Biotemplating Magnetic Nanoparticles on Patterned Surfaces for Potential Use in Data Storage
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Biotemplating Magnetic Nanoparticles on Patterned Surfaces for Potential Use in Data Storage Johanna M. Galloway*, Scott M. Bird, Jonathan P. Bramble, Kevin Critchley and Sarah S. Staniland School of Physics and Astronomy, The University of Leeds, Woodhouse Lane, Leeds, LS2 9JT, UK. ABSTRACT Thin-films of magnetic nanoparticles (MNPs) with high coercivities are deposited onto surfaces for use in data storage applications. This usually requires specialist clean-room facilities, sputtering equipment and high temperatures to achieve the correct crystallographic phases. One possible cheaper and more environmentally friendly alternative could be to use biomolecules. Many biomineralization and biotemplating molecules have been identified that are able to template a wide range of technologically relevant materials using mild, aqueous chemistry under physiological reaction conditions. Here, we have designed a dual affinity peptide (DAP) sequence to template MNPs onto a surface. One end of the DAP has a high binding affinity for SiO2 and the other for MNPs of the L10 phase of CoPt, a high coercivity magnetic material. Images of the biomineralized substrates show that nanoparticles of CoPt are localized onto the areas that were functionalized with the biotemplating DAP. Magnetic force microscopy (MFM) plots of the biotemplated nanoparticles show that there is magnetic contrast on the patterned surface. INTRODUCTION Magnetic nanoparticles (MNPs) are used in a wide range of technological applications, which includes the storage of electronic data on computer hard disks [1-3]. It is essential that the magnetic response of the MNPs is consistent and predictable, so that their behavior when an external field is applied is reliably known [4]. The magnetic properties of a material are not only dependent on the material an MNP is made from, but also on its size, shape and crystal structure [3-5]. As such, the MNPs used in any application must be uniform in all of these respects to ensure the required consistency in magnetic behavior. To synthesize such monodispersed MNPs from a bulk solution usually requires high temperatures and toxic reagents [6-9], which is not environmentally friendly. In the natural world, biomineralization proteins are able to template the formation of at least 60 different biominerals [10]. These proteins precisely control the composition, specific crystallographic phases and hierarchical ordering of mineral-organic hybrid structures, which often have superior properties to their artificially synthesized counterparts [9, 11-14]. Excitingly, some of these biomineralization proteins, as well as smaller biotemplating peptide sequences, are able to direct the formation of consistent, uniform nanoparticles from aqueous solutions at room temperature in vitro [7, 8, 14-19]. MNPs must be attached to surfaces and the particles should have a high coercivity (i.e. be magnetically hard) to be useful in data storage. This usually requires clean-room facilities, photolithography and sputtering at high temperatures and under
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