Boric-Acid-Functionalized Covalent Organic Framework for Specific Enrichment and Direct Detection of cis-Diol-Containing Compounds by Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry

4-Mercaptobenzoic acid as a MALDI matrix for highly sensitive analysis of metals

4-Mercaptobenzoic acid (MBA) is introduced as a matrix for laser desorption/ionization time-of-flight mass spectrometry (MS) analysis of metals, exhibiting matrix-interference-free background, greatly enhanced MS signal intensity, and excellent reproducibility. The developed method was successfully extended for the rapid screening and sensitive determination of ultratrace metals in fine particulate matter (PM_2.5).

Hybrid MoS2/g-C3N4-assisted LDI mass spectrometry for rapid detection of small molecules and polyethylene glycols and direct determination of uric acid in complicated biological samples

A novel matrix-assisted laser desorption/ionization time-of-flight mass spectrometric method (MALDI-TOF MS) for determination of highly sensitive small molecular compounds was developed based on molybdenum disulfide nanosheets hybridized with ultrathin graphitic carbon nitride (MoS₂/g-C₃N₄) as the matrix. With this approach, the synergistic effects of MoS₂ and g-C₃N₄ enhance the UV absorption of MoS₂/g-C₃N₄, increase both desorption and ionization efficiency in LDI MS, and induce higher signal-to-noise ratio of analytes when compared with the bare MoS₂ and g-C₃N₄ matrix in the determination of amino acids, antibiotics, neutral oligosaccharides, uric acid, and polyethylene glycols (PEGs). The detection limits of these small molecular compounds are in the ranges 0.1 to 10 μg mL^-1, 1*10^-3 to 1.0 μg mL^-1, 1.0 to 10 μg mL^-1, and 2*10^-4 μg mL^-1, respectively, and the polydispersity index of these PEGs is less than 1.02. Moreover, high salt tolera`nce and homogeneous deposition on the spot results in good reproducibility. The relative standard deviations (RSDs) of shot-to-shot and spot-to-spot (n = 15) of these compounds are less than 10.1% and 12.5%, respectively. With MoS₂/g-C₃N₄, the uric acid in complicated biological samples can be directly determined in combination with LDI-TOF MS. We synthesized MoS₂/g-C₃N₄ nanohybrid as an efficient matrix for MALDI-TOF MS analysis of small molecules as well as quantitative detection of uric acid in human urine.

Synthesis of magnetic metal organic framework/covalent organic framework hybrid materials as adsorbents for magnetic solid-phase extraction of four endocrine-disrupting chemicals from milk samples

RATIONALE

Endocrine-disrupting chemicals (EDCs), widespread and easily ingested through the simple food chain, have been suggested to pose potential carcinogenic threats to human health. Considering food safety and public health, it is urgent to establish a sensitive and effective method to enrich and determine EDCs in food samples.

METHODS

Novel hybrid nanocomposites Fe₃ O₄ @A-TpBD@NH₂ -MIL-125(Ti) were synthesized through the formation of amide bonds. The as-prepared Fe₃ O₄ were innovatively encapsulated with 4-aminobenzoic acid functionalized COF(A-TpBD) to generate bare carboxyl (-COOH), which formed amide bonds with the NH₂ -MIL-125(Ti), generating well-defined and hierarchical hybrid materials. The Fe₃ O₄ @A-TpBD@NH₂ -MIL-125(Ti) materials were used as the adsorbents for magnetic solid-phase extraction (MSPE) coupled with high-performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS) to enrich and determine EDCs (E1, E2, E3 and BPA) from milk samples.

RESULTS

Fe₃ O₄ @A-TpBD@NH₂ -MIL-125(Ti) exhibited improved adsorption efficiency and selectivity based on π-π stacking interaction, hydrogen bonding, electrostatic interaction, and the interaction between the hydroxyl group in EDCs and titanium ions (IV, [Ti]⁴⁺ ). Under the optimized conditions, Fe₃ O₄ @A-TpBD@NH₂ -MIL-125(Ti)-based MSPE coupled with HPLC/MS/MS showed good linearity with correlation coefficient (R² ) ≥0.9983 and high sensitivity with limits of detection (LODs) in the range of 0.37-0.85 μg/L. Moreover, the developed method was successfully employed to detect EDCs in milk samples.

