Imaging Metabolites in Agar‐Based Bacterial Co‐Cultures with Minimal Sample Preparation using a DIUTHAME Membrane in Surface‐Assisted Laser Desorption/Ionization Mass Spectrometry

While the imaging of bacteria, directly on agar-based media, has been reported in matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI), such samples usually require laborious and time-consuming preparation prior to analysis. Furthermore, the MALDI sample preparation may require desiccation, potentially causing sample deformation and/or degradation. Other issues may be associated with the use of a matrix in MALDI-MSI. Here, we propose an alternative approach to image a co-culture of Pseudomonas and Bacillus bacteria, grown on agar, in the positive and negative ionization modes, using surface-assisted laser desorption/ionization (SALDI) MSI. A rapid and easy sample preparation was performed using a “desorption/ionization using through-hole alumina membrane” (DIUTHAME) with a blotting method. The porous DIUTHAME membrane was used (1) for the transfer of the metabolites from the sample to the membrane, and (2) as assisting material in SALDI-MSI. The advantages and limitations of this new sample preparation are discussed in this paper.