MULTI ion source with innvoative postionization modules for enabling a flexible analysis of complex samples in biomedical laser mass spectrometry

基于质谱学的分析方法是生物医学研究中的关键技术。细胞和组织具有复杂的分子组成。对化学成分高度不同的成分进行全面的MS分析通常需要使用不同的电离方法。MALDI-MS成像(MALDI-MSI)能够以约10微米的横向分辨率显示组织切片中的生物分子。然而，该方法依赖于在复杂的单个事件中的解吸/电离耦合，而且，每个辐照像素只有很少的物质可用。因此，低电离效率和离子抑制效应经常阻碍该方法的广泛应用。在该项目中，将开发一种基于离子漏斗的模块化多离子源。该源代码将包含一套创新的，但经济的定位模块。该项目的一个关键要素是产生瞬变气相反应堆(TGR)，它由在良好真空气氛中碰撞冷却的分析物或分析物/基质混合物组成。我们将利用TGR通过外部刺激来启动初级和次级类MALDI电离过程。通过这种方式，我们期望有效地后电离相关类别的生物分子(例如，脂类和化学上不同种类的代谢物)，并实现分析灵敏度的关键增强。此外，多离子源的布局还将使传统的MALDI-MS(I)、ESI-MS以及MALDI-2-MS分析成为可能。作为分析器，我们希望使用高分辨率的Orbitrap质谱仪。具体地说，将探索以下正位化方法来激发TGR：(I)通过介质阻挡放电产生的冷等离子体，(Ii)通过宽带非相干UV-C光，(Iii)通过单光子电离，(Iv)通过与电喷雾电离束重叠，以及(V)通过与金属离子形成加合形成的方式。为了有效地刺激TGR，最佳的正位束与TGR的重叠是必不可少的。因此，该项目的主要部分将致力于准确描述TGR的膨胀动力学和化学成分。为此，我们将应用以下诊断方法：(I)通过快速闪光成像和差示荧光激发的光学方法，(Ii)通过朗缪尔探针确定电荷分布的电子方法，以及(Iii)使用定位化激光光束的质谱学。为了优化模块和确定可根据个别定位方法修改的分析物类别，我们将使用标准和冰冻切片的匀浆组织。在与我们来自医学、化学和生物学的合作伙伴建立的合作中，我们将以选定的生物医学研究问题为例，探索和展示该仪器的潜力。

Mass spectrometry-based analysis methods represent key techniques in biomedical research. Cells and tissues are characterized by a complex molecular composition. A comprehensive MS analysis of the chemically highly diverse constituents typically requires use of different ionization methods. MALDI-MS imaging (MALDI-MSI) enables visualization of biomolecules in tissue sections with a lateral resolution of approximately 10 µm. However, the method depends on coupled desorption/ionization in a convoluted single event and, moreover, only little material is available per irradiated pixel. As consequence, low ionization efficiencies and ion suppression effects frequently hamper a wider use of the methodology.Within this project, an ion funnel-based modular MULTI ion source will be developed. The source will contain a set of innovative, yet economical postionization modules. A key element of the project is the generation of a transient gas phase reactor (TGR), which consists of collisional-cooled analyte or analyte/matrix-mixtures within a fine vacuum atmosphere. We will exploit the TGR for initiating primary and secondary MALDI-like ionization processes by means of external stimuli. In this way, we expect to effectively post-ionize relevant classes of biomolecules (e.g., lipids and chemically heterogeneous metabolites) and to achieve a critical enhancement of the analytical sensitivity. Moreover, the layout of the MULTI ion source will also enable use of conventional MALDI-MS(I), ESI-MS as well as MALDI-2-MS analyses. As analyzer we would like to employ an Orbitrap mass spectrometer with high resolving power.Specifically, the following postionization methods will be explored to stimulate the TGR: Excitation via (i) a cold plasma generated by a dielectric barrier discharge, (ii) by means of broadband incoherent UV-C-light, (iii) via single photon ionization, (iv) by overlap with an electrospray ionization beam, and (v) by means of adduction formation with metal ions.For effective stimulation of the TGR an optimal overlap of the postionization beams with the TGR is essential. Therefore, a major part of the project will be devoted to a precise characterization of the expansion dynamics and chemical composition of the TGR. For this, we will apply the following diagnostic methodologies: (i) optical by means of fast flash imaging and differential fluorescence excitation, (ii) electronic by means of Langmuir probes for determination of the charge distributions, and (iii) mass spectrometric by use of a postionization laser beam.For optimization of the modules and determination of the analyte classes that are amendable to the individual postionization approaches, we will use standards and cryo-sections of homogenized tissue. Within established collaborations with our partners from medicine, chemistry, and biology we will explore and demonstrate the potential of the instrument at the example of selected biomedical research questions.