A Bioinspired Approach to Data Storage By: Scott Michael Bird A thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy The University of Sheffield Faculty of Science Department of Chemistry March 2016 I For Ann and Craig Without their unwavering support and endless sacrifices none of this would have been possible. II III Abstract Traditional magnetic data storage devices are reaching the limits of their capabilities, and new technologies must be sought if the remarkable pace of improvement in performance and storage capacity seen over the last 60 years is to continue. Bit-patterned media (BPM) has the potential to continue this development and significantly increase the storage densities of magnetic hard disks, but developing a cost-effective route to manufacture this technology has so far remained elusive. This work takes inspiration from nature, to develop a bioinspired and green approach to forming magnetic nanoparticles (MNPs) on surfaces, as a novel approach to BPM. Magnetotactic bacteria (MTB) form highly uniform MNPs of the magnetic material of magnetite inside specialised lipid organelles called magnetosomes, under mild aqueous conditions. Control over the magnetite crystal formed is exerted through the use of biomineralisation proteins. One of these proteins from the MTB Magnetospirillum magneticum AMB-1, termed Mms6, has been shown to control the formation of magnetite nanoparticles in vitro. In this work, a modified version of the Mms6 protein, engineered to contain an N-terminal cysteine, is patterned and immobilised onto gold surfaces to biotemplate the growth of MNP arrays of magnetite. Furthermore, different patterning methods are explored to control the location of Mms6, with the aim of producing MNP arrays that are suitable for BPM. Magnetite is a magnetically soft material that is unlikely to ever be used for data storage, but Mms6 has been shown to biotemplate the magnetically harder material of cobalt-doped magnetite and this is also explored as an alternative. This approach is also highly adaptable, and could be used for the production of a wide range of different nanomaterials on surfaces through the use of alternative biomolecules. The patterning approaches developed in this work are also used to pattern artificial biomolecules to biotemplate materials that are more technologically relevant and not found in nature, such as L10 phase CoPt, as a route to developing an environmentally friendly, scalable and bioinspired approach to the challenge of BPM. IV Table of Contents ABSTRACT ........................................................................................................................................................... III LIST OF FIGURES ................................................................................................................................................. VII LIST OF TABLES .................................................................................................................................................. XIX BIBLIOGRAPHY ................................................................................................................................................... XX ACKNOWLEDGEMENTS ...................................................................................................................................... XXI INTELLECTUAL PROPERTY STATEMENT ............................................................................................................. XXII ABBREVIATIONS AND DEFINITIONS ................................................................................................................. XXIV 1. INTRODUCTION ................................................................................................................................................ 1 1.1 OVERVIEW .................................................................................................................................... 2 1.2 MAGNETISM ................................................................................................................................. 3 1.2.1 History of Magnetic Materials .................................................................................................. 3 1.2.2 Fundamental Principles of Magnetism ..................................................................................... 3 1.2.3 Properties of Magnetic Materials ............................................................................................. 7 1.2.4 Magnetic Domains .................................................................................................................... 9 1.2.5 Magnetisation Curves and Magnetic Hysteresis ..................................................................... 11 1.2.6 Magnetic Anisotropy ............................................................................................................... 13 1.2.7 Magnetic Materials ................................................................................................................. 14 1.2.8 Magnetism on the Nanoscale ................................................................................................. 17 1.2.9 Magnetic Nanoparticles (MNPs) ............................................................................................. 19 1.3 MAGNETIC DATA STORAGE ................................................................................................................... 23 1.3.1 History and Basic Principles of Magnetic Data Storage .......................................................... 23 1.3.2 Data Storage Technologies ..................................................................................................... 27 1.3.3 The Future of Magnetic Data Storage ..................................................................................... 29 1.3.4 Fabrication of Bit-Patterned Media (BPM) ............................................................................. 31 1.4 BIOMINERALISATION PROTEINS .............................................................................................................. 35 1.4.1 Biomineralisation .................................................................................................................... 35 1.4.2 Discovery of Magnetotactic Bacteria (MTB) ........................................................................... 37 1.4.3 Magnetotaxis .......................................................................................................................... 37 1.4.4 Phylogeny of MTB ................................................................................................................... 39 1.4.5 Magnetosome Formation ....................................................................................................... 40 1.4.6 The Biomineralisation Protein Mms6 ...................................................................................... 43 1.4.7 Recombinant Protein Synthesis ............................................................................................... 45 1.4.8 Designing New Biomolecules for Biomineralisation ................................................................ 46 1.4.9 Immobilising Proteins on Surfaces .......................................................................................... 48 1.5 SELF-ASSEMBLED MONOLAYERS (SAMS) ................................................................................................ 50 1.5.1 Overview ................................................................................................................................. 50 1.5.2 Basics of SAM Formation ........................................................................................................ 50 1.5.3 Alkanethiol SAMs .................................................................................................................... 51 1.5.4 Patterning SAMs ..................................................................................................................... 53 1.6 PROJECT OUTLINE ............................................................................................................................... 59 1.6.1 Biomineralised MNP Arrays .................................................................................................... 59 1.6.2 Summary of Chapters .............................................................................................................. 60 2. METHODS ....................................................................................................................................................... 61 2.1 BIOMOLECULES FOR BIOMINERALISATION ................................................................................................. 62 2.1.1 Cysteine-Tagged Mms6 ........................................................................................................... 62 V 2.1.2 Peptide Based on the C-terminal Region of Mms6 (Mms6Peptide) ............................................. 62 2.1.3 Magnetite Interacting Adhiron 1 (MIA-1) ................................................................................ 62 2.1.4 CoPt Binding Peptide ............................................................................................................... 63 2.2 PATTERNING BIOMOLECULES ON GOLD SURFACES ...................................................................................... 64 2.2.1 Overview of Patterning Biomolecules on Gold Surfaces .........................................................