光谱学与光谱分析, 2019, 39 (5): 1354, 网络出版: 2019-05-13  

近场光学用于激光解吸飞行时间质谱的亚微米级空间分辨成像

Laser Desorption Time-of-Flight Mass Spectrometer for Sub-Micrometer-Scale Mass Spectrometry Imaging Using Near-Field Optics Technique
作者单位
厦门大学化学化工学院, 谱学分析与仪器教育部重点实验室, 福建 厦门 361005
摘要
基于激光离子源的飞行时间质谱法作为一门新兴的成像方法, 已经被广泛应用于材料、 地质、 环境、 药物和生命科学领域中。 但受限于光学衍射极限、 聚焦透镜的焦距和数值孔径等因素, 使其难以实现亚微米尺寸的高空间分辨率成像。 近场技术的引入成功地解决了光学衍射极限的限制, 将近场技术与激光电离技术相结合, 可以实现对固体样品表面纳米级弹坑的剥蚀。 此外, 传统的质谱成像技术常常假设样品表面是平整的, 忽略其表面形貌的高低起伏, 但这往往会导致信号强度不稳定和成像假象。 为此, 不仅需要获得样品中的化学组成与空间分布, 还需同时获得样品表面的形貌信息, 才能实现多功能的原位表征。 在自行研制的激光解吸/电离飞行时间质谱的基础上, 采用近场纳米有孔针尖离子源代替传统的远场激光聚焦, 以532 nm波长激光为第一束解析激光, 355 nm波长激光为后电离激光, 音叉式原子力显微镜控制系统针尖与样品之间的距离维持在近场范围内, 对酞菁铜镀层样品表面进行了弹坑剥蚀实验, 获得了直径为550~850 nm的弹坑点阵; 并对7.5 μm×7.5 μm的标准酞菁铜网格样品进行了铜离子亚微米级的高分辨率成像; 此外, 纳米有孔针尖离子源作为原子力显微镜的一种变体, 还可同时获得成像区域的表面形貌信息, 这一结合优势大大拓展了质谱技术在微纳尺度下的原位表征能力。
Abstract
Laser-based ionization time-of-flight mass spectrometry techniques, as an emerging mass spectrometry imaging technique, has been widely used in material, geology, environment, pharmacology, and especially life science. However, it is difficult to achieve sub-micrometer-scale imaging resolution due to the limits of diffraction limit of light, focusing distance and numerical aperture of focusing lens. The introduction of the near-field optics technique has overcome this limitation. By combining the near-field optics technique and laser ionization mass spectrometry, nanoscale crater on the solid surface could be achieved. In addition, traditional mass spectrometry imaging techniques usually neglect the topographical information of the irregular sample surface and cause unreal imaging. So it is important for multifunctional in-situ characterization to get the chemical and topographical information simultaneously. In this paper, a near-field nanometer aperture tip desorption postionization time-of-flight mass spectrometer was developed for sub-micrometer-scale chemical and topographical analysis. 532 and 355 nm laser were used as the desorption and postionizationlaser respectively. A tuning fork based AFM system was used to control the distance between the tip and sample. Copper phthalocyanine molecular layers was ablated to produce a series of nanoscale craters with the size from 550 to 850 nm, which indicated that the technique could achieve sub-micrometer-scale lateral resolution. Furthermore, a mass spectrometry imaging with high lateral resolution was carried out on a 7.5 μm×7.5 μm copper phthalocyanine grid pattern sample. As the results showed, the chemical imaging of the sample surface was achieved simultaneously with the topographical information, expanding the in-situ characterization ability of the mass spectrometry imaging techniques.

李晓萍, 殷志斌, 程肖玲, 刘蓉, 杭纬. 近场光学用于激光解吸飞行时间质谱的亚微米级空间分辨成像[J]. 光谱学与光谱分析, 2019, 39(5): 1354. LI Xiao-ping, YIN Zhi-bin, CHENG Xiao-ling, LIU Rong, HANG Wei. Laser Desorption Time-of-Flight Mass Spectrometer for Sub-Micrometer-Scale Mass Spectrometry Imaging Using Near-Field Optics Technique[J]. Spectroscopy and Spectral Analysis, 2019, 39(5): 1354.

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