[Detection of Ethoprophos Using SERS Coupled with Magnetic Fe3O4/Ag Composite Materials].

The magnetic Fe3O4/Ag composite materials were synthesized by reducing AgNO3 with sodium citrate in the presence of Fe3O4 which were prepared by co-precipitation firstly. The enrichment and extraction of ethoprophos assembled on Fe3O4/Ag were achieved with the applied magnetic field. The different concentrations of ethoprophos adsorbed on Fe3O4/Ag were analyzed by SERS and it was showed that the trace analysis of ethoprophos had been established, while the enhancement factor of probe molecules on Fe3O4/Ag was 1. 48 X 10(5). The structure and morphology of Fe3O4/Ag were characterized by UV-Vis, EDX and TEM. Compared with Ag, the UV-Vis absorption peak of Fe3O4/Ag shifted from 417 to 369 nm, and the UV-Vis of Fe3O4 almost had no characteristic absorption peak in this region. At the same time, it was showed that the surface properties of Fe3O4/Ag changed with Raman enhancement effect during the aggregation process of Ag around the surface of Fe3O4. Further EDX images of micro area element analysis suggested that the chemical composition of products were Ag, Fe and O while the Cu peak was from the copper mesh. In addition, TEM images indicated that the average particle size of Fe3O4 was between 30 and 60 nm with shape tended to be spherical. And the silver nanoparticles were attached to the Fe3O4 particles and agglomeration occured. Density functional theory calculations which can be applied to qualitative judgment of molecule was carried out to obtain the molecular optimization structure and theoretical Raman spectra. It was found that the stabilized SERS signals were detected under the saturated adsorption equilibrium after 15 min. Finally, Raman response of ethoprophos was achieved with lower than 2 X 10(-8) mol . L-1 , indicatint that the established method had reached the requirements of ethoprophos residues detection and could be used for analysis of sulfur-containing organophosphorus pesticide.

[Chemical characteristics of Nickel(II) 2,3-dimercaptosuccinate complexes modified on gold electrodes].

2,3-Dimercaptosuccinic acid (DMSA) and its complex Nickel(II) 2,3-Dimercaptosuccinate (DMSA-Ni(II)) were assembled on the electrochemically activated Au electrode and the modified films were investigated by ex-situ SERS, SEM and electro-reduction. The coordination ratio (1:2) and stability constant (4.716 X 10(7)) of DMSA and Nickel(II) were firstly confirmed by UV. Then, the SERS spectra showed that DMSA was absorbed on the surface of activated Au and the coordinate bond of DMSA-Ni(II) was existed as S-Ni-O. Meanwhile, two reduction peaks of DMSA-Ni(II) on Au electrode were presented at negative potential. The first peak (from positive to negative values) was related to the RS-Au group which was produced by the mutual absorption of DMSA and Au. The second reduction peak was related to Nickel(II). Finally, it was further confirmed by calculating the surface coverage and comparison of molecular area. And it was found that the molecular arrangement of DM-SA-Ni(II) on Au electrode generated as monolayer which was dispersed or connected partly instead of concentrated or overlapped.

[Chemical adsorption of thiosalicylic acid on silver surface investigated by surface-enhanced Raman scattering].

Surface-enhanced Raman scattering (SERS) of thiosalicylic acid (TSA) with sulfydryl group was investigated on the surface of electrochemically roughed silver electrode. The result shows that SERS enhancement effect was relative to the concentration and pH, and 1 x 10(-3) mol x L(-1) and pH 4 were the optimal condition. While the concentration increased, the enhancement effect decreased quickly because of steric hindrance. S--Ag peak position by the absorption of TSA was basically consistent, but pH significantly affected its intensity. The distribution and mechanism of TSA at different pH were further investigated. It was showed that TSA was adsorbed on the active silver surface via the sulfydryl group without H of neutral C4H4 (COOH)SH molecule. Competitive adsorption of negative valence C4H4 (COO-) SH and OH- may bring non-SERS under the strong base condition. At the same time, the sulfydryl group significantly influenced the carboxyl vibration peak's change and the distribution of electron cloud of benzene ring conjugate system.