Transfer-Based Thin-Section-Free MALDI Mass Spectrometry Imaging Using a Platinum-Coated Porous Plate Formed of Glass Beads

Matrix- and surface-assisted laser desorption/ionization mass spectrometry imaging (MALDI- and SALDI-MSI) are widely used for visualizing molecular distributions not only in medical and pharmaceutical applications but also in plant and food analysis. To overcome limitations associated with sample hardness or fragility, a transfer-based approach was recently developed as an alternative to thin sectioning. In particular, Pt-coated porous plates formed of glass beads (transfer plates) have been introduced as robust substrates for thin-section-free SALDI-MSI. In this study, we demonstrate for the first time that these transfer plates also support thin-section-free MALDI-MSI by transferring the entire strawberry cross-section onto the plate. First, SALDI-MSI was performed; then, a matrix was applied to the same sample on the transfer plate, which was followed by MALDI-MSI. Sequential imaging using both modalities enabled comparison under identical conditions. Ion images of hexose, citric acid, and sucrose obtained using both modalities showed qualitative agreement, indicating that the prior SALDI-MSI and the delocalization caused by subsequent matrix spraying had no substantial effect on the MALDI-MSI results while using a 200-μm step size. In addition, anthocyanins localized to the strawberry skin, which could not be detected by SALDI-MSI, were successfully visualized by MALDI-MSI, thereby validating the method. These results confirm that MALDI-MSI can be performed on transfer plates without sectioning, expanding the utility of this sampling platform. The proposed approach utilizing a transfer plate enables efficient acquisition of both SALDI and MALDI data, which is particularly useful when conventional sectioning or sample duplication is impractical.