Efficient capture and highly sensitive analysis of okadaic acid by three-dimensional covalent organic frameworks with hydroxyl surface engineering.

A novel three-dimensional covalent organic framework (3D-COF) with content-tunable and active hydroxyl groups (OH) on the pore walls was developed and adopted for the high-performance capture of okadaic acid (OA) marine toxins. Using pore-surface engineering, the integration of linear building blocks (4,4'-diamino-3,3'-biphenyldiol, BD(OH)2 and benzidine, BD) with the 3D structural building block backbone (4,4',4'',4'''-methane-tetrayltetrabenzaldehyde, TFPM) was achieved. By adjusting the ratio of BD(OH)2, functional multicomponent-COFs [OH]x-BD-TFPM COFs (X = 25%) were synthesized, which offered ideal access to convert a conventional COF into a functional platform with multiple-mode interactions of hydrophobic and hydrophilic groups for OA capture. [OH]x-BD-TFPM was characterized using SEM, XRD, FT-IR, and BET. The adsorption features and analytical performance of OA were screened and evaluated. Optimization of dispersive solid-phase extraction using [OH]25-BD-TFPM was accomplished, and the method was verified for sensitive quantitative detection of OA in clam and mussel samples. Coupled with LC-MS/MS, the resultant [OH]25-BD-TFPM COF demonstrated the ability to analyze OA, and the limit of detection for OA in shellfish was determined to be 0.005 µg/kg. A significant improvement in trace OA detection was observed compared to previously reported SPE materials without adjustable hydrophilic interactions. The recoveries of OA in the fortified clam and mussel samples were in the ranges of 93.9‒105.1% and 96.7‒110.2%, respectively. This study highlights that OH-group surface engineering in channel walls is a facile and powerful strategy for developing functional 3D-COFs with multiple interactions for high-performance target capture.

Towards highly specific aptamer-affinity monolithic column by efficient UV light-initiated polymerization in "one-pot".

Time-consuming or tedious operation in multiple-step process might is the obstacle for efficiently preparing aptamer-affinity monolithic column. Here, a new and facile strategy to prepare aptamer-based hybrid affinity monolith in "one-pot" at room temperature was exploited, in which UV light-initiated free-radical polymerization and "thiol-ene" click reaction were implemented simultaneously. Only 7 min was cost for finishing the polymerization reaction, which was only 1/100 of that for the traditional thermal polymerization. Using ochratoxin A (OTA) as the model analyte, the recipe for photo-initiated polymerization was optimized, and SEM morphology, FTIR, EDS, pore size distribution and specific recognition performance were also studied. Compared with traditional thermal polymerization, the resultant monolith was achieved more facilely and displayed better results such as more homogeneous skeleton structure, higher reaction efficiency of aptamer (>88.2%) and better specific selectivity to OTA. Besides, an extremely low nonspecific adsorption of analogues was obtained and showed a level at only 1/25 of that in the similar aptamer-affinity monolith prepared by thermal polymerization. Applied to beer and red wine samples, good recovery yields about 99.7 ± 4.0% -101.2 ± 2.3% (n = 3)was achieved with the acceptable RSDs. It would open up a rapid and promising access to efficiently preparing high-performance aptamer-based affinity monolithic columns for online specific recognition.

Heteroporous 3D covalent organic framework-based magnetic nanospheres for sensitive detection of bisphenol A.

Covalent organic frameworks (COFs) showed great promise in effective adsorption of target molecule via size selectivity. Although various magnetic 2D COFs composites have been studied and exhibited the intensive applications, the incorporation of 3D COFs and magnetic nanoparticles to form a new class of magnetic adsorbents with enhanced function still has no reports. Herein, a novel Fe3O4@3D COF with heteroporous structure matching to the sizes of bisphenol A (BPA) was firstly synthesized for better adsorption of BPA than common magnetic 2D-COFs. Three Fe3O4@3D COFs nanospheres were synthesized under the solvothermal conditions in autoclave, and the optimum Fe3O4@3D-COF denoted as Fe3O4@COF-TpTAM (Tp, 1,3,5-triformylphloroglucinol; TAM, tetra(p-aminophenyl)-methane) was selected and employed. Detailed characteristics of Fe3O4@COF-TpTAM were evaluated via various techniques including TEM, FTIR, TGA, XRD and BET. Excellent chemical and thermal stability, high surface area (294.6 m2 g-1) and pore volume (0.2 m3 g-1) with multiple pore sizes comparable with the simulated three-dimensional sizes of BPA were exhibited. A high adsorption capacity of BPA up to 209.9 mg/g that was better than common 2D-COFs was achieved, and the sensitive MSPE-LC-MS method with wide linear range (10-5000 pg/mL), low detection limit (4 pg/mL, S/N = 3) was built. Satisfactory recoveries of BPA as 93.8 ± 1.4%-101.4 ± 5.1% (n = 3) and 100.4 ± 1.9% ~ 107.3 ± 1.2% (n = 3) were obtained in milk and river water samples, respectively. This work demonstrates the promising application of Fe3O4@3D COF as efficient adsorbents of trace BPA, and opens up a new access for the efficient MSPE in sample pretreatment for food or environmental safety analysis.

