Author ORCID Identifier

https://orcid.org/0000-0003-3000-4195

Semester

Spring

Date of Graduation

2025

Document Type

Dissertation (Campus Access)

Degree Type

PhD

College

Eberly College of Arts and Sciences

Department

Physics and Astronomy

Committee Chair

Matthew Johnson

Committee Co-Chair

Stephen Valentine

Committee Member

Stephen Valentine

Committee Member

Alan Bristow

Committee Member

Tudor Stanescu

Committee Member

Raymond Raylman

Abstract

Abstract

Native Mass Spectrometry using Capillary Vibrating Sharp-Edge Spray Ionization and Surface Analysis on Thin Films used in Superconducting Detectors

Vikum Kanishka Dewasurendra

My thesis is made up of two projects. The main project involves using a novel native mass spectrometry (MS) source to investigate biomacromolecules, including proteins and DNA. A smaller project involves x-ray photoelectron spectroscopy (XPS) to analyze superconducting thin films in NASA’s microwave kinetic inductance detectors (MKID) used for far infrared imaging.

In native mass spectrometry, a gentle ion source takes large biomacromolecules in solution and transfers them to the gas phase, preserving their native state. Once in the gas phase, such large molecules can be mass analyzed using MS-based techniques to characterize conformational features and even break apart the biomacromolecule to determine its underlying structure. We collaborated with Profs. Valentine and Li (Chemistry, WVU) to better understand their novel capillary Vibrating Sharp-edge Spray Ionization (cVSSI) source. These sources use an ultrasonically vibrating capillary tip to directly nebulize a solution into a cloud of droplets. This work began by measuring droplet diameters from cVSSI sources, including under conditions where a bias voltage was applied between the solution in the capillary and the MS inlet. We measured droplet diameters in the range of 25 µm that decreased slightly with increased bias voltage and even more so by increasing the capillary vibration amplitude. Through measurements of the electric current carried by the nebulized droplets, we found that the droplet current at high +ve bias voltage was +ve, as expected, but surprisingly at low +ve bias it was –ve. Based on this unexpected result, we were able to propose different pathways from initial (large) droplets, final progeny droplets to charged gas-phase macromolecules. Applying this to MS studies of the protein ubiquitin under +ve applied bias voltage, we were able to understand why we observe bimodal charge state distributions (CSDs), especially at low voltage and identify low charge states (2+ to 6+) as native-like conformer and high charge states >6+ as extended conformer ensembles. Our studies show that cVSSI can maintain native conformers and due to its tunability, we can reproducibly access multiple conformations. For our work on Triplex DNA, we started by optimizing the cVSSI source parameters (bias voltage and inlet temperature) to maximize the Triplex ion current. Then we developed tools to identify fragmentation patterns associated with the Triplex, and Triplex Forming Oligonucleotide (TFO) to better understand the fragmentation processes.

The NASA collaboration involves using XPS to investigate surface and buried interface oxide layers associated with the superconductor thin films used in MKIDs for far-infrared detectors. XPS, with its chemical sensitivity, is well suited to investigating surface oxides, however, for buried interfaces, sputter depth profiling is required, and sputtering alters chemistry so that firm conclusions are difficult. In this thesis, I present challenges and strategies developed to overcome them.

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