Simple fabrication of hydrophobic surface target for increased sensitivity and homogeneity in matrix-assisted laser desorption/ionization time-of-flight mass spectrometry analysis of peptides, phosphopeptides, carbohydrates and proteins.

To enhance sample signals and improve homogeneity in matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF) analysis, a simple, rapid, and efficient sample preparation method was developed in this study. Polydimethylsiloxane (PDMS) was coated on a stainless steel MALDI plate, forming a transparent, hydrophobic surface that enhanced sample signals without producing observable background signals. Compared to the use of an unmodified commercial metal MALDI plate, peptide signals were enhanced by ~7.1-11.0-fold due to the reduced sample spot area of the PDMS-coated plate, and showed improved peptide mass fingerprinting (PMF) and MS/MS peptide sequencing results. In the analysis of phosphopeptides and carbohydrates with a 2,5-dihydroxybenzoic acid (DHB) matrix, the PDMS-coated plate showed improved sample homogeneity and signal enhancements of ~5.2-8.2-fold and ~2.8-3.2-fold, respectively. Improved sensitivity in the observation of more unique fragment ions by MS/MS analysis, to successfully distinguish isomeric carbohydrates, was also illustrated. In protein analysis with a sinapinic acid (SA) matrix, a ~3.4-fold signal enhancement was observed. The PDMS film coating was easily removed and refabricated to avoid sample carryover, and was applicable to diverse commercial MALDI plates. The PDMS-coated approach is a simple, practical, and attractive method for enhancing analyte signals and homogeneity.