The Ames Laboratory, US Department of Energy, Iowa State University, Ames, Iowa 50011-3111, United States.
Anal Chem. 2012 May 15;84(10):4300-6. doi: 10.1021/ac203355a. Epub 2012 May 3.
Total internal reflection (TIR) Raman and reflectivity spectra were collected for nonresonant analytes as a function of incident angle at sapphire or sapphire/smooth 50 nm gold interfaces using 785 nm excitation. For both interfaces, the Raman signal as a function of incident angle is well-modeled by the calculated interfacial mean square electric field (MSEF) relative to the incident field times the thickness of the layer being probed in the Raman measurement (D(RS)). The Raman scatter was reproducibly enhanced at the interface containing a gold film relative to the sapphire interface by a factor of 4.3-4.6 for aqueous pyridine or 2.2-3.7 for neat nitrobenzene, depending on the analyzed vibrational mode. The mechanism for the increased Raman signal is the enhanced MSEF at incident angles where propagating surface plasmons are excited in the metal film. The background from the TIR prism was reduced by 89-95% with the addition of the gold film, and the percent relative uncertainty in peak area was reduced from 15 to 1.7% for the 1347 cm(-1) mode of nitrobenzene. Single monolayers of benzenethiol (S/N = 6.8) and 4-mercaptopyridine (S/N = 16.5) on gold films were measured by TIR Raman spectroscopy with 785 nm excitation (210 mW) without resonant enhancement in 1 min.
全内反射（TIR）拉曼和反射光谱是在蓝宝石或蓝宝石/光滑 50nm 金界面上，使用 785nm 激发，作为入射角的函数收集的非共振分析物。对于这两个界面，拉曼信号作为入射角的函数可以通过计算界面均方电场（MSEF）与入射场的比值以及在拉曼测量中被探测层的厚度（D（RS））来很好地建模。与蓝宝石界面相比，在含有金膜的界面处，拉曼散射可以通过 4.3-4.6 倍的因子（对于水溶液吡啶）或 2.2-3.7 倍的因子（对于纯硝基苯）得到重复性增强，具体取决于分析的振动模式。增强拉曼信号的机制是在金属膜中激发传播表面等离子体时增强的 MSEF。通过添加金膜，TIR 棱镜的背景降低了 89-95%，并且对于硝基苯的 1347cm(-1)模式，峰面积的相对不确定度从 15%降低到 1.7%。使用 785nm 激发（210mW），无需共振增强，在 1 分钟内通过 TIR 拉曼光谱测量了金膜上的苯硫醇（S/N=6.8）和 4-巯基吡啶（S/N=16.5）的单层。
