|Abstract: ||This thesis describes the synthesis of iron oxide nanoparticles for use as contrast agents in biomedical imaging, specifically for MRI. The limitations of single imaging modalities can be overcome by the synergistic combination of two or more imaging techniques, e.g. the low sensitivity but high resolution of MRI complements the high sensitivity but low resolution of PET. The large surface area of superparamagnetic iron oxide nanoparticles (SPION) allows relatively simple functionalisation. The large size of a single combined nanoparticle MRI/PET probe would slow down in vivo movement, diminishing radioactivity before reaching its target. Pre-targeting using a magnetic nanoparticle followed by the injection of the radio-labelled molecule at the correct time will ensure radioactivity remains sufficiently high. Thus, the investigation of dual-modality probe development is also a focus of the thesis.
Chapter 2 discusses the preparation of iron oxide nanoparticles with a core diameter of 6 nm via the high temperature thermal decomposition of iron salts. Direct modification to the surface of the nanoparticles was carried out using various small molecules with differing anchoring groups, the most successful being sodium alendronate, a bisphosphonate ligand.
Chapter 3 describes the further functionalisation of the nanoparticles. One way this was achieved was by the incorporation of PEG chains of different lengths to increase water solubility and biocompatibility. Functionalisation with a strained alkyne for eventual in vitro/in vivo copper-free cycloaddition with an azide group was also achieved. The PET moiety was designed to be a 68Ga-azido-DOTA complex. Prior to radiolabelling with gallium-68, the copper-free cyclised resultant nanoparticles were characterised by the use of lanthanide analogues (Eu, Tb and Gd). Eu and Tb allowed for fluorescence spectroscopy, while the Gd allowed for relaxivity measurements to be carried out. Unexpected fluorescence results were observed for the Eu and Tb analogues.
The Gd-NP conjugates are further investigated in Chapter 4. Combination of both a T1 and T2 moiety results in changes to the relaxivity of the resultant nanoparticle which can act as a dual-weighted MRI probe. The relaxivities are found to vary with modifications to the nanoparticle construct.
Finally, preliminary in vitro experiments with macrophages were carried out to investigate whether there was significant preferential uptake between M1 and M2 macrophages. A single-chain variable fragment (scFv) specific to Fractalkine, a chemokine important in the progression of atherosclerosis was prepared, for use as a targeting moiety towards the imaging of vulnerable plaque.|