Hemoglobin-driven iron-directed assembly of gold nanoparticles

The ability to form complex 3D architectures using nanoparticles (NPs) as the building blocks and complex macromolecules that direct these assemblies remains a challenging objective for nanotechnology. Here we report results in which the partial substitution of classical Turkevich citrate-capped gold NPs by a novel, heteroaromatic ligand (L) results in NPs able to form coordination-driven assemblies mediated by free or protein-bound iron ions. The morphology of these assemblies can be tuned depending on the source of iron. To prove the concept, classical citrate and novel NPs were reacted with iron-containing protein hemoglobin (Hb). To diminish the influence of possible electrostatic interactions of native Hb and gold NPs, the reaction was performed at the isoelectric point of Hb. Moreover, thiol groups of Hb were protected with p-quinone to exclude thiol–gold bond formation. As expected, citrate-capped gold NPs are well dispersed in functionalized Hb, while L-functionalized NPs form assemblies. The blue shift of the Soret band of the functionalized Hb, when reacted with novel NPs, unambiguously confirms the coordination of a NP-anchored heteroaromatic ligand with the heme moiety of Hb. Coarse-grained molecular dynamics of this system were performed to gain information about aggregation dynamics and kinetics of iron- and hemoglobin-templated assemblies of L–NPs. A multi-scale simulation approach was employed to extend this model to longer time scales. The application of this model towards novel coordination-based assemblies can become a powerful tool for the development of new nanomaterials.