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Shoronia Cross1 Katalin Korpany1 Dorothy Majewski1 Amy Blum1

1, McGill University, Montreal, Quebec, Canada

The challenge of developing ultradense magnetic data storage technologies is the production of nanoscale magnetic bits, capable of being individually switched, and which can be assembled in a close-packed array with minimum bit-bit coupling. It has been shown that magnetic coupling can occur between neighboring magnetic nanoparticles (MNPs) in self-assembled nanoring structures, generating chiral, bistable domains, known as flux closure (FC) states. The magnetostatic fields within these FC states are confined within the ring structure, thus minimizing stray fields, and making MNP nanoring structures appealing as magnetic bits. Reported self-assembled MNP ring structures, however, are produced by evaporative techniques, and produce low yields of oblong, polydisperse rings with relatively large diameters, which cannot be assembled into organized arrays or layers. Constructing nanoscale assemblies with positional control at the nanometer level requires a templating method with high specificity and monodispersity, such as that offered by tobacco mosaic virus (TMV) coat protein, which, as a biomolecule, is inherently monodisperse in size, shape and surface chemistry. As a scaffold for nanoparticle self-assembly, TMV disks not only produce well-defined nanostructures, but close-packed structures wherein coupling between neighboring nanoparticles, which is essential to forming FC states, can occur. The EDC coupling reaction is utilized to conjugate propargylamine to the surface of superparamagnetic iron oxide nanoparticles (IONP) coated in 3,4-dihydroxyphenylacetic acid (DOPAC), to yield solution exposed alkyne groups on the IONP surface (IONP-alkyne). The solution exposed N-terminal amines of the TMV disks are similarly used to conjugate 5-azidopentanoic acid to the outer surface of the TMV disk, yielding solution exposed azide groups (TMV-azide), through EDC coupling. The copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction is then applied to covalently bind the IONP-alkyne to the TMV-azide disks, in order to form templated self-assembled ring structures for further characterization and FC studies. These structures not only open novel potential avenues for the assembly of ultradense data storage devices through the self-assembly of virus-templated superparamagnetic IONPs, but also provide an assembly, upon which, the fundamentals of FC states can be studied.

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