Tanya Prozorov

 

Assistant Scientist III,  Division of Materials Sciences and Engineering, US DOE Ames Laboratory

136B WIlhelm Hall,
Ames Lab,
Ames IA,  50011
USA
Office: 1-515-2943376
  Lab:  1-515-2941255

Emergent Atomic and Magnetic Structures

 Determining the nature of the macromolecule-mediated magnetic nanoparticle formation. Magnetic nanoparticles with narrow size distribution, controlled magnetic anisotropy and large magnetic moment per particle and are in high demand in various technologically important areas, — from data storage and quantum computing, to magnetocaloric refrigeration and cancer therapy. For most applications, uniform size, controlled shape and well-defined magnetic properties are essential. Bio-inspired synthetic routes offer room-temperature pathways to the production of a variety of magnetic nanostructures with the exceptional control over nanoparticles nucleation and growth, and ultimately enable the fabrication of structurally perfect magnetic nanocrystals with sizes and shapes not realizable via conventional techniques. Inspired by Nature, biomimetics allows low-temperature fabrication of new magnetic functional nanostructures, using synthetic polymers, viruses, peptides, DNA molecules, proteins and various polymer-based hybrid materials as matrices, scaffolds and templating agents. Protein-driven nucleation plays an important role in formation and growth of templated nanocrystals. Our research is aimed at determining the nature of macromolecule-mediated magnetic nanoparticle formation: i.e., the mechanism of particle nucleation, growth, the emergence of crystal structure and development of ferromagnetism in the individual bio-templated magnetic nanocrystal by utilizing advanced electron microscopy techniques.


    

Visualization of synthesized magnetic nanoparticles. Analysis of nanostructured materials frequently employs Transmission Electron Microscopy, where specimens are routinely prepared by placing a drop of nanoparticles suspension on a suitable electron microscopy (EM) grid. Solvent-induced interactions, often resulting in self-organization of the suspended nanoparticles, can be misleading in terms of both the observed interactions between the individual nanoparticles, and resulting geometries. Moreover, solvent evaporation can induce unwanted aggregation of suspended nanoparticles, and comprehensive analysis of such a system can be challenging due to the presence of a large number of randomly oriented, overlapping features of interest. The issue can be further exacerbated when working with magnetic nanoparticles. Using various biomolecular templating agents, we are working on optimization of the novel on-the-EM-grid synthesis of magnetic iron oxides as a tool for direct evaluation of the individual templated magnetic nanocrystal formation and growth, free of artifacts associated with the conventional sample preparation and characterization.  Controlled synthesis directly on the surface of the EM grid, followed by the strategic Cryo-plunging of the specimens, allows for an arrested small-scale growth of the templated nanoparticles. In addition to minimizing both the solvent-induced nanoparticles interactions and the effect of solvent evaporation on a resulting nanoparticles arrangement on the EM grid, such an approach reduces the overall number of the nanoparticles subject to analysis and minimizes their overlapping, thus permitting high-resolution imaging of the vitrified specimens. We are currently carrying out the Cryo-EM analysis on vitrified specimens to identify suitable data collection modes.


 Magnetosome magnetite. While the controlled, low-temperature chemical synthesis of structurally perfect, single domain magnetic nanoparticles with narrow size distribution can be challenging, magnetotactic bacteria, present in many natural aquatic environments, produce these particles under a strict biological control over the mineralization process. Such a control results in particles with a well-ordered crystal structure, nearly perfect stoichiometry, narrow size distribution, and their well-defined magnetic properties. As a result, magnetite nanoparticles biomineralized of by these microorganisms, are a topic of great interest in a variety of fields, from nanotechnology to Astrobiology. Magnetosomes offer many characteristics superior to those of synthetic magnetite analogues, and have attracted a great interdisciplinary interest. Magnetite nanocrystals in magnetosomes are of the order of 35-120 nm in size, are permanently magnetic and function for the bacteria at ambient conditions.

Despite the obvious difficulties, it is possible to “dope” the magnetosome magnetite by introducing the foreign metal into the media where the bacteria grow. Such a “doping” results in a significant change in magnetization of the bacterial magnetite. Applying a variety of techniques to study of magnetic behavior of the bacterial cultures grown in such a way, may yield a unique information regarding the number of Borh-magnetones per the individual cell, or even per individual magnetite nanocrystal.