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ZrO2−carbon nanotube (CNT) composites have been successfully synthesized via decompositoin of Zr(NO3)4·5H2O in supercritical carbon dioxide−ethanol solution with dispersed CNTs at relatively low temperatures. The samples were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction spectroscopy (XRD), transmission electron microscopy (TEM), and energy-dispersive X-ray (EDX) analyses. It was demonstrated that CNTs were fully coated with an amorphous ZrO2layer, and the coating layer was nominally complete and uniform. In addition, the thickness of the coating sheath could be readily controlled by tuning the Zr(NO3)4·5H2O/CNTs ratio used. Furthermore, the chemiluminescent sensor prepared from ZrO2−carbon nanotube composites exhibited dramatic sensitivity as well as high stability and selectivity to ethanol. [ABSTRACT FROM AUTHOR]

Molecular analysis at cellular and subcellular levels, whether on selected molecules or at the metabolomics scale, is still a challenge now. Here we propose a method based on probe ESI mass spectrometry (PESI-MS) for single cell analysis. Detection of metabolites at cellular and subcellular levels was successfully achieved. In our work, tungsten probes with a tip diameter of about 1 μm were directly inserted into live cells to enrich metabolites. Then the enriched metabolites were directly desorbed/ionized from the tip of the probe for mass spectrometry (MS) detection. The direct desorption/ionization of the enriched metabolites from the tip of the probe greatly improved the sensitivity by a factor of about 30 fold compared to those methods that eluted the enriched analytes into a liquid phase for subsequent MS detection. We applied the PESI-MS to the detection of metabolites in single Allium cepa cells. Different kinds of metabolites, including 6 fructans, 4 lipids, and 8 flavone derivatives in single cells, have been successfully detected. Significant metabolite diversity was observed among different cells types of A. cepa bulb and different subcellular compartments of the same cell. We found that the inner epidermal cells had about 20 fold more fructans than the outer epidermal cells, while the outer epidermal cells had more lipids. We expected that PESI-MS might be a candidate in the future studies of single cell "omics". [ABSTRACT FROM AUTHOR]

A simple and fast (<5 s) method for in situarsenic speciation on solid surfaces has been developed based on desorption electrospray ionization-tandem mass spectrometry (DESI-MS). Arsenic-polluted environmental samples such as animal feed and plant tissues could be directly monitored by DESI-MS. Each arsenic species in this study, including monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), arsenobetaine (AsB), arsenocholine (AsC), 4-arsanilic acid (p-ASA), 4-hydroxyphenylarsonic acid (4-OH), Nitarsone, Roxarsone and two inorganic arsenic species, arsenate As(v) and arsenite As(iii), could be detected by their typical m/zand collision induced dissociation (CID) behavior respectively. By the characteristic information, mixtures of different arsenic species could be detected without any sample preparation and separation process. This method could give absolute detection limits of the arsenic species at ng/mm2to pg/mm2level with a best RSD of 5.3% (n= 5). The method could be potentially applied to in situenvironmental monitoring of arsenic pollution, especially that caused by arsenic pesticides, animal feed additives, herbicides and wood treatment. [ABSTRACT FROM AUTHOR]

The effects of SeIV on the structure and function of recombinant human arsenic (+3 oxidation state) methyltransferase (AS3MT) purified from the cytoplasm of Escherichia coli were studied. The coding region of human AS3MT complementary DNA was amplified from total RNA extracted from HepG2 cell by reverse transcription PCR. Soluble and active human AS3MT was expressed in the E. coli with a Trx fusion tag under a lower induction temperature of 25 °C. Spectra (UV–vis, circular dichroism, and fluorescence) were first used to probe the interaction of SeIV and recombinant human AS3MT and the structure–function relationship of the enzyme. The recombinant human AS3MT had a secondary structure of 29.0% α-helix, 23.9% β-pleated sheet, 17.9% β-turn, and 29.2% random coil. When SeIV was added, the content of the α-helix did not change, but that of the β-pleated sheet increased remarkably in the conformation of recombinant human AS3MT. SeIV inhibited the enzymatic methylation of inorganic AsIII in a concentration-dependent manner. The IC50 value for SeIV was 2.38 μM. Double-reciprocal (1/ V vs. 1/[inorganic AsIII]) plots showed SeIV to be a noncompetitive inhibitor of the methylation of inorganic AsIII by recombinant human AS3MT with a Ki value of 2.61 μM. We hypothesized that SeIV interacts with the sulfhydryl group of cysteine(s) in the structural residues rather than the cysteines of the active site (Cys156 and Cys206). When SeIV was combined with cysteine(s) in the structural residues, the conformation of recombinant human AS3MT changed and the enzymatic activity decreased. Considering the quenching of tryptophan fluorescence, Cys72 and/or Cys226 are deduced to be primary targets for SeIV. [ABSTRACT FROM AUTHOR]