Magnetic covalent organic frameworks for extraction and determination of endocrine-disrupting chemicals in beverage and water samples.

BACKGROUND: Phenolic endocrine-disrupting chemicals (EDCs) are widespread and easily ingested through the food chain. They pose a serious threat to human health. Magnetic solid-phase extraction (MSPE) is an effective sample pre-treatment technology to determine traces of phenolic EDCs. RESULTS: Magnetic covalent organic framework (COF) (Fe3 O4 @COF) nanospheres were prepared and characterized. The efficient and selective extraction of phenolic EDCs relies on a large specific surface and the inherent porosity of COFs and hydrogen bonding, π-π, and hydrophobic interactions between COF shells and phenolic EDCs. Under optimal conditions, the proposed magnetic solid-phase extraction-high-performance liquid chromatography-ultra violet (MSPE-HPLC-UV) based on the metallic covalent organic framework method for phenolic EDCs shows good linearities (0.002-6 µg mL-1 ), with R2 of 0.995 or higher, and low limits of detection (6-1.200 ng mL-1 ). CONCLUSION: Magnetic covalent organic frameworks (Fe3 O4 @COFs) with good MSPE performance for phenolic EDCs were synthesized by the solvothermal method. The magnetic covalent organic framework-based MSPE-HPLC-UV method was applied successfully to determine phenolic EDCs in beverage and water samples with satisfactory recoveries (90.200%-123%) and relative standard deviations (2.100%-12.100%). © 2023 Society of Chemical Industry.

A colorimetric sensor for Staphylococcus aureus detection based on controlled click chemical-induced aggregation of gold nanoparticles and immunomagnetic separation.

Staphylococcus aureus (S. aureus) is a pathogen closely associated with foodborne diseases. We prepared a reliable colorimetric sensor to detect S. aureus using click chemical reaction and immunomagnetic separation. Aptamer-functionalized and ALP-labeled Fe3O4 NPs act as separation and signal transduction elements. Under the optimized conditions, the Cu+ generated by signal transduction triggers a click chemistry reaction, which causes the aggregation of azides and alkyne-AuNPs and a color change. The net extinction ratio of Δ(A530/A760) was linearly correlated with the S. aureus concentration from 10 to 106 cfu mL-1, and the limit detection was 2.4 cfu mL-1. The recoveries were 91.15 ~ 106.36% for the analysis of spiked food and water samples without pre-enrichment. Therefore, we believe that the detection platform can be easily and accurately used for S. aureus detection, providing a broad prospect for on-site visual detection.

Core-shell-structured magnetic covalent organic frameworks for effective extraction of parabens prior to their determination by HPLC.

Covalent organic framework (COF)-decorated magnetic nanoparticles (Fe3O4@DhaTab) with core-shell structure have been synthesized by one-pot method. The prepared Fe3O4@DhaTab was well characterized, and parameters of magnetic solid-phase extraction (MSPE) for parabens were also investigated in detail. Under optimized conditions, the adsorbent dosage was only 3 mg and extraction time was 10 min. The developed Fe3O4@DhaTab-based MSPE-HPLC analysis method offered good linearity (0.01-20 µg mL-1) with R2 (0.999) and low limits of detection (3.3-6.5 µg L-1) using UV detector at 254 nm. The proposed method was applied to determine four parabens in environmental water samples with recoveries in the range 64.0-105% and relative standard deviations of 0.16-7.8%. The adsorption mechanism was explored and indicated that porous DhaTab shell provided π-π, hydrophobic, and hydrogen bonding interactions in the MSPE process. The results revealed the potential of magnetic-functionalized COFs in determination of environmental contaminants.

Ratiometric fluorescent probe based on gold nanoclusters and alizarin red-boronic acid for monitoring glucose in brain microdialysate.

Glucose monitoring with high sensitivity and accuracy in the cerebrospinal fluid is a challenge for evaluating the role of glucose in the physiological and pathological processes. In this work, a ratiometric fluorescent probe for sensing glucose was developed. In the probe, the gold nanoclusters protected by ovalbumin played the role as the reference of fluorophore and the Alizarin Red S-3-aminophenyl boronic acid immobilized on the poly(N-acryloxysuccinimide) acted as both the response signal and specific recognition unit for sensing glucose. Once the ratiometric fluorescent probe reacted with glucose in the biological system, its fluorescence intensity at 567 nm was quenched, while the fluorescence intensity at 610 nm was essentially unchanged. In addition, the prepared ratiometric fluorescent probe showed higher stability against environmental effects. As a result, the present ratiometric fluorescent probe was successfully used for monitoring of glucose in the rat brain following the cerebral calm/ischemia.

A multichromatic colorimetric detection method for Vibrio parahaemolyticus based on Fe3O4-Zn-Mn nanoenzyme and dual substrates.

IMPORTANCE: The Fe3O4-Zn-Mn nanomimetic enzyme demonstrates significant importance in dual-substrate colorimetric detection for V. parahaemolyticus, owing to its enhanced sensitivity, selectivity, and rapid detection capabilities. Additionally, it offers cost-effectiveness, portability, and the potential for multiplex detection. This innovative approach holds promise for improving the monitoring and control of V. parahaemolyticus infections, thereby contributing to advancements in public health and food safety.

Multicolor colorimetric visual detection of Staphylococcus aureus based on Fe3O4-Ag-MnO2 composites nano-oxidative mimetic enzyme.

