Investigation and application of the plasmonic enhancement effect from inverse plasmonic nanostructures on chiral light-matter interaction

在“反向等离子体纳米结构对手性光-物质相互作用的等离子体增强效应的研究和应用”的提案中，我们计划理解和利用等离子体结构来放大手性光-中红外光谱范围内的物质相互作用，以期能够通过使用具有成本效益的仪器来确定和研究微量样品的手性。研究建议旨在在两个相互关联的场景中解决两个不同的问题。在第一种情况下，手性激发和手性纳米结构用于增强手性分子的CD响应。我们已经通过实验证明，基于这种情况，对映体的区分是可能的，但到目前为止，基于理论的工作原理的解释是不可能的。在这一部分中，我们将通过系统地改变等离子体结构，对增强效应对等离子体结构的依赖性进行全面而系统的研究。结果将被用作第二种情况的输入。在第二种情况下，线性偏振激发和由金膜中的椭圆纳米孔组成的非手性基底将被用于增强手性分子的圆二色性。这种方法的优点是手性光场仅在纳米结构的近场中局部产生。因此，一个有效的结构将有三个好处。首先，线偏振激发大大降低了实验装置的成本，因为不需要昂贵的VCD光谱仪与光弹性调制器。其次，线性偏振照明允许VCD与光学显微镜的组合，从而实现空间分辨的显微VCD分析。最后，使用线性偏振照明和非手性基底提供了对来自分子的VCD信号的无背景检测，因为热区外部的分子和等离子体结构都不会对信号有贡献。因此，我们将研究手性分子的圆二色性，通过评估从椭圆形纳米孔填充分析物在扩展的金膜的传输信号。预期的实验也将允许确定这是否确实是等离子体增强圆二色光谱的最佳方案。如果成功，该研究将为超灵敏手性分析提供一个简单有效的平台。

Within the proposal “Investigation and application of the plasmonic enhancement effect from inverse plasmonic nanostructures on chiral light-matter interaction” we plan to understand and make use of plasmonic structures to amplify chiral light-matter interactions in the mid infrared spectral range with the vision of being able to determine and investigate the chirality of minute amounts of samples by employing cost effective instruments.The research proposal aims at addressing two different questions in two scenarios which are mutually interconnect. In the first scenario, chiral excitation and chiral nanostructures are used to enhance the CD response of chiral molecules. We have already proved by experiment that based on this scenario the differentiation of enantiomers is possible, but so far an explanation for the working principle based on theory is not possible. For this part, we will carry out comprehensive and systematic investigations of the dependence of the enhancement effects on the plasmonic structures by varying them systematically. The results will be used as input for the second scenario.In the second scenario, linearly polarized excitation and an achiral substrate consisting of elliptical nanopores in a gold film will be used to enhance the circular dichroism of chiral molecules. This approach has the advantage that the chiral optical field is only generated locally in the near field of the nanostructure. Therefore, a working structure would have three benefits. First, linearly polarized excitation greatly reduces the cost of the experimental setup because no expensive VCD spectrometers with photoelastic modulators are needed. Secondly, linearly polarized illumination allows the combination of VCD with optical microscopes, enabling spatially resolved micro-VCD analysis. Finally, using linearly polarized illumination and achiral substrates provides a background-free detection of the VCD signals from the molecules as neither molecules outside of the hot zone nor the plasmonic structure will contribute to the signal. Accordingly, we will investigate the circular dichroism of chiral molecules by evaluating the transmission signal from elliptical nanopores filled with analyte in an extended gold film. The intended experiments will also allow to determine if this is indeed the best scenario for plasmon-enhanced circular dichroism spectroscopy. If successful, the study will lead to a simple and effective platform for ultrasensitive chiral analysis.