https://www.spintec.fr/wp-content/uploads/2025/10/Plaquette_Spintec_2026.pdf
Context
Magnetotactic bacteria are specific microorganisms sharing the ability to intracellularly form nanoparticles called magnetosomes. These are magnetic crystals typically made of magnetite (Fe3O4) embedded in a phospholidic membrane. The magnetosomes are aligned in chains along the long axis of the bacteria, functioning as a compass to passively orient the cells along the magnetic field lines of the Earth. Off-axis electron holography in the transmission electron microscope (TEM) is a powerful technique to quantitatively assess the magnetic properties of nanocrystals at the single particle level. It was used about 30 years ago to demonstrate that magnetite crystals were all single magnetic domains, and that the magnetization directions of small superparamagnetic crystals were constrained by magnetic interactions with larger crystals in the chains1. However, this study was performed on a very reduced amount of samples that in addition were not fully representative of the variability encountered in biological samples in general. Over the years, genetic as well as chemical techniques have been developed to experimentally modify the dimension and the organization of magnetosomes in vivo. There is thus now a demand of characterization of nanocrystals structure, organization and alignment to the light of their magnetic properties. Here, we thus propose to profit from recent developments to construct a magnetic state phase diagram depicting the magnetic state (superparamagnetic vs stable single domain) depending on the particle size as well as the interparticle spacing within the chains. In addition, we aim at correlating the magnetic structure of the particles as determined with electron holography with the structure of the crystals as determined by High Resolution Transmission Electron Microscopy. In the best-case scenario, the experimental data will be compared with analytical models of superparamagnetism, which will account for size, spacing, crystal shape and crystal structure.
[1] - Science 282 (1998), 1868-1870, Magnetic microstructure of magnetotactic bacteria by electron holography
(Free version : https://www.rafaldb.com/papers/J-1998-Science-magnetotactic-bacteria.pdf)
Work program & Skills acquired during internship
The candidate will learn basic microbiological techniques and sample preparation for electron microscopy. She/He will then learn high resolution and magnetic imaging (electron holography) in a TEM as well as data treatment. She/He will develop a deep physical understanding of nanobiomagnetism providing a solid and broad basis to start a scientific research career, which we aim to be extended with a PhD project that is already funded. The biological samples will be prepared at the University of Latvia (Riga, Latvia) in the Living Materials group (D. Faivre). Electron microscopy studies and data treatment are performed @ Grenoble PFNC – Minatec in the Spin-Textures team of Spintec (A. Masseboeuf).
Requested background:
- Biophysics / Soft Matter,
- Solid-State Physics
- Data (Image) Treatment
- Experimentalist flavor