Magnetotactic bacteria biosynthesize magnetite nanoparticles of high structural and chemical purity that allow them to orientate in the geomagnetic field. In this work we have followed the process of biomineralization of these magnetite nanoparticles. We have performed a time-resolved study on magnetotactic bacteria Magnetospirillum gryphiswaldense strain MSR-1. From the combination of magnetic and structural studies by means of Fe K-edge X-ray absorption near edge structure (XANES) and high-resolution transmission electron microscopy we have identified and quantified two phases of Fe (ferrihydrite and magnetite) involved in the biomineralization process, confirming the role of ferrihydrite as the source of Fe ions for magnetite biomineralization in M. gryphiswaldense. We have distinguished two steps in the biomineralization process: the first, in which Fe is accumulated in the form of ferrihydrite, and the second, in which the magnetite is rapidly biomineralized from ferrihydrite. Finally, the XANES analysis suggests that the origin of the ferrihydrite could be at bacterial ferritin cores, characterized by a poorly crystalline structure and high phosphorus content.

Magnetotactic bacteria are aquatic microorganisms that internally biomineralize chains of magnetic nanoparticles (called magnetosomes) and use them as a compass. Here it is shown that magnetotactic bacteria of the strain Magnetospirillum gryphiswaldense present high potential as magnetic hyperthermia agents for cancer treatment. Their heating efficiency or specific absorption rate is determined using both calorimetric and AC magnetometry methods at different magnetic field amplitudes and frequencies. In addition, the effect of the alignment of the bacteria in the direction of the field during the hyperthermia experiments is also investigated. The experimental results demonstrate that the biological structure of the magnetosome chain of magnetotactic bacteria is perfect to enhance the hyperthermia efficiency. Furthermore, fluorescence and electron microscopy images show that these bacteria can be internalized by human lung carcinoma cells A549, and cytotoxicity studies reveal that they do not affect the viability or growth of the cancer cells. A preliminary in vitro hyperthermia study, working on clinical conditions, reveals that cancer cell proliferation is strongly affected by the hyperthermia treatment, making these bacteria promising candidates for biomedical applications.

Ambient temperature sodium-ion batteries are emerging as an exciting alternative to commercially dominant lithium-ion batteries for larger scale stationary applications. In order to realize such a sodium-ion battery, electrodes need to be developed, understood, and improved. Here, Na 3 V 2 O 2 (PO 4 ) 2 F is investigated from the perspective of sodium. Reaction mechanisms for this cathode during battery function include the following: a region comprising at least three phases with subtly varying sodium compositions that transform via two two-phase reaction mechanisms, which appears at the lower potential plateau-like region during both charge and discharge; an extended solid solution region for majority of the cycling process, including most of the higher potential plateau; and a second two-phase region near the highest charge state during charge and between the first and second plateau-like regions during discharge. Notably, the distinct asymmetry in the reaction mechanism, lattice, and volume evolution on charge relative to discharge manifests an interesting question: Is such an asymmetry beneficial for this cathode? These reaction mechanisms are inherently related to sodium evolution, which shows complex behavior between the two sodium crystallographic sites in this compound that in turn mediate the lattice and reaction evolution. Thus, this work relates atomiclevel sodium perturbations directly with electrochemical cycling.