Magnetic Study of Co-Doped Magnetosome Chains

Abstract

Magnetotactic bacteria synthesize a chain of magnetic nanoparticles, called magnetosome chain, used to align and swim along the geomagnetic field lines. In particular, Magnetospirillum gryphiswaldense biomineralize magnetite, Fe3O4. Growing this species in a Co-supplemented medium, Co-doped magnetite is obtained, tailoring in this way the magnetic properties of the magnetosome chain. Combining structural and magnetic techniques such as transmission electron microscopy, energy-dispersive x-ray spectroscopy, X-ray absorption near edge structure, and X-ray magnetic circular dichroism, we determine that ∼1% of Co2+ substitutes Fe2+ located in octahedral places in the magnetite, thus increasing the coercive field. In the framework of the Stoner–Wohlfarth model, we have analyzed the evolution of the hysteresis loops as a function of temperature determining the different magnetic anisotropy contributions and their evolution with temperature. In contrast with the control magnetosome chains, whose effective anisotropy is uniaxial in the whole temperature range from 300 to 5 K, the effective anisotropy of Co-doped magnetosome chains changes appreciably with temperature, from uniaxial down to 150 K, through biaxial down to 100 K, to triaxial below 100 K.

Magnetosomes could be protective shields against metal stress in magnetotactic bacteria

“…Note that, according to EDS (see the supplementary information), the Co content in the magnetosomes is only 1.6% at./Fe, thus the Co ferrite in the magnetosomes is not stoichiometric ( Co 0.05 Fe 2.95 O 4 ). In spite of the low Co content, it has been previously reported that the magnetic properties of Co-magnetosomes change notably with respect to the undoped ones [20][21][22] .…”

Exploring the potential of the dynamic hysteresis loops via high field, high frequency and temperature adjustable AC magnetometer for magnetic hyperthermia characterization

“…It should be noted that, such form of thermal dependence (as M 2 ) cannot be extrapolated to lower temperatures in our case, due to the presence of the Verwey phase transition at around 100 K. A detailed analysis of this issue requires the collection of additional data as a function of temperature and a more complex modeling to take account for the thermal dependence of the magnetocrystalline contribution to the anisotropy that is out of the scope of this work. This type of study have been already done in the literature, either with magnetosome [64], whose thermal behavior is expected to be similar to the samples presented in this work, or very recently with Mn-Zn ferrites [65]. The overall agreement between experiments and simulations in both SAR evolution ( Figure 10) as well as in AC hysteresis loops (see Supporting Information Figure S13) is quite surprising since simplifications made in the modeling are really strong: size distribution has been not taken into account and, most importantly, magnetic dipolar interactions have not been explicitly considered.…”

Transient Magnetothermal Neuronal Silencing Using the Chloride Channel Anoctamin 1 (TMEM16A)

“…Laboratory synthesized nanoparticles require encapsulation in biopolymers to be biocompatible and to remain stable in suspension inside the body over long periods of time. Already biocompatible alternatives are natural or engineered biosynthesized magnetite nanoparticles from bacteria ( Hergt et al, 2005 ; Fantechi et al, 2014 ; Elfick et al, 2017 ; Marcano et al, 2018 ). Genetically controlled in situ syntheses of nanoparticles in neurons could in the future completely remove the need for particle delivery but so far has failed to produce particles showing clear heating ( Wesolowski et al, 2009 ; Pollithy et al, 2011 ; Stanley et al, 2015 ).…”