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

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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.