Silver nanoparticles (Ag NPs) modified with sodium 2-mercaptoethanesulfonate (mesna) exhibit strong surface-enhanced Raman scattering (SERS). Their specific and strong interaction with heavy metal ions led to a labelfree assay for Hg(II). The covalent bond formed between mercury and sulfur is stronger than the one between silver and sulfur and thus prevents the adsorption of mesna on the surface of Ag NPs. This results in a decrease of the intensity of SERS in the presence of Hg(II) ions. The Raman peak at 795 cm −1 can be used for quantification. The effect of the concentration of mesna, the concentration of sodium chloride, incubation time and pH value on SERS were optimized. Under the optimal conditions, the intensity of SERS decreases with increasing concentration of Hg(II). The decrease is linear in the 0.01 and 2 μmol L −1 concentration range, with a correlation coefficient (R 2 ) of 0.996 and detection limit (S/N03) is 0.0024 μmol L −1 . The method was successfully applied to the determination of the Hg(II) in spiked water samples.

Au/Ag core/shell bipyramids were used as surface-enhanced Raman scattering (SERS) substrates to determine the thiram. The metallic substrates showed high SERS performance and are very suitable for the analytical sensors. The fabrication and characterization of the Au/Ag core/shell bipyramids were described. The influence of experimental parameters, such as the thickness of Ag shell of the bipyramids, sodium chloride concentration, and pH value on SERS of thiram was examined and optimized. Under the optimum conditions, thiram molecules were effectively adsorbed onto bipyramids and the SERS intensity is proportional to the concentration of thiram in the range of 3.3 to 400.0 ng mL -1 . The corresponding correlation coefficient of the linear equation is 0.997, which indicates that there is a good linear relationship between SERS intensity and thiram concentration. The limit of detection for thiram is 2.0 ng mL -1 . The experimental results indicate that the proposed method is a viable method for determination of thiram. Some environmental water samples were analyzed and the analytical results were satisfactory.

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In this paper, we consider the asymptotic regularity of Daubechies scaling functions and construct examples of M-band scaling functions which are both orthonormal and cardinal for M ¢ 3. ᭧ 1999 Academic Press