Dissecting the Suitability of DESI-MSI for Molecular Fingerprinting.

Since its inception in 2004, Desorption Electrospray Ionization Mass Spectrometry (DESI MS) has seen a significant increase in its application to the pharmaceutical and clinical setting, supported by a steady improvement of the sensitivity, mass accuracy, mass resolution, spatial resolution and usability, as well as by the advantages offered by its ambient nature. However, in comparison to the rapid growth for tissue imaging, the uptake of DESI-MSI in fingerprint imaging has not grown a substantial body of knowledge, compared to MALDI-MSI. In this work, we set off to dissect the application of DESI-MSI to fingerprint imaging to explore both the advantages and the potential challenges that might have slowed the uptake, taking stock from our previous work and that of others in this area. During this endeavor we have highlighted advantages but also discovered that, under a range of optimized operating conditions, fingerprint imaging by DESI-MSI is affected by a delocalization phenomenon which we termed "the bleeding effect". This phenomenon has been shown to be specific to fingerprints, as sample type, as opposed to biological tissues, and may be one of the contributing factors to a seemingly slower uptake of this technique in molecular fingerprinting. Therefore, a description of the observed effect, how to minimize it, and its implications in operational work are discussed.