A Mass Spectrometry Imaging approach for the fundamental study of Surface-Assisted Laser Desorption/Ionisation mechanisms

Surface-Assisted Laser Desorption/Ionisation Mass Spectrometry (SALDI-MS), which employs inorganic nanosubstrates to promote desorption/ionisation of analytes, is a promising technique for the analysis of small molecules. Indeed, SALDI-MS does not require any organic matrix, reducing the desorption/ionisation of interfering organic ions (in low m/z region) and requiring no co-crystallisation, which simplifies the sample preparation. However, while most papers are focused on the development of new nanosubstrates, the fundamental aspects of SALDI-MS have not been studied in detail yet. Indeed, SALDI-MS involves complicated processes, which make the understanding of SALDI-MS desorption/ionisation mechanisms less straightforward. Our study aims at investigating the SALDI-MS processes for various nanosubstrates. We observed that the ionisation of the metallic nanosubstrates occurs during SALDI-MS experiments and that each nanomaterial is increasingly ionised from a different energy threshold. Moreover, the desorption/ionisation and fragmentation of model molecules (benzylpyridinium salts) seem to be correlated with the appearance of the metallic nanosubstrates ions, demonstrating that the nanosubstrate destruction/restructuring may be involved in the desorption/ionisation processes.