Many modern technologies, such as high density data storage, require monodispersed magnetic nanoparticles (MNPs), which have a consistent magnetic behavior, specifically immobilized onto a patterned surface. Current methods for synthesizing uniform MNPs require high temperatures and harsh chemicals, which is not environmentally friendly. Also, the particles are expensive to make and expensive to pattern using conventional lithography methods. Magnetic bacteria are able to synthesize consistent MNPs in vivo using biomineralization proteins inside magnetosome vesicles to control particle size and shape and make single domain MNPs. Mms6 is a biomineralization protein that is able to template cubo-octahedral MNP formation in vitro. It is thought the N-terminus helps integrate the protein into the magnetosome membrane, and the C-terminus interacts with magnetite during nucleation and/or MNP growth. By selectively attaching Mms6 to a patterned self assembled monolayer via the N-terminus, patterns of uniform magnetite MNPs are templated in situ. This also requires careful selection of the mineralization solution used to mineralize the patterned Mms6. Here we evaluate some low temperature (room temperature to <100°C) methods of magnetite formation to produce monodispersed magnetite MNPs onto immobilized Mms6. Room temperature co-precipitation (RTCP) was found to be unsuitable, as the magnetite does not form on the immobilized Mms6, but appears to form rapidly as base is added. Partial oxidation of ferrous hydroxide (POFH) was found to be able to form consistent magnetite MNPs on the immobilized Mms6, as the reactants gradually mature to form magnetite over a few hours (at 80°C) or a few days (room temperature). By carefully controlling the type of base used, the ratio of the reactants and the temperature and duration of the POFH mineralization reaction, this system was optimized to produce consistent MNPs (340 ± 54 nm, coercivity 109 Oe) on the immobilized Mms6, with scarcely any mineralization on the anti-biofouling background. The MNPs are ferrimagnetic, and appear to be exchange coupled across multiple particles in MFM measurements. The specificity of this method towards precise magnetite mineralization under relatively mild conditions may be adapted to nanoscale patterning of multiple biotemplated materials, by using other biomineralization proteins or peptides. This would allow the fabrication of cheaper, more environmentally friendly components for devices of the future.
|Number of pages||20|
|Journal||Journal of Nano Research|
|Publication status||Published - Feb 2012|
- magnetic nanoparticles
- iron oxides
- surface pattern
- protein attachment