Speaker
Description
Magnetotactic bacteria are microorganisms capable of aligning with and navigating along geomagnetic field lines thanks to the presence of one or more chains of magnetic nanoparticles synthesized within their cells. These chains behave as intracellular compass needles under an external magnetic field. The biomineralized nanoparticles, known as magnetosomes, have attracted considerable attention because they combine high chemical purity and crystallinity. Their distinctive properties have motivated the use of magnetosomes and magnetotactic bacteria in biomedical applications [1]. In the last years, several groups have proposed different strategies, focused on in vivo processes [2-3] to tune the composition of the magnetosomes to overcome the natural limitations. However, only limited amounts of dopant elements are generally incorporated into the magnetosome structure, resulting in minor modifications of their room-temperature magnetic properties [4].
In this work, we go one step further by evaluating the optimal stage for cobalt addition during magnetosome biomineralization in Magnetospirillum gryphiswaldense. We observe that the timing of Co supplementation directly affects the doping dynamics. Magnetic measurements reveal enhanced magnetic hardness, particularly when cobalt is added at more advanced stages of the biomineralization process. In addition, the hysteresis loops suggest the progressive emergence of two magnetic phases as Co incorporation takes place later during magnetosome formation. XAS and XMCD at the Fe and Co L3-edges reveal that cobalt is incorporated as Co2+ in octahedral positions, directly influencing the magnetocrystalline anisotropy of the doped nanoparticles. Furthermore, comparison of Fe L3-edge XMCD measurements acquired in transmission mode (bulk-sensitive) and total electron yield mode (surface-sensitive) provides not only quantitative information on cobalt incorporation, but also insight into its location within the magnetosome particles as a function of the Co-addition timing.
References
• [1] Fdez-Gubuieda, M.L., et al., J. Appl. Phys. 2020, 128, 070902.
• [2] Staniland, S.; et al., Nat. Nanotechnol. 2008, 3, 158-162.
• [3] Marcano, L.; et al. J. Phys. Chem. C 2018, 122, 7541-7550.
• [4] Muñoz, D., Marcano, L.; et al.; Sci. Rep. 2020, 10, 11430.
• [5] Fdez-Gubuieda, M.L., et al., ACS Nano, 2013, 7, 3297–3305.