Abstract
Nanoparticles are a diverse subset of nanomaterials with a plethora of usesin areas such as therapeutics, diagnostics, optical materials design, cataly-
sis, and metal sensing to name just a few. Many of the most widespread
techniques for nanoparticle characterisation rely on optical methods, explic-
itly requiring knowledge of optical constants such as their refractive index to
draw conclusions. This problem is tackled here through the use of backscat-
tering interferometry (BSI), a technique that is typically used to facilitate
determination of kinetic parameters for protein binding in solution. By using
Rayleigh theory, the scope of BSI was broadened to encompass nanoparticle
suspensions, allowing determination of the ensemble average refractive index
of nanoparticles. This was extended further to functionalised nanoparticles,
facilitating the experimental observation of sub-nanometer surface coverage
on carbon dots, which was confirmed by complementary techniques. As BSI
could measure differences in surface functionalisation, a theory was developed
to describe the refractive index change observed due to binding. Proof of bind-
ing was experimentally verified for N -acetylglucosamine functionalised carbon
dots and wheat germ agglutinin, however, the model and experiment showed
a discrepancy in signal direction. This was due to the parameters required to
fit the model to the system possibly being ill-defined. Through this process,
it was found that the optical theory behind the various modalities of BSI was
conflicting or lacking. To this end, a composite ray tracing model based on
prior literature was created for one system based on glass capillaries, with a
completely new ray tracing model put forward for another system based on
etched semicircular channels. Finally, BSI was further applied to the com-
plex case of extracellular vesicles, lipid-delimited particles excreted from cells.
Their core-shell, and highly variable, morphology makes them difficult sam-
ples, with their refractive index a highly debated topic. When analysed with
BSI, the refractive index determined was found to be overestimated. This
could not be reconciled to nanoparticle tracking analysis (NTA) data after
the addition of smaller liposomal particle invisible to NTA, suggesting that
dilutant-supernatent mismatch due to processing steps was the cause.
| Date of Award | 27 Sept 2022 |
|---|---|
| Original language | English |
| Awarding Institution |
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| Supervisor | Henkjan Gersen (Supervisor), Ian D Lindsay (Supervisor) & Andy M. Chapman (Supervisor) |