Sustainable and Well-Dispersed Cu-Doped Magnetic Vortex Nanorings for Highly Specific Separation of His-Rich Proteins

The combination of magnetic nanomaterials with the immobilized metal affinity (IMA) technique has emerged as a powerful method to specifically separate histidine (His)-rich proteins. However, obtaining a high-performance and sustainable magnetic adsorbent with good dispersibility and minimal copper leakage remains a major challenge. Herein, we propose a simple ligand-free method to acquire Cu-doped magnetic nanorings (Fe₃O₄–Cu NR) for the highly selective enrichment of His-rich proteins. Importantly, the Fe₃O₄–Cu NR with unique ring-like structural features offers numerous exposed Cu²⁺ binding sites for His-rich proteins while maintaining a high magnetic behavior (61.7 emu g^–1). Thus, the Fe₃O₄–Cu NR exhibits a remarkable adsorption capacity (932.2 mg g^–1) and high selectivity (SF < 0.1) for bovine hemoglobin (BHb), surpassing most of the reported IMA magnetic adsorbents. Moreover, Fe₃O₄–Cu NR can be easily regenerated with negligible copper ion leakage (<0.1 μmol L^–1) and without requiring a reincubation step, demonstrating reusability for up to six cycles. In addition, the removal efficiency and recovery of Fe₃O₄–Cu NR for BHb in the diluted bovine blood were found to be 89.79 and 70.25%, respectively, further indicating the specificity of Fe₃O₄–Cu NR to BHb in complex biological samples.