DESI-Enabled Signature-Ion-Guided Natural Product Imaging (DESIGNi) for Rapid Screening of Aromatic Acylated Derivatives in Plant Tissues

Mass spectrometry imaging (MSI) enables in situ visualization of small-molecule distributions in plants. However, MSI data interpretation often relies on extensive prior chemical knowledge, limiting the rapid screening of specific compound classes. Furthermore, structural analysis via LC/MS typically depends on tandem mass spectrometry, which is not routinely integrated into standard MSI workflows. To address this, we established a desorption electrospray ionization (DESI)-enabled, signature-ion-guided natural product imaging (DESIGNi) method. By acquiring high-resolution fragment ion data using a multi-reflecting time-of-flight (MRT) mass spectrometer, this approach enables rapid visualization of compounds containing specific building blocks based on their diagnostic fragment ions. As a proof of concept, we focused on aromatic acylated derivatives. The method was developed and optimized using the phenylethanoid glycosides in Forsythia fruit, and the accuracy of the resulting distributions was validated by LC/MS. We applied this approach to seven additional medicinal or edible plants and mapped the distribution of phenylethanoid glycosides, phenolic acid oligomers, benzyl ester glycosides, amides, and diarylheptanoids. By tracing signature ions to their corresponding full-scan spectra, MSI enabled the discovery and preliminary identification of rare or potential novel compounds. This study presents a new strategy for rapid visual screening of plant natural products using MSI.