CONCLUSIONS

Fe₃ O₄ @A-TpBD@NH₂ -MIL-125(Ti) possess good adsorption capability and selectivity for EDCs. In addition, the proposed MSPE-HPLC/MS/MS method based on Fe₃ O₄ @A-TpBD@NH₂ -MIL-125(Ti) is effective and sensitive for the determination of EDCs in real samples, which can be used as a robust alternative method to monitor EDCs in complex matrices.

A novel fluorescent covalent organic framework containing boric acid groups for selective capture and sensing of cis-diol molecules

Owing to specific formation of five-membered or six-membered cyclic esters between boric acid groups and cis-diol molecules, boric acid bearing fluorescent materials can not only selectively capture but also specifically identify cis-diol substances. In this work, a novel covalent organic framework containing boric acid groups (COF-BA) was prepared through post-modification via the aza-Diels-Alder cycloaddition reaction. COF-BA with good stability, a permanent pore structure, a high specific surface area (606 m2 g-1) and a uniform pore size (2.59 nm) exhibited unique selectivity toward the cis-diol guest molecule 1,2-dihydroxyanthracene-9,10-dione (1,2-Doa) with a high adsorption capacity of 177.95 mg g-1. However, as for the isomers of 1,2-Doa (1,4-dihydroxyanthracene-9,10-dione and 2,6-dihydroxyanthracene-9,10-dione), the corresponding uptake capacities are distinctively decreased to 40.86 mg g-1 and 3.05 mg g-1, respectively. It is worth noting that the COF-BA can be recovered and recycled. Moreover, because the formation of the quinoline enhanced the conjugation effect of the COF skeleton, it was unexpectedly found that COF-BA possessed an intrinsic fluorescence property and could be used as an optical sensor for 1,2-Doa.

Recent development of nanoparticle-assisted metabolites analysis with mass spectrometry

Metabolomics systematically studies the changes of metabolites in biological systems in the temporal or spatial dimensions. It is a challenging task for comprehensive analysis of metabolomics because of diverse physicochemical properties and wide concentration distribution of metabolites. Used as enrichment sorbents, chemoselective probes, chromatographic stationary phases, MS ionization matrix, nanomaterials play excellent roles in improving the selectivity, separation performance, detection sensitivity and identification efficiency of metabolites when mass spectrometry is employed as the detection technique. This review summarized the recent development of nanoparticle-assisted metabolites analysis in terms of assisting the pretreatment of biological samples, improving the separation performance and enhancing the MALDI-MS detection.

Nanoscale covalent organic frameworks as theranostic platforms for oncotherapy: synthesis, functionalization, and applications

Cancer nanomedicine is one of the most promising domains that has emerged in the continuing search for cancer diagnosis and treatment. The rapid development of nanomaterials and nanotechnology provide a vast array of materials for use in cancer nanomedicine. Among the various nanomaterials, covalent organic frameworks (COFs) are becoming an attractive class of upstarts owing to their high crystallinity, structural regularity, inherent porosity, extensive functionality, design flexibility, and good biocompatibility. In this comprehensive review, recent developments and key achievements of COFs are provided, including their structural design, synthesis methods, nanocrystallization, and functionalization strategies. Subsequently, a systematic overview of the potential oncotherapy applications achieved till date in the fast-growing field of COFs is provided with the aim to inspire further contributions and developments to this nascent but promising field. Finally, development opportunities, critical challenges, and some personal perspectives for COF-based cancer therapeutics are presented.

Boric-acid-modified Fe3O4@PDA@UiO-66 for enrichment and detection of glucose by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Herein, boric-acid-modified multifunctional Zr-based metal-organic frameworks (denoted as Fe₃O₄@PDA@B-UiO-66) were synthesized by hydrothermal reaction and surface modification. Compared to traditional matrix, Fe₃O₄@PDA@B-UiO-66 has the advantages of high ionization efficiency, high surface area, low matrix background, porous structure, and numerous boric-acid-active sites. By combining matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), Fe₃O₄@PDA@B-UiO-66 was used as an adsorbent and matrix for enrichment and detection of glucose, based on a specific reaction between boric acid and glucose. The limit of detection was 58.5 nM. The proposed method provides a simple and efficient approach for the sensitive and quantitative detection of glucose in complex samples based on MALDI-TOF MS. Design and synthesis of boric-acid-modified multifunctional magnetic metal-organic frameworks (designated as Fe₃O₄@PDA@B-UiO-66) applied as adsorbent and matrix for the matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) analysis of glucose in complex biosamples.

