Abstract
We report a high spatial resolution mass spectrometry (MS) system that allows us to image live hippocampal tissue slices under open-air atmospheric pressure (AP) and ambient temperature conditions at the subcellular level. The method is based on an efficient desorption process by femtosecond (fs) laser assisted with nanoparticles and a subsequent ionization step by applying nonthermal plasma, termed AP nanoparticle and plasma assisted laser desorption ionization (AP-nanoPALDI) MS method. Combining the AP-nanoPALDI with microscopic sample scanning, MS imaging with spatial resolution of 2.9 µm was obtained. The observed AP-nanoPALDI MS imaging clearly revealed the differences of molecular composition between the apical and basal dendrite regions of a hippocampal tissue. In addition, the AP-nanoPALDI MS imaging showed the decrease of cholesterol in hippocampus by treating with methyl β-cyclodextrin, which exemplifies the potential of AP-nanoPALDI for live tissue imaging for various biomedical applications without any chemical pretreatment and/or labeling process.
Highlights
We report a high spatial resolution mass spectrometry (MS) system that allows us to image live hippocampal tissue slices under open-air atmospheric pressure (AP) and ambient temperature conditions at the subcellular level
All the MS images presented in this study were obtained using a ×20 objective lens (NA = 0.45; LUCPlanFLN 20X, Olympus, Japan), and the diameter of the focused laser beam could be reduced to 1.2 μm
For precise positioning of a region of interest (ROI) at the micrometer level and sample moving at a constant velocity for raster scanning, a programmable motorized XY scanning stage was mounted on the inverted optical microscope
Summary
We report a high spatial resolution mass spectrometry (MS) system that allows us to image live hippocampal tissue slices under open-air atmospheric pressure (AP) and ambient temperature conditions at the subcellular level. The desorption electrospray ionization (DESI) method[10,14], AP matrix-assisted laser desorption ionization (AP-MALDI) method[15], and laser ablation electrospray ionization (LAESI)[16] method have been regarded as prominent AP desorption/ionization methods capable of producing MS imaging of biological samples Owing to their limited spatial resolution, these AP-MS imaging techniques still face several challenges for practical bioimaging applications[17]. The AP-nanoPALDI MS analysis for live mouse hippocampal tissue slices provided information on the distribution of lipids and metabolites in the apical and the basal dendrite regions without any chemical or fixative treatment It showed the decrease of cholesterol in hippocampus by treating with methyl β-cyclodextrin. The APnanoPALDI MS imaging technique is expected to be applicable to various label-free bioimaging applications, such as accurate molecular histology for fresh tissues and tissue-based drug screening
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