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Abstract
In this thesis, metrology and physicochemical characterisation of L-cysteine-modified gold nanoparticles (AuNPs) with different techniques are described. Stabilisation of the mixture of dilute gold colloid and L-cysteine (Cys) solution was first investigated. It has been found that a small amount of L-cysteine can induce gold nanoparticle clustering under the current experimental condition, while L-cysteine in large excess can retard the evolution of gold nanoparticle clusters to some extent.
Subsequently, to measure mass fractions of trace element sulfur and main element gold in the functionalised AuNPs, an optimised ICP-DRC-MS (inductively coupled plasma mass spectrometry with dynamic reaction cell technology) method in which pre-digestion of samples with aqua regia is required was in-house validated and the combined uncertainty was estimated according to the Guide to the Expression of Uncertainty in Measurement. Preliminary studies show that the method may be transferred to other ICP-DRC-MS systems by re-optimising cell gas flow.
Thirdly, the potential of using differential centrifugal sedimentation (DCS) for sizing gold nanoparticle clusters induced by L-cysteine·HCl was probed. For comparison the same sample was measured by nanoparticle tracking analysis (NTA) in parallel. The two techniques yielded quite different size distributions and average diameters. An explanation is proposed based on the theory of breakup of colloidal clusters under hydrodynamic conditions. Additional evidence is presented from corresponding UV-visible attenuation spectra, transmission electron microscopy (TEM) images, and validation of measurement accuracy for DCS and NTA.
Next, the slow clustering of gold colloid in the presence of a small concentration of L-cysteine·HCl was followed by NTA, DCS, UV-visible spectroscopy, second order scattering (SOS) spectroscopy and TEM. The diameters of agglomerates measured by NTA are much greater than those measured by DCS, or diameters implied by fitting UV measurements. TEM reveals small linear clusters that become open linked chains of fractal-like structures after several hours of clustering. The variation of morphology shows a great impact on the linear/non-linear optics of AuNPs due to surface plasmon resonance.
Lastly, size and state characterisation of AuNPs in bovine serum albumin (BSA) - supplemented DMEM culture medium using NTA and single particle ICP-MS was studied, mainly in optimisation of operating conditions. The size distributions given by both the two techniques indicate that the presence of BSA can stabilise AuNPs in the complicated medium for a given period of time.