Synthesis of bifunctional TiO2@SiO2-B(OH)2@Fe3O4@TiO2 sandwich-like nanosheets for sequential selective enrichment of phosphopeptides and glycopeptides for mass spectrometric analysis.

In this work, the bifunctional TiO2@SiO2-B(OH)2@Fe3O4@TiO2 sandwich-like nanosheets were designed and synthesized for the sequential selective enrichment of phosphopeptides and glycopeptides. Due to the bifunctional property of the titanium dioxide and the boronic acid group, the nanosheets were successfully applied to the enrichment of phosphopeptides and glycopeptides sequentially, evaluated by capturing phosphopeptides from tryptic digestion of model phosphoprotein bovine β-casein diluted to 0.02 ng/μL (8 × 10(-16) mol/μL) and glycopeptides from tryptic digestion of model glycoprotein horseradish peroxidase (HRP) diluted to 0.1 ng/μL (2.5 × 10(-15) mol/μL). The enrichment selectivity of the bifunctional nanosheets was evaluated by capturing phosphopeptides from a peptide mixture of β-casein and bovine serum albumin (BSA) with the molar ratio of 1:1000 (8.3 × 10(-12) mol of β-casein and 8.3 × 10(-9) mol of BSA in 100 μL) and glycopeptides from a peptide mixture of HRP and BSA up to the ratio of 1:50 (5.0 × 10(-11) mol of HRP and 2.5 × 10(-9) mol of BSA in 100 μL). Graphical Abstract A workflow of the sequential enrichment strategy for phosphopeptides and glycopeptides by the bifunctional TiO2@SiO2-B(OH)2@Fe3O4@TiO2 sandwich-like nanosheets.