We are developing a single molecule protein sequencing technology that aims to combine the advantages of mass spectrometry with those of nanopores. The basic idea is to cleave the individual amino acids from a protein molecule as they transit a small hole in sequence and then identify each one by determining its mass-to-charge ratio in a mass spectrometer. This talk will focus on a step toward that goal. I will describe a nanopore ion source for mass spectrometry that delivers ions directly into high vacuum from aqueous solutions. Ions escape a nanoscale, electrified meniscus by ion evaporation and travel along collisionless trajectories to the ion detector. We measure mass spectra of 16 different amino acid ions as well as post-translationally modified variants of glutathione in unsolvated states using the nanopore ion source. The current emitted by the nanopore source is composed of ions rather than charged droplets, and the majority of the current can be recovered in a distant collector. The nanopore ion source could enable more sensitive proteomic analyses. It circumvents the sample loss mechanisms inherent to conventional electrospray ionization (ESI), where charged droplets are sprayed into a background gas that scatters ions and degrades their transmission.
