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

有了这个奖项，化学测量和成像项目资助了德克萨斯大学的Katherine Willets的研究，以开发研究表面详细结构的新技术。这些技术将改善各种化学传感器的功能，特别是基于表面增强拉曼散射或SERS现象的类型。虽然SERS是一种非常有前途的传感技术，但它的商业利用受到一些问题的限制，这些问题似乎是由于表面不均匀，没有很好地表征或控制。目前的研究旨在通过研究添加金和银的小颗粒时从表面发出的信号来改善基于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过的表面时，产生的SERS信号会增强，有时会增强一百万倍以上。为了了解这种增强是如何发生的，更重要的是，如何控制这种增强，研究人员正在将各种分析技术应用于该系统。这项工作正在对新的化学传感技术的发展产生广泛的影响。这项工作的长期目标是开发新的SERS探针，将有更大的商业化机会，从而利用这种类型的传感器的易用性，便携性和相对便宜。通过包括高中学生在内的各级学生参与研究调查，它正在对下一代科学家的培训产生进一步的广泛影响。该项目的重点是了解分子如何与支持SERS中局部表面等离子体的金和银纳米粒子相互作用。等离子激元的激发会在纳米颗粒表面产生强烈增强的电磁场，通过将分子置于这些增强的表面磁场中，分子发出的光信号就会增加。特别是拉曼散射，它提供了分子“指纹”，对各种化学传感应用都很有用，这些纳米颗粒大大增强了拉曼散射。大多数理解等离子体激元和SERS的工作都集中在纳米粒子如何增强激发场上，但忽略了分子发射的作用，尽管它在产生被测量信号中很重要。该项目探讨了分子与等离子体纳米粒子相互作用的作用，以便更好地了解导致感兴趣的分子目标产生最强信号的因素。为了更精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，利用电致化学发光探测等离子体耦合发射。超分辨率光学成像也被用于探测等离子体纳米粒子表面分子的位置如何影响发射以低于10纳米的分辨率耦合到远场的方式和位置。波长分辨版本的超分辨成像用于同时实现光谱和空间分辨率，以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耦合到远场的。这些研究将提供一个更好的理解，说明分子如何可能重新定义一个“热点”区域的强增强局部电磁场的传统图像。

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.