Facile extraction and determination of organophosphorus pesticides in vegetables via magnetic functionalized covalent organic framework nanocomposites

Facile enrichment and determination of trace organophosphorus pesticides (OPPs) in foods has been a constantly pursuing goal in food safety field. Herein, Zr⁴⁺-immobilized covalent organic frameworks (Fe₃O₄@COF@Zr⁴⁺) have been first constructed and utilized as the powerful adsorbents for magnetic solid-phase extraction (MSPE) of OPPs. Owing to the π-π stacking interaction, hydrogen bonding and Zr⁴⁺-phosphate coordination reaction, the composites exhibited excellent selectivity and superior affinity to OPPs. Under optimized conditions, the proposed MSPE method coupled with GC-FPD showed good linearity (R² ≥ 0.9990) and yielded low limits of detection (0.7-3.0 μg kg^-1) for OPPs. Moreover, the developed method was successfully employed for the quantitation of OPPs in spiked vegetable samples and obtained satisfactory recoveries in the range of 87-121% with the relative standard deviations (RSDs) ≤ 8.9%. These results demonstrated that the prepared nanoparticles hold unique advantages for trace OPPs analysis in foodstuffs.

A spherical covalent-organic framework for enhancing laser desorption/ionization mass spectrometry for small molecule detection

A spherical vinyl-functionalized covalent-organic framework (COF-V) was prepared at room temperature by a facile method and applied as a novel substrate for surface-enhanced laser desorption/ionization mass spectrometry (SELDI-MS).

Thiol-Ene Click Synthesis of Phenylboronic Acid-Functionalized Covalent Organic Framework for Selective Catechol Removal from Aqueous Medium

We report a thiol-ene click strategy for the preparation of a novel phenylboronic acid-functionalized covalent organic framework (COF) for selective removal of catechol in aqueous solution. Vinyl-functionalized 2,5-diallyloxyterephthalaldehyde (Da-V) was prepared as a building ligand. Da-V was then condensed with 1,3,5-tris(4-aminophenyl)benzene (Tab) to give a vinyl-functionalized COF DhaTab-V. Subsequently, 4-mercaptophenylboronic acid (4-MPBA) was covalently linked on DhaTab-V via thiol-ene click reaction to give phenylboronic acid-functionalized COF DhaTab-PBA. The adsorption isotherms, energetics and kinetics, and reusability of DhaTab-PBA for the adsorption and removal of catechol from aqueous solution were investigated in detail. This phenylboronic acid-functionalized COF is promising as sorbent for selective removal of catechol from aqueous medium with large adsorption capacity and good reusability.

Recent advances in the construction of functionalized covalent organic frameworks and their applications to sensing

Covalent organic frameworks (COFs), as an emerging class of porous crystalline polymers, are built by the combination of the light elements through the strong covalent bonds. In the past decade, COFs have been reported to show plenty of unique properties (such as ordered channels, large specific surface area, highly tunable porosity, optional building blocks, predictable and stable structure, and abundant functional groups), and have been widely applied in multiple fields. Recently, to further improve the potential performances of COFs and extend their applicability, a number of COFs with various functionalities have been successfully developed through the functionalization modification. In this review, we summarized the advanced design and construction of functionalized COFs, including COFs with post-synthetic modification, COFs-based composites (e.g. COFs-metal nanoparticles composites, COFs-metal oxide nanoparticles composites, COFs-MOFs composites, and COFs-enzyme composites), and molecularly imprinted COFs. Impressively, the applications of functionalized COFs to sensing also have been comprehensively summarized, including colorimetric sensing, fluorescent sensing, electrochemical sensing, and other sensing (such as quartz crystal microbalance (QCM) sensing, photoelectrochemical sensing, and humidity sensing). In the end, future opportunities and challenges in this promising field are tentatively proposed.

Recent advances in covalent organic frameworks (COFs) as a smart sensing material

Recent advances in covalent organic frameworks (COFs) as a smart sensing material are summarized and highlighted.