Facile synthesis of Fe3O4@PDA core-shell microspheres functionalized with various metal ions: A systematic comparison of commonly-used metal ions for IMAC enrichment

Metal ions differed greatly in affinity towards phosphopeptides, and thus it is essential to systematically compare the phosphopeptides enrichment ability of different metal ions usually used in the IMAC techniques. In this work, for the first time, eight metal ions, including Nb5+, Ti4+, Zr4+, Ga3+, Y3+, In3+, Ce4+, Fe3+, were immobilized on the polydopamine (PDA)-coated Fe3O4 (denoted as Fe3O4@PDA-Mn+), and systematically compared by the real biosamples, in addition to standard phosphopeptides. Fe3O4 microspheres were synthesized via the solvothermal reaction, followed by self -polymerization of dopamine on the surface. Then through taking advantage of the hydroxyl and amino group of PDA, the eight metal ions were easily adhered to the surface of Fe3O4@PDA. After characterization, the resultant Fe3O4@PDA-Mn+ microspheres were applied to phosphopeptides enrichment based on the binding affinity between metal ions and phosphopeptides. According to the results, different metal ions presented diverse phosphopeptides enrichment efficiency in terms of selectivity, sensitivity and the enrichment ability from real complex samples, and Fe3O4@PDA-Nb5+ and Fe3O4@PDA-Ti4+ showed obvious advantages of the phosphopeptides enrichment effect after the comparison. This systematic comparison may provide certain reference for the use and development of IMAC materials in the future.