Conductive Adhesive Film Expands the Utility of Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry Imaging

The matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) technique is a promising approach for detecting the distribution of small molecules in a section of biological tissue. However, when a cryosection is created from fragile, hard, or whole-body samples, obtaining a high-quality section that maintains the distribution of the various components has been difficult. Since adhesive films have the potential to obtain high-quality cryosections, we attempted to utilize a conductive adhesive film for MALDI-MSI. To this end, cryosections of the whole body of a 9-day-old mouse were directly prepared on indium tin oxide (ITO) glass slides, nonconductive adhesive films, or conductive adhesive films, and the signal intensities from each section were measured by MALDI-MSI. We measured the differences in the ion intensity among these three slides/films by means of multivariate analyses and found that both the nonconductive and conductive adhesive films gave rise to high-quality sections in comparison with the ITO glass slide. The conductive adhesive film gave higher signals that were comparable to those of the ITO glass slide in comparison with the nonconductive adhesive film. We divided the frozen sections into two groups, a freeze-dried group and a thawed group, to examine the freeze thaw effect on the signals of representative compounds of amino acids, cholesterol, and phosphatidylcholines. The freeze-dried samples were found to be useful for the analysis. These results indicate that the sections made with the conductive adhesive film under a freeze-dried condition can expand the utility of the MALDI-MSI analysis.