Single-Cell 5 μm-Resolution Dual-Polarity MALDI-MS Imaging without Matrix Reapplication

High-resolution mass spectrometry imaging (MSI) plays a vital role in lipidomics, yet challenges persist in analyzing lipids at the single-cell level due to limitations in spatial resolution and lipid coverage. While existing strategies based on a single matrix application step for dual-polarity provide high lipid coverage from the same sample and enable easy sample preparation, matrix depletion limits their spatial resolution to 10 μm, preventing their application to single-cell imaging. Here, we present a single-cell/subcellular resolution strategy for dual-polarity matrix-assisted laser desorption and ionization mass spectrometry imaging (MALDI-MSI) that eliminates the need for matrix reapplication. This approach achieves 5 μm spatial resolution while maintaining lipid coverage comparable to multistep single-cell imaging methods. This is enabled by a fine-tuned matrix deposition technique that fully utilizes the high sensitivity of N-(1-naphthyl)-ethylenediamine dihydrochloride (NEDC) in dual polarities and optimized acquisition conditions, allowing single-deposition workflows without the need for washing, repreparation, or image recalibration. This single-cell resolution MALDI-MSI strategy successfully imaged a broader range of lipid species with distinctive spatial detail in mouse kidney tissue and lung carcinoma cells (A549). Using spatial probabilistic latent semantic analysis (PLSA), we identified three distinct lipid distribution patterns within a single-cell population in both polarities, and histogram analysis revealed substantial cell-to-cell lipidomic heterogeneity. This strategy overcomes limitations of traditional dual-polarity MSI and provides a powerful tool for advancing cellular lipidomics, elucidating disease mechanisms, and investigating environmental toxicology.