Biotemplating arrays of nanomagnets using the biomineralisation protein Mms6

High quality magnetic nanoparticles (MNPs) are used in applications such as electronic data storage. Current methods for synthesising the consistent MNPs required use high temperatures, harsh chemicals and bespoke equipment. As this is energy intensive, expensive and not very environmentally friendly, cheaper and „greener‟ alternatives are being sought. Mms6 is a biomineralisation protein from a magnetic bacterium (Magnetospirillum magneticum AMB-1), which is able to biotemplate the formation of uniform cubo-octahedral magnetite nanoparticles in vitro under mild reaction conditions. The N-terminal section is hydrophobic, and may cause the protein to self-assemble in aqueous solution. This self-assembly may facilitate the biotemplating ability of the protein, but it is the acidic C-terminal section of the protein that is the most important for binding iron and templating uniform MNPs. Attachment of Mms6 via the N-terminus to a micro-contact printed (μCP) patterned self-assembled monolayer (SAM) allows the protein to biotemplate uniform, ferrimagnetic magnetite MNPs in situ. These biotemplated MNPs were investigated with magnetic force microscopy (MFM), which found that they form multi-particle zones of attraction and repulsion. This is likely to be due to exchange-coupling of MNPs on the surface, with the long-axis of these magnetic features running parallel to the long axis of the assembly of patterned nanoparticles. As magnetite is magnetically soft, the system was doped with cobalt to increase the coercivity of the MNPs, both when templated onto a surface and in a bulk solution. To create biotemplated MNPs for use in data storage, a high coercivity is necessary to ensure that the magnetic orientation, and therefore the data recorded, is retained. The work presented here demonstrates that biotemplating can be used to produce high quality magnetic materials under far milder conditions than required in current industrial synthesis techniques, which should allow the development of more environmentally friendly bioinspired devices in the future.