NSOM/HRTEM Characterization of Biologically Derived Cubo–Octahedral Nanomagnets

Nanomagnets synthesized by the magnetotactic bacterium Magnetospirillum gryphiswaldense have been characterized. Transmission electron microscopy (TEM) shows that the nanomagnets have a mean diameter of 38 nm plusmn 10 nm. Structural analysis done using high-resolution TEM (HRTEM) indicates that, while the nanomagnets appear spherical in shape, crystal planes of magnetite are observed on the cubo-octahedral facets. Microdiffraction analysis suggests that the magnetic nanoparticles have a composition close to Fe₃O₄ and are crystalline. Utilizing a near-field scanning optical microscope (NSOM), we report insights into the magnetic properties of the nanomagnets inside bacterial cells with imaging done on single cells. The experimental design relied on performing magnetization measurements using the magneto-optic Kerr effect (MOKE). The NSOM-MOKE image clearly shows the magnetization of the nanomagnets, while still aligned in continuous chains inside the bacterial cells.