Magnetic molecular imprinted covalent organic framework composite for the magnetic solid-phase extraction of bisphenol AF.

A magnetic molecular imprinted covalent organic framework composite (MCOF-MIP) that possessed the 'dual-selectivity' of a covalent organic framework and molecular imprinted polymer (MIP) with rapid response performance was successfully prepared for the removal of bisphenol AF (BPAF) from real water and blood samples. First, the MCOF was separately synthesized using magnetic Fe3O4 as the magnetic core, 1,3,5-triaminobenzene and 2,5-dibromobenzene-1,4-diformaldehyde as precursors and a deep eutectic solvent (DES) as the solvent using a solvothermal synthesis method. The MCOF showed high crystallinity and good adsorption capacities for BPAF (107.4 mg g-1), bisphenol A (113.6 mg g-1), bisphenol S (120.0 mg g-1) and bisphenol F (82.1 mg g-1). To further improve the selectivity for BPAF, an MIP, which uses BPAF as a template, was introduced to form the MCOF-MIP. Due to the dual selectivity of MCOF and MIP, the MCOF-MIP exhibited relatively high selective adsorption capacity to BPAF (243.1 mg g-1) compared to that for the MCOF (107.4 mg g-1), while the adsorption capacities (149.7-109.4 mg g-1) for the other three compounds were not significantly improved. Furthermore, a magnetic solid-phase extraction (MSPE) method was established, and MSPE parameters such as adsorbent dosage, adsorption time, desorption solvent and desorption time were optimized. Combined with high-performance liquid chromatography with diode-array detection (HPLC-DAD) analysis, a rapid and sensitive method was developed to detect BPAF, which showed good linearity (r > 0.9969) ranging from 0.1 to 400 µg mL-1. Low limits of detection (0.04 µg mL-1, S/N = 3) and quantitation (0.1 µg mL-1, S/N = 10) and good precision with low relative SDs (<1.2 % for intra-day and <1.1 % for inter-day) were also obtained. Finally, MSPE coupled with HPLC-DAD was employed for the analysis of BPAF in water and blood samples, and the recoveries of BPAF were satisfactory (91.1-112.6 %).

Sulfuric acid induced-synthesis coupled with ethanol extraction-water precipitation purification method for orange fluorescent carbon dots with dual-emission: Application for methyl blue detection and cell imaging.

In this work, by adjusting the sulfuric acid content in reaction solvent of ethanol, orange fluorescent carbon dots (O-FCDs) with dual-emission wavelength and blue fluorescent carbon dots (B-FCDs) with single-emission wavelength were successfully prepared using 1,3-dihydroxynaphthalene as precursor. Coupling with ethanol extraction-water precipitation purification method, pure O-FCDs and B-FCDs with yields of 9.0 % and 21.3 %, quantum yields (QYs) of 43.0 % and 13.7 % were obtained, respectively. The structures and optical properties of O-FCDs and B-FCDs were investigated by TEM, AFM, Raman, FT-IR, XPS, UV-vis, fluorescence analysis etc. The results revealed that sulfuric acid promoted the carbonization and the oxidation of precursor in the reaction process. In comparison with the B-FCDs, O-FCDs showed narrower lattice spacing and band gap, demonstrating the important role of sulfur-doping in fluorescence tuning. Additionally, O-FCDs showed good sensitivity for methyl blue with a linear response range of 0.05-100 µM (LOD was 20 nM) and the satisfactory results were obtained when O-FCDs were applied to the detection of methyl blue in real fish sample. Moreover, two FCDs showed good biocompatibility and negligible cytotoxicity proved by MTT experiment, while, O-FCDs showed better cell imaging effects than that of B-FCDs. Therefore, the O-FCDs had a broad application prospect as sensing platform in detection of methyl blue and for imaging in biological field.

Sulfuric-acid-mediated synthesis strategy for multi-colour aggregation-induced emission fluorescent carbon dots: Application in anti-counterfeiting, information encryption, and rapid cytoplasmic imaging.

