采用化学还原法制备了以Au为核、包覆Ag的双金属核壳Au@Ag纳米粒子, 并成功地用于表面增强拉曼光谱(SERS)分析测试。通过改变制备液中Ag/Au的量比来调控Ag壳包覆厚度。采用透射电子显微镜(TEM)和紫外-可见光谱仪(UV-Vis)对Au@Ag纳米粒子的构貌进行表征。TEM显示明显存在核壳结构, 且Ag壳层随Ag/Au的量比的增加而逐渐变厚; UV-Vis表明随着Ag/Au的量比的增加, Au@Ag纳米粒子出现了Au核与Ag壳吸收峰的2个等离子体共振峰, 同时伴随着Au峰的蓝移和Ag峰的红移。以双甲脒为分析物, 考察了不同Ag/Au的量比时的Au@Ag纳米粒子的SERS活性。结果表明, SERS活性随Ag/Au的量比的增加先增大后减小, 在6∶5时其SERS增强效应最佳, 此时Ag壳厚度约为6 nm。以对巯基苯胺(4-ATP)、结晶紫(CV)和双甲脒为分析测试对象, 对比了Au@Ag、Ag、Au 3种基底的SERS活性。结果表明, 所制备的Au@Ag纳米粒子的SERS活性要明显优于单纯的Au、Ag纳米粒子。

Au@Ag core-shell bimetallic nanoparticles were prepared by chemical reduction method and successfully applied to surface-enhanced Raman scattering (SERS) analysis. The thickness of the coated Ag shell is regulated by changing the Ag/Au molar ratios in the preparation solution. The morphology of the Au@Ag nanoparticles were characterized by TEM and further confirmed by UV-Vis. TEM spectra show that Au@Ag nanoparticles have obvious core-shell structure, and the Ag shell layer becomes thicker with the increasing of Ag/Au molar ratio. UV-Vis spectra show that Au@Ag nanoparticles exhibit two plasmon resonance absorption peaks assigned to Au and Ag plasmonic absorption. When Ag/Au molar ratio increases, the Au core resonance is blue-shifted and the Ag shell resonance is red-shifted. The enhanced effects of Au@Ag nanoparticles with different Ag/Au molar ratios in SERS were investigated by using amitraz as a probe. It is found that the SERS intensity of amitraz is enhanced firstly and then becomes weaker with the increasing of Ag/Au molar ratios, The optimum SERS signal appeares when the Ag/Au molar ratio is 6∶5 and the thickness of Ag shell is 6 nm. Moreover, the SERS effects of Au@Ag, Ag and Au nanparticles were further compared by using p-mercaptoaniline (4-ATP), crystal violet (CV) and amitraz as analytes. The results show that the SERS effect of Au@Ag nanoparticles is obviously stronger than that of pure Au or Ag nanoparticles.