On-Plate Desalting and SALDI-MS Analysis of Peptides with Hydrophobic Silicate Nanofilms on a Gold Substrate

Abstract

We report the use of silicate nanofilms for on-plate desalting and subsequently direct laser desorption/ionization-mass spectrometric (LDI-MS) analysis of peptides. A hydrophobic octadecyltrichlorosilane (OTS) monolayer is formed on a calcinated nanofilm on a gold substrate to facilitate sample deposition and interaction with the surface that allows effective removal of MS-incompatible contaminants such as salts and surfactants by simple on-plate washing while the peptides are retained on the spot. By eliminating interferences from matrix-related ions and contaminants, sensitivity of MS analysis has been enhanced over ca. 20 times, leading to improved detection of peptides at the low-fmol level. A high recovery rate of the peptides is obtained by using relatively rough nanofilms, which are prepared through a modified layer-by-layer (LbL)-deposition/calcination process. The performance of the films has been investigated with peptide samples in the presence of high salts (NaCl and sodium acetate) and urea. Compared to MALDI analysis with CHCA-matrix, LDI with on-plate desalting offers marked improvement for analysis of peptides due to low background ions and reduction of sample complexity. Additionally, selective capture of the hydrophobic components of a protein can be achieved, providing a highly useful strategy for specific peptide enrichment. LDI with on-plate desalting approach has also been successfully applied to peptide analysis from protein digests.

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