Muramoto Shin, Graham Daniel J, Wagner Matthew S, Lee Tae Geol, Moon Dae Won, Castner David G
National ESCA and Surface Analysis Center for Biomedical Problems, University of Washington, Seattle, WA 98195.
J Phys Chem C Nanomater Interfaces. 2011 Dec 15;115(49):24247-24255. doi: 10.1021/jp208035x.
In time-of-flight secondary ion mass spectrometry (ToF-SIMS), the choice of primary ion used for analysis can influence the resulting mass spectrum. This is because different primary ion types can produce different fragmentation pathways. In this study, analysis of single-component protein monolayers were performed using monatomic, tri-atomic, and polyatomic primary ion sources. Eight primary ions (Cs(+), Au(+), Au(3) (+), Bi(+), Bi(3) (+), Bi(3) (++), C(60) (+)) were used to examine to the low mass (m/z < 200) fragmentation patterns from five different proteins (bovine serum albumin, bovine serum fibrinogen, bovine immunoglobulin G and chicken egg white lysozyme) adsorbed onto mica surfaces. Principal component analysis (PCA) processing of the ToF-SIMS data showed that variation in peak intensity caused by the primary ions was greater than differences in protein composition. The spectra generated by Cs(+), Au(+) and Bi(+) primary ions were similar, but the spectra generated by monatomic, tri-atomic and polyatomic primary ion ions varied significantly. C(60) primary ions increased fragmentation of the adsorbed proteins in the m/z < 200 region, resulting in more intense low m/z peaks. Thus, comparison of data obtained by one primary ion species with that obtained by another primary ion species should be done with caution. However, for the spectra generated using a given primary ion beam, discrimination between the spectra of different proteins followed similar trends. Therefore, a PCA model of proteins created with a given ion source should only be applied to datasets obtained using the same ion source. The type of information obtained from PCA depended on the peak set used. When only amino acid peaks were used, PCA was able to identify the relationship between proteins by their amino acid composition. When all peaks from m/z 12-200 were used, PCA separated proteins based on a ratio of C(4)H(8)N(+) to K(+) peak intensities. This ratio correlated with the thickness of the protein films and Bi(1) (+) primary ions produced the most surface sensitive spectra.
在飞行时间二次离子质谱分析（ToF-SIMS）中，用于分析的一次离子的选择会影响最终的质谱图。这是因为不同类型的一次离子会产生不同的碎裂途径。在本研究中，使用单原子、三原子和多原子一次离子源对单组分蛋白质单层进行了分析。八种一次离子（Cs(+)、Au(+)、Au(3)(+)、Bi(+)、Bi(3)(+)、Bi(3)(++)、C(60)(+)）用于研究吸附在云母表面的五种不同蛋白质（牛血清白蛋白、牛血清纤维蛋白原、牛免疫球蛋白G和鸡卵清溶菌酶）的低质量（m/z < 200）碎裂模式。对ToF-SIMS数据进行主成分分析（PCA）处理表明，一次离子引起的峰强度变化大于蛋白质组成差异。由Cs(+)、Au(+)和Bi(+)一次离子产生的光谱相似，但单原子、三原子和多原子一次离子产生的光谱差异显著。C(60)一次离子增加了m/z < 200区域内吸附蛋白质的碎裂，导致更低m/z峰的强度增加。因此，比较由一种一次离子物种获得的数据与由另一种一次离子物种获得的数据时应谨慎。然而，对于使用给定一次离子束产生的数据，不同蛋白质光谱之间的区分遵循相似的趋势。因此，用给定离子源创建的蛋白质PCA模型应仅应用于使用相同离子源获得的数据集。从PCA获得的信息类型取决于所使用的峰集。当仅使用氨基酸峰时，PCA能够通过氨基酸组成识别蛋白质之间的关系。当使用m/z 12 - 200的所有峰时，PCA根据C(4)H(8)N(+)与K(+)峰强度的比率分离蛋白质。该比率与蛋白质膜的厚度相关，并且Bi(1)(+)一次离子产生最表面敏感的光谱。
