Novel Blotting Method for Mass Spectrometry Imaging of Metabolites in Strawberry Fruit by Desorption/Ionization Using Through Hole Alumina Membrane

Abstract

Mass spectrometry imaging (MSI) using matrix-assisted laser desorption/ionization (MALDI) is a powerful technique for visualizing metabolites in the strawberry fruit. During sample preparation for MALDI-MSI, sectioning of the samples is usually required. In general, MALDI-MSI analysis of strawberry fruits that are larger than a single glass slide is difficult because thin sections cannot be prepared. In this study, we attempted to visualize metabolites in large strawberry fruits by MSI, employing a blotting method that uses desorption ionization using a through-hole alumina membrane (DIUTHAME) chip. Large strawberry fruits were cut and a DIUTHAME chip was set on the cross-section to blot the metabolites. After drying the DIUTHAME chip, the metabolites were measured in positive and negative ion modes using a commercial MALDI-type mass spectrometer. Several peaks were detected in both the ion modes. Various metabolites related to food quality, such as sugars, organic acids, and anthocyanins, were detected and successfully visualized by blotting on a DIUTHAME chip in MSI. These results suggest that blotting using a DIUTHAME chip in MSI is useful for visualizing the metabolites present in the strawberry fruit.

Keywords: blotting; desorption ionization using through hole alumina membrane (DIUTHAME); mass spectrometry imaging; metabolites; strawberry.

Figure 1

Workflow of the blotting method involving desorption ionization using through-hole alumina membrane (DIUTHAME) chip in mass spectrometry imaging.

Figure 2

Mass spectra of strawberry fruit by blotting using desorption ionization using through-hole alumina membrane (DIUTHAME) chip in mass spectrometry imaging. (a) Optical image of the analyzed cross-section of strawberry fruit. (b) Optical image of DIUTHAME chip blotted with a cross-section of strawberry fruit. Dotted white line indicates the analyzed region. Scale bar = 20 mm. Mass spectra obtained using (c) positive and (d) negative ion modes. Peaks with platinum (Pt) are derived from Pt coated on the through porous hole alumina membrane.

Figure 3

Visualization of the tentatively assigned metabolites in strawberry fruit. Optical images of (a) cross-section of strawberry fruit and (b) desorption ionization using through hole alumina membrane (DIUTHAME) chip blotted by the strawberry fruit. Ion images of m/z (c) 104.0, (d) 179.0, (e) 219.0, (f) 231.0, (g) 271.0, (h) 301.0, (i) 341.1, and (j) 381.1. Dotted white line indicates the analyzed region. Scale bar = 20 mm.