Bare magnetic iron oxides for binding and selective elution of lactoferrin from acid whey

Bare iron oxide nanoparticles (BIONs) can isolate the dilute but valuable protein lactoferrin (LF) from dairy by-products through magnetic separation. While BIONs can be produced in large quantities at a reasonable price and can act as ion-exchanging material, the binding behaviors of biomolecules to BIONs in complex mixtures need to be better understood. Using a combination of static binding studies and zeta potential measurements, we investigated how whey salts and the whey proteins β-lactoglobulin, bovine serum albumin, and α-lactalbumin influence the binding of LF to BIONs. Zeta potential measurements revealed that whey salts induce a surface charge reversal on BIONs, enabling them to function as cation exchangers at acidic pH. The cationic LF exhibited preferential binding to BIONs in single- and multicomponent binding experiments. Even in native acid whey, where LF accounted for less than 3 % of the whey protein, it constituted over 43 % of surface-bound whey protein on BIONs. By selectively controlling whey protein elution with simple salt buffers, we achieved complete LF elution with over 84 % purity. This study represents the first in-depth analysis of BIONs for the selective isolation of an untagged natural protein from a complex mixture, demonstrating their reusability over multiple cycles. Our findings enhance the understanding of bio-nano interactions and demonstrate the potential of magnetic separation with BIONs as a scalable and cost-effective solution for recovering valuable biomolecules from industrial by-products.