It was found that chloroauric acid (HAuCl(4)) could be directly reduced by the luminescent reagent luminol in aqueous solution to form gold nanoparticles (AuNPs), the size of which depended on the amount of luminol. The morphology and surface state of as-prepared AuNPs were characterized by transmission electron microscopy, UV/visible spectroscopy, X-ray photoelectron spectroscopy, FTIR spectroscopy, and thermogravimetric analysis. All results indicated that residual luminol and its oxidation product 3-aminophthalate coexisted on the surface of AuNPs through the weak covalent interaction between gold and nitrogen atoms in their amino groups. Subsequently, a luminol-capped AuNP-modified electrode was fabricated by the immobilization of AuNPs on a gold electrode by virtue of cysteine molecules and then immersion in a luminol solution. The modified electrode was characterized by cyclic voltammetry, electrochemical impedance spectroscopy, and scanning electron microscopy. The as-prepared modified electrode exhibited an electrochemiluminescence (ECL) response in alkaline aqueous solution under a double-step potential. H2O2 was found to enhance the ECL. On this basis, an ECL sensor for the detection of H2O2 was developed. The method is simple, fast, and reagent free. It is applicable to the determination of H2O2 in the range of 3x10(-7)-1x10(-3) mol L(-1) with a detection limit of 1x10(-7) mol L(-1) (S/N=3).

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Tobacco leaf obtained from different geographical areas in China was profiled using gas chromatography-mass spectrometry (GC-MS) coupled with multivariate data analyses. Hierarchical cluster analysis (HCA) and principal component analysis (PCA) showed that the tobacco metabolome was clearly dependent on geographical origins; climatic conditions, such as temperature and precipitation, imposed a greater impact on metabolite levels than the cultivars. By orthogonal partial least-squares-discrimination analysis (OPLS-DA), 20 metabolites that contributed to the discrimination were screened, including primary metabolites (sucrose, D-fructose, D-mannose, D-glucose, inositol, maleic acid, citric acid, malic acid, L-threonic acid, L-proline, L-phenylalanine), secondary metabolites (chlorogenic acid, α- and β-4,8,13-duvatriene-1,3-diol, nicotine, quinic acid), and four unknown metabolites. The results suggest that metabolic profiling using GC-MS combined with multivariate analysis can be used to discriminate tobacco leaf of different geographical origins and to provide potential indicators of tobacco origins.

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It was found that luminol could react with AgNO 3 in the presence of gold colloid to generate chemiluminescence (CL) at 425 nm. UV-visible spectra and X-ray photoelectron spectra showed that AgNO 3 was reduced by luminol to Ag in the CL reaction, which covered on the surface of gold nanoparticles to form Au/Ag core/ shell nanoparticles. The luminophor was identified by the CL spectrum as 3-aminophthalate. The effects of Au/Ag core/shell nanoparticles with various compositions on the luminol-AgNO 3 system and the CL kinetics were also studied. On this basis, a CL reaction mechanism involving catalysis is proposed. When Au colloid was injected into the mixture of luminol and AgNO 3 , AgNO 3 reacted rapidly with luminol under the catalysis of gold nanoparticles to produce Ag and luminol radicals, which reacted with the dissolved oxygen, accompanying a light emission; then, with instant deposition of Ag atoms on the surface of Au particles, the catalytic activity declined, leading to a sharp decrease in CL intensity and a slow growth of core/shell nanoparticles. The new CL system has the advantages of low background and good stability, and gold nanoparticles have excellent biocompatible property. It may find future applications in immunoassay and DNA detection.