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.