Optical approaches to characterising engineered nanoparticles for size and shape in aquatic systems.

Engineered nanoparticles are increasingly being used in a wide range of commercial products including paints, personal care products, textiles, and coatings. As a result, increasingly large quantities of engineered nanoparticles are being released into the environment via a range of different pathways. While there are a wide selection of available tools capable of making measurements of engineered nanoparticles in the environment, these all have their own unique drawbacks. In this thesis, a range of optical techniques for the measurement of engineered nanoparticles are critically assessed. One of these, nanoparticle tracking analysis, was selected for further investigation. This investigation commenced with a conventional nanoparticle fate and behaviour study using an existing commercial solution in order to get a better understanding of the capabilities of currently available systems. One of the primary issues identified was the inability of available commercial equipment to operate effectively at concentrations as low as those predicted for the natural environment. Following this, further development of the nanoparticle tracking analysis paradigm resulted in the twin capabilities of shape determination directly from light-scattering data (which has never been successfully achieved before) and an improvement in low-concentration performance by three orders of magnitude. Finally, a simple nanoparticle aggregation study from the literature was repeated, this time at concentrations leveraging the new, lower-concentration capability. The profoundly different outcome from running this experiment at environmentally relevant conditions – that aggregation proceeded at a sufficiently reduced rate that the nanoparticles were effectively stabilised – demonstrates the importance of this development: at environmentally relevant concentrations nanoparticles behave in very different ways compared to the current standard of lab-based studies at artificially high concentrations. Using this newly-developed low-concentration approach it is possible to cheaply and quickly work at these concentrations.