Dynamic magnetic properties of magnetosomes

Magnetosomes are found in magnetotactic bacteria, and consist of linear chains of tens of single-domain magnetic nanoparticles of Fe3O4 (magnetite) or Fe3S4 (greigite), enclosed in a lipid bilayer membrane. The particles are typically in the size range 30–120 nm, and are practically monodisperse. Harnessing the power of biomineralisation could lead to efficient strategies for synthesising semiflexible dipolar filaments, and the development of optimum materials for applications, including in biomedicine. Brownian dynamics simulations of noninteracting magnetosomes, containing 1 ⩽ N ⩽ 64 ferromagnetic nanoparticles, have been used to determine static properties, and the dynamical response to a weak AC magnetic field. Results are presented for the radius of gyration Rg, the static magnetic susceptibility χ(0), the dynamic magnetic susceptibility χ(ω), and the effective Brownian rotation time τrot, all as functions of N. The results are compared to theoretical predictions of the flexibility, susceptibility, and rotational dynamics of such magnetic filaments.