Shear disassembly of hierarchical superparamagnetic Fe₃O₄ hollow nanoparticle necklace chains

Supramolecular amide hydrogen-bond interactions between bundles of necklace-like chains based on superparamagnetic hollow Fe₃O₄ nanoparticle beads could be indirectly quantified by shear stress and magnetorheological analyses. First, a facile magnetic field-induced method was developed for the preparation of the superparamagnetic Fe₃O₄ hierarchical chain structures. Primary Fe₃O₄ hollow nanospheres, hollow nanosphere-assembled chains, and partially hollow nanosphere-assembled chains were successfully prepared. These superparamagnetic nanoparticles and chains could be well dispersed in aqueous solutions. The magnetic hollow nanoparticle chains possess a strong magnetorheological effect in aqueous solutions. Bundle wire-like structures based on chains or nanospheres could be formed with different magnetic field alignments. The hollow nanostructure greatly strengthens the as-formed bundle wire-like structures such that the chains have a larger magnetorheological effect than that of the hollow nanospheres. It is envisaged that a specific cell transfection mechanism of chains and wires could involve a partial disassembly from bundles to individual chains/wires before endocytosis. The force that is exerted on this disassembly from bundles to individual chains/wires in a specific medium, which are quantified by shear stress and magnetorheological analyses, would shed light on cell magnetofection mechanisms.