Fusion of MALDI Spectrometric Imaging and Raman Spectroscopic Data for the Analysis of Biological Samples.

Oleg Ryabchykov,Juergen Popp,Thomas Bocklitz

doi:10.3389/fchem.2018.00257

Abstract

Despite of a large number of imaging techniques for the characterization of biological samples, no universal one has been reported yet. In this work, a data fusion approach was investigated for combining Raman spectroscopic data with matrix-assisted laser desorption/ionization (MALDI) mass spectrometric data. It betters the image analysis of biological samples because Raman and MALDI information can be complementary to each other. While MALDI spectrometry yields detailed information regarding the lipid content, Raman spectroscopy provides valuable information about the overall chemical composition of the sample. The combination of Raman spectroscopic and MALDI spectrometric imaging data helps distinguishing different regions within the sample with a higher precision than would be possible by using either technique. We demonstrate that a data weighting step within the data fusion is necessary to reveal additional spectral features. The selected weighting approach was evaluated by examining the proportions of variance within the data explained by the first principal components of a principal component analysis (PCA) and visualizing the PCA results for each data type and combined data. In summary, the presented data fusion approach provides a concrete guideline on how to combine Raman spectroscopic and MALDI spectrometric imaging data for biological analysis.

Highlights

Different analytical methods could be utilized for biomedical analysis to highlight a certain aspect of the sample e.g., morphological microstructure, distribution of electronic chromophores, molecule classes, or special proteins
We described the most significant corrupting effects influencing the analysis of Raman spectroscopic and matrix-assisted laser desorption/ionization (MALDI) mass spectrometric imaging data
The importance of data weighting prior to data fusion is highlighted, especially when the data are obtained from different sources and have different scales and dimensionalities

Summary

Introduction

Different analytical methods could be utilized for biomedical analysis (e.g., cells, and tissues, etc.) to highlight a certain aspect of the sample e.g., morphological microstructure, distribution of electronic chromophores, molecule classes, or special proteins. MALDI is a soft ionization technique utilized for mass-spectrometric imaging (Gessel et al, 2014) to determine large organic molecules and biomolecules undetected by conventional ionization techniques. This technique was employed in clinical parasitology (Singhal et al, 2016), microbial identification (Urwyler and Glaubitz, 2016), and cancer tissue investigation (Hinsch et al, 2017)

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Conclusion