Facile preparation of stainless steel microextraction fiber via in situ growth of metal-organic framework UiO-66 and its application to sensitive analysis of polycyclic musks.

A functional stainless steel microextraction fiber easily prepared by in situ growing metal-organic framework UiO-66 was presented and used for high-performance analysis of polycyclic musks. Via the robust Ag-SH bonding reaction, mercaptoacetic acid was easily anchored on Ag film to provide carboxyl group on the stainless steel fiber, then in situ grown UiO-66 was fulfilled via the coordination reaction between Zr4+ and carboxyl group. Good characteristics including large surface area, high thermal stability, and good adsorption property were achieved. Sensitive detection limits (0.015-0.040 ng/L) were achieved for polycyclic musks by coupling with gas chromatography with mass spectrometry, and it could be stable enough for 150 extraction cycles without a significant loss of extraction efficiency. Compared with the classical commercial fibers, 2.2-11.4 times higher enhancement factors were shown. Applied to the analysis of fortified river water samples, five typical polycyclic musks were well detected with the recoveries of 90.2-101.8%, respectively. It showed a facile approach for preparing stainless steel microextraction fiber via chemically bonding in situ grown metal-organic framework for high-performance enrichment.

Highly hydrophilic polyhedral oligomeric silsesquioxane (POSS)-containing aptamer-modified affinity hybrid monolith for efficient on-column discrimination with low nonspecific adsorption.

A novel polyhedral oligomeric silsesquioxane (POSS)-containing aptamer-modified hybrid affinity monolith with excellent hydrophilicity and unique architecture without Si-OH groups is presented herein, and the nonspecific adsorption caused by the hydrophobic nature of the monolithic column or polar interaction with silanol groups is minimized. Via a simple "one-pot" procedure, hydrophilic monomers were facilely polymerized with the POSS-methacryl substituted (POSS-MA) and aptamer; a highly hydrophilic nature was obtained and the lowest contact angle of 11° was achieved. By using ochratoxin A (OTA) as the model analyte, highly selective recognition of OTA in the mixture was achieved and the control of nonspecific interactions and the cross-reactivity of OTB and AFB1 were significantly improved. The recovery yield of OTB caused by nonspecific adsorption in the resultant monolith was only about 0.1% and remained steady even with the coexistence of a high OTB content (OTA : OTB = 1 : 50), which reached the best level to date and was obviously less than the 6.1% occurring in the hydrophobic POSS-containing control monolith, 8.3% in the POSS-PEI@AuNPs@aptamer affinity monolith and 18.7% in the silica-hybrid affinity monolith. When applied to wine and wheat samples, the nonspecific adsorption was significantly reduced and efficient discrimination of OTA was obtained with better results than that of the hydrophobic POSS-containing affinity column. This provides an attractive tool for minimizing the nonspecific adsorption for highly selective on-column recognition.

Study on the degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) and 2-methyl-4-chloro-phenoxyacetic sodium (MCPA sodium) in natural agriculture-soils of Fuzhou, China using capillary electrophoresis.

A new method of analyzing trace 2,4-Dichlorophenoxyacetic acid (2,4-D) and 2-methy-4-chloro-lphenoxyacetic sodium (MCPA sodium) in soils by capillary electrophoresis (CE) has been developed in this study. The optimum analytical conditions including chemical component and concentration of buffer solution, pH, separation voltage and sample injection time were studied in detail. Under the optimum conditions, 2,4-D and MCPA sodium in soils can be speedy separated and determined within 20 min with detection limits of 0.15 microg/g (2,4-D) and 0.25 microg/g (MCPA sodium) , a RSD (n=6)<5% and a recovery>89%. With the help of analytical method developed in this study, the degradations of 2,4-D and MCPA sodium in natural agriculture-soils of Fuzhou were studied. The experimental results indicated that the degradations of 2,4-D and MCPA sodium follow first-order kinetics with degradation constants of 0.1509 day(-1) (2,4-D) and 0.2722 day(-1) (MCPA sodium) respectively. The degradation half-life were calculated to be 4.6 days (2,4-D) and 2.6 days (MCPA sodium) at 27 degrees C, implied that 2,4-D and MCPA sodium can be speedy degraded in natural agriculture-soils of Fuzhou, China.