Iron Oxide/Niobium Oxide Core–Shell Magnetic Nanoparticle-Based Phosphopeptide Enrichment from Biological Samples for MALDI MS Analysis

The feasibility of using niobium oxide-coated magnetic nanoparticles (NPs) as affinity probes for selectively trapping phosphopeptides from peptide mixtures including tryptic digest of caseins, serum, and cell lysate was demonstrated in this study. Phosphopeptide enrichment was rapid when subjecting these systems to microwave heating for 1 min; the probe-target species, which were readily isolated through magnetic separation, were then analyzed using matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS). Only signals for phosphopeptides were present in the resulting mass spectra. The detection limit for monophosphopeptide was as low as 5 fmol.