Phytic acid functionalized magnetic bimetallic metal-organic frameworks for phosphopeptide enrichment.

Highly specific enrichment of phosphopeptides from complex biological samples was a precondition for further studying its physiological and pathological processes due to the important and trace amounts of phosphopeptides. In this work, phytic acid (PA) functionalized magnetic cerium and zirconium bimetallic metal–organic framework nanocomposites (denoted as Fe3O4@SiO2@Ce–Zr-MOF@PA) were fabricated by a facile yet efficient method. The as-prepared nanomaterial exhibited high sensitivity (0.1 fmol μL−1), high selectivity toward phosphopeptides from β-casein tryptic digests/BSA (1 : 800), and good reusability of five cycles for enriching phosphopeptides. This affinity probe was applied to biological samples, and 19, 4 and 15 phosphopeptides were identified from non-fat milk, human serum and human saliva, respectively. The above marked advantages are attributed to the strong affinity of the abundant Ce–O and Zr–O nanoclusters on the surface of the MOF shell with the improved hydrophilicity from a great number of phosphate groups. Therefore, the novel Fe3O4@SiO2@Ce–Zr-MOF@PA nanospheres could not only enrich phosphopeptides effectively, but also reduce the adsorption of phosphopeptides, manifesting great potential in the identification and further analysis of low abundance phosphopeptides in complex biological samples.