Trapping performance of Fe3O4 @ Al2O3 and Fe3O4 @ TiO2 magnetic nanoparticles in the selective enrichment of phosphopeptides from human serum

Abstract

We have previously demonstrated that both alumina-coated iron oxide magnetic nanoparticles (Fe3O4 @ Al2O3) and titania-coated iron oxide magnetic nanoparticles (Fe3O4 @ TiO2) are effective affinity probes for phosphopeptides from the tryptic digests of phosphoproteins. The major advantage of these two types of affinity probe is the ease of isolating the affinity probe-target species conjugates from complex samples based on their magnetic property. Only a short time is required to enrich phosphorylated species in sufficient amounts for MALDI MS analysis by vigorously mixing the suspension of the sample and affinity nanoparticles through pipeting in and out of a sample vial for 30 sec. We herein evaluate the trapping performance of Fe3O4 @ Al2O3 and Fe3O4 @ TiO2 magnetic nanoparticles as the affinity probes to selectively enrich phosphopeptides from human serum under the same experimental condition. The peaks derived from fibrinopeptide A containing a phosphorylated serine dominate the matrix-assisted laser desorption/ionization (MALDI) mass spectra of the sample obtained after using the affinity probes to selectively enrich their target species from human serum. Furthermore, only phosphorylated fibrinopeptide A residues, which appeared in the MALDI mass spectrum, as Fe3O4 @ Al2O3 magnetic nanoparticles are employed as the affinity probes for the serum sample. However, non-phosphopeptides also appear in the MALDI mass spectrum when using Fe3O4 @ TiO2 magnetic nanoparticles as the affinity probes for the same serum sample. The results suggest that the specificity of Fe3O4 @ Al2O3 magnetic nanoparticles for phosphopeptide is superior to that of Fe3O4 @ TiO2 magnetic nanoparticles.