Abstract
Applications of mass spectrometry imaging (MSI), especially matrix-assisted laser desorption/ionization (MALDI) in the life sciences are becoming increasingly focused on single cell analysis. With the latest instrumental developments, pixel sizes in the micrometer range can be obtained, leading to challenges in matrix application, where imperfections or inhomogeneities in the matrix layer can lead to misinterpretation of MS images. Thereby, the application of premanufactured, homogeneous ionization-assisting devices is a promising approach. Tissue sections were investigated using a matrix-free imaging technique (Desorption Ionization Using Through-Hole Alumina Membrane, DIUTHAME) based on premanufactured nanostructured membranes to be deposited on top of a tissue section, in comparison to the spray-coating of an organic matrix in a MALDI MSI approach. Atmospheric pressure MALDI MSI ion sources were coupled to orbital trapping mass spectrometers. MS signals obtained by the different ionization techniques were annotated using accurate-mass-based database research. Compared to MALDI MSI, DIUTHAME MS images captivated with higher signal homogeneities, higher contrast and reduced background signals, while signal intensities were reduced by about one order of magnitude, independent of analyte class. DIUTHAME membranes, being applicable only on tissue sections thicker than 50 µm, were successfully used for mammal, insect and plant tissue with a high lateral resolution down to 5 µm.
Highlights
Mass spectrometry imaging (MSI) has proven to be a valuable and versatile tool for spatially resolved chemical analysis of surfaces [1,2,3]
To characterize the ionization behavior of DIUTHAME, mouse brain tissue sections were analyzed and compared to the results obtained from matrix-assisted laser desorption/ionization (MALDI) and LDI MSI experiments
We demonstrated the applicability of DIUTHAME membranes for MSI at a high lateral resolution of 5 μm pixel size under atmospheric-pressure conditions
Summary
Mass spectrometry imaging (MSI) has proven to be a valuable and versatile tool for spatially resolved chemical analysis of surfaces [1,2,3]. Matrix-assisted laser desorption/ionization (MALDI) MSI [4,5] under atmospheric pressure (AP) is known for its ease of sample handling, morphological authenticity and the possible combination with highly accurate, highly mass resolving Fourier-transformation-based mass spectrometers [3,6,7]. The achievable lateral resolution is predominantly defined by the focal diameter of the laser beam on the sample surface and thereby the sample area from which analytes are desorbed and ionized. For small laser spot sizes, a high ion yield is essential, predominantly influenced by the chosen matrix material [8]. Optimizing protocols for matrix application to achieve homogeneous surface coverage and small matrix crystals while retaining high ion yields is crucial but time-consuming, as it relies on many parameters [10]. Introducing new matrices for high lateral resolution is challenging
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