Thermophoresis of gold nanorods from surface enhanced Raman scattering and real-time Rayleigh scattering in solution
Thermophoresis of gold nanorods from surface enhanced Raman scattering and real-time Rayleigh scattering in solution
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DOI：
10.1039/c9ay00104b
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发表时间：
2019-05-14
影响因子：
3.1
通讯作者：
Hafner, Jason H.
中科院分区：
文献类型：
--
作者：
Makihara, Takuma;Demers, Steven M. E.;Hafner, Jason H.
悬浮在溶液中的金和银纳米粒子的表面增强拉曼散射（SERS），相对于聚集的纳米粒子和粗糙的金属基底的SERS，可以进行更定量的分析。这是由于由分离的纳米颗粒产生的更可预测和一致的近场增强区域，以及在测量期间通过激发束扩散的许多纳米颗粒的平均。然而，我们发现聚焦激发对溶液的局部加热会导致热泳，从而改变焦点体积中的纳米棒浓度，从而影响定量分析。由于许多现象可能影响拉曼信号，我们记录了金纳米粒子溶液中的瑞利散射和拉曼散射。这使我们能够区分分子过程和激发光束中纳米粒子的损耗。我们观察到纳米棒的浓度可以在100秒的时间尺度内消耗到其原始值的50%以下，这与热泳效应驱动纳米颗粒离开光束点一致。我们还发现，粒子运动驱动对流在样品细胞，进一步有助于信号的不稳定性。
Surface-enhanced Raman scattering (SERS) from gold and silver nanoparticles suspended in solution enables a more quantitative level of analysis relative to SERS from aggregated nanoparticles and roughened metal substrates. This is due to the more predictable and consistent near field enhancement regions created by isolated nanoparticles, and to averaging over the many nanoparticles that diffuse through the excitation beam during the measurement. However, we find that localized heating of the solution by the focused excitation leads to thermophoresis which alters the nanorod concentration in the focal volume and therefore impacts quantitative analysis. Since many phenomena may impact the Raman signal, we record both the Rayleigh and Raman scattering from gold nanoparticle solutions. This allows us to distinguish molecular processes from depletion of nanoparticles in the excitation beam. We observe that the concentration of nanorods can deplete to less than 50% of its original value over 100 second timescale, which are consistent with a thermophoretic effect driving nanoparticles from the beam spot. We also find that the particle motion drives convection within the sample cell that further contributes to signal instabilities.