ionic liquids (ILs); however, it is challenging to develop such a synergistic catalyst that combines high efficiency, stability, the capability of maintaining immobilized ILs and active components, and high recovery efficiency. In this study, we successfully developed a magnetic MOF sub-nanostructured carrier by integrating organic UiO-66 with magnetic nanoparticles (MNPs). The resulting magnetic pore-confined catalyst, named MAG-UiO-66-IL(OAc), was prepared by in-situ self-assembly of pore-confining [C4mim] [OAc] within the nano-cavities of the magnetic MOF carrier. The morphology, structure, and thermal properties of the magnetic pore-confined catalyst were comprehensively characterized using various techniques. The novel catalyst MAG-UiO-66-IL(OAc) demonstrated remarkable catalytic efficiency in transforming cyclic carbonates and aryl amines to aryl-oxazolidinones, achieving yields up to 95% under mild solvent-free conditions. Furthermore, the catalyst showed exceptional recyclability, retaining its catalytic activity after ten successive reuses. Notably, the catalyst displayed excellent performance for reactions involving large-size reactants, expanding the range of substrate usability beyond previously reported solid-loading catalysts. Theoretical calculations were also conducted to complement the experimental results, providing valuable insights into the structure–activity relationship between the magnetic MOF carrier and the ionic liquid. These findings emphasize the significance of molecular-scale confinement on reactant diffusion and the overall reaction process, offering valuable guidance for the design of catalyst microstructures and the modulation of reaction performance.

Enhanced Electrochemical Characterization of the Immune Checkpoint Protein PD-L1 using Aptamer-Functionalized Magnetic Metal-Organic Frameworks.

Programmed death ligand 1 (PD-L1) is highly expressed in cancer cells and participates in the immune escape process of tumor cells. However, as one of the most promising biomarkers for cancer immunotherapy monitoring, the key problem ahead of practical usage is how to effectively improve the detection sensitivity of PD-L1. Herein, an electrochemical aptasensor for the evaluation of tumor immunotherapy is developed based on the immune checkpoint protein PD-L1. The fundamental principle of this method involves the utilization of DNA nanotetrahedron (NTH)-based capture probes and aptamer-modified magnetic metal-organic framework nanocomposites as signaling probes. A synergistic enhancement is observed in the electrocatalytic effect between Fe3O4 and UiO-66 porous shells in Fe3O4@UiO-66 nanocomposites. Therefore, the integration of aptamer-modified Fe3O4@UiO-66@Au with NTH-assisted target immobilization as an electrochemical sensing platform can significantly enhance sensitivity and specificity for target detection. This method enables the detection of targets at concentrations as low as 7.76 pgmL-1 over a wide linear range (0.01 to 1000ngmL-1). The authors have successfully employed this sensor for in situ characterization of PD-L1 on the cell surface and for monitoring changes in PD-L1 expression during drug therapy, providing a cost-effective yet robust alternative to highly expensive and expertise-dependent flow cytometry.

Bioluminescence assay for rapid detection of live Staphylococcus aureus based on the enrichment of egg yolk antibody modified magnetic metal organic framework immunobeads.

Specific and rapid detection of live Staphylococcus aureus (S.A) in environmental and food samples is critically important for protecting human health. In order to fulfill this purpose, two kinds of novel egg yolk antibody (IgY) immobilized immunomagnetic beads (IMBs; mSiO2-IgY and mMOF-IgY), with core-shell mSiO2 and mMOF as substrate, were prepared for selectively enriching S.A from samples. Furthermore, the IMBs with captured S.A were collected and re-dissolved in 0.5 mL PBS. After that, a cotton swab coated with sodium dodecylsulfate (SDS) was put in the solution to lyse S.A cells and emit ATP bioluminescence of the luciferin/luciferase system. Finally, a portable bioluminescence detector was used for quantification of ATP corresponding to S.A concentration. The results demonstrated that mMOF-IgY can enrich more S.A than mSiO2-IgY and emit a stronger signal. The reasons may be due to the higher immobilization amount of IgY on the IMBs. Under optimal conditions, the calibration line of S.A concentration was 10-105 CFU mL-1 by mMOF-IgY within 30 min. The low detection limit of S.A was 3 CFU mL-1. The results demonstrated that the assay takes much shorter time than plate counting. Its portability and excellent detection capability are suitable for rapid monitoring of specific pathogens in foods.

