Impact of Analyte-Surface Spacing on the Performance of Desorption/Ionization on Porous Silicon Mass Spectrometry (DIOS-MS)

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Title: Impact of Analyte-Surface Spacing on the Performance of Desorption/Ionization on Porous Silicon Mass Spectrometry (DIOS-MS)
Author: Shah, Abhilasha Parag
Advisors: Morteza Khaledi , Committee Member
Edmond Bowden, Committee Member
Lin He , Committee Chair
Abstract: Desorption/ionization on porous silicon (DIOS), a matrix free-laser desorption mass spectrometric technique shows potential for direct analysis of biological compounds in the low mass region. However, the geometric scale of the porous silicon is significantly smaller than the biological samples used in MS imaging and suspect to limit an effective direct analysis of analyte. Herein, I have investigated the effect of the spacing distance between analytes and a porous substrate in DIOS-MS. In particular, organic polymer films were used to simulate the biological tissue between analyte and porous substrate. These films circumvent biological complexity that simplifies data analysis. The thicknesses of polymer film on the substrate controlled by varying spin coating condition. Different classes of analytes were used as standard molecules to evaluate the analyte-substrate spacing effect. In all cases, the standard molecules were successfully detected atop of the polymer film in DIOS-MS. The insulating layer of polymer shift the laser threshold compare to bare DIOS. Relatively stable signal-to-background (S/B) ratios across the tested spacing distances suggest that the analyte detection is less dependent of the distance between analyte and porous surface. The total ion current (TIC) of the analytes however, decreases as the distance increases suggesting distance effect on desorption/ionization. Moreover, the TIC was limited by the amount of analyte accessible for detection. In addition, the ultra-thin SiOx film showed improvement in analyte detectability over the tested thickness. Analyte detection on the DIOS surface greatly influence by surface chemical functionality; oxidized surface is advantageous for positive mode detection whereas the amine derivatized surface showed improvement in negative mode detection.
Date: 2009-08-08
Degree: MS
Discipline: Chemistry

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