Molecular Mapping of Neutral Lipids Using Silicon Nanopost Arrays and TIMS Imaging Mass Spectrometry

Abstract

We demonstrate the utility of combining silicon nanopost arrays (NAPA) and trapped ion mobility imaging mass spectrometry (TIMS IMS) for high spatial resolution and specificity mapping of neutral lipid classes in tissue. Ionization of neutral lipid species such as triglycerides (TGs), cholestryl esters (CEs), and hexosylceramides (HexCers) from biological tissues has remained a challenge for imaging applications. NAPA, a matrix-free laser desorption ionization substrate, provides enhanced ionization efficiency for the above-mentioned neutral lipid species, providing complementary lipid coverage to matrix-assisted laser desorption ionization (MALDI). The combination of NAPA and TIMS IMS enables imaging of neutral lipid species at 20 μm spatial resolution while also increasing molecular coverage greater than 2-fold using gas-phase ion mobility separations. This is a significant improvement with respect to sensitivity, specificity, and spatial resolution compared to previously reported imaging studies using NAPA alone. Improved specificity for neutral lipid analysis using TIMS IMS was shown using rat kidney tissue to separate TGs, CEs, HexCers, and phospholipids into distinct ion mobility trendlines. Further, this technology allowed for the separation of isomeric species, including mobility resolved isomers of Cer­(d42:2) (m/z 686.585) with distinct spatial localizations measured in rat kidney tissue section.

Atmospheric-Pressure Infrared Laser-Ablation Plasma-Postionization Mass Spectrometry Imaging of Formalin-Fixed Paraffin-Embedded (FFPE) and Fresh-Frozen Tissue Sections with No Sample Preparation

“…Encouragingly, given the very different sample processing steps applied to FFPE tissue compared to FF, those ions with shared matched identities also show similar spatial distributions, either between FFPE and FF (G/H, I/J), positive and negative ion (E/F, K/L), or across all four (M–P). Several interesting spatial distributions are also observed here including image D, where a distribution in the pelvic region (or local adipose tissue) and parts of the capsule are seen, in common with a similar recently published TG distribution in MALDI MSI …”

“…Several interesting spatial distributions are also observed here including image D, where a distribution in the pelvic region (or local adipose tissue) and parts of the capsule are seen, in common with a similar recently published TG distribution in MALDI MSI. 28 …”

“…Several interesting spatial distributions are also observed here including image D, where a distribution in the pelvic region (or local adipose tissue) and parts of the capsule are seen, in common with a similar recently published TG distribution in MALDI MSI. 28 The study presented here goes beyond previous approaches for the analysis of FFPE tissue removing the need for all sample pretreatment when analyzing FFPE tissues. This approach enables the detection and imaging of a broad range of low mass metabolite and lipid species to complement more common approaches such as UV-MALDI and DESI MSI.…”

Ion Mobility Mass Spectrometry for the Separation and Characterization of Small Molecules

“…228 The type of matrix has a significant effect on the ionization of compounds in MALDI, and a silicon nanopost array matrix can significantly improve the ionization efficiency of neutral lipids. 229 In addition, a laser-based post-ionization strategy called MALDI-2 can also improve sensitivity, and the output of ions can be increased by 2−3 orders of magnitude. 224 Bien et al 202 used MALDI-2-TIMS-MSI to map the spatial distribu- tion of more than 30 different sterol species in different parts of the symbiotic system.…”

Analysis of Immunogenic Galactose-α-1,3-galactose-Containing N-Glycans in Beef, Mutton, and Pork Tenderloin by Combining Matrix-Assisted Laser Desorption/Ionization-Mass Spectroscopy and Capillary Electrophoresis Hyphenated with Mass Spectrometry via Electrospray Ionization

“…26,27 Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) allows one to address this by generating two-dimensional illustrations of selected analytes by scanning the surface of biological samples (Figure 1b). 28−30 This methodology is generally used to detect analytes such as proteins, 31 peptides, 32 lipids, 33 and metabolites, 34 but various studies also report on its usage to explore the distribution of the N-glycome. 35−40 While MALDI-MSI has already been applied in food studies, 41,42 this technique has, to the best of our knowledge, not yet been exploited to investigate the N-glycome distribution of various meats.…”