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    LASER ELECTROSPRAY MASS SPECTROMETRY: INSTRUMENTATION AND APPLICATION FOR DIRECT ANALYSIS AND MOLECULAR IMAGING OF BIOLOGICAL TISSUE

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    Genre
    Thesis/Dissertation
    Date
    2017
    Author
    Shi, Fengjian
    Advisor
    Levis, Robert J.
    Committee member
    Levis, Robert J.
    Valentine, Ann M.
    Strongin, Daniel R.
    McEwen, Charles N., 1942-
    Department
    Chemistry
    Subject
    Chemistry, Analytical
    Chemistry, Physical
    Medical Imaging
    Ambient Ionization
    Biological Tissue
    Electrospray Ionization
    Femtosecond Laser Desorption
    Mass Spectrometry
    Mass Spectrometry Imaging
    Permanent link to this record
    http://hdl.handle.net/20.500.12613/2371
    
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    DOI
    http://dx.doi.org/10.34944/dspace/2353
    Abstract
    This dissertation elucidates the instrumentation and application of a hybrid ambient ionization source, laser electrospray mass spectrometry (LEMS), for the direct analysis and molecular imaging of biological tissue without matrix deposition. In LEMS, laser pulses from a Ti:Sapphire laser amplifier (60 fs, 800 nm, and 1 mJ) interact with surface analytes and transfer them from the condensed phase into the gas phase without the requirement of either exogenous matrix or endogenous water in the sample. The laser vaporized analytes are captured and ionized by an electrospray source, and finally detected by a mass analyzer. It was found that a turn-key, robust femtosecond fiber laser with longer wavelength, longer duration, and lower pulse energy at 1042 nm, 425 fs, and 50 µJ, respectively, provided comparable results with the Ti:Sapphire laser. Vaporization of intact, dried or aqueous cytochrome c and lysozyme samples was demonstrated by the fiber laser. A charge states distribution at lower charge states indicating folded conformation of proteins and the hemoglobin α subunit-heme complex from whole blood was observed. Endogenous anthocyanins, sugars, and other metabolites were detected and revealed the anticipated metabolite profile for the flower petal and leaf samples by the fiber laser. Phospholipids, especially phosphatidylcholine, were identified from a fresh mouse brain section sample. These lipid features were suppressed in both the fiber laser and Ti:Sapphire LEMS measurement in the presence of optimal cutting temperature compounds which are commonly used in animal tissue cryosectioning. This dissertation also details the design of an automated mass spectrometry imaging source based on the Ti:Sapphire LEMS. The laser, translation stage, and mass analyzer are synchronized and controlled using a customized user interface to enable step-by-step scanning of the area of interest on a given tissue sample. The imaging source is coupled with a high resolution accurate mass quadrupole time-of-flight (QTOF) mass analyzer with tandem mass analysis capability. A lateral resolution of 60 µm was demonstrated on a patterned ink film by LEMS imaging. Plant metabolites including sugar and anthocyanins were directly imaged from a leaf sample. Small metabolites, lipids and proteins were simultaneously imaged from a single tissue section of a pig liver sample. Biomarkers of blood-brain barrier damage and traumatic brain injury (TBI) that occurred during the injury were detected and imaged from a TBI mouse brain. The loading values from principal component analysis (PCA) were shown to be useful for identification of features of interest from the large LEMS imaging dataset.
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