Aggregation-induced emission fluorescent carbon dots (AIE-CDs) have applications in the fields of multi-colour anti-counterfeiting, information encryption, and imaging. In this study, four AIE-CDs (B-AIE-CDs, G-AIE-CDs, Y-AIE-CDs, and O-AIE-CDs) with blue, green, yellow, and orange fluorescence at high concentrations were fabricated using crystal violet as a precursor, solutions with different sulfuric acid concentrations as solvents under different temperatures and reaction times for the first time. The structural properties and fluorescence behaviour of the AIE-CDs were investigated. The results revealed that the sulfuric acid concentration had a significant effect on the fluorescence colour of the AIE-CDs because sulfuric acid can affect the degree of carbonisation, the type and content of nitrogen. Moreover, the reaction temperature and time affected the surface-defect state and the degree of carbonisation of the AIE-CDs, which affected the emission wavelength and quantum yield (QY) of the AIE-CDs. Furthermore, to exploit the unique characteristics (polychromatic aggregation fluorescence and acid-sensitive properties) of the obtained-AIE-CDs, anti-counterfeiting and information encryption methodologies (i.e., acid-stimuli-response producing multi-colour fluorescence) were preliminarily developed. Finally, B-AIE-CDs with a high QY of 43.5% were successfully used for rapid cytoplasmic imaging, demonstrating their applicability in biological fields.

A novel hydroxyl-riched covalent organic framework as an advanced adsorbent for the adsorption of anionic azo dyes.

Considering the highly carcinogenic and mutagenic of anionic azo dyes to the environment and humans, the development of high efficiency adsorbent for them are of great significance. In this study, a novel hydroxyl-riched covalent organic framework (denoted as COF-OH), which can act as an advance adsorbent for anionic azo dyes, was fabricated for the first time. The as-prepared COF-OH demonstrated good dispersion in water, remarkable adsorption performances and good selectivity for anionic azo dyes including eriochrome black T, eriochrome blue black R and congo red. The adsorption capacities of them ranged from 90.71 to 229.12 mg g-1, and the extraction efficiencies of them (>75.91%) were much higher than other dyes (e.g. Methylene blue, direct red 80, 1.46%-39.57%). By optimizing the adsorption conditions (adsorbent dosage, adsorption time, pH, and salt concentration) and desorption conditions (desorption solvent, desorption time and desorption frequency), a dispersive micro solid-phase extraction (D-µ-SPE) method was developed. Further, coupled D-µ-SPE with HPLC-PDA analysis, an effective method was fabricated for the extraction and detection of three selected dyes. The method showed good linearity in the range of 0.1-200 µg mL-1 (R2 > 0.9966), low limits of quantification (0.10 µg mL-1-2.00 µg mL-1), low limits of detection (0.03-1.50 µg mL-1) and good precision. Finally, the COF-OH based D-µ-SPE was successfully applied to extract three selected dyes from water samples (recoveries ranged from 73.90 to 104.00%) and congo red from beverages (recoveries ranged from 81.40 to 111.80%). Besides, by using computer simulation, FT-IR and UV-vis analysis, the adsorption mechanisms of COF-OH to three selected dyes were explored preliminarily.

Preparation of sulphuric acid-mediated N,S-codoped red emissive carbon dots: Applications in food dyes detection, solid-state luminescence and cell imaging.

As diseases such as cardiovascular disease and cancer caused by food problems are more and more frequent, food safety has received great attention. Among them, the safety problem caused by food dyes is more prominent. Thus, it is of great value to develop sensitive detection methods for food dyes. In present study, sulphuric acid-mediated N,S-codoped red emissive carbon dots (namely as R-CDs) had been manufactured by using N-phenyl-o-phenylenediamine as precursor, sulfuric acid as additive for the first time. The structural and fluorescence properties of R-CDs had been systematically studied. The results demonstrated that R-CDs showed uniform spherical morphology and had a graphite-like structure, for which the average diameters size was 5.05 nm. Due to the various functional groups such as hydroxyl, pyridinic N, pyrrolic N and -C-SO4, R-CDs emitted bright red fluorescence. Importantly, because of the interactions between the functional groups of R-CDs with the selected food dyes, three dyes including amaranth, brilliant blue FCF and methylene blue can sensitively quench the fluorescence of R-CDs through IFE and static quenching effects. The linearity ranges of them were separately detected as 0.20 µM -20 µM, 10 nM-1 µM and 60 nM-8 µM. The limits of detection (LODs) of them were 70 nM, 4 nM and 20 nM, respectively. Further, R-CDs was successfully applied to the sensitive detection of three dyes from various food samples. To maximize the fluorescence properties of R-CDs, a R-CDs/PVA composite gel was fabricated to make R-CDs fluoresce in solid state condition. The potential of R-CDs/PVA composite gel for preliminary visualization analysis of three dyes was studied. Finally, ascribed to the low toxicity and good biocompatibility, the potential of R-CDs as probe for cell imaging was explored preliminarily.

Hydroxyl-riched covalent organic framework for solid-phase microextraction of flavonoids aglycones or their metabolites in mice's plasma: Luteolin and quercetagetin as examples.

Herein, a hydroxyl­riched covalent organic framework (named COF-DES-1) was synthesized using 1,3,5-tris(4-aminophenyl)benzene and 2,5-dihydroxyterephthalaldehyde as building blocks and employed as a coating of solid-phase microextraction (SPME) fiber. Ascribed to the advantages (e.g. suitable pore size and rich functional group characteristics) of coating, the SPME fiber showed good adsorption capacities to flavonoids aglycones including luteolin and quercetagetin, and the maximum adsorption capacities for them were 145.31 µg and 84.75 µg, respectively. Due to the size exclusion property of COF-DES-1, SPME fiber showed good protein exclusion effects on seven selected proteins with high exclusion efficiencies (>93%). Accordingly, an attractive strategy of the combination of COF-DES-1 based SPME fiber and HPLC-MS/MS was proposed for the extraction and determination of luteolin, quercetagetin or their metabolites. The results revealed that the fiber can be effectively applied to extract luteolin and its metabolites, and quercetagetin from mice's palsma. Compared with the traditional protein precipitation methods, the extraction effects of SPME fiber based extraction method were much better, indicating the promising applicability of the fiber for the enrichment of flavonoids aglycones or their metabolites in biological samples.

Highly Crystalline Covalent Organic Frameworks Act as a Dual-Functional Fluorescent-Sensing Platform for Myricetin and Water, and Adsorbents for Myricetin.

Selective detection of active ingredients in complex samples has always been a crucial challenge because there are many disturbing compounds, especially structural analogues that interfere with the detection. In this work, a fluorescent covalent organic framework (named COF-TD), which can be used for the selective fluorescence detection and enrichment of myricetin from complex samples, was reported for the first time. The highly crystalline COF-TD with bright blue fluorescence was formed through a solution polymerization method by the condensation reaction between 4,4',4″-(1,3,5-triazine-2,4,6-triyl)trianiline and 2,5-dihydroxy-1,4-benzenedicarboxaldehyde. Due to spatial size selectivity, multisites hydrogen bonding, and π-π interaction, myricetin can quench the fluorescence of COF-TD with an inner filter effect (IFE) and static quenching mechanisms as well as can be enriched on COF-TD. Myricetin can observably eliminate the interference of other compounds and selectively quench the fluorescence of COF-TD with a limit of detection (LOD) of 0.30 µg·mL-1. The high adsorption ability of COF-TD (Q = 124.6 mg·g-1) to myricetin was also obtained. Finally, a sensing platform based on COF-TD for myricetin was successfully developed and applied for the detection of myricetin from vine teas. In addition, COF-TD also showed good water sensing ability and could be used effectively to detect water content in organic solvent (1-18% water in acetone, 0.5-5% water in acetonitrile, 1-4.5% water in ethyl acetate, v/v). To the best of our knowledge, this is the first report where COF-TD was used to detect water in a relatively wide concentration range. In all, this work provided dual-functional fluorescent COFs with the properties of an adsorbent, opening up new methodologies for the simple, selective, and enrichment detection method for myricetin.

N,Cl-Codoped Carbon Dots from Impatiens balsamina L. Stems and a Deep Eutectic Solvent and Their Applications for Gram-Positive Bacteria Identification, Antibacterial Activity, Cell Imaging, and ClO- Sensing.

In this study, we first synthesized metal-free N,Cl-doped carbon dots (N,Cl-CDs) using Impatiens balsamina L. stems as green precursors in a deep eutectic solvent (DES). The obtained N,Cl-CDs were characterized through transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) spectroscopy, fluorescence (FL) spectroscopy, and ultraviolet (UV) spectroscopy. In addition to the common features of carbon dots (CDs), such as high light stability, small size, low toxicity, good aqueous solubility, and favorable biocompatibility, these N,Cl-CDs exhibited excellent recognition and selectivity for Gram-positive bacteria by doping with N and Cl elements using DES. The N,Cl-CDs with positive charge cannot only differentiate Gram-positive bacteria by selective fluorescence imaging but also have antibacterial effects on Gram-positive bacteria. Through potential, ROS, and morphological analyses of bacteria before and after treatment with N,Cl-CDs, the antibacterial mechanisms of bacteriostasis, Enterococcus faecium, Staphylococcus aureus, Bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa, and Salmonella were explored. In addition, N,Cl-CDs demonstrated low cytotoxicity and good cell imaging ability in cancer and normal cells. Moreover, they can be used as a fluorescence sensor for the detection of ClO- with a detection range from 100 nM to 40 µM and a limit of detection (LOD) of 30 nM. In summary, the prepared N,Cl-CDs could be applied as environmentally friendly Gram-positive bacterial identification and antibacterial agents. Additionally, their cell imaging and ClO- detection abilities were outstanding.