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Zhang Y.,Southwest University | Zhang Y.,Laboratory of Quality and Safety Risk Assessment for Citrus Products | Zhang Y.,Quality Supervision and Testing Center for Citrus and Seedling | Zhao Q.,Southwest University | And 10 more authors.
Food Analytical Methods | Year: 2015

A rapid, efficient, and environmentally friendly method using vortex-assisted ionic liquid dispersive liquid-liquid microextraction (VA-IL-DLLME) prior to high-performance liquid chromatography coupled with photodiode array detection (HPLC-PDA) has been developed for the determination of six triazole fungicides (triazolone, triadimenol, epoxiconazole, flusilazole, tebuconazole, and diniconazole) in various fruit juices. 1-Hexyl-3-methylimidazolium hexafluorophosphate ([C6MIM][PF6]) and acetonitrile were used as extraction and dispersive solvents, respectively. A single factor experiment was selected to obtain the significant variables from the several related parameters that could affect the extraction efficiencies, such as the volume of IL and acetonitrile, extraction time, centrifugation time, and salt addition. Under the optimum conditions, an excellent linearity with correlation coefficients higher than 0.997 was obtained. Enrichment factors and average recoveries in three concentration levels ranged from 51 to 72, and 71.0 to 104.5 %, respectively, and the relative standard deviations (RSDs) from 1.4 to 11.8 %. The limits of detection (LODs) (S/N = 3) for the six triazole fungicides were between 0.4 and 6.7 μg L−1. The proposed method was successfully applied for the determination of trace amounts of triazole fungicides in various fruit juices including peach, apple, and orange juices. © 2015 Springer Science+Business Media New York Source


He Y.,Southwest University | He Y.,National Citrus Engineering Research Center | Jiao B.-N.,Southwest University | Jiao B.-N.,National Citrus Engineering Research Center
RSC Advances | Year: 2015

In this work, a novel fluorescent method for protein detection has been developed based on terminal protection of small molecule-linked DNA by target protein and the difference in affinity of graphene oxide (GO) for single-stranded DNA (ssDNA) containing different numbers of bases in length. A probe ssDNA, which is labeled carboxyfluorescein (FAM) at the 5′ end and a small molecule at the 3′ end, is designed for the detection of target protein. In the absence of target protein, the probe ssDNA can be hydrolyzed into mononucleotides by Exo I. The introduction of GO into the sensing solution results in weak quenching of the fluorescence of FAM due to the weak affinity of the short FAM-labeled oligonucleotide fragment to GO. Conversely, and very importantly, in the presence of target protein, the specifically binding of target protein to the small molecule of probe ssDNA can protect probe ssDNA from the Exo I-catalyzed digestion. Then the adsorption of the probe ssDNA on GO makes FAM close proximity to GO surface resulting in high efficiency quenching of fluorescence of FAM, and the fluorescence intensity gradually decreases with increasing concentration of target protein. Taking folate receptor (FR) as an example in this work, we can determine the protein in a linear range from 1 to 80 ng mL-1 with a detection limit of 0.81 ng mL-1. Besides satisfactory sensitivity, the developed strategy also shows high selectivity, excellent reproducibility, and low cost, implying that this technique may have great potential applications in the future. © The Royal Society of Chemistry. Source


He Y.,Southwest University | He Y.,National Citrus Engineering Research Center | Jiao B.,Southwest University | Jiao B.,National Citrus Engineering Research Center
RSC Advances | Year: 2014

