Analysis of biological molecules on surfaces using stimulated desorption photoionization mass spectrometry

Mass spectrometry plays a pivotal role in the rapid advances of analytical and biological sciences. Improvements in sample preparation, instrumentation, desorption, and ionization methods are highly beneficial to the developments of mass spectrometric techniques for high-throughput analysis of biological molecules in complex systems.; Surface-assisted laser desorption/ionization mass spectrometry (SALDI MS) is a novel technique for direct analysis of organic and biological molecules. In this matrix-free method, specific surfaces are selected to trap analytes and to assist/enhance the laser desorption/ionization process. Amino acids, dipeptides, and organoselenium compounds were successfully detected by SALDI on carbon and silicon surfaces. Surface effects, solvent effects, temperature effects and pH effects were studied. A possible mechanism of SALDI is proposed based on observed results.; In general, stimulated desorption results in neutral yields that are much larger than ion yields. Thus, we have exploited and further developed laser desorption single photon ionization mass spectrometry (LD/SPI MS) as a means of examining biomolecules. LD/SPI MS uses one laser to desorb intact neutral molecules from the sample surface and another vacuum ultraviolet (VUV) laser to ionize the desorbed neutral molecules. The experimental results clearly demonstrate that LD/SPI MS is a very useful and fast analysis method with uniform selectivity and high sensitivity.; Selenium (Se) is an essential ultra-trace element in the human body. Se metabolites, especially organoselenium compounds, have been linked to toxicity, antioxidant enzymes, endocrine processes, and proper functioning of the immune system. In efforts to obtain more useful information of Se-containing metabolites in human urine, exact mass determination of unknown organoselenium compounds in biological matrices using SALDI MS was investigated. In another approach, several selenium metabolites in human urine were successfully detected by LD/SPI MS. A HPLC-MS/MS method was also developed for a quantitative case study of selenium metabolites in human urine after ingestion of selenomethionine.; Low-energy electrons (LEE, 3-20 eV) have been shown to induce single and double strand breaks (SSB and DSB) in plasmid DNA. LEE-induced DNA strand breaks were related to the formation and decay of transient negative ion (TNI) states localized on various components of DNA (i.e. bases, phosphates, deoxyribose, hydration water, etc). To understand the genotoxic effects due to secondary species of high-energy radiation, we investigate the role of TNIs and the specificity in LEE-DNA damage by examining the neutral product yields using low electron stimulated dissociation SPI MS. The neutral yields as a function of incident electron energy are then correlated with the SSBs and DSBs measured using post-irradiation gel electrophoresis. The results provide further insight concerning the mechanisms of LEE-induced damage to DNA.; Overall, this research provided an in-depth understanding of non-thermal surface processes and the development of new mass spectrometric techniques for the analysis of biomolecules. It demonstrated that SD/PI MS is a uniquely advantageous tool for direct analysis of small molecules in complex biochemical systems and electron induced damage on large biological molecules. Furthermore, LD/SPI MS shows great potential for future work in the analysis of metabolites, drug discovery, and biomarker imaging.