Direct Oligosaccharide Profiling Using Thin-Layer Chromatography Coupled with Ionic Liquid-Stabilized Nanomatrix-Assisted Laser Desorption-Ionization Mass Spectrometry

The in-depth characterization of glycan structures is crucial to understanding their structure–function relationships and their effects on health and various diseases. Despite advances in rapid analysis, the utility of matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS) is limited for complex mixtures of carbohydrates due to their low ionization efficiency and the difficulty in separating oligosaccharides because of their high structural similarity. In this study, we developed an ionic liquid (IL)-stabilized, nanomatrix-decorated, thin-layer chromatography (TLC)-MALDI MS method for simultaneous and rapid separation, detection, and identification of oligosaccharides to achieve efficient profiling. The IL demonstrated good dispersion and stabilization for the spin coating of dihydroxybenzoic acid-functionalized magnetic nanoparticles (DHB@MNPs) on the TLC plate with spot homogeneity, which contributed to the observed high reproducibility (<20% CV) and 12- and 28-fold signal enhancement. Although the TLC was not able to separate isomeric glycans, the DHB@MNPs generate diagnostic glycosidic and cross-ring cleavage ions, enabling on-spot structural elucidation of composition, sequence, branching, and linkage of glycans in each separated spot. Without chemical derivatization of glycan samples, glycan visualization by TLC and tandem MS, our integrated platform, allowed the identification of 25 oligosaccharides from human milk, and heatmap analysis revealed the variability in the oligosaccharide abundance in samples from individual donors at different lactation times, which may provide insight into the microbiota and immunity of infants. With the demonstrated simplicity of our sample preparation method along with the achieved separation and in-depth structural characterization, our approach can be used for the rapid screening of other oligosaccharide-rich samples.