Existing detectors for time-of-flight (TOF) mass spectrometry of intact proteins in low charge states, such as microchannel plates and electron multipliers, rely upon the emission of secondary electrons for ion detection. Unfortunately, the efficiency of this secondary electron generation falls-off severely with increasing mass of the incident ions, dramatically reducing detection sensitivity and limiting the ability of TOF mass spectrometers to provide useful mass information on large biomolecules. This problem in ion detection is one of the major reasons that biological mass spectrometry as currently practiced is predominantly directed towards the analysis of small peptides rather than towards whole intact proteins, a critical limitation in the technology. We have developed a new type of ion detector to address this problem, based upon the mechanical deformation and vibration of a nanomembrane. An incoming ion packet initiates oscillations of the nanomembrane, which are then detected by corresponding oscillations in field emission electron current from the membrane. We propose here to develop our initial prototype detector into a powerful, robust, and well- characterized device for the mass spectrometry of intact proteins up to a megadalton in size. This new detector technology will open many new opportunities in biological mass spectrometry, in areas such as biomarker discovery and monitoring, the elucidation of protein variation, and the imaging of tissue by MALDI mass spectrometry.

Public Health Relevance

This project seeks to develop a novel detector technology to dramatically improve the mass spectrometric analysis of intact high molecular weight proteins present at low abundance and/or in complex biological samples. Research in areas such as protein variation, biomarker discovery and mass spectrometric imaging will greatly benefit from this technology, opening new possibilities in the diagnosis and treatment of disease.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Research Project (R01)
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Instrumentation and Systems Development Study Section (ISD)
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Sheeley, Douglas
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University of Wisconsin Madison
Schools of Arts and Sciences
United States
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Li, Qiyao; Shortreed, Michael R; Wenger, Craig D et al. (2017) Global Post-Translational Modification Discovery. J Proteome Res 16:1383-1390
Shortreed, Michael R; Frey, Brian L; Scalf, Mark et al. (2016) Elucidating Proteoform Families from Proteoform Intact-Mass and Lysine-Count Measurements. J Proteome Res 15:1213-21
Cesnik, Anthony J; Shortreed, Michael R; Sheynkman, Gloria M et al. (2016) Human Proteomic Variation Revealed by Combining RNA-Seq Proteogenomics and Global Post-Translational Modification (G-PTM) Search Strategy. J Proteome Res 15:800-8
Shortreed, Michael R; Wenger, Craig D; Frey, Brian L et al. (2015) Global Identification of Protein Post-translational Modifications in a Single-Pass Database Search. J Proteome Res 14:4714-20
Liu, Ranran; Li, Qiyao; Smith, Lloyd M (2014) Detection of large ions in time-of-flight mass spectrometry: effects of ion mass and acceleration voltage on microchannel plate detector response. J Am Soc Mass Spectrom 25:1374-83