High resolution MALDI mass spectrometry imaging with laser-induced postionization

MALDI质谱成像（MALDI-MSI）能够直接从基质包被的组织切片中同时无标记记录多种生物分子，如脂质、肽和代谢物。然而，有限的离子产率和离子抑制效应通常限制了该方法的适用性，尤其是在每个照射像素只有很少材料可用的高分辨率应用中。我们最近推出了传统MALDI的扩展，称为MALDI-2。通过使用第二激光器和精细真空离子源，可以启动MALDI样二次电离过程，并且到目前为止，脂质、糖缀合物和脂溶性维生素的MSI信号强度增加多达两个数量级[Soltwisch et al.，Science 348（2015）211]。该研究项目旨在开发这种创新技术，并深入了解MALDI-2的基本过程。因此，它可以分为两个紧密相连的部分：在第一个主要部分>Methodisch-instrumentelle Entwicklungen und Anwendungen<中，我们寻求进一步提高不同类别分析物的分析灵敏度，其中包括使用高光束强度的Nd：YAG激光器，开发改进的MALDI-2基质系统，以及使用直接共振双光子电离分析代谢物。在这种情况下，我们还将探讨是否可以positionized有效地从组织解吸的直接红外激光解吸的手段代谢物。在工作计划的另一部分中，我们试图通过将MALDI-2与所谓的传输模式几何结构耦合，将横向分辨率提高到1-2 µm。在与领先的同事合作中，优化的技术也将应用于一些选定的生物医学研究问题，其中包括改善糖脂的可视化，糖脂作为病原微生物及其毒素的受体。在第二个主要部分的基础研究中>Mechanismen der MALDI-2<材料消融和电离过程将被研究。我们将表征MALDI基质的物理化学性质，以实现有效的定位，invrstigate哪些分析物类别在原则上服从MALD-2和直接2-光子电离，并优化定位照射条件在这两种情况下。通过进行扩展波长研究，将揭示电离过程的精细特征，并通过表征不同实验条件下材料羽流的膨胀动力学，例如解吸激光束的不同焦点直径、离子源中缓冲气体的压力和激发类型。（顶部照明与透射模式几何结构/ UV-与IR-激光解吸），将获得对MALDI-2机制的进一步重要见解。

MALDI mass spectrometry imaging (MALDI-MSI) enables simultaneous label-free recording of numerous biomolecules such as lipids, peptides, and metabolites directly from matrix-coated tissue slices. However, limited ion yields and ion suppression effects often restrict the applicability of the method, not least in high resolution applications where only little material is available per irradiated pixel. We recently introduced an extension of conventional MALDI, called MALDI-2. By using a second laser and a fine-vacuum ion source, MALDI-like secondary ionization processes could be initiated and the MSI signal intensities of - so far - lipids, glycoconjugates and liposoluble vitamins increased by up to two orders of magnitude [Soltwisch et al., Science 348 (2015) 211]. The research project aims at the development of this innovative technology and at obtaining a deeper knowledge about the processes underlying MALDI-2. Therefore, it can be broken down into two closely linked sections:Within the first main part >Methodisch-instrumentelle Entwicklungen und Anwendungen< we seek to further increase the analytical sensitivity for different classes of analytes, among others by using a Nd:YAG laser of high beam intensity, the development of improved MALDI-2 matrix systems, and by use of direct resonant 2-photon ionization for the analysis of metabolites. In this context, we will also explore whether metabolites could be postionized efficiently that are desorbed from tissue by means of direct IR-laser desorption. In a further section of the work program we seek to improve the lateral resolution to values of 1-2 µm by coupling MALDI-2 with the so-called transmission mode geometry. In collaboration with leading colleagues, the optimized technique will also be applied to a few selected biomedical research questions, among others for an improved visualization of glycolipids, serving as receptors for pathogenic microorganisms and their toxins.Within the fundamental investigations of the second main part >Mechanismen der MALDI-2< the processes of material ablation and ionization will be studied. We will characterize which physico-chemical properties of a MALDI-Matrix arre equired to enable an effective postionization, invrstigate which analyte classes are in principle amenable to MALD-2 and to direct 2-photon ionization, and optimize postionization irradiation conditions in both cases. By conducting extended wavelength studies, fine features of the ionization processes will be revealed and by characterizing the expansion dynamics of the material plume at varying experimental conditions, such as different focal diameters of the desorption laser beam, pressure of the buffer gas in the ion source, and the type oft excitation (top illumination vs. transmission mode geometry / UV- vs. IR-laser desorption), further important insight into the MALDI-2 mechanisms will be obtained.