High Resolution Mass Spectrometric Imaging for Single Cell Metabolic Analysis

Abstract

Mass spectrometry imaging makes possible simultaneous measurement of a large number of biomolecules of lipids, peptides, proteins, etc. from the same sample. Of special interest are ambient ionization techniques that can be carried out at room temperature in air. We report the development of a new type of ambient mass spectrometry named laser desorption ionization droplet delivery mass spectrometry (LDIDD-MS). It utilizes a pulsed laser for desorption of molecules from cells or tissue substrates. The desorbed ions are picked up and delivered with directed sprayed liquid droplets on the laser-irradiated region to a mass spectrometer. By translating desorption region on XY moving stage, two-dimensional images of the desorbed/ionized ions can be formed. As the region of desorption/ionization of LDIDD-MS is spatially limited to the laser beam spot size, the spatial resolution can be ideally reduced to several microns.We obtained spatial resolution as low as 2.4 μm in microcontacted standard samples and ∼7 μm for a pancreas tissue sample. We employed the LDIDD-MS imaging for single cell analysis and observed a significant heterogeneity in cellular apoptosis of HEK cells. LDIDD-MS also enables real-time measurement/imaging of exocytosed biomolecules in live cells. Exocytosis of neuropeptides and enzymes in PC12 upon biochemical or biophysical stimulation has been acquired and we believe that this will make it possible for use to obtain spatiotemporally resolved maps of neurosecretions at single-cell resolution.