Martin Körsgen oral presentation (PB2-Mon4-1-5)
Molecular ME-ToF-SIMS Yield as a Function of Matrix Layer Thicknesses Obtained from Mouse Brain Sections Coated by Sublimation/Deposition Techniques
1 University of Münster, Physikalisches Institut, Wilhelm Klemm Str. 10, 48149 Münster, Germany
2 University of Münster, Institute for Hygiene, Robert-Koch-Str. 41, 48149 Münster, Germany
3 University of Münster, Interdisciplinary Center for Clinical Research, Domagkstr. 3, 48149 Münster, Germany
Due to its ability to provide chemical information on a sub-micrometer scale, the use of ToF-SIMS is of increasing interest for biological and medical applications. However, the detection of larger biomolecules such as phospholipids and peptides is often hampered due to high fragmentation rates and low ionization efficiencies.
A way to increase secondary ion molecular yield is to chemically modify the surface using the matrix-enhanced SIMS (ME-SIMS) approach, where an organic matrix is placed upon the surface. Common matrices used in ME-SIMS are MALDI matrices like 2,5-dihydroxybenzoic acid (DHB) or α-Cyano-4-hydroxycinnamic acid (HCCA). Sample preparation is particularly important. Solvent based matrix preparations can lead to high molecular ion yields even deep within the matrix crystals , but lateral resolution is limited by analyte migration during the crystallization process. A solvent-free sample preparation technique like sublimation/deposition of matrix onto the sample surface should be able to achieve higher lateral resolution. The influence of the matrix on the secondary ion yield depends on matrix layer thickness.
In this study, a solvent-free matrix sublimation/deposition technique was developed for coating a mouse brain section with a thin layer of a DHB matrix to produce samples for ME-SIMS analysis with Bi3+ primary ions . Differences in normalized secondary ion intensities and ion yields as a function of layer thickness were investigated.
Signal enhancements for ME-SIMS up to a factor of 18 greater than ToF-SIMS were observed. The matrix layer thickness was found to play an important role in the efficiency of yield enhancement. An ion yield increase with layer thickness up to approximately 80 nm was found. However, a much thicker matrix layer of approximately 160 nm produced a lower ion yield. This indicates that there should be an optimum matrix layer thickness. In addition, a complex influence of the matrix layer on various signals was observed.
Our study shows that matrix sublimation/deposition can provide enhanced secondary ion yield and an optimized protocol holds great promise for sensitive ME-SIMS of physiologically important biomolecules at sub-µm lateral resolution.
 M. Körsgen, A. Pelster, K. Dreisewerd, H. F. Arlinghaus, J. Am. Soc. Mass Spectrom. 2016, 27, 277-284.
 M. Körsgen, A. Pelster, S. Vens-Cappell, O. Roling, H. F. Arlinghaus, Surf. Interface Anal. 2016, 48, 34-39.