NOM-assisted, amyloid-enriched, hierarchical self-assembled nanostructures of maghemite nanoparticles and their plastic deformation: role of magnetic fields, Pb2+, and biomolecular conformations

Abstract

Sequential sorption of bovine serum albumin (BSA)–humic acid (HA)–BSA on weakly ferromagnetic maghemite nanoparticles has achieved the formation of amyloid scaffold-controlled self-assembly (B2-GFeNPs) at pH 4. Unlike BSA-modified maghemite (B1-GFeNPs), which has stronger magnetic dipolar interaction-mediated random aggregation, the liquid crystalline nature and nanoconfinement effects of the amyloid scaffold controlled the growth of highly ordered colloidal assemblies of B2-GFeNPs. These assembled structures undergo topotactic transformations due to Helfrich membrane bending when the suspension pH is increased from 4 to 7. In the presence of an external magnetic field, and at pH 4 these self-assembled structures underwent screw dislocation-driven growth; for example, nanowires and helicoidal and disc-like colloidal crystals. The formations of micropipe-like open core screw defects with a higher magnitude of the Burgers vector of the colloidal clusters were also observed. The interaction of Pb²⁺ (0–100 μg L⁻¹) within the amyloid backbone of B2-GFeNP clusters at pH 4 produced an FCC-like geometry and resulted in moderate to severe plastic deformation, including slip, with increasing concentrations of heavy metal ions. The signatures of plastic deformation, including dislocation dipoles, prismatic loops, stacking fault tetrahedra, and twin boundaries were observed. At pH 7, the topological transformation of B2-GFeNPs and Pb²⁺-induced elastic strain caused a dislocation pile-up, which represented the zincblende {111} face. The dislocation reactions produced from the mutual interactions between the Shockley partials (which evolved from the stacking faults) with Burgers vectors and that moved along {111} planes resulted in the formation of a Lomer–Cottrell (LC) barrier with a stair-rod geometry. Therefore, Fe–NOM coprecipitate interactions with heavy metal ions or soil colloids isolated from metal-contaminated soils may provide the morphological signatures of elastic strain-mediated geometries.