Single-molecule and single-nanoparticle SERS: Examining the roles of surface active sites and chemical enhancement
Single-molecule and single-nanoparticle SERS: Examining the roles of surface active sites and chemical enhancement
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DOI：
10.1021/jp011730b
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发表时间：
2002-01-17
影响因子：
3.3
通讯作者：
Nie, SM
中科院分区：
文献类型：
--
作者：
Doering, WE;Nie, SM
最近几个小组的研究已经确定了一类新的金属胶体纳米粒子，它能够将表面增强拉曼散射（SERS）的效率提高10(14)-10（15）倍。这种巨大的增强使单分子检测和光谱在室温下成为可能。以往的单分子和单粒子研究已经对电磁场增强的机制产生了重要的见解，但对表面活性位点和化学增强的贡献知之甚少。在这里，我们报告了使用集成流动注射和超灵敏光学成像/光谱系统对化学增强的直接检查。其关键特征是将胶体银纳米颗粒固定在微流装置内的玻璃表面上，当固定的颗粒在流池中经过化学试剂处理时，可以实时观察到单颗粒SERS信号。空间隔离粒子的原位表面等离子体散射研究表明，化学处理后它们的电磁特性没有改变。因此，观察到的SERS光谱变化应该主要来自表面活性位点的化学增强。我们的实验数据表明，三种卤化物离子（Cl-， Br-和I-）具有显著的激活作用，而其他离子（如柠檬酸盐，硫酸盐和氟化物）对单颗粒SERS的影响很小或没有影响。硫代硫酸盐离子的“猝灭”效应完全破坏了SERS活性。估计罗丹明6G分子吸附在单个Ag纳米颗粒上的化学增强因子约为10(2)-10(3)。
Recent research in several groups has identified a new class of metal colloidal nanoparticles that is able to enhance the efficiencies of surface-enhanced Raman scattering (SERS) by as much as 10(14)-10(15) fold. This enormous enhancement allows single-molecule detection and spectroscopy at room temperature. Previous single-molecule and single-particle studies have yielded important insights into the mechanism of electromagnetic field enhancement, but little is known about the contributions of surface active sites and chemical enhancement. Here we report a direct examination of chemical enhancement by using an integrated flow injection and ultrasensitive optical imaging/spectroscopy system. A key feature is that colloidal silver nanoparticles are immobilized on a glass surface inside a microflow device and that single-particle SERS signals are observed in real time while the immobilized particles are treated by chemical reagents in the flow cell. In situ surface plasmon scattering studies of spatially isolated particles indicate that their electromagnetic properties do not change after chemical treatment. Thus, the observed SERS spectral changes should primarily come from chemical enhancement at surface active sites. Our experimental data reveal that three halide ions (Cl-, Br-, and I-) have a substantial activating effect, whereas other ions such as citrate, sulfate, and fluoride have little or no effect on single-particle SERS. A "quenching" effect is observed for thiosulfate ions, which completely destroys the SERS activity. The chemical enhancement factors are estimated to be about 10(2)-10(3) for rhodamine 6G molecules adsorbed on single Ag nanoparticles.