Triple-enzyme mimetic activity of Fe3O4@C@MnO2 composites derived from metal-organic frameworks and their application to colorimetric biosensing of dopamine.

Novel Fe3O4@C@MnO2 composites were successfully synthesized for the first time via an interfacial reaction between magnetic porous carbon and KMnO4, in which the magnetic porous carbon was derived from the pyrolysis of Fe-MIL-88A under N2 atmosphere. Interestingly, the obtained Fe3O4@C@MnO2 composites were found to have triple-enzyme mimetic activity including peroxidase-like, catalase-like, and oxidase-like activity. As a peroxidase mimic, Fe3O4@C@MnO2 composites could catalyze the oxidation of TMB into a blue oxidized product by H2O2. As a catalase mimic, Fe3O4@C@MnO2 could catalyze the decomposition of H2O2 to generate O2 and H2O. As an oxidase mimic, Fe3O4@C@MnO2 could catalyze the direct oxidation of TMB to produce a blue oxidized product without H2O2. Reactive oxygen species measurements revealed that the oxidase-like activity originated from 1O2 and O2-∙and little∙OH generated by the dissolved oxygen, which was catalyzed by the Fe3O4@C@MnO2 in the TMB oxidation reaction. The oxidase-like activity of Fe3O4@C@MnO2 was investigated in detail. Under the optimized conditions, a rapid, sensitive, visual colorimetric method for dopamine detection was developed based on the inhibitory effect of dopamine on the oxidase-like activity. The proposed method allows for dopamine detection with a limit of detection of 0.034 µM and a linear range of 0.125-10 µM. This new colorimetric method was successfully used for the determination of dopamine in human blood samples.

Functional Covalent Organic Frameworks' Microspheres Synthesized by Self-Limited Dynamic Linker Exchange for Stationary Phases.

Synthesizing uniform functional covalent organic framework (COF) microspheres is the prerequisite of applying COFs as novel stationary phases for liquid chromatography. However, the synthesis of functionalized COF microspheres is challenging due to the difficulty in maintaining microspheric morphology when conferring functions. Here, a facile and universal "self-limited dynamic linker exchange" strategy is developed to achieve surface functionalization of uniform COF microspheres. Six different types of COF microspheres are constructed, showing the universality and superiority of the strategy. The library of COF microspheres' stationary phases can be further enriched on demand by varying different functional building blocks. The "self-limited dynamic linker exchange" is attributed to the result of a delicate balance of reaction thermodynamics and molecular diffusion energy barrier. As a demonstration, the chiral functional COF microspheres are used as stationary phases of chiral chromatography and realized effective enantioseparation.

[Recent advances in the research of chromatographic separation materials based on click chemistry].

Since Nobel Laureate K. B. Sharpless first introduced the concept of click chemistry in 2001, such reactions have become a powerful modular synthesis tool. Click chemistry reactions have rapidly expanded into many scientific fields, such as materials and life science, owing to their distinct advantages, which include mild conditions, fast reaction rates, high yields, low by-product generation, and simple separation and purification procedures. Nowadays, click chemistry reactions have become an essential means of designing and preparing separation materials; thus, interest in this synthetic technique has quickly grown. Here, the development of click chemistry and its unique advantages are briefly described firstly. The reports on click chemistry-based chromatographic separation materials published in the past five years are then systematically reviewed, focusing on two major separation fields: column chromatography and membrane chromatography. Meanwhile, recent advances in the separation materials obtained from three common types of click reactions, namely, azido-alkyne, thiol-alkene, and thiol-alkyne, are summarized. Finally, an outlook on the future of click chemistry is provided in developing efficient chromatographic separation materials.

Facile in situ microwave synthesis of Fe3O4@MIL-100(Fe) exhibiting enhanced dual enzyme mimetic activities for colorimetric glutathione sensing.

In recent decades, artificial nanozymes with excellent stability, low cost and availability have been gradually explored to avoid the limits of natural enzymes such as poor stability, high cost and difficult preparation. Herein, for the first time, we investigated the capability of nanoscale Fe3O4@MIL-100(Fe) as a nanozyme, which was quickly synthesized in situ by a microwave-assisted method within 20 min using Fe3O4 as the metal precursor. The obtained Fe3O4@MIL-100(Fe) showed satisfactory intrinsic dual enzyme mimetic activities, including peroxidase (POD)- and catalase (CAT)-like activities. Moreover, a simple and effective colorimetric biosensor was fabricated to detect glutathione (GSH) based on its POD-like activity. The proposed measurement had a linear range of 1-45 µM and a limit of detection (LOD) of 0.26 µM (3.3 δ/S). It was proved that the established colorimetric sensing system could be successfully applied to detect GSH in actual biological samples. Importantly, the outstanding reusability and stability made it extremely valuable as a catalyst. The present work implied that Fe3O4@MIL-100(Fe) synthesized in situ by the microwave-assisted method was a very promising candidate for biocatalyst and biosensing.

Development and application of metal-organic framework@GA based on solid-phase extraction coupling with UPLC-MS/MS for the determination of five NSAIDs in water.

MIL-101(Cr) and graphene aerogel (GA) were hybridized as a multifunctional adsorbent for the preconcentration of trace analytes. The novel MIL-101(Cr)@GA was prepared and characterized by FTIR, XRD and SEM, where GA is serving as a carrier for MIL-101(Cr). The synthesized composite as a solid phase extraction (SPE) sorbent combined with UPLC-MS/MS was applied for the determination and quantification of five NSAIDs (phenacetin, meloxicam, naproxen, diclofenac sodium and carprofen) in different environmental water samples. The parameters influencing the whole extraction process were systematically optimized. Under the most favorable. conditions, good sensitivity was achieved with a limit of detection between 0.006 and 0.012 ng mL-1, the linear range of 0.02-2 ng mL-1 for phenacetin, meloxicam and 0.05-5 ng mL-1 for naproxen, diclofenac sodium, carprofen (r2 ≥ 0.9940). The satisfactory recoveries of the target analytes were in the range from 77.2 to 103.3% with relative standard deviation (RSD) from 0.6% to 8.4%. The established method was proved to be simple, highly sensitive and accurate. The adsorbent could be reusable up to nine cycles without any decrease in performance, which provides economic strategy and little waste generation. Adsorption behaviors were explored by choosing two typical types of NSAIDs as models to measure the adsorption capacity of MIL-101(Cr)@GA. The maximum adsorption capacities for PHE and NAP were 232.5 and 333.3 mg g-1, respectively.