Sample preparation free tissue imaging using Laser Desorption – Rapid Evaporative Ionisation Mass spectrometry (LD-REIMS)

Laser desorption ionisation (LDI) is generally considered to be an inferior ionisation modality to matrix assisted LDI (MALDI), providing information solely on lipids with low sensitivity. The current study demonstrates that the combination of ambient LDI with in-source surface-induced declustering provides sensitivity and chemical coverage comparable to MALDI. The setup was characterised for infrared laser desorption using two different laser systems and was successfully used for ambient mass spectrometric imaging. 20 µm spatial resolution was achieved with oversampling, approaching single-cell resolution, while metabolites and lipids ranging from amino acids through carbohydrates and nuclear bases to complex glycolipids were successfully detected. The technique was also tested as a platform for MS-guided surgery, raising the possibility of using a single technique for generating histological and in-vivo data. The results suggest that the new method can form the basis for a new histological classification system for surgery and pathology environments closing this 150 year old diagnostic gap.