Application of Polyethylenimine Modified Nickel Ferrite Graphene Oxide Composite in the Enrichment of Phosphopeptides

Abstract

A polyethyleneimine (PEI)‑modified nickel ferrite‑graphene oxide composite material, GO@PEI‑NiFe₂O₄, was prepared for the selective purification and enrichment of phosphopeptides from biological samples. The Ni²⁺ and Fe³⁺ ions on its surface can coordinate with phosphate groups, thereby selectively adsorbing phosphopeptides. The modified PEI enhances the hydrophilicity of the composite, which facilitates its binding to phosphopeptides. In addition, NiFe₂O₄ in the composite is magnetic, enabling its rapid separation from solution. Using β‑casein as a sample, the enrichment performance of the composite for phosphopeptides in tryptic digest was investigated, and the results were compared with those enriched by GO@NiFe₂O₄ (without PEI modification). The adsorption mechanism of the composite was also discussed. The static and dynamic adsorption curves of the composite for pTyr were determined using the phosphopeptide pTyr, and the maximum adsorption capacity reached 36.2 μg/mg. The results showed that this composite could effectively remove the interference of non‑phosphopeptides and efficiently enrich phosphopeptides in complex matrices. After enrichment of tryptic digest of rat liver proteins, 1535 phosphopeptides were identified by mass spectrometry, and the enrichment effect was significantly better than that of a commercial Fe³⁺‑IMAC kit. This study provides a highly selective material for the enrichment of phosphopeptides and shows potential application in phosphoproteomics research.