Fig. 1: Comparison of conventional electrospray ion source with nanopore ion source.
From: Nanopore ion sources deliver individual ions of amino acids and peptides directly into high vacuum
a Schematic of conventional electrospray ionization highlighting the background gas that stimulates evaporation of solvent from droplets, as well as the transfer capillary where significant ion loss occurs. P represents pressure. b Schematic of a nanopore ion source showing the liquid-filled nanopipette tip, the extractor electrode, and the extraction voltage VE applied between them. Inset shows an scanning electron microscopy image of the tip of a pulled quartz nanopipette with a tip ID of 30 nm. c Schematic of the mass spectrometer used in this study. Ion optics comprising an extractor electrode and an Einzel lens extract ions from the liquid meniscus at the ion source and focus them through a quadrupole mass filter and an electrostatic ion bender. The transmitted ions strike a channel electron multiplier detector which is sensitive to single ions. d Mass spectrum of 100 mM arginine in aqueous solution obtained with a 41 nm ID nanopore ion source in our quadrupole mass spectrometer. Peaks are labeled as Arg+(H2O)n, where Arg+ represents protonated arginine [Arg + H]+, and n denotes the number of attached water molecules. Source data are provided as a Source Data file.
