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Caught in the act: protein-templated nucleation of iron oxide in situ
Tanya Prozorov
DOE Ames National Laboratory, USA
Mardi 18/11/2014, 10:00
LSI - École Polytechnique Palaiseau,

Tanya Prozorov received her PhD in Materials Chemistry from the University of Illinois at Urbana-Champaign, USA, in 2004 working on the applications of high-intensity ultrasound for synthesis and modification of nano-materials. In 2005 she joined the US DOE Ames National Laboratory focusing on bioinspired synthesis magnetic nanoparticles. She is the recipient of DOE Early Career award and currently is a staff scientist at the Division of Materials Sciences and Engineering at the Ames National Laboratory leading the Emergent Atomic and Magnetic Structures group focusing on in situ TEM studies of nanomaterials in liquid cell.

Abstract: Magnetotactic bacteria biomineralize ordered chains of nearly perfect magnetic crystals (magnetosomes) and serve as an inspiration and source of a number of proteins used for the biomimetic synthesis of magnetic nanomaterials [1].  Using in situ fluid cell Scanning Transmission Electron Microscopy (STEM), we have imaged the process at nanometer resolution as it occurs in liquid [2].  Bacterial protein Mms6 first self-assembles into micelles, which become visible after binding iron from FeCl3 in the solution.  Upon addition of NaOH, a dense liquid precursor forms on the micelle.  When more NaOH is added, the goo-like layer condenses to give birth to tiny iron oxide nanoparticles. In confining the nucleation to its surface, Mms6 suppresses undesired random particle formation elsewhere in the solution [2].  Recently, we extended the in situ analysis to probing the mechanism of bacterial magnetosome biomineralization.  We used a correlative scanning transmission electron microscopy (STEM) and fluorescence microscopy to image viable magnetotactic bacteria in their native environment and worked to determine radiation damage thresholds and bacterial cell damage mechanisms in the fluid cell STEM [3].  The post-STEM fluorescence imaging confirms presence of viable bacterial cells [3].  This is the first step toward in vivo studies of magnetite biomineralization in magnetotactic bacteria.  Understanding the steps of the crystal formation , both in vivo and in vitro, will allow mimicking Nature’s own technology and develop better synthetic nanomaterials.

[1] Prozorov, T.; Bazylinski, D. A.; Mallapragada, S. K.; Prozorov, R. Mater. Sci. Eng. R  2013, 74, 133.
[2] Kashyap, S.; Woehl, T. J.; Liu, X.; Mallapragada, S. K.; Prozorov, T. ACS Nano 2014, 8, 9097.
[3] Woehl, T. J.; Kashyap, S.; Firlar, E.; Perez-Gonzalez, T.; Faivre, D.; Trubitsyn, D.; Bazylinski, D. A.; Prozorov, T. Sci. Rep. 2014, 4, 6854.

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