Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Científicas , Cantoblanco, 28049 Madrid, Spain.
Departamento de Física, Escuela Politécnica Superior, Universidad Carlos III de Madrid , Avenida Universidad 30, Leganés, 28911 Madrid, Spain.
ACS Appl Mater Interfaces. 2017 Feb 1;9(4):4119-4125. doi: 10.1021/acsami.6b12490. Epub 2017 Jan 18.
The detection, identification, and quantification of different types of molecules and the optical imaging of, for example, cellular processes are important challenges. Here, we present how interference-enhanced Raman scattering (IERS) in adequately designed heterostructures can provide amplification factors relevant for both detection and imaging. Calculations demonstrate that the key factor is maximizing the absolute value of the refractive indices' difference between dielectric and metal layers. Accordingly, Si/Al/AlO/graphene heterostructures have been fabricated by optimizing the thickness and roughness and reaching enhancement values up to 700 for 488 nm excitation. The deviation from the calculated enhancement, 1200, is mainly due to reflectivity losses and roughness of the Al layer. The IERS platforms are also demonstrated to improve significantly the quality of white light images of graphene and are foreseen to be adequate to reveal the morphology of 2D and biological materials. A graphene top layer is adequate for most organic molecule deposition and often quenches possible fluorescence, permitting Raman signal detection, which, for a rhodamine 6G (R6G) monolayer, presents a gain of 400. Without graphene, the nonquenched R6G fluorescence is similarly amplified. The wavelength dependence of the involved refractive indices predicts much higher amplification (around 10) for NIR excitation. These interference platforms can therefore be used to gain contrast and intensity in white light, Raman, and fluorescence imaging. We also demonstrate that surface-enhanced Raman scattering and IERS amplifications can be efficiently combined, leading to a gain of >10 (at 488 nm) by depositing a Ag nanostructured transparent film on the IERS platform. When the plasmonic structures deposited on the IERS platforms are optimized, single-molecule detection can be actively envisaged.
检测、识别和量化不同类型的分子，以及对细胞过程等进行光学成像，是重要的挑战。在这里，我们展示了如何在适当设计的异质结构中增强拉曼散射（IERS），为检测和成像提供相关的放大因子。计算表明，关键因素是最大化介电层和金属层之间折射率差值的绝对值。因此，通过优化厚度和粗糙度，制备了 Si/Al/AlO/石墨烯异质结构，在 488nm 激发下达到了高达 700 的增强值。与计算出的增强值 1200 的偏差主要归因于 Al 层的反射率损失和粗糙度。IERS 平台还被证明可以显著提高石墨烯的白光图像质量，并有望揭示二维和生物材料的形貌。石墨烯顶层对于大多数有机分子的沉积是足够的，并且通常会猝灭可能的荧光，从而允许检测拉曼信号，对于单层罗丹明 6G（R6G），可获得 400 的增益。没有石墨烯，未猝灭的 R6G 荧光也会被类似地放大。所涉及的折射率的波长依赖性预测了近红外激发下更高的放大（约 10 倍）。因此，这些干涉平台可用于在白光、拉曼和荧光成像中获得对比度和强度增益。我们还证明了表面增强拉曼散射和 IERS 放大可以有效地结合，通过在 IERS 平台上沉积 Ag 纳米结构透明膜，可以获得 >10 的增益（在 488nm 处）。当沉积在 IERS 平台上的等离子体结构被优化时，可以积极地考虑进行单分子检测。
