Department of Civil and Environmental Engineering , Virginia Tech , Blacksburg , Virginia 24061 , United States.
Virginia Tech Institute of Critical Technology and Applied Science (ICTAS) Sustainable Nanotechnology Center (VTSuN) , Blacksburg , Virginia 24061 , United States.
Anal Chem. 2018 Mar 6;90(5):3227-3237. doi: 10.1021/acs.analchem.7b04667. Epub 2018 Feb 13.
The application of surface-enhanced Raman spectroscopy (SERS) for everyday quantitative analysis is hindered by the point-to-point variability of SERS substrates that arises due to the heterogeneous distribution of localized electromagnetic fields across a suite of plasmonic nanostructures. Herein, we adopt surface-enhanced elastic scattering as a SERS internal standard. Both elastic and inelastic (i.e., Raman) scattering are simultaneously enhanced by a given "hot spot", and thus, the surface-enhanced elastic scattering signal provides a localized intrinsic internal standard that scales across all of the plasmon-enhanced electromagnetic fields within a substrate. Elastically scattered light originates from the amplified spontaneous emission (ASE) of the commercial laser, leading to the formation of a low-wavenumber pseudo band that arises from the interaction of the ASE and the edge filter. A theoretical model was developed to illustrate the underlying mechanism supporting this normalization approach. The normalized Raman signals are independent of the incident laser intensity and the density of "hot spots" for numerous SERS substrates. Following "hot-spot" (HS) normalization, the coefficient of variation for the tested SERS substrates decreases from 10 to 60% to 2%-7%. This approach significantly improves SERS quantitation of four chloroanilines and enables collection of highly reproducible analyte adsorption results under both static and dynamic imaging conditions. Overall, this approach provides a simple means to improve SERS reproducibility without the need to use additional chemicals as internal standards.
表面增强拉曼光谱（SERS）在日常定量分析中的应用受到 SERS 衬底的点对点可变性的阻碍，这种可变性是由于局域电磁场在一系列等离子体纳米结构中不均匀分布引起的。在此，我们采用表面增强弹性散射作为 SERS 内标。弹性和非弹性（即拉曼）散射都同时被给定的“热点”增强，因此，表面增强弹性散射信号提供了一个局部的固有内标，它可以扩展到衬底中所有的等离子体增强电磁场。弹性散射光源于商用激光的放大自发辐射（ASE），导致形成一个低波数的伪带，这是 ASE 和边缘滤波器相互作用的结果。建立了一个理论模型来解释支持这种归一化方法的基本机制。对于许多 SERS 衬底，归一化后的拉曼信号不依赖于入射激光强度和“热点”密度。经过“热点”（HS）归一化后，测试 SERS 衬底的变异系数从 10%到 60%降低到 2%-7%。这种方法显著提高了四种氯代苯胺的 SERS 定量分析能力，并在静态和动态成像条件下实现了高度可重复的分析物吸附结果的收集。总的来说，这种方法提供了一种简单的方法来提高 SERS 的重现性，而不需要使用额外的化学物质作为内标。
