Smart Hydrophilic Modification of Magnetic Mesoporous Silica with Zwitterionic l-Cysteine for Endogenous Glycopeptides Recognition

There are still few reports about endogenous glycosylated peptides although the significance of the study of them has been confirmed since they may provide higher sensitivity and specificity in clinical practice. In this work, magnetic mesoporous silica microspheres were endowed with strong hydrophilicity by a simple and smart modification way to l-cysteine, which was attributed to the bond formation of Fe–S. The microsphere (denoted as l-Cys-Fe3O4@mSiO2) was composed of Fe3O4 core, mesoporous silica layer, and innumerable perpendicularly aligned mesopores, as well as abundant l-cysteine in the mesopores. Thanks to the excellent hydrophilicity of l-cysteine probe, the l-Cys-Fe3O4@mSiO2 microspheres showed strong recognition ability toward glycopeptides. Owing to the superparamagnetic cores well encapsulated in microspheres, the whole process is quite time-saving by magnetic separation. Also, due to the appropriate pore size of the l-Cys-Fe3O4@mSiO2 microspheres, the extraction method exhibited good size-exclusion effect toward large-sized proteins. Finally, the glycopeptidome analysis method based on the l-Cys-Fe3O4@mSiO2 microspheres was proven to be highly efficient in enriching endogenous glycopeptides in healthy and gastric cancer human saliva directly.