Core-Shell Structured Nickel@polydopamine Magnetic Composite Nanotubes for Chelator-Free Protein Removal: Self-Released Ni2+-Mediated Selective Adsorption of Histidine-rich Proteins

Construction of magnetic nanotubes and transition metal ion generated by acid etching form its own surface (defined as “self-released” systems) can effectively address the issues of complex operation and poor adsorption performance associated with traditional immobilized metal affinity chromatography (IMAC) materials. Based on the magnetic Ni core and polydopamine (PDA) shell, a core-shell structured Ni@PDA magnetic composite nanotubes and thier acid-etched product (defined as Ni@PDA-T) were developed and synergistically provided excellent magnetic responsiveness, low cell toxixity and more active sites, enabling efficient magnetic separation and surface Ni 2+ self-release. Surface self-released Ni 2+ enabled coordinate capture of histidine-rich proteins without requiring exogenous metal ion supplementation after fixed onto PDA with pH 8.0, simplifying operation and enhancing adsorption efficiency. Given the differences in histidine content among Bovine hemoglobin (BHb), Bovine serum albumin (BSA), and Lysozyme (LYZ), Ni@PDA-T exhibited a maximum adsorption capacity of 4556 mg/g for BHb, which is rich in histidine residues. Density functional theory (DFT) calculations indicate that p-d orbital coordination interactions dominate the His protein's immobilization onto the Ni site and result in superior adsorption behavior for the His protein by DOPAm-Ni 2+ functional group. SDS-PAGE analysis of mixed protein systems and actual bovine blood samples further confirmed the selective adsorption of BHb by Ni@PDA-T. Chelator-free blood purification was achieved through synergistic coordination between self-released Ni 2+ and histidine residues, overcoming the reliance on traditional chelating agents.