Synthesis, Characterization and Toxicity of Nanoparticles for Real World Applications

Nanotechnology involves the synthesis and characterization of materials at the atomic, molecular and macromolecular scales, which results in a controlled manipulation of structures and devices that have at least one dimension that is approximately 1-100 nm in length. Objects at this scale, referred to as “nanoparticles” (NPs), exhibit physical properties differing from that of their bulk or micron scale counterparts. Unique properties such as small size, improved solubility, surface tailorability and large surface-to-volume ratio open up many research and application avenues for the materials scientist, the biologist and the engineer. These novel properties enable cross-disciplinary researchers the opportunity to improve existing products and to design and develop new products. The primary aim of this work was to design studies and formulate methodologies that offer valuable insight into the complexities that are often encountered with understanding environmental/human health impacts of a nanotechnology. This dissertation investigates two scenarios of a nanotechnological application. First, a current nanotechnology-based consumer application was considered. Specifically, the incorporation of titanium dioxide NPs into paints and lacquers was studied. A valuable way to gather information critical to the development of safe nanomaterial-containing consumer products is by employing a product life cycle approach. The primary focus here was to formulate methodologies to produce nano-enabled coatings in-house and assess the impacts/benefits of a nanotechnological application that is currently in the marketplace using a life cycle approach. Material characterization and toxicological evaluations of NPs in their pristine and end-of-life stages were assessed. Next, a potential nanotechnological application was explored. Specifically, the modification of silver NPs for insect vector control was investigated. The research developed here was the first of its kind in engineering a novel silver NP-pesticide conjugate. The efficacy of the newly developed conjugate and the cellular effects in model cell culture systems were evaluated. The findings of this work will provide a useful initial framework in prioritizing future nanotechnological research needs and have a significant impact on material scientists, toxicologists and engineers alike

Characterizing Nanoparticles in Biological Matrices: Tipping Points in Agglomeration State and Cellular Delivery In Vitro.

Understanding the delivered cellular dose of nanoparticles is imperative in nanomedicine and nanosafety, yet is known to be extremely complex because of multiple interactions between nanoparticles, their environment, and the cells. Here, we use 3-D reconstruction of agglomerates preserved by cryogenic snapshot sampling and imaged by electron microscopy to quantify the "bioavailable dose" that is presented at the cell surface and formed by the process of individual nanoparticle sequestration into agglomerates in the exposure media. Critically, using 20 and 40 nm carboxylated polystyrene-latex and 16 and 85 nm silicon dioxide nanoparticles, we show that abrupt, dose-dependent "tipping points" in agglomeration state can arise, subsequently affecting cellular delivery and increasing toxicity. These changes are triggered by shifts in the ratio of the total nanoparticle surface area to biomolecule abundance, with the switch to a highly agglomerated state effectively changing the test article midassay, challenging the dose-response paradigm for nanosafety experiments. By characterizing nanoparticle numbers per agglomerate, we show these tipping points can lead to the formation of extreme agglomeration states whereby 90% of an administered dose is contained and delivered to the cells by just the top 2% of the largest agglomerates. We thus demonstrate precise definition, description, and comparison of the nanoparticle dose formed in different experimental environments and show that this description is critical to understanding cellular delivery and toxicity. We further empirically "stress-test" the commonly used dynamic light scattering approach, establishing its limitations to present an analysis strategy that significantly improves the usefulness of this popular nanoparticle characterization technique

Processing and Characterization of Stable, pH-Sensitive Layer-by-Layer Modified Colloidal Quantum Dots

Quantum Dots (QDs) stabilized with dihydrolipoic acid (DHLA) were used as a template for layer-by-layer (LbL) modification to study the effect on the QD optical properties. We studied several different polyelectrolytes to determine that large quantities of monodisperse DHLA-QDs could only be obtained with the weak polyelectrolyte pair of poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA). The key to this success was the development of a two-step method to split the LbL process into adsorption and centrifugation phases, which require different pH solutions for optimum success. Solution pH is highlighted as an important factor to achieve sufficient QD surface coverage and QD recovery during wash cycles. We optimized the process to scale up synthesis by introducing a solvent precipitation step before ultracentrifugation that, when coupled with the correct pH conditions, results in a mean QD recovery of 86–90% after three wash cycles. We found that adsorption of PAH had a negligible effect on the quantum yield and lifetime but an additional layer of PAA resulted in a substantial decrease in both quantum yield and lifetime that could not be recovered by the addition of more layers. The PAH coating provides a protective coating that extends DHLA-QDs stability, prevents photo-oxidation mediated aggregation, alleviates concerns over batch variability, and results in pH-dependent emission

Characterizing Nanoparticles in Biological Matrices: Tipping Points in Agglomeration State and Cellular Delivery <i>In Vitro</i>

Understanding the delivered cellular dose of nanoparticles is imperative in nanomedicine and nanosafety, yet is known to be extremely complex because of multiple interactions between nanoparticles, their environment, and the cells. Here, we use 3-D reconstruction of agglomerates preserved by cryogenic snapshot sampling and imaged by electron microscopy to quantify the “bioavailable dose” that is presented at the cell surface and formed by the process of individual nanoparticle sequestration into agglomerates in the exposure media. Critically, using 20 and 40 nm carboxylated polystyrene-latex and 16 and 85 nm silicon dioxide nanoparticles, we show that abrupt, dose-dependent “tipping points” in agglomeration state can arise, subsequently affecting cellular delivery and increasing toxicity. These changes are triggered by shifts in the ratio of the total nanoparticle surface area to biomolecule abundance, with the switch to a highly agglomerated state effectively changing the test article midassay, challenging the dose–response paradigm for nanosafety experiments. By characterizing nanoparticle numbers per agglomerate, we show these tipping points can lead to the formation of extreme agglomeration states whereby 90% of an administered dose is contained and delivered to the cells by just the top 2% of the largest agglomerates. We thus demonstrate precise definition, description, and comparison of the nanoparticle dose formed in different experimental environments and show that this description is critical to understanding cellular delivery and toxicity. We further empirically “stress-test” the commonly used dynamic light scattering approach, establishing its limitations to present an analysis strategy that significantly improves the usefulