Subcellular-Resolution Molecular Pathology by Laser Ablation–Rapid Evaporative Ionization Mass Spectrometry

This work demonstrates the combination of ambient laser ablation (LA) with in-source surface-induced declustering, originally developed for rapid evaporative ionization mass spectrometry (REIMS). This combination, termed laser ablation REIMS (LA-REIMS), provides sensitivity, spatial resolution, and chemical coverage comparable to matrix-assisted laser desoprtion ionization (MALDI) but without the requirement for matrix deposition. The atmospheric pressure interface setup was subjected to detailed characterization with regard to geometric and thermal parameters augmented by in-silico flow modeling. The resulting platform was tested using aerosol formed by the infrared laser ablation of tissues. Three different laser systems were successfully employed for ambient mass spectrometric imaging: a carbon dioxide laser (λ = 10.6 μm, τ_L = ∼100 μs), an optical parametric oscillator (OPO; λ = 2.94 μm, τ_L = 8 ns), and an optical parametric amplifier (OPA; λ = 3.0 μm, τ_L = ∼30 ps). Single-cell imaging was achieved using the high-resolving capabilities of the OPA systems, and 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.