溶液酸碱性对金纳米粒子在端基功能化单分子膜表面组装影响的SERS光谱研究

Study on the Effect of Solution pH Value on Assembling of Gold Nanoparticles on 4,4'-Dithiodipyridine Self-assembled Monolayers by Surface-enhanced Raman Scattering Spectroscopy

在4,4’-二硫联吡啶在Au表面形成自组装单分子层膜的基础上,采用表面增强拉曼散射光谱(SERS)研究了在不同pH值条件下金纳米粒子在4,4’-二硫联吡啶自组装单分子膜/Au体系表面的组装。研究结果表明,由于处于单分子膜表面的吡啶环中氮原子的质子化程度随溶液环境中pH值的变化而变化,使得金纳米粒子与单分子膜表面间的结合作用程度不同,由此会引起金纳米粒子在单分子膜表面的覆盖度存在差异,并最终导致所观测到的4-巯基吡啶自组装单分子膜的SERS光谱强度存在明显的差异。而且,令人感兴趣的是,所观测到的SERS谱峰强度随金纳米粒子组装时pH值的变化呈现出明显的规律性。结合分子结构特征的分析,初步阐明了SERS谱峰强度随pH值这一组装条件的改变而发生规律性变化的内在原因。

After having obtained the 4, 4＇ - dithiodipyridine self - assembled monolayers （SAMs） on gold, we have applied surface- enhanced Raman scattering（SERS） technique to investigate the assembly of gold nanoparticles on the composite system of 4,4＇ - dithiodipyridine SAMs modified gold substrate at different pH values. The results obtained here show that protonation degree of nitrogen atoms in the pyridine rings, which make up the surface of the SAMs, changes with solution pH value. This results in the change of interaction strength between gold nanoparticles and the SAMs surface. Consequently it finally causes the variation of the coverage of gold nanoparticles on the SAMs surface. As a result, corresponding to the change mentioned as above, obvious change of intensity of characteristic SERS bands of the SAMs can be observed in our experiment. Moreover, it is interesting that intensities of these characteristic SERS bands vary regularly with change of solution pH at which gold nanoparticles were assembled on the SAMs surface. Essential and intrinsic origin to cause such regular changes in SERS intensities is elucidated by analysis with molecular structural features in the corresponding process.