Novel Fe3O4-Ag-MnO2 composites were successfully synthesized. It was noteworthy that the obtained Fe3O4-Ag-MnO2 composites were found to possess three types of enzyme-mimicking activities, including peroxidase-like, catalase-like and oxidase-like activities. Taking advantage of the oxidase properties of Fe3O4-Ag-MnO2, the direct oxidation of TMB could be catalyzed to generate blue oxidation products without H2O2. The oxidase-like activity of Fe3O4-Ag-MnO2 were carefully studied. Based on the Fe3O4-Ag-MnO2-TMB system, a fast, sensitive and intuitive multicolor colorimetric method for Staphylococcus aureus (S. aureus) detection was established under the optimized conditions. The proposed method allows the detection of S. aureus with a detection limit of 3.7 cfu mL-1 and a linear range of 10-106 cfu mL-1. This new colorimetric method has been successfully proved to be applicable to the detection S. aureus of food samples.

Rapid and sensitive determination of ascorbic acid based on label-free silver triangular nanoplates.

In this study, a new method for the detection of ascorbic acid (AA) was proposed. It was based on the protective effect of AA on silver triangular nanoplates (Ag TNPs) against Cl- induced etching reactions. Cl- can attack the corners of Ag TNPs and etch them, causing a morphological shift from triangular nanoplates to nanodiscs. As a result, the solution changes color from blue to yellow. However, in the presence of AA, the corners of Ag TNPs can be protected from Cl- etching, and the blue color of the solution remains unchanged. Using this effect, a selective sensor was designed to detect AA in the range of 0-40.00 µM with a detection limit of 2.17 µM. As the concentration of AA varies in this range, color changes from yellow to blue can be easily observed, so the designed sensor can be used for colorimetric detection. This method can be used to analyze fruit juice samples.

Construction of an ultra-small hydrazone-linked covalent organic polymer for selective fluorescent detection of ferric ion in aqueous solution.

A novel ultra-small hydrazone-linked covalent organic polymer (UHCOP) was synthesized based on the Schiff-base reaction between 2,4,6-trihydroxy-1,3,5-benzenetricarbaldehyde and 1,4-benzenedicarbohydrazide at room temperature and utilized as a sensitive fluorescent sensor for rapid (<2 min) and selective detection of Fe3+ in aqueous solution. The prepared UHCOP displayed ultra-small size with the diameter of 7.98 ± 0.97 nm and gave a stable fluorescent emission at 510 nm. UHCOP exhibited good sensitivity and highly selectivity towards Fe3+. The coordination interaction between UHCOP and Fe3+ resulted in the obviously aggregation-caused quenching response of UHCOP. The linear range was from 5.0 µM to 1.4 mM (R2 = 0.999) with the detection limit of 2.5 µM. Finally, UHCOP has been successfully applied in the detection of Fe3+ in real water samples, proving the fabricated UHCOP is promising as a sensitive fluorescent sensor for selective detection of Fe3+ in aqueous solution.

Fabrication of magnetic covalent organic framework for effective and selective solid-phase extraction of propylparaben from food samples.

Efficient magnetic solid phase extraction using crystalline porous polymers can find important applications in food safety. Herein, the core-shell Fe3O4@COFs nanospheres were synthesized by one-pot method and characterized in detail. The porous COF shell with large surface area had fast and selective adsorption for propylparaben via π-π, hydrogen bonding and hydrophobic interactions. The extraction and desorption parameters were evaluated in detail. Under the optimized conditions, the extraction equilibrium was reached only in 5 min, the maximum adsorption capacity for propylparaben was 500 mg g-1 and the proposed Fe3O4@DhaTab-based-MSPE-HPLC-UV method afforded good linearity (4-20000 µg mL-1) with R2 (0.997), low limits of detection (0.55 µg L-1) and limits of quantification (1.5 µg L-1). Furthermore, the developed method was applied to determine propylparaben in soft drinks with the recoveries (97.0-98.3%) and relative standard deviations (0.61 to 3.75%). These results revealed the potential of Fe3O4@DhaTab as efficient adsorbents for parabens in food samples.

Immobilization of glyceraldehyde-3-phosphate dehydrogenase on Fe3O4 magnetic nanoparticles and its application in histamine removal.

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) from Lactobacillus plantarum is a novel biocatalyst in the degradation of histamine, but its properties need enhancement before practical application. Herein, we used Fe3O4 magnetic nanoparticles (MNPs) as the carrier core to prepare immobilized GAPDH. GAPDH was cloned, expressed in E. coli and purified, followed by immobilization on Fe3O4 MNPs and characterization by TEM and FT-IR. Then, characteristic comparisons between immobilized enzyme and its free form showed that the optimal pH and temperature of the former shifted to 7.5 and 40 °C, respectively, and pH tolerance and thermostability were separately broadened to 4.5-8.5 and 50-60 °C. In a wine-making experiment, including grape and black raspberry wines, using the immobilized enzyme, the results showed that over 81 %, 75 % and 59 % of histamine was removed after each treatment. These findings demonstrate that immobilizing GAPDH onto Fe3O4 MNPs is facile and efficient for histamine removal in fermented beverages.

In†Situ Growth of Covalent Organic Framework Shells on Silica Microspheres for Application in Liquid Chromatography.

A facile, in situ growth strategy for the synthesis of monodispersed COF@SiO2 microspheres is reported. The microspheres have uniform and controllable COF shells, and are used as the stationary phase for HPLC. The TpBD COF, constructed from 1,3,5-triformylphloroglucinol (Tp) and benzidine (BD), is taken as the COF shell, and aminosilica (SiO2 -NH2 ) is employed as the core to support the TpBD shell. The TpBD shell thickness is adjusted by controlling the concentrations of the Tp and BD monomers. The TpBD@SiO2 packed columns show excellent hydrophobic selectivity, and good reproducibility for the separation of neutral (toluene and ethylbenzene, polycyclic aromatic hydrocarbons), acidic (hydroquinone, p-cresol, and p-chlorophenol), and basic molecules (nucleobases, nucleosides, and deoxynucleosides).