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，我们计划了解和利用等离子体结构来放大中红外光谱范围内的手性光物质相互作用，以期能够通过采用成本有效的仪器来确定和研究微量样品的手性。该研究计划旨在解决两个相互关联的场景中的两个不同问题。在第一种情况下，使用手性激发和手性纳米结构来增强手性分子的CD响应。我们已经通过实验证明，在这种情况下，对映体的区分是可能的，但迄今为止，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进行全面系统的研究。结果将用作第二个场景的输入。在第二种情况下，将使用线极化激发和由金薄膜中的椭圆纳米孔组成的非手性底物来增强手性分子的圆二色性。这种方法的优点是手性光场只在纳米结构的近场局部产生。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，因为不需要昂贵的带有光弹性调制器的VCD光谱仪。其次，线偏振照明允许VCD与光学显微镜相结合，实现空间分辨的微VCD分析。最后，使用线偏振照明和非手性衬底提供了来自分子的VCD信号的无背景检测，因为热区外的分子和等离子体结构都不会对信号产生影响。因此，我们将通过评估填充分析物的椭圆纳米孔在延伸金膜中的传输信号来研究手性分子的圆二色性。计划中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.