Nanoparticles (NPs), defined by their size (1-100 nm), are increasingly incorporated into commercial and industrial products due to their high surface area and unique properties. They can be designed for specific applications by manipulating composition, size, shape, and surface functionalization. As NP production and complexity increases, there is a need to rapidly assess relevant parameters to prioritize hazard testing and ultimately predict behavior upon release into the environment. Robust and reproducible characterization of toxicity and physicochemical properties of NPs in solution are needed for reliable model development. In this dissertation, I address significant challenges regarding NP dispersion consistency and characterization of NP properties.
Current practices of NP dispersion preparation that utilize sonication to break apart agglomerates were evaluated for consistently across nanotoxicology studies, and it was determined that they vary greatly in the type of ultrasonicator used, total energy input, and reporting of associated metadata. To facilitate comparison across studies, I demonstrate a method to deliver equivalent energy to NP dispersions using three different ultrasonicator systems with various power settings and dispersion media. This can improve uniformity of NP exposures for better reproducibility of toxicity and characterization data.
The hydrophobicity of NPs, a key property determining environmental fate and bioavailability, was evaluated with two potential methods optimized for use with NPs, hydrophobic interaction chromatography (HIC) and dye adsorption, and compared results to those obtained using the octanol water partitioning method commonly used for organic and dissolved chemicals. Measures of hydrophobicity were determined for both agglomerated and surface functionalized NPs.
Finally I address the need for a quantitative measure of redox behavior of NPs to inform the design of catalytic nanomaterials as well as to model potential toxic interactions. The use of methylene blue (MB) as a colorimetric probe to quantify the catalytic redox behavior of NPs is proposed in Chapter 4. The redox assay was compared to modified abiotic methods to evaluate reactive oxygen species (ROS) production (dichlorofluorescein diacetate, DCFH-DA) and antioxidant capacity (Trolox Equivalent Antioxidant Capacity, TEAC) of NPs to determine relationships and trends based on methodology used and NP properties.
The studies presented in this dissertation provides the basis for improved reproducibility of NP exposures for toxicity data and addresses clear data gaps for determining fate and toxicity descriptors of NPs. This work will contribute to comprehensive NP characterization that is ultimately needed for predictive fate and toxicity models for sustainable nanotechnology development.