Facile synthesis of Fe3O4@CS@ZIF-67 for the magnetic solid phase extraction-high performance liquid chromatographic determination of benzoylurea insecticides in tea infusions

In this paper, a novel magnetic metal–organic framework composite with chitosan as linker (Fe3O4@CS@ZIF-67) was synthesized by a facile method at normal pressure and normal temperature. After characterization, Fe3O4@CS@ZIF-67 was used as adsorbent for the magnetic solid phase extraction of benzoylurea insecticides (BUs) in tea infusions prior to high performance liquid chromatographic analysis. The effects of the amount of adsorbent, ionic strength, pH, adsorption time, type of eluent and elution time were investigated. The adsorption could be completed in 1.5 min with only 15 mg adsorbent for the extraction of 10 mL sample solution. Good linearity was obtained for the analysis of BUs with R2 between 0.9988 and 0.9999. The limits of detection were in the range of 0.72–1.48 μg·L−1. Relative standard deviations (RSDs) for intra-day precision and inter-day precision were in the range of 2.62–4.32 % and 3.60–6.29 %, respectively. RSDs for batch-to-batch precision of Fe3O4@CS@ZIF-67 were between 0.41 % and 7.52 %. The spiked recoveries ranged from 75.7 % to 112.5 %. The proposed method has been successfully applied to the determination of BUs in tea infusion samples.

Facile fabrication of Fe3O4@UiO-66-NH2/popcorn-like gold nanoparticles based SERS substrate for selective enrichment and real-time detection of residual enrofloxacin in milk

In this study, a magnetic metal-organic frameworks (MOFs) based hybrid substrate was designed and fabricated for SERS detection of enrofloxacin (ENR) in milk. The magnetic MOF (Fe3O4@UiO-66-NH2) was synthesized by a facile microwave-assisted method, then loaded with popcorn-like Au nanoparticles (NPs) through electrostatic interaction. The as-prepared SERS substrate (Fe3O4@UiO-66-NH2/Au NPs) integrated the abundant hot spots of popcorn-like Au NPs with porous Fe3O4@UiO-66-NH2, which greatly improved its SERS activity and stability. More importantly, benefiting from the fingerprint characteristics of SERS and adsorption performance of Fe3O4@UiO-66-NH2, the SERS substrate exhibited high selectivity and sensitivity in detecting ENR. Under the optimal detection condition, a good linearity (R2 = 0.996) was obtained with ENR concentration of 1.0 × 10−9–1.0 × 10−6 M in spiked milk, the LOD was as low as 5.26 × 10−10 M, and the recoveries were in the range of 76.1–86.1 % at three different spiking levels. The whole detection process including sample pretreatment took about 50 min, which indicating that the prepared substrate has great potential in sensitive and real-time detection of ENR in milk.

Magnetic solid phase extraction for the determination of Pb(II) and Cd(II) in high salt foods

The conventional method for the determination of heavy metals in food is acid digestion followed by atomic absorption spectrometry or induced coupled plasma mass spectrometry. However, for high salt foods, due to the strong matrix effect, the detection results are seriously inaccurate. In this work, sulfur-functionalized magnetic metal-organic frameworks (Fe3O4@UiO-66-SH) were synthesized by coating Fe3O4 nanospheres with sulfydryl-functionalized UiO-66. The Fe3O4@UiO-66-SH possesses both the magnetic properties of Fe3O4 and the diverse properties of metal-organic framework (MOF) in one material, which has the superiority of high surface area, easy-operation and strong adsorb ability with Pb (II) and Cd(II), is used to separate and determine Pb (II) and Cd(II) in high salt foods by magnetic solid phase extraction-induced plasma mass spectrometry. The detection limits (LODs) for Pb (II) and Cd(II) were 0.17 and 0.21µg/kg, respectively, and the quantification limits (LOQs) were 0.56 and 0.66µg/kg. Analyzing the certified reference material of soy sauce (CFAPA-QC1728-4, P41839) and estimating the spiked recoveries proved the accuracy and precision of the proposed method. The determined values agreed well with the reference values, and the recoveries for spiking sample varied from 85.8–100.5%.