Polarity switching mass spectrometry imaging of healthy and cancerous hen ovarian tissue sections by infrared matrix-assisted laser desorption electrospray ionization (IR-MALDESI)

Abstract

Mass spectrometry imaging (MSI) is a rapidly evolving field for monitoring the spatial distribution and abundance of analytes in biological tissue sections. It allows for direct and simultaneous analysis of hundreds of different compounds in a label-free manner. In order to obtain a comprehensive metabolite and lipid data, a polarity switching MSI method using infrared matrix assisted laser desorption electrospray ionization (IR-MALDESI) was developed and optimized where the electrospray polarity was alternated from one voxel to the next. Healthy and cancerous ovarian hen tissue sections were analyzed using this method. Distribution and relative abundance of different metabolites and lipids within each tissue section were discerned, and differences between the two were revealed. Additionally, the utility of using mass spectrometry concepts such as spectral accuracy and sulfur counting for confident identification of analytes in an untargeted method are discussed.

TransOmic analysis of forebrain sections in Sp2 conditional knockout embryonic mice using IR-MALDESI imaging of lipids and LC-MS/MS label-free proteomics

“…The list of lipids comprised phospholipids, as well as ceramides, sulfatides, and acylglycerides. These results are in excellent accordance with previous studies from adult mouse brains, e.g., [38, 39], as well as previous IR-MALDESI studies from different tissue types [5, 40]. …”

IR-MALDESI Mass Spectrometry Imaging at 50 Micron Spatial Resolution

“…Cholesterol was chosen as it was the most abundant ion detected by IR-MALDESI and, therefore, would require the least volume of ablated tissue to be detected. Methods to improve ion abundance including reoptimization of the IR-MALDESI source geometry to improve ablation and electrospray plume overlap [21], the use of a higher repetition rate laser to reduce ion loss in the MS C-trap, and ionization agent optimization [28, 30, 31] will be the focus of future work.…”

Infrared matrix-assisted laser desorption electrospray ionization mass spectrometry imaging analysis of biospecimens

“…This permits selection of aqueous and organic solvent system to be optimized for particular class of compounds 41 , although to date, only binary solvent systems have been investigated. Additionally, the ionization agent can be adjusted for operation in positive or negative ionization mode 42 using typical ionization agents such as formic acid or ammonium hydroxide. Some instruments, like the Q Exactive, allow rapid change of polarity such that a polarity switching imaging experiment may be performed on the same sample 42–44 .…”

“…Additionally, the ionization agent can be adjusted for operation in positive or negative ionization mode 42 using typical ionization agents such as formic acid or ammonium hydroxide. Some instruments, like the Q Exactive, allow rapid change of polarity such that a polarity switching imaging experiment may be performed on the same sample 42–44 . In this case, the electrospray solvent system must be selected as a compromise in performance between the polarities.…”