High Spatial Resolution Ambient Ionization Mass Spectrometry Imaging Using Microscopy Image Fusion

Mass spectrometry imaging (MSI) using ambient ionization technique enables a direct chemical investigation of biological samples with minimal sample pretreatment. However, detailed morphological information of the sample is often lost due to its limited spatial resolution. We demonstrated that the fusion of ambient ionization MSI with optical microscopy of routine hematoxylin and eosin (H&E) staining produced predictive high-resolution molecular imaging. In this study, desorption electrospray ionization (DESI) and nanospray desorption electrospray ionization (nanoDESI) mass spectrometry were employed to visualize lipid and protein species on mice tissue sections. The resulting molecular distributions obtained by ambient ionization MSI-microscopy fusion were verified with matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) MSI and immunohistochemistry (IHC) staining. Label-free molecular imaging with 5-μm spatial resolution could be acquired using DESI and nanoDESI, whereas the typical spatial resolution of ambient ionization MSI is ~100 μm. In this regard, sharpened molecular histology of tissue sections was achieved, providing complementary references to the pathology. Such multi-modality integration enabled the discovery of potential tumor biomarkers. After image fusion, we identified about 70% more potential biomarkers that could be used to determine the tumor margins on a metastatic mouse lung tissue section.