Iron oxide/tantalum oxide core-shell magnetic nanoparticle-based microwave-assisted extraction for phosphopeptide enrichment from complex samples for MALDI MS analysis

A new type of metal-oxide-coated magnetic nanoparticles (NPs)-tantalum-oxide-coated magnetic iron oxide (Fe(3)O(4)@Ta(2)O(5)) NPs-which are used as affinity probes for selectively trapping phosphopeptides from complex samples, is demonstrated in this study. In this approach, phosphopeptide enrichment was achieved by incubating the NPs with sample solutions under microwave heating within 1 min. The NP-target species conjugates were readily isolated from samples by magnetic separation followed by matrix-assisted laser desorption/ionization (MALDI) mass spectrometric analysis. When using human serum as the sample, phosphorylated fibrinopeptide-A-derived ions are the only ions observed in the MALDI mass spectra after enrichment by the Fe(3)O(4)@Ta(2)O(5) NPs. Furthermore, only phosphopeptides appear in the MALDI mass spectra after using the affinity probes to selectively trap target species from the tryptic digest of a cell lysate and milk sample. The results demonstrated that the Fe(3)O(4)@Ta(2)O(5) NPs have the capability of selectively trapping phosphorylated peptides from complex samples. The detection limit of this approach for a phosphopeptide (FQpSEEQQQTEDELQDK) was similar to 10 fmol.