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Description:
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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 . |