Harmonic and superparamagnetic nanoparticles for biomedical imaging and diagnostic applications

Abstract

Diagnosing certain diseases and tracking their progression requires the ability to 'see' into the body. This is typically achieved by taking advantage of intrinsic contrast in biological tissues (such as in X-ray or magnetic resonance imaging) or by labelling structures with markers such as dyes, fluorescent tags or quantum dots. Each method has limitations – not all structures have sufficient contrast for high resolution imaging, fluorescence fades and quantum dots blink randomly. Nanomaterials were developed for in vitro imaging applications which can overcome the limitations of conventional imaging probes by combining harmonic nanocrystals with superparamagnetic nanoparticles in a multimodal/multifunctional diagnostic tool. Nanocrystals of nonlinear optical bismuth ferrite were prepared by a sol-gel route. In order to enhance the purity of the nanocrystals and hence improve their nonlinear optical response, a variety of chelating agents were substituted in the sol-gel synthesis and the enhancements were quantified by Hyper Rayleigh Scattering. Stable dispersions of the nanocrystals were used as seeds for the synthesis of superparamagnetic magnetite nanoparticles by co-precipitation. Magnetite and bismuth ferrite nanoparticles and composites were combined into silica nanowires to enhance their biocompatibility. This was achieved by incorporating silica sol-gel in which nanoparticles or composites were suspended into the pores of anodic alumina templates, annealing the silica and then dissolving the templates to release the wires. These procedures resulted in novel nanomaterials whose physico-chemical properties such as size-distribution, morphology, colloidal stability, crystal structure and magnetic and nonlinear optical response were extensively characterised by a suite of analytical techniques, including Dynamic Light Scattering, Transmission Electron Microscopy, Zeta-potential measurements, X-ray Diffraction, Vibrating Sample Magnetometry and Second Harmonic Microscopy. A safety assessment of the nanomaterials and composites was carried out using High Content Screening to examine cytotoxicity. Three cell lines were selected to represent different potential exposure routes: human lung cell epithelial cells, human vein endothelial cells and monocyte-derived macrophages. The response of these cell lines was evaluated with respect to cell count, cell viability and lysosomal mass/pH changes after exposure to each of the nanomaterials and composites for 24, 48 and 72 hours. Composites were functionalised to target specific markers such as epidermal growth factor receptor. The uptake, specificity and sensitivity of the probes of the functionalised nanomaterials was evaluated using colorimetric analysis, and the targeting and localisation were assessed using Epifluorescence and Confocal Microscopy. As proof-of-concept of their multifunctionality and multimodality, the composites were magnetically separated from biological media, and imaged using Magnetic Resonance Imaging and Second Harmonic Microscopy, which was also used to illustrate the advantages of nonlinear optical probes over conventional, fluorescent markers. The work carried out in this thesis involved many methods to optimise the synthesis of harmonic and superparamagnetic nanomaterials and composites and demonstrated their suitability for use as multifunctional diagnostic probes in multimodal in vitro imaging.