Abstract
Nanoparticles have a greater role in both multimodal and multifunctional molecular imaging. Whilst fluorescent probes are routinely used, their limitations such as photobleaching and short emission lifetimes, mean that new and better imaging agents are needed. The most well-known fluorescent nanoparticle, the quantum dot, shows excellent photoluminescence properties as well as photo-stability, tuneable emission and increased functionality. However, as quantum dots are normally composed of toxic heavy metals, there is a need for a different agent that can meet the demands of being both suitable for biological imaging as well as being further enhanced for diagnostics. In this thesis the use of a novel agent, and how it is generated, is discussed.Conjugated polymers are proving successful as an optical imaging tool. These organic semiconductors span the entire spectral range, have high quantum yields, are tuneable and biocompatible. The hydrophobic nature of conjugated polymers, however, requires use of self-assembling co-polymers to generate a robust system for nanoparticles synthesis. By utilising the nanoprecipitation method, it was possible to make conjugated polymers nanoparticles with a size of 50 nm, that have bright emission and quantum yields.
The conjugated polymer nanoparticles have been studied by optical absorption spectroscopy, photoluminescence spectroscopy, transmission electron microscopy, dynamic light scattering, confocal fluorescent imaging and magnetic measurements. By utilising an oxidising agent, it was possible to tune the emission of conjugated polymers. The rate of tuneability could be increased by decreasing the polymer concentration. In this way, it was possible to tune MEH-PPV, a known emitter at 550nm, to have an emission profile ranging from 405nm to 600nm.
Whilst conjugated polymers span the entire visible spectral region, red to near-infra red emitting conjugated polymers were utilised for nanoparticle generation. CN-PPV, a conjugated polymer that emits in the yellow region when dissolved in solvents, red-shifts when encapsulated as a nanoparticle (to emit around 630 nm). CN-FO-DPD, was a relatively new true-red emitting conjugated polymer, with emission properties the same in solvent as well as when encapsulated as a nanoparticle. Two NIR emitting conjugated polymers were also used, where the emission properties were related to how borylated they were. Addition of superparamagnetic iron oxide nanoparticles allowed for early stage development of a bimodal imaging agent.
Different types of co-polymers were investigated to determine what influence they had on the optical and physical properties of the nanoparticles. Changing the molecular weight of poly(ethylene glycol)-poly lactic-co-glycolic acid (PEG-PLGA) presented nanoparticles between 70 and 150 nm. Changing the ratio of conjugated polymer to pluronic, a well-researched co-polymer, and adding a silica shell created hollow shelled silica nanoparticles, the nanoparticles had a size of 30 nm and emission profiles ranging from 550 to 630nm. This trend was also seen when using poly(styrene-co-maleic anhydride), another type of co-polymer that had carboxylic acid groups on the surface of the nanoparticle. Studies with different cell types showed nanoparticle uptake, with limited to no cytotoxicity.
| Date of Award | 1 Dec 2019 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Mark Green (Supervisor) & Lea Ann Dailey (Supervisor) |