Determination of the Optimum Pixel Size for the Highest Spatial Resolution in Molecular Images Produced by Continuous Laser Raster Sampling Technique with Imaging Mass Spectrometry

Abstract

Imaging mass spectrometry can be used to reveal the relative distribution of peptides and proteins throughout a biological tissue section. In matrix assisted laser desorption/ionization (MALDI) imaging mass spectrometry, molecular images are produced by ablating each site on the sample and assigning different colors to each interested molecular mass in the spectra.  Continuous laser raster sampling technique was introduced to improve the spatial resolution of molecular images and to reduce the scanning time compared to the original scanning technique known as the spot-to-spot sampling. The smallest pixel size of images produced by the spot-to-spot sampling technique is same as the size of the laser spot. But which is in continuous laser raster sampling technique is determined by the instrumental and sample performance. In this paper, the optimum pixel size for the highest spatial resolution is determined.  This is evaluated using a molecular image of a chemically blotted fine mesh produced by a MALDI orthogonal-injection time-of-flight (TOF) mass spectrometer. A Nd-YAG laser firing at the frequency of 500 Hz ablates the sample moving the sample stage at the velocity of 200 µm/s. The molecular image of a scanned raster line is reproduced with different pixel sizes and the spatial resolution is evaluated. According to the results, the maximum spatial resolution was produced at the pixel size of 3 µm under the used instrumental and sample condition of the experiment.