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Controlling the Au/Iron oxide interface to optimise plasmonic resonance for magneto-optic diagnostics

Davies, Josh 2021. Controlling the Au/Iron oxide interface to optimise plasmonic resonance for magneto-optic diagnostics. PhD Thesis, Cardiff University.
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Abstract

Sepsis is one of the biggest causes of child mortality across the globe accounting for 1 in 5 deaths. Often these deaths could have been prevented with faster diagnosis. This can be achieved by developing point of care diagnostics which can be carried out in a pharmacy or general practitioners office. One way to develop portable diagnostics such as this is the use of the unique magnetic and optical properties possessed by anisotropic nanoparticles. A possible method to identify sepsis is through the presence of bacterial endotoxins. These can be detected magneto-optically by monitoring the rotational dynamics of anisotropic nanoparticles in an external magnetic field. Nanoparticles of hematite and cerium phosphate were synthesised and evaluated for their use as sensors in magneto-optical diagnosis. The sensitivity of such a probe depends upon a combination of magnetic and plasmonic properties. These are affected by morphology, magnetic susceptibility, and surface plasmon resonance. The hydrothermal growth mechanisms of hematite nanorods were examined and the relationship between directing agent concentration, reaction temperature and time was examined. The effect of 1,2 propanediamine and alkali metal phosphates acting as directing agents were evaluated on hematite, resulting in the formation of tuneable nanorods with aspect ratios between 3-10 and 1-7 respectively. The rotational dynamics of these hematite particles was assessed in glycerol solution and shown to be sensitive to changes in viscosity at different frequencies of rotation. Cerium phosphate nanorods were prepared with a tuneable length from 78 nm to 432 nm and aspect ratios of 3-27. The magnetic susceptibility of these rods was changed through the addition of W, Fe, Ni and Mn ions. The addition of Co ions had only a minimum effect n the magnetic susceptibility. The particles were rotated in external magnetic fields and were shown to be sensitive to changes in the viscosity of a solution based on changes in phase shift. Hematite and cerium phosphate core shell particles were produced. The cores were coated in gold through the seed-mediated method and the morphology of the Au shell was shown to depend heavily upon the number of gold seeds pre-deposited on the ii surface as well as the concentration of the gold growth solution. Using this understanding of the growth mechanism, nanorods with smooth gold surfaces which would produce strong plasmonic signals were synthesised.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Chemistry
Date of First Compliant Deposit: 19 October 2021
Last Modified: 20 Oct 2021 10:00
URI: https://orca.cardiff.ac.uk/id/eprint/144939

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