Nanostructure and field-induced arrangement of magnetosomes studied by SANSPOL

Magnetosomes are intracellular magnetic structures formed by biological mechanism in magnetotactic bacteria. They consist of nano-sized magnetite crystals, covered by protein and lipid membranes. Here we present a small-angle scattering investigation using polarised neutrons (SANSPOL) on magnetosomes extracted from cultivated bacteria (Magnetospirillum gryphiswaldense). Samples of different concentrations and dissolved in H2O/D2O mixtures have been studied. In very diluted samples the simultaneous fits of the two polarisation states revealed the existence of magnetic core-shell particles with an averaged core radius of 21.8 nm and a water-impenetrable shell of 3.4 nm. Sizes and distributions have been found to depend on the biological cultivation conditions. In case of higher concentrated samples, particles are aggregated in segments of chains, which were found aligned in the direction of an applied magnetic field