Poly-l-lysine-functionalized magnetic graphene for the immobilized metal affinity purification of histidine-rich proteins

Abstract

In this work, we prepared poly-L-lysine (PLL) functionalized magnetic graphene through a simple covalent bonding process. The composite was further conjugated with aspartic acid (Asp) and chelated copper ions to obtain a metal affinity PLL-functionalized magnetic graphene composite (MGPLA-Cu). Various characterizations via FT-IR, XRD, TGA, VSM and SEM/TEM confirm its physicochemical properties. Owing to the strong metal affinity forces between metal affinity groups and the residual histidine in proteins, the MGPLA-Cu composite exhibits highly selective adsorption performance toward histidine-rich proteins, i.e., hemoglobin (Hb) in this case. A high adsorption efficiency of ca. 100% was achieved for 200 mg L⁻¹ Hb in a phosphate buffer at pH 8. The equilibrium adsorption isotherm of Hb on the MGPLA-Cu composite well fitted to the Langmuir theoretical model (R² = 0.9969), along with the maximum adsorption capacity (q_max) at 334 mg g⁻¹. The adsorption kinetics was favorably described by the pseudo-second-order kinetic model. The retained Hb could be effectively recovered with a 0.2 mol L⁻¹ carbonate buffer containing 0.05 mol L⁻¹ imidazole at pH 10, giving rise to a recovery of ca. 97%. The MGPLA-Cu composite showed favorable reusability, and a high adsorption efficiency (>80%) was maintained after five adsorption–desorption operation cycles. The practical application demonstrates that the MGPLA-Cu composite can isolate Hb from human whole blood with high selectivity and high purity.