An ultrasensitive and straightforward fluorescent sensing platform for S1 nuclease activity has been developed based on S1 nuclease-induced DNA strand scission and the difference in affinity of cytochrome c (Cyt c) for single-stranded DNA (ssDNA) containing different numbers of bases. This sensing platform consists of a negatively charged fluorophore carboxyfluorescein (FAM) labeled 20-mer ssDNA (20F) and a positively charged protein Cyt c. In the absence of S1 nuclease, the electrostatic and hydrophobic interaction between 20F and Cyt c makes the FAM be in close proximity to Cyt c, resulting in efficient quenching of the fluorescence of FAM. Conversely, and very importantly, in the presence of S1 nuclease, it cleaves 20F into small fragments. The introduction of Cyt c into the sensing solution results in weak quenching of the fluorescence of FAM due to the relatively weak electrostatic interaction between the fragmented ssDNA chains and Cyt c, making the FAM move away from Cyt c, and thus the fluorescence intensity gradually increases with increasing concentration of S1 nuclease. S1 nuclease can be detected in a range of 4.0 × 10-3 to 4.0 × 10-2 units per mL with a detection limit of 8.3 × 10-4 units per mL and good selectivity. Moreover, the sensing system is used for the detection of an inhibitor of S1 nuclease with satisfying results. © 2014 the Partner Organisations. Source


He Y.,Southwest University | He Y.,National Citrus Engineering Research Center | Jiao B.,Southwest University | Jiao B.,National Citrus Engineering Research Center | Tang H.,Wuhan University
RSC Advances | Year: 2014

As a new, water-soluble material, graphene oxide (GO) has gained growing interest for sensing applications. Particularly interesting is the interaction of nucleic acids with GO. Recently, it was found that short single-stranded DNA (ssDNA) had weaker affinity to GO than long ssDNA. This property makes it possible to prepare a novel bioassay platform for metal ions, antibiotics, and nuclease detection via the DNA(RNA) cleavage reaction. While practical analytical applications have been successfully demonstrated, few studies are focused on the mechanism of this phenomenon. In this work, we use fluorescence spectroscopy to deeply investigate the binding mechanism of ssDNA with GO to reveal the reason for this affinity difference caused by DNA length. Through computing with literature models, the main binding force, the binding constant, and number of binding sites between ssDNA and GO are obtained. Besides, our results show that the binding constant of short ssDNA with GO is much lower than that of long ssDNA with GO, which is the strongest evidence to prove the affinity difference between short ssDNA and long ssDNA with GO. Finally, based on these basic understandings of the interaction between ssDNA and GO, we develop a GO based biosensor for S1 nuclease and an inhibitor of S1 nuclease with satisfying results. © 2014 The Partner Organisations. Source


He Y.,Southwest University | He Y.,National Citrus Engineering Research Center | Jiao B.,Southwest University | Jiao B.,National Citrus Engineering Research Center
RSC Advances | Year: 2015

As the extracellular nuclease of Staphylococcus aureus (S. aureus), micrococcal nuclease (MNase), which preferentially digests single-stranded nucleic acids, can be used as the standard to identify S. aureus and can be used to evaluate the pathogenicity of S. aureus. So the assay of MNase is of high importance. However, traditional methods for the assay of MNase activity have intrinsic limitations such as sophisticated synthesis processes, the need for functionalizing thiol (or dye)-modified oligonucleotide probes or critical operation conditions. Herein, a simple and convenient fluorescence sensing platform for MNase activity has been developed based on N-methyl mesoporphyrin IX (NMM)/G-quadruplexes. In the absence of MNase, the G-rich single stranded DNA (ssDNA) folds into a quadruplex in the presence of monovalent ions, thus greatly enhancing the fluorescence of NMM (a specific G-quadruplex binder). In the presence of MNase, the G-rich ssDNA was digested into small fragments. As a result, the fluorescence of the solution decreases with increase of MNase activity. Under the optimized conditions, the fluorescence intensity exhibits a linear correlation to MNase concentration in a wide range of 1.2 × 10-4-2.4 × 10-3 units per mL with a detection limit of 7.1 × 10-5 units per mL and good selectivity. The detection limit is much better or at least comparable to previous reports. Given its simplicity, easy operation, sensitivity and cost-effectiveness, this method can be extended to other nuclease assays. © The Royal Society of Chemistry 2015. Source

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