The analytical utility of gold nanoparticles (AuNPs) for laser
desorption/ionization mass spectrometry (LDI-MS) is examined here. An evaluation of
the parameters that affect desorption/ionization show that careful treatments of AuNPs is
needed, as subtle changes in the solution environment can result in subsequent changes
in the mass spectra. A thorough evaluation of the parameters that affect
desorption/ionization of peptides is presented here, and these parameters include: (i)
AuNP-to-analyte ratio, (ii) AuNP size, (iii) solvent, (iv) AuNP surface composition, (v)
pH and buffer effects, (vi) amino acid sequence, and (vii) additives such as fructose or
glycerol. Specifically, controlling the AuNP-to-analyte ratio, pH, peptide composition,
and AuNP size are important parameters for ionization. Additionally, effects of
passivating the AuNP surface with halides or oxyanions was investigated. The presence
of NaF, NaCl, NaBr, and NH4X (X = F, Cl, Br, I) were shown to not significantly affect
analyte ion abundances, whereas addition of NaI strongly suppressed analyte ion yields.
Further physical characterization of the NPs showed that etching had occurred, which
suggests that the surface chemistry of the NPs is important for desorption/ionization. Throughout these investigations, questions remain as to what the internal energies of
peptides are after the desorption/ionization event, and how energy is deposited. Peptide
ion fragmentation is examined under different solution conditions to evaluate the relative
internal energies of peptides, and the fragmentation pattern examined for insight into
fragmentation mechanisms. The data suggest that radical species are important for
fragmentation of peptides when using AuNPs. However, it is likely that multiple
processes are actually directing the fragmentation. Finally, based on the data presented
in this dissertation, a thermal desorption mechanism of pre-formed ions is proposed.
This fundamental research is intended to lay foundations for optimizing the use of
nanoparticles in routine LDI-MS analysis as well as giving insight into nanoparticle
ionization mechanisms. Since very little work has been done in this area, this dissertation
investigates, in detail, many of the subtle characteristics that affect desorption/ionization
of biomolecules when using NPs.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-3127 |
| Date | 15 May 2009 |
| Creators | Stumpo, Katherine Anne |
| Contributors | Russell, David H. |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | electronic, application/pdf, born digital |
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