Live single‐cell video‐mass spectrometry for cellular and subcellular molecular detection and cell classification

The molecular content from the cytoplasm of a live, single mammalian cell and its organelle were trapped with a nano‐electrospray ionization (ESI) tip acting as a micropipette under a video microscope, and hundreds of small molecular peaks were detected by direct nano‐ESI mass spectrometry (MS). Granule‐ or cytoplasm‐specific peaks in a mast cell (RBL 2H3) model were extracted by paired t ‐test to demonstrate their specific localization. Some of the typical and specific molecules were successfully identified by MS/MS analysis. This method was also applied to the cell classification of seven types of cell lines at the single‐cellular level by principal component analysis (PCA), revealing seven clusters in the multivariate score plot.