Extending singlet oxygen lifetime to enhance sensitivity of isomer-selective lipid imaging using nanospray desorption...

Identifying and localizing lipid CC positional isomers in biological tissues remains a major analytical challenge for isomer-selective mass spectrometry imaging (iMSI). Herein, we report a straightforward yet powerful strategy to enhance the efficiency of singlet oxygen (¹O₂) reactions used for iMSI of lipids by extending the ¹O₂ lifetime using deuterated solvents. Replacing the conventional 9:1 (v/v) MeOH/H₂O nanospray desorption electrospray ionization (nano-DESI) solvent with its deuterated counterpart, CD₃OD/D₂O, enhances the efficiency of lipid hydroperoxide (LOOH) formation by at least a factor of two. The resulting increase in signals of diagnostic fragments of LOOHs enhances sensitivity of nano-DESI iMSI for fatty acids and both mono- and polyunsaturated lipid species. Using this optimized solvent system, we achieved a deeper molecular coverage of isomeric lipids in nano-DESI iMSI of mouse brain tissue, enabling the detection and spatial mapping of lipid isomers previously undetectable with MeOH/H₂O. Overall, the use of deuterated solvents is a practical and broadly applicable strategy for enhancing the sensitivity and coverage of photochemical derivatization-based nano-DESI iMSI, which will offer new insights into lipid structure and spatial distribution in complex biological systems.