Surface-Assisted Laser Desorption/Ionization-Mass Spectrometry (SALDI-MS) of Controlled Nanofeatures and the Associated Thermal Properties

Abstract

Surface-Assisted Laser Desorption/Ionization-Mass Spectrometry (SALDI-MS) utilizes a solid surface as an energy transfer medium for desorption/ionization. The purpose of this research was to generate controlled feature size and distribution so that the proposed mechanisms of desorption/ionization could each be studied in turn. The thermal contribution to desorption/ionization and how it relates to MS response was studied in this segment.

In this study, substrates with feature changes from 20 to 60 percent porosity. Peptides, sugars and low molecular weight proteins are used to determine MS performance of the substrates. Pore size and distribution of 100 nm each on Si (0.002-0.005 Ohm/cm) shows the best SALDI-MS signal/noise among those tested. The thermal properties of the substrates were evaluated using thermography in which the temperature changes from different substrates under the same conditions were measured. This measured temperature change was found to be directly related to substrate porosity and MS response. These results confirmed our hypothesis that SALDI-MS is thermally induced and that the increased density of pores on the surface aid in the thermal desorption of the analyte.

The optimized substrate generated was used to profile metabolites in a complex biological plant system. Arabidopsis thaliana was transgenically modified with a human inositol 5 phosphatase enzyme and used as a model to test SALDI-MS performance. The small molecules commonly found in the SALDI-MS data include amino acids, organic acids and steroids. Simple sugars required derivatization to increase ionization efficiency. Suppression effects did not allow for the observation of sugar alcohols, even after derivatization.