Understanding plasmon-enhanced electromagnetic hot spots for surface-enhanced spectroscopies

有了这个奖项，化学测量和成像计划将资助德克萨斯大学的凯瑟琳·威利茨的研究，以开发新的技术来研究表面的详细结构。这些技术将改善各种化学传感器的功能，特别是一种基于表面增强拉曼散射(SERS)现象的传感器。虽然表面增强拉曼散射是一种非常有前途的传感技术，但它的商业应用一直受到一些问题的限制，这些问题似乎是由于表面不均匀，没有得到很好的表征或控制。目前的研究旨在通过研究加入小颗粒金银时来自表面的信号，来改善基于SERS技术的设备的功能。当分子接触到用这些小块金和银处理的表面时，产生的SERS信号被增强，有时增强了一百万倍以上。为了了解这种增强是如何发生的，以及更重要的是，如何控制它，研究人员正在将各种分析技术应用到这个系统上。这项工作对新的化学传感技术的发展产生了广泛的影响。这项工作的长期目标是开发新的SERS探测器，这种探测器将有更大的商业化机会，从而利用这种传感器的易用性、便携性和相对廉价。通过包括高中在内的各级学生参与研究调查，该项目对下一代科学家的培训产生了进一步广泛的影响。该项目的重点是了解分子如何与金和银纳米粒子相互作用，这些纳米粒子支持表面增强拉曼散射中的局域表面等离子激元。等离子体激子的激发导致纳米粒子表面电磁场的强烈增强，通过将分子放入这些增强的表面场中，可以增加来自分子的光信号。特别是，这些纳米粒子大大增强了拉曼散射，它提供了分子的“指纹”，并可用于各种化学传感应用。大多数理解等离子体和SERS的工作都集中在纳米粒子如何增强激发场上，而忽略了分子发射的作用，尽管它在产生测量信号方面很重要。该项目探索分子与等离子体纳米颗粒相互作用的作用，以更好地了解导致来自感兴趣的分子靶标的最强可能信号的因素。为了更准确地了解分子如何与等离子体纳米粒子耦合，正在研究分子和纳米粒子之间的光谱和空间重叠。在没有等离子体增强光激发的情况下，电致化学发光被用来探测等离子体耦合发射。超分辨率光学成像也被用来探测分子在等离子体纳米颗粒表面的位置如何影响发射如何以及在哪里耦合到分辨率低于10 nm的远场。为了显示不同的拉曼模式是如何通过波长相关的等离子体耦合进入远场的，我们使用了一种波长分辨的超分辨率成像来实现光谱和空间分辨率的同时。这些研究将提供一个更好的理解，即解释分子如何潜在地重新定义强烈增强的局部电磁场的“热点”区域的传统图景。

With this award, the Chemical Measurement and Imaging Program is funding the research of Katherine Willets at the University of Texas to develop new techniques to study the detailed structure of surfaces. These techniques will improve the functioning of a variety of chemical sensors, in particular a type based on a phenomenon known as surface-enhanced Raman scattering, or SERS. While SERS is an intensely promising sensing technology, its commercial utilization has been limited by problems that appear to be due to non-uniform surfaces that are not well-characterized or controlled. The current research seeks to improve the functioning of devices based on SERS technology by studying the signals that come from the surface when small particles of gold and silver are added. When molecules come into contact with surfaces treated with these small bits of gold and silver, the resulting SERS signal is enhanced, sometimes by more than a million-fold. The investigators are bringing a variety of analysis techniques to bear on this system in order to understand how this enhancement occurs and, more importantly, how it can be controlled. The work is having a broad impact on the development of new chemical sensing technologies. The long-term goal of the work is to develop new SERS probes that will have greater commercialization opportunities, thus exploiting the ease, portability and relative cheapness of this type of sensor. It is having a further broad impact on the training of the next generation of scientists through the involvement of students at all levels, including high school, in the research investigations.This project is focused on understanding how molecules interact with gold and silver nanoparticles that support localized surface plasmons in SERS. Excitation of plasmons leads to strongly enhanced electromagnetic fields at the surface of the nanoparticles, and by placing molecules into these enhanced fields at the surface, optical signals from the molecules can be increased. In particular, Raman scattering, which provides a molecular 'fingerprint' and is useful for a variety of chemical sensing applications, is strongly enhanced by these nanoparticles. Most work on understanding plasmons and SERS has focused on how excitation fields are enhanced by the nanoparticles, but has neglected the role of emission by the molecule, despite its importance in generating the measured signals. This project probes the role of the molecule interacting with plasmonic nanoparticles, in order to better understand the factors that lead to the strongest possible signals from molecular targets of interest. To more precisely understand how molecules couple to plasmonic nanoparticles, both spectral and spatial overlap between the molecules and the nanoparticles are being investigated. Electrogenerated chemiluminescence is used to probe plasmon-coupled emission in the absence of plasmon-enhanced optical excitation. Super-resolution optical imaging is also being used to probe how the location of molecules on the surface of plasmonic nanoparticles influences how and where the emission is coupled into the far-field with sub-10 nm resolution. A wavelength-resolved version of super-resolution imaging is used to achieve simultaneous spectral and spatial resolution in order to show how different Raman modes are coupled into the far-field via wavelength-dependent plasmon coupling. These studies will provide an improved understanding of how accounting for the molecule can potentially redefine the conventional picture of a 'hot spot' region of strongly enhanced local electromagnetic fields.