Description
- Abstract:
- My research is motivated by an idea for a new method of sequencing individual biopolymers, including proteins and nucleic acids, that combines mass spectrometry with nanopores. The basic idea is to take advantage of a mass spectrometer’s ability to identify monomers by their mass, paired with a nanopore’s ability to force biopolymers into a linear configuration so that their monomers are delivered into the mass spectrometer in sequence. I address two major challenges for such a method to succeed. First, monomers must be ionized and transferred to the gas phase, necessary for mass analysis. Second, before monomers are transferred into vacuum, but after they are cleaved in solution from their parent polymer, they undergo random thermal motion which tends to randomize their sequential order. This order between neighboring monomers must be preserved between when they are cleaved and when they exit into this charged gas phase. If a strong electric field is applied to the liquid surface at the tip of a solution filled needle-like capillary, it will emit a spray of ions through a process known as electrospray. Ions emitted in this spray can leave the liquid surface in two main ways. They can leave inside large multiply charged liquid drops usually on the order of 100's nm in diameter, or they can leave the surface individually as partially solvated ions, called ion clusters. Since monomer ions trapped in drops would prevent us from obtaining sequence information, I conducted experiments on a version of electrospray known as ion evaporation in which ion clusters in solution are emitted directly from the electrospray capillary’s liquid surface. I have helped to build and test a machine capable of investigating this mechanism of ion production from electrospray using capillaries with nanoscale tip openings. I present measurements of the voltages necessary to produce electrospray for capillaries in this nanoscale regime. Generally, the electrospray is composed of both ion clusters and charged droplets, and the latter must be suppressed for the success of this sequencing strategy. I compare the number of ion clusters that reach our mass spectrometer with the total number of ions leaving our nanocapillaries to explore the conditions under which ion cluster production is favored over drop formation. Finally, I present a simplified one dimensional model of the dynamics of Brownian particles in the electric fields at the tips of these electrospraying capillaries to estimate the conditions under which sequential information is preserved.
- Notes:
- Thesis (Ph. D.)--Brown University, 2018
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Citation
Maulbetsch, William,
"Nanopore Mass Spectrometry"
(2018).
Physics Theses and Dissertations.
Brown Digital Repository. Brown University Library.
https://doi.org/10.26300/06sw-2s29
