Development of core-shell structure Fe3O4@Ta2O5 microspheres for selective enrichment of phosphopeptides for mass spectrometry analysis. 
Protein phosphorylation is one of the most important post-translational modifications.  Due to the dynamic nature and low stoichiometry of the protein phosphorylation, enrichment of phosphopeptides from proteolytic mixtures is often necessary prior to their characterization by mass spectrometry.  Many metal oxides such as titanium dioxide and zirconium dioxide have been successfully applied to isolation and enrichment of phosphopeptides.  Recently, niobium pentoxide was proved to have the ability for selective enrichment of phosphopeptides.  Considering the proximity of tantalum to niobium, we supposed that Ta(2)O(5) can be used as affinity probes for phosphopeptide enrichment.  In the work, we synthesized Fe(3)O(4)@Ta(2)O(5) magnetic microspheres with core-shell structure for selective enrichment of phosphopeptides.  To demonstrate its ability for selective enrichment of phosphopeptides, we applied Fe(3)O(4)@Ta(2)O(5) magnetic microspheres to isolation and enrichment of the phosphopeptides from tryptic digestion of standard proteins and real samples, and then the enriched peptides were analyzed by matrix-assisted laser desorption mass spectrometry analysis (MALDI-MS) or liquid chromatography coupled to electrospray ionization mass spectrometry (LC-ESI-MS).  Experiment results demonstrate that Ta(2)O(5) coated-magnetic microspheres show the excellent potential for selective enrichment of phosphopeptides.