Terahertz Photonics (THP) Group, Photon Beam Science Research Division, Institute of Laser Engineering, Osaka University, Suita, Osaka 565-0971, Japan.
Department of Chemistry, Faculty of Science, Kyushu University, Fukuoka 819-0395, Japan; RIKEN Center for Biosystems Dynamics Research, Suita, Osaka 565-0874, Japan.
J Chromatogr A. 2023 Nov 8;1710:464384. doi: 10.1016/j.chroma.2023.464384. Epub 2023 Sep 17.
Terahertz (THz) time-domain spectroscopy (TDS) is a recently emerging analysis method which can provide unique information on molecular vibration and rotation induced by inter/intra-molecular interactions. Although the application of THz-TDS to high-performance microscale separation methods like capillary electrophoresis (CE) has been anticipated, it has been hindered due to the diffraction limit of THz wave (typically, hundreds µm). In order to realize CE-THz-TDS, in this study, we placed a narrow open-tubular capillary on the surface of a GaAs semiconductor substrate as a "localized" THz-emitter. By focusing femtosecond pulsed laser beams at the surface of a gallium arsenide (GaAs) substrate closest to the capillary, THz waves were locally generated to pass through the capillary, so that THz absorbance spectra were obtained from the capillary which has narrower inner diameter than the diffraction limit. As a typical result from acetic acid analysis in the CE-THz-TDS platform, information on the refractive index and extinction coefficient was obtained, which showed non-linear and linear concentration dependence, respectively, similar to conventional THz-TDS using large liquid cells. Finally, CE-THz-TDS analysis of several carboxylic acids was demonstrated. Two acids were successfully separated and detected with THz-TDS, where their electrophoretic mobility values were estimated as close to those obtained with conventional contactless conductivity detection. Our proposed CE-THz-TDS showed the potential for the systematic analysis of inter/intra-molecular weak interactions like hydrogen bonds, which are unable to obtain with conventional detectors.
太赫兹时域光谱（THz-TDS）是一种新兴的分析方法，它可以提供分子振动和旋转的信息，这些信息是由分子间/内相互作用引起的。虽然人们已经预期太赫兹时域光谱（THz-TDS）可以应用于高性能微尺度分离方法，如毛细管电泳（CE），但由于太赫兹波的衍射极限（通常为数百微米），这种应用一直受到阻碍。为了实现 CE-THz-TDS，在本研究中，我们将一根窄的开管式毛细管放置在砷化镓（GaAs）半导体衬底的表面上，作为一个“局部”的太赫兹发射器。通过聚焦飞秒脉冲激光在最接近毛细管的砷化镓（GaAs）衬底表面上，局部产生太赫兹波并穿过毛细管，从而从内径小于衍射极限的毛细管获得太赫兹吸收光谱。作为 CE-THz-TDS 平台中乙酸分析的典型结果，获得了折射率和消光系数的信息，它们分别表现出非线性和线性浓度依赖性，类似于使用大液体池的传统太赫兹时域光谱（THz-TDS）。最后，演示了几种羧酸的 CE-THz-TDS 分析。两种酸都可以通过太赫兹时域光谱（THz-TDS）进行分离和检测，其电泳迁移率值与使用传统非接触式电导检测获得的值非常接近。我们提出的 CE-THz-TDS 显示了分析分子间/内弱相互作用（如氢键）的潜力，而这些相互作用是传统检测器无法获得的。
