Biotemplated synthesis of magnetic filaments

Abstract

With the aim of creating one-dimensional magnetic nanostructures, we genetically engineered flagellar filaments produced by Salmonella bacteria to display iron- or magnetite-binding sites, and used the mutant filaments as templates for both nucleation and attachment of the magnetic iron oxide magnetite. Although nucleation from solution and attachment of nanoparticles to a pre-existing surface are two different processes, non-classical crystal nucleation pathways have been increasingly recognized in biological systems, and in many cases nucleation and particle attachment cannot be clearly distinguished. In this study we tested the magnetite-nucleating ability of four types of mutant flagella previously shown to be efficient binders of magnetite nanoparticles, and we used two other mutant flagella that were engineered to periodically display known iron-binding oligopeptides on their surfaces. All mutant filaments were demonstrated to be efficient as templates for the synthesis of one-dimensional magnetic nanostructures under ambient conditions. Both approaches resulted in similar final products, with randomly oriented magnetite nanoparticles partially covering the filamentous biological templates. In an external magnetic field, the viscosity of a suspension of the produced magnetic filaments showed a twofold increase relative to the control sample. The results of magnetic susceptibility measurements were also consistent with the magnetic nanoparticles occurring in linear structures. Our study demonstrates that biological templating can be used to produce one-dimensional magnetic nanostructures under benign conditions, and that modified flagellar filaments can be used for creating model systems in which crystal nucleation from solution can be experimentally studied.

Characterisation of the magnetic response of nanoscale magnetic filaments in applied fields

“…49 Linear, filament-like assemblies of ferromagnetic nanoparticles have been made using biological agents and bio-templates. 50,51 Magnetic nanochains have been made by causing chain-like assembly applying external magnetic fields on super-paramagnetic nanoparticle clusters, fixed by an additional layer of silica. 52 In summary, one can divide available MF systems in two classes: those containing magnetisable (or super-paramagnetic) particles and those made of ferromagnetic particles.…”

Tuning properties of biomimetic magnetic nanoparticles by combining magnetosome associated proteins

“…According to the results of Bereczk-Tompa et al . 43 and being the iron binding by negatively charged amino acids (in extended surfaces) a less specific process than the binding of previously formed nuclei, magnetite nucleation induced by the ionotropic effect is probably kinetically favoured in the case of MamC 44 . HRTEM images of MamC-mediated magnetite crystals in Lopez-Moreno et al .…”

Sensing Layer for Ni Detection in Water Created by Immobilization of Bioengineered Flagellar Nanotubes on Gold Surfaces

“…Previous studies demonstrated that binding proteins, enzymes, or reporter proteins can be inserted into the variable central portion of the flagellin protein, resulting in a plethora of building blocks applicable for functionalized nanotube formation. − Flagellin-based fusion proteins with catalytic and molecular recognition functionalities can be assembled to form mixed or block copolymers in a rationally designed manner, opening new horizons for applications in medical diagnostics, environmental monitoring, or bionanotechnology.…”

“…Its terminal regions are highly conserved and required for filament formation, in contrast to the variable middle portion that forms the D3 domain exposed on the surface of the filaments. The D3 domain can be modified or replaced by heterologous segments, enabling the introduction of specific functionalities into the host molecule. − These flagellin variants reengineered in the D3 region typically retain their polymerization ability and can be used to make functionalized protein nanotubes in vitro . They can be readily produced by bacteria because they form filaments on the cell surface, which can be removed and purified easily.…”