A new three-dimensional graphene oxide-wrapped melamine foam was prepared and used as a solid-phase extraction substrate. β-Cyclodextrin was fabricated onto the surface of three-dimensional graphene oxide-wrapped melamine foam by a chemical covalent interaction. In view of a specific surface area and a large delocalized π electron system of graphene oxide, in combination with a hydrophobic interior cavity and a hydrophilic peripheral face of β-cyclodextrin, the prepared extraction material was proposed for the determination of flavonoids. In order to demonstrate the extraction properties of the as-prepared material, the adsorption energies were theoretically calculated based on periodic density functional theory. Static-state and dynamic-state binding experiments were also investigated, which revealed the monolayer coverage of flavonoids onto the β-cyclodextrin/graphene oxide-wrapped melamine foams through the chemical adsorption. H NMR spectroscopy indicated the formation of flavonoids-β-cyclodextrin inclusion complexes. Under the optimum conditions, the proposed method exhibited acceptable linear ranges (2-200 μg/L for rutin and quercetin-3-O-rhamnoside; 5-200 μg/L for quercetin) with correlation coefficients ranging from 0.9979 to 0.9994. The batch-to-batch reproducibility (n = 5) was 3.5-6.8%. Finally, the as-established method was satisfactorily applied for the determination of flavonoids in Lycium barbarum (Goji) samples with relative recoveries in the range of 77.9-102.6%.

No abstract

A method is described for extracting and detecting the fluorescent reaction product (2',7'-dichlorofluorescein, DCF) that is formed by reaction of reactive oxygen species (ROS) with dichlorodihydrofluorescein diacetate (DCFH-DA). DCF is extracted by using porous polyaniline nanotubes (PPN) which have a large specific surface and pore volume which favor the adsorption capacity. Additional attractive features include an appropriate pore size distribution, hydrophobic surface, and electron-attracting groups which contribute to DCF adsorption. A variety of methods was applied to characterize the morphology of PPN. Under optimal conditions and by performing DCF in 0.08-1.0 μM concentrations, the correlation coefficient of the calibration plot is 0.999. The limits of detection for standard DCF solutions is 20 nM. Compared with commercial sorbents for solid-phase extraction (SPE) such as commercially available carbon or Welchrom® C18, the use of the new sorbent results in better retraction recovery (92%) and longer reuse times (30 times). Doxorubicin and X-ray radiation were used to externally stimulate the ROS production in HepG2 and Hela cells. ROS was stabled by DCFH-DA and quantified by DCF. Following SPE, DCF was detected by HPLC and the concentration ROS was calculated. Graphical abstract ᅟ.