TiO2-modified fibrous core-shell mesoporous material to selectively enrich endogenous phosphopeptides with proteins exclusion prior to CE-MS analysis

As an important post-translational modification of proteins, phosphorylation plays a key role in regulating a variety of complicated biological reactions. Owing to the fact that phosphopeptides are low abundant and the ionization efficiency could be suppressed in mass spectroscopic detection, highly efficient and selective enrichment methods are essential to identify protein phosphorylation by mass spectrometry. Here, we develop novel titanium oxide coated core shell mesoporous silica (CSMS@TiO 2 ) nanocomposites for enrichment of phosphopeptides with simultaneous exclusion of massive proteins. The CSMS@TiO 2 nanocomposites have essential features, including uniform 1.0 μm diameter, 120 nm thick shell, 7.0 nm mesopores perpendicular to the surface, large surface area of 77 m 2 /g and pore volume of 0.15 cm 3 /g, therefore can greatly improve the sensitivity for identifying phosphopeptides by capillary electrophoresis-mass spectrometry. The proposed CSMS@TiO 2 nanocomposites are applied for analysis of β-casein tryptic digest and bovine serum albumin (BSA) protein mixture, respectively. The results show that the number of phosphopeptides detected is tremendously increased by using CSMS@TiO 2 nanocomposite, proving selectively enriching phosphopeptides due to the size-exclusive and specific interaction of the TiO 2 -modified mesopores. The enrichment of the phosphopeptides is achieved even for the digests at very low concentration of β-casein (1 fmol/μL). This research would open up a promising idea to utilize mesoporous materials in peptidomics analysis.