PNNL

Abstract

Mass spectrometry imaging (MSI) enables label-free spatial mapping of hundreds of biomolecules in tissue sections. This capability provides valuable information on tissue heterogeneity, which is difficult to obtain using population-averaged assays. Despite the significant developments in both the instrumentation and methodology, MSI of tissue samples at a single-cell resolution remains challenging. Herein, we describe a protocol for robust imaging of tissue sections with a high spatial resolution of better than 10 µm using nanospray desorption electrospray ionization (nano-DESI) mass spectrometry, an ambient ionization technique that does not require sample pretreatment prior to analysis. In this protocol, mouse uterine tissue is used as a model system to illustrate both the workflow and data obtained in these experiments. We provide a detailed description of the nano-DESI MSI platform, fabrication of the nano-DESI and shear force probes, shear force microscopy experiments, spectral acquisition, and data processing. We also describe an improved strategy for acquiring both positive and negative mode imaging data in the same experiment. This is achieved by alternating between positive and negative data acquisition modes during consecutive line scans. Using our imaging approach, hundreds of histology-quality ion images were obtained from a single uterine section. This protocol enables sensitive and quantitative imaging of lipids and metabolites in heterogeneous tissue sections with increased throughput and high spatial resolution, which is critical to understanding biochemical processes occurring in biological tissues of interest to drug discovery, molecular biology, and clinical research.