Mass spectrometry imaging of small molecule in situ in Lepidium meyenii (Maca) using gold nanoparticles matrix

Lepidium meyenii Walp. (Maca), a functional food, has been used as a drug and food in Peru for more than two thousand years because Maca is rich in nutrition and rational in nutritional structure. Due to their uniform size and little interference in the low molecular weight region, Au nanoparticles (AuNPs) have been applied as a matrix to analyze the components of Maca extract and to visualize them of fresh root tissue in situ by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). The result shows that imidazole alkaloids including Lepidiline A (1,3-dibenzyl-4,5-dimethylimidazolium chloride), Lepidiline B (1,3-dibenzyl-2,4,5-trimethylimidazolium chloride), Lepidiline C (3-benzyl-1-(3-methoxybenzyl)-4,5-dimethylimidazolium chloride), Lepidiline D (3-benzyl-1-(3-methoxybenzyl)-2,4,5-trimethylimidazolium chloride), 1, 3-dibenzyl-2-pentyl-4,5-dimethylimidazilium and 1, 3-dibenzyl-2-phenyl-4,5-dimethylimidazilium are the products of Maca after drying proess. Additionally, the distribution of amino acids, amide alkaloids, imidazolium alkaloids and saccharide in the upper, middle, and lower parts of Maca root tissue can be clearly visualized in situ with the synthesized AuNPs matrix by MALDI mass spectrometry imaging (MSI). The report provides a meaningful reference to study active components from natural product in situ.