Development of and Application of Plasmonic Nanomaterials for Mass Spectrometry Based Biosensing
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The 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.