Patterning Matrix Droplets for Quantitative Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry Imaging

Abstract

Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI) enables analysis of a wide range of biomolecules and provides their spatial distribution on biological samples with advantages such as high sensitivity and soft ionization for minimal fragmentation of biomolecules. Quantitative analysis, however, is challenging due to ionization suppression effects, nonuniform matrix crystals, and formation of hot-spots. Challenges associated with the ionization suppression or the heterogeneous cocrystals can be resolved, for instance, by internal standards and isotope labelling. Thus, a key challenge in quantitative MALDI-MSI is to be able to apply matrix, with precision, convenience, and reproducibility over the entire imaging area. In this work, we demonstrate a simple approach for forming uniform and controlled array of matrix crystals for quantitative MALDI mass spectrometry imaging of peptides. An array of elastomeric microwells filled with matrix solution is stamped onto a sample. The well between microwells helps to preserve spatial information of the peptides by efficiently blocking mixing of analytes across neighboring wells. Peeling off the stamp transfers the matrix solution onto the substrate, thereby concentrating the extracted analytes. Mass signal from each matrix crystals is directly proportional to surface coverage of the peptides. The result suggests that our approach is promising for quantitative MALDI-MSI.