Zhang Kaifeng, Bao Yifan, Cao Maofeng, Taniguchi Shin-Ichi, Watanabe Masahiro, Kambayashi Takuya, Okamoto Toshihiro, Haraguchi Masanobu, Wang Xiang, Kobayashi Kei, Yamada Hirofumi, Ren Bin, Tachizaki Takehiro
Research & Development Group, Hitachi, Ltd., Yokohama 244-0817, Kanagawa, Japan.
Department of Electronic Science and Engineering, Kyoto University, Kyoto 615-8510, Japan.
Anal Chem. 2021 Jun 1;93(21):7699-7706. doi: 10.1021/acs.analchem.1c00806. Epub 2021 May 20.
Tip-enhanced Raman spectroscopy (TERS) is a nano-optical approach to extract spatially resolved chemical information with nanometer precision. However, in the case of direct-illumination TERS, which is often employed in commercial TERS instruments, strong fluorescence or far-field Raman signals from the illuminated areas may be excited as a background. They may overwhelm the near-field TERS signal and dramatically decrease the near-field to far-field signal contrast of TERS spectra. It is still challenging for TERS to study the surface of fluorescent materials or a bulk sample that cannot be placed on an Au/Ag substrate. In this study, we developed an indirect-illumination TERS probe that allows a laser to be focused on a flat interface of a thin-film waveguide located far away from the region generating the TERS signal. Surface plasmon polaritons are generated stably on the waveguide and eventually accumulated at the tip apex, thereby producing a spatially and energetically confined hotspot to ensure stable and high-resolution TERS measurements with a low background. With this thin-film waveguide probe, TERS spectra with obvious contrast from a diamond plate can be acquired. Furthermore, the TERS technique based on this probe exhibits excellent TERS signal stability, a long lifetime, and good spatial resolution. This technique is expected to have commercial potential and enable further popularization and development of TERS technology as a powerful analytical method.
针尖增强拉曼光谱（TERS）是一种纳米光学方法，能够以纳米精度提取空间分辨的化学信息。然而，在商业TERS仪器中常用的直接照明TERS情况下，来自照明区域的强荧光或远场拉曼信号可能作为背景被激发。它们可能会淹没近场TERS信号，并显著降低TERS光谱的近场与远场信号对比度。对于TERS来说，研究荧光材料的表面或无法放置在金/银基底上的块状样品仍然具有挑战性。在本研究中，我们开发了一种间接照明TERS探针，该探针能使激光聚焦在远离产生TERS信号区域的薄膜波导的平坦界面上。表面等离激元极化激元在波导上稳定产生，并最终在针尖顶端积累，从而产生一个空间和能量受限的热点，以确保在低背景下进行稳定且高分辨率的TERS测量。使用这种薄膜波导探针，可以获得与金刚石平板形成明显对比的TERS光谱。此外，基于该探针的TERS技术表现出优异的TERS信号稳定性、长寿命和良好的空间分辨率。该技术有望具有商业潜力，并能使TERS技术作为一种强大的分析方法得到进一步的推广和发展。
