Bioinspired Materials: Aptamer-Mediated Templates for Hybrid Elastic Nanostructures

Program Scope: Creation of a new class of biomimetic hybrid materials involving magnetite nanocrystals embedded in hierarchically self-assembling polymers. Controlling nanoscale magnetite synthesis using bacterial mineralization proteins and using DNA/RNA aptamers for achieving specificity of non-covalent binding within the polymer. Investigation of these novel materials and processes using experimental characterization tools as well as theoretical approaches combining modern polymer theory and the theory of micro-magnetism.

Major Program Achievements: We have successfully cloned the sequence for the bacterial mineralization protein mms6 from M. Magneticum and expressed it in E. Coli. Since most of the recombinant mms6 protein was insoluble and found in inclusion particles, the protein was renatured and successfully separated by affinity chromatography. Both the native as well as refolded mms6 proteins were found to facilitate formation of uniform cubo-octahedral nanocrystals of magnetite in solution with sizes of about 40 nm, as seen by transmission electron micrography. It is very difficult to synthesize nanocrystals with similar size and morphology by using other synthetic techniques. The magnetite nanocrystals obtained exhibited strong superparamagnetic behavior, which is typical for monodomain nanoparticles. In the presence of a self-assembling polymer gel, the formation of these magnetite nanocrystals was found to be much more controlled than in free solution. The nanocrystals formed in the presence of ferritin, another iron-binding protein as control, did not exhibit the uniform sizes and shapes seen in the presence of mms6. DNA and RNA aptamers are being developed to bind to mms6 as well as the self-assembling polymers. The approach was also used to synthesize cobalt ferrite nanocrystals in vitro using mms6 as a templating agent, because of their enhanced magnetic properties. Even though mms6 is not involved in the production of cobalt ferrite nanocrystals in Nature, the use of the mineralization protein was found to promote the formation of uniform cobalt ferrite nanocrystals in vitro, making it a truly general bioinspired approach for synthesis of uniform nanocrystals under ambient conditions.

Program Impact: The use ofbacterial mineralization proteins to create uniform, monodisperse, monodomain nanocrystals of magnetite and cobalt ferrite in vitro represents a new paradigm for nanocrystal synthesis and processing using bioinspired methods. The non-covalent linkages and the hierarchical self-assembly processes enable bottom-up approaches for materials design.

Contact Information:
Surya Mallapragada

Selected Publications