Development of immobilized Sn⁴⁺ affinity chromatography material for highly selective enrichment of phosphopeptides

In this work, we first immobilized tin(IV) ion on polydopamine-coated magnetic graphene (magG@PDA) to synthesize Sn⁴⁺ -immobilized magG@PDA (magG@PDA-Sn⁴⁺ ) and successfully applied the material to highly selective enrichment of phosphopeptides. The material gathered the advantages of large surface area of graphene, superparamagnetism of Fe₃ O₄ , good hydrophilicity and biocompatibility of polydopamine, and strong interaction between Sn⁴⁺ and phosphopeptides. The enrichment performance of magG@PDA-Sn⁴⁺ toward phosphopeptides from digested β-casein at different concentrations, with and without added digested BSA was investigated and compared with magG@PDA-Ti⁴⁺ . The results showed high selectivity and sensitivity of the Sn⁴⁺ -IMAC material toward phosphopeptides, as good as the Ti⁴⁺ -IMAC material. Finally, magG@PDA-Sn⁴⁺ was applied to the analysis of endogenous phosphopeptides from a real sample, human saliva, with both MALDI-TOF MS and nano-LC-ESI-MS/MS. The results indicated that the as-synthesized Sn⁴⁺ -IMAC material not only has good enrichment performance, but also could serve as a supplement to the Ti⁴⁺ -IMAC material and expand the phosphopeptide coverage enriched by the single Ti⁴⁺ -IMAC material, demonstrating the broad application prospects of magG@PDA-Sn⁴⁺ in phosphoproteome research.