e-MALDI: An Electrowetting-Enhanced Drop Drying Method for MALDI Mass Spectrometry

The performance of matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) is frequently compromised by the heterogeneous distribution of matrix and analyte deposits on the target plate arising during the conventional drop drying sample preparation procedure. It was recently shown that this so-called coffee stain effect can be suppressed by exciting evaporating complex fluids throughout the drying process using AC-electrowetting. Here, we demonstrate that electrowetting-assisted drying of solutions of common MALDI matrix materials and a variety of common low molecular weight pharmaceutical molecules indeed leads to substantially smaller and more homogeneous sample spots on special electrowetting-functionalized e-MALDI target plates. The improved spot quality enables 2-30X enhanced MALDI-1VIS signals along with substantial reductions of the typical lateral variations of the MALDI-MS. The latter largely eliminates the time-consuming need to search for sweet spots.