Browsing by Subject "Gold Nanoparticles"
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Item Development of and Application of Plasmonic Nanomaterials for Mass Spectrometry Based Biosensing(2014-05-05) Gamez, RobertoThe use of nanomaterials for sensing and biological applications has recently gained interest owing to the unique physical, chemical and optical properties that arise when materials are reduced to the nanoscale. The unique optical properties exhibited by gold (Au) and silver (Ag) nanomaterials have made for versatile platforms in a wide range of applications including surface plasmon biosensing techniques and laser desorption/ionization mass spectrometry (LDI-MS). A primary driver for this work is the relative ease performing surface modifications to nanoparticles (NPs), which can be used to enhance the selectivity of ionization and/or facilitate analyte capture. The research presented here focuses on the development of AuNP and AgNP based biosensors for selective capture and ionization of low abundance compounds from complex mixtures and subsequent detection by LDI-MS and Matrix Assisted Laser Desorption Ionization- Mass Spectrometry (MALDI-MS). First, a ?strategy? for selective capture and ionization of specific compound classes based on chemical derivatization of gold nanorods (AuNRs) and infrared laser desorption ionization (IR-LDI) is described. LDI is performed at near infrared wavelengths (1064 nm) that overlap with the longitudinal surface plasmon resonance (LSPR) mode of AuNRs which allows absorbed energy from the laser to facilitate the desorption and ionization of the analyte. Capture of hydrophobic species using surfactant coated AuNRs and subsequent detection by IR-LDI-MS was also demonstrated in these experiments. Second, the fabrication of a label-free MS and optical detection based biosensor platform consisting of a phospholipid layer partially tethered to the surface of a gold nanorod for the detection of low abundance lipophilic analytes from complex mixtures is described. In these experiments, stable phospholipid capped AuNRs are produced by tethering some of the phospholipids to the surface of the AuNRs though a covalent, gold-thiol linkage. The effectiveness of the biosensor is demonstrated for the label-free detection of a membrane active lipophilic drug from aqueous solution and of a lipopeptide from fetal bovine serum. Lastly, porous AgNP embedded thin films were fabricated by the sol-gel method and utilized as matrix-free LDI-MS biosensors applicable to several chemical classes. In these experiments, UV laser irradiation (337 nm) of the AgNP facilitates desorption and ionization of a number of peptides, triglycerides, and phospholipids. Preferential ionization of sterols from vesicles composed of olefinic phosphosphatidylcholines is also demonstrated.Item Explorations of Functionalized Gold Nanoparticle Surface Chemistry for Laser Desorption Ionization Mass Spectrometry Applications(2012-07-11) Gomez Hernandez, Mario 1980-Functionalized nanoparticles provide a wide range of potential applications for Biological Mass Spectrometry (MS). Particularly, we have studied the effects of chromophore activity on the performance of gold nanoparticles (AuNPs) capped with substituted azo (-N=N-) dyes for analyte ion production in Laser Desorption Ionization Mass Spectrometry (LDI-MS) conditions. A series of aromatic thiol compounds were used as Self-Assembled Monolayers (SAM) to functionalize the surface of the AuNPs. Results indicate that AuNPs functionalized with molecules having an active azo chromophore provide enhanced analyte ion yields than the nanoparticles capped with the hydrazino analogs or simple substituted aromatic thiols. We have also conducted experiments using the azo SAM molecules on 2, 5, 20, 30, and 50 nm AuNPs exploring the changes of Relative Ion Yield (RIY) with increased AuNP diameters. Our results indicate that the role of the SAM to drive energy deposition decreases as the size of the AuNP increases. It was determined that 5 nm is the optimum size to exploit the benefits of the SAM on the ionization and selectivity of the AuNPs.Item Size-selected 2, 5, and 10 nm gold nanoparticles for laser desorption/ionization mass spectrometry(2009-05-15) Stumpo, Katherine AnneThe 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.