Synthesis of shape-controlled magnetic nanoparticles and a novel route for their surface modification in suspension for biomedical applications

Abstract

Superparamagnetic nanoparticles (SNPs) have many potential biomedical applications, for instance as MRI contrast agents, which was of specific interest in this work. Various techniques were used to synthesise spherical and non-spherical SNPs of a desired size in suspension. The size, shape and composition of the resulting NPs were characterised by DLS, TEM, TGA, ICP-MS, elemental analysis and IR spectroscopy. Magnetic properties of the NPs in solid form were characterised by VSM and SQUID, and further discussed within the context of their size, shape, crystallinity and the synthetic methods used to produce the NPs. Langevin function fitting to M-H curves yielded the magnetic moment of the particles (μ) and a magnetic domain size (d). Magnetic resonance properties of the NPs in suspension were characterised through NMRD measurements, and further analysed according to a well-accepted superparamagnetic theory. Finally, the magnetometry results were compared with those obtained from NMRD analysis.

Competitive stabiliser desorption (CSD)-based cluster growth in the presence of silica was exploited in this thesis. A series of experiments were performed in order to gain an understanding of the mechanism of this process. Parameters which govern the CSD-based growth of clusters were identified. Next, a novel CSD-ligand exchange method performed on the surface of iron oxide nanoparticle (IONP) clusters and discrete particles in suspension was successfully developed. Various secondary ligands were trialled which rendered the NPs dispersible in more polar solvents. A new molecule, 2-azido-2-methyl-propionic acid 2-phoshonooxy-hexyl ester (C6), was synthesised and used in the CSD-ligand exchange process. ATR-IR spectroscopy was appointed as an effective method for the pre-selection of a potential secondary ligand which could be utilised during the CSD-ligand exchange procedure.

Various experimental vessels were developed in order to scale up the CSD-cluster growth and ligand exchange experiments, and to address some technical issues that arose while performing the experiments on a small scale. The results of the CSD-cluster growth and ligand exchange procedures performed in these vessels were presented and discussed. Moreover, a glass vessel with a Teflon holder for TLC plates was successfully developed and used for both CSD-cluster growth and ligand exchange procedures. This approached not only enabled the scale-up of the experiments, but also allowed an advantageous change from silica gel to silica gel-covered TLC plates.