We presented a new aptasensor for mycotoxins, which was based on multiplexed fluorescence resonance energy transfer (FRET) between multicolor upconversion fluorescent nanoparticles (UCNPs) as donors and graphene oxide (GO) as the entire and effective acceptor. BaY(0.78)F(5):Yb(0.2), Er(0.02) and BaY(0.78)F(5):Yb(0.7), Tm(0.02) upconversion nanoparticles were synthesized and functionalized, respectively, with immobilized ochratoxin A (OTA)-aptamers and fumonisin B(1) (FB(1))-aptamers. On the basis of the strong π-π stacking effect between the nucleobases of the aptamers and the sp(2) atoms of GO, the aptamer modified-UCNPs can be brought in close proximity to the GO surface. The strong upconversion fluorescence both of BaY(0.78)F(5):Yb(0.2), Er(0.02) and BaY(0.78)F(5):Yb(0.2), Tm(0.02) can be completely quenched by the GO, because of a good overlap between the fluorescence emission of multicolor UCNPs and the absorption spectrum of GO. In contrast, in the presence of OTA and FB(1), the aptamers preferred to bind to their corresponding mycotoxins, which led to changes in the formation of aptamers, and therefore, aptamer modified-UCNPs were far away from the GO surface. Our study results showed that the fluorescence intensity of BaYF(5):Yb Er and BaYF(5):Yb Tm were related to the concentration of OTA and FB(1). We therefore developed a sensitive and simple platform for the simultaneous detection of OTA and FB(1) with multicolor UCNPs and GO as the FRET pair. The aptasensor provided a linear range from 0.05 to 100 ng·mL(-1) for OTA and 0.1 to 500 ng·mL(-1) for FB(1); the detection limit of OTA was 0.02 ng·mL(-1) and FB(1) was 0.1 ng·mL(-1). As a practical application, the aptasensor was used to monitor OTA and FB(1) level in naturally contaminated maize samples with the results consistent with that of a classic ELISA method. More importantly, the novel multiplexed FRET was established for the first time based on multiplexed energy donors to the entire energy acceptor; this work was expected to open up a new field of FRET system applications for various targets.

Graphene oxide (GO) nanosheets have been immobilized onto SiO(2) particles through electrostatic interactions by surface assembly. The surface-assembled composite material was characterized by means of SEM and FTIR and UV/Vis spectroscopy to reveal an assembling ratio of 2.3% (w/w, GO/SiO(2)). The GO/SiO(2) composites were subsequently used, for the first time, as adsorbents for the adsorption/isolation of proteins. Selective isolation of proteins of interest, namely, hemoglobin (Hb) in this case, from complex sample matrices, for example, human whole blood, could be obtained by carefully manipulating the adsorption/desorption process. At pH 7, an adsorption of 85% was achieved for Hb (70 mg L(-1)) in sample solution (1.0 mL) by the GO/SiO(2) composites (3.0 mg). The adsorption behavior was consistent with the Langmuir adsorption model, corresponding to a theoretical adsorption capacity of 50.5 mg g(-1) for Hb. The retained Hb could be readily recovered by using a Tris-HCl buffer at pH 8.9 to give a recovery of 80%. Circular dichroism and specific activity investigations indicated that the GO/SiO(2) composites exhibited favorable biocompatibility, characterized by virtually no effect on the conformation and activity of Hb after adsorption/desorption. The composites were used for the selective isolation of Hb from human whole blood and achieved satisfactory results by assaying with sodium dodecyl sulfate polyacrylamide gel electrophoresis.

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Catalytic Janus nanosheets were synthesized by using an anion-exchange reaction between heteropolyacids (HPAs) and the modified ionic-liquid (IL) moieties of Janus nanosheets. Their morphology and surface properties were characterized by using SEM, energy-dispersive spectroscopy (EDS), FTIR spectroscopy, and X-ray photoelectron spectroscopy (XPS) studies. Because of their inherent Janus structure, the nanosheets exhibited good amphipathic character with ILs and oil to form a stable ILs-in-oil emulsion. Therefore, these Janus nanosheets can be used as both emulsifiers and catalysts to perform emulsive desulfurization. During this process, sulfur-containing compounds at the interface could be easily oxidized and efficiently removed from a model oil. Application of this Janus emulsion brings an efficient, useful, and green procedure to the desulfurization process. Compared with the desulfurization catalyzed by using HPAs in a conventional two-phase system, the sulfur removal of dibenzothiophene (DBT) achieved in a Janus emulsion system was improved from 68 to 97 % within 1.5 h. Moreover, this emulsion system could be demulsified easily by simple centrifugation to recover both the nanosheets and the ILs. Owing to the good structural stability of the Janus nanosheets, the sulfur removal efficiency of DBT could still reach 99.9 % after the catalytic nanosheets had been recycled at least six times.

The rational design of active photoanodes for photoelectrochemical (PEC) water splitting is crucial for future applications in sustainable energy conversion. A combination of catalysts with photoelectrodes is generally required to improve surface kinetics and suppress surface recombination. In this study, we present WO photoanode modified with the iridium complex [(H dphbpy)Ir (Cp*)Cl]Cl (Ir-PO H ; H dphbpy=2,2'-bipyridine-4,4'-bisphosphonic acid, Cp*=pentamethylcyclopentadiene (WO +Ir-PO H )- for PEC water oxidation. When Ir-PO H is anchored to a WO electrode, the photoanode shows a significant improvement in both photocurrent and faradaic efficiency compared to the bare WO photoanode. Under simulated sunlight illumination (AM 1.5G, 100 mW cm ) with an applied bias of 1.23 V (vs. reversible hydrogen electrode), the photoanode exhibits a photocurrent of 1.16 mA cm in acidic conditions, which is double that of the bare WO photoanode. The faradaic efficiency is promoted from 56 % to 95 %. Kinetic studies reveal that Ir-PO H exhibits a different interfacial charge-transfer mechanism on the WO photoanode for PEC water oxidation compared to iridium oxide. Ir-PO H , as a water-oxidation catalyst, can accelerate the surface charge transfer through rapid surface kinetics.