Direct Analysis of Micro-biopsy Samples by Polarity Gradient Focusing Dip-and-Go Mass Spectrometry

Abstract

Direct analysis of micro-biopsy samples by mass spectrometry at single-cell level still faces major challenges. In this work, we developed a polarity gradient focusing dip-and-go strategy (PGF-Dip&Go) during induced electrospray ionization mass spectrometry (iESI-MS) analysis for real-time enrichment and spatial separation of compounds such as lipids, alkaloids, fatty amines, and drugs. Compared with direct iESI-MS analysis, enrichment of analytes (enrichment factor of 5.0−100.0) and spatial separation between different analytes were achieved. Owing to the enrichment effect and salt cleanup effect, the sensitivity of PGF-Dip&Go has been improved by 25−10,000 times compared with direct iESI-MS. PGF-Dip&Go has been successfully applied for the analysis of lipids in a 200 pL micro-biopsy section from an individual fish egg. Lysophosphatidylcholine (LPC), phosphatidylcholine (PC), and triglyceride (TG) were significantly enriched and separated according to their polarity differences, proving the potential of PGF-Dip&Go to be a noninvasive and powerful analytical tool for in situ analysis of complex small volumes in the future.

Familiarize Students with Direct MS Analysis Methods: Localization of Components in Citrus Peel by Induced Electrospray Ionization

“…to directly sample nanoliter extracts (freehand sampling) from either oil glands or the flavedo for MS analysis. The DC-iESI method used in this course was a robust method previously developed by us for single cell analysis in 2015. − It can ionize analytes without direct contact between the electrode and the sample solution (Figure S1 and Figure S2), which is suitable for the analysis of volume-limited samples in a safe way. The mass spectra obtained by DC-iESI could tell the difference of compounds between two microregions.…”