Department of Chemistry, W. M. Keck Institute for Proteomics Technology and Applications, George Washington University , Washington, District of Columbia 20052, United States.
Anal Chem. 2014 May 6;86(9):4308-15. doi: 10.1021/ac500007t. Epub 2014 Apr 15.
Ambient ionization methods, such as laser ablation electrospray ionization (LAESI), facilitate the direct analysis of unperturbed cells and tissues in their native states. However, the lack of a separation step in these ionization techniques results in limited molecular coverage due to interferences, ion suppression effects, and the lack of ability to differentiate between structural isomers and isobaric species. In this contribution, LAESI mass spectrometry (MS) coupled with ion mobility separation (IMS) is utilized for the direct analysis of protein mixtures, megakaryoblast cell pellets, mouse brain sections, and Arabidopsis thaliana leaves. We demonstrate that the collision cross sections of ions generated by LAESI are similar to the ones obtained by ESI. In various applications, LAESI-IMS-MS allows for the high-throughput separation and mass spectrometric detection of biomolecules on the millisecond time scale with enhanced molecular coverage. For example, direct analysis of mouse brain tissue without IMS had yielded ∼300 ionic species, whereas with IMS over 1 100 different ions were detected. Differentiating between ions of similar mass-to-charge ratios with dissimilar drift times in complex biological samples removes some systematic distortions in isotope distribution patterns and improves the fidelity of molecular identification. Coupling IMS with LAESI-MS also expands the dynamic range by increasing the signal-to-noise ratio due to the separation of isobaric or other interfering ionic species. We have also shown that identification of potential biomarkers by LAESI can be enhanced by using the drift times of individual ions as an additional parameter in supervised orthogonal projections to latent structures discriminant analysis. Comparative analysis of drift time versus mass-to-charge ratio plots was performed for similar tissue samples to pinpoint significant metabolic differences.
环境电离方法，如激光消融电喷雾电离 (LAESI)，便于在其天然状态下直接分析未受干扰的细胞和组织。然而，这些电离技术缺乏分离步骤，导致由于干扰、离子抑制效应以及缺乏区分结构异构体和等质异位体的能力，分子覆盖范围有限。在本研究中，我们利用 LAESI 质谱 (MS) 与离子淌度分离 (IMS) 直接分析蛋白质混合物、巨核细胞沉淀、小鼠脑切片和拟南芥叶片。我们证明了由 LAESI 产生的离子的碰撞截面与通过 ESI 获得的离子的碰撞截面相似。在各种应用中，LAESI-IMS-MS 允许在毫秒时间尺度上以高通量分离和质谱检测生物分子，并且具有增强的分子覆盖范围。例如，直接分析未经 IMS 的小鼠脑组织仅产生了约 300 种离子，而通过 IMS 检测到了超过 1100 种不同的离子。在复杂的生物样品中，通过分辨具有相似质荷比但淌度时间不同的离子，可以消除同位素分布模式中的一些系统偏差，并提高分子鉴定的准确性。将 IMS 与 LAESI-MS 耦合还可以通过分离等质异位体或其他干扰离子来增加信号与噪声比，从而扩展动态范围。我们还表明，通过将单个离子的淌度用作监督正交投影到潜在结构判别分析的附加参数，LAESI 鉴定潜在生物标志物的能力可以得到增强。为了确定显著的代谢差异，我们对相似组织样本进行了淌度与质荷比关系图的比较分析。
