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Spatial lipidomics is a powerful technique for understanding the complexity of the lipidome in biological systems through mass spectrometry imaging (MSI). Recent advancements have enabled isomer-selected MSI (iMSI) of lipids in biological samples using both online and off-line derivatization strategies. Despite these impressive developments, most iMSI techniques are limited to either positive or negative ion mode analysis, restricting the molecular coverage achievable in a single experiment. Additionally, derivatization efficiency often varies across lipid classes, presenting challenges for comprehensive lipid analysis. In this study, we introduce tetrakis(4-carboxyphenyl)porphyrin (TCPP) as a universal photosensitizer that facilitates online lipid derivatization in both positive and negative ionization modes via singlet oxygen (1O2) reaction. This method enables the identification and localization of both acyl chain compositions and lipid carbon-carbon (C=C) isomers in liquid extraction-based ambient ionization techniques. We have also employed sodium fluoride (NaF) as a solvent dopant to enhance the analysis of low-abundance and poorly ionizable biomolecules. By integrating these online derivatization and signal enhancement strategies with nanospray desorption electrospray ionization (nano-DESI), we achieved dual polarity iMSI within the same sample. We demonstrate imaging of low-abundance isomeric lipids, which were otherwise below the noise level. Notably, TCPP significantly enhances the efficiency of the online derivatization of unsaturated fatty acids, for which other photosensitizers are inefficient. This novel approach allows for the imaging of isomeric fatty acids and phospholipids from multiple classes in the same experiment, revealing their distinct spatial localization within biological tissues.
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Imaging and Analysis of Isomeric Unsaturated Lipids through Online Photochemical Derivatization of Carbon–Carbon Double Bonds**
Abstract Unraveling the complexity of the lipidome requires the development of novel approaches for the structural characterization of lipid species with isomer‐level discrimination. Herein, we introduce an online photochemical approach for lipid isomer identification through selective derivatization of double bonds by reaction with singlet oxygen. Lipid hydroperoxide products are generated promptly after laser irradiation. Fragmentation of these species in a mass spectrometer produces diagnostic fragments revealing the C=C locations in the unreacted lipids. This approach uses an inexpensive light source and photosensitizer making it easy to incorporate into any lipidomics workflow. We demonstrate the utility of this approach for the shotgun profiling of C=C locations in different lipid classes present in tissue extracts using electrospray ionization (ESI) and ambient imaging of lipid species differing only by the location of C=C bonds using nanospray desorption electrospray ionization (nano‐DESI).
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- Award ID(s):
- 1808136
- PAR ID:
- 10224254
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Angewandte Chemie International Edition
- Volume:
- 60
- Issue:
- 14
- ISSN:
- 1433-7851
- Page Range / eLocation ID:
- p. 7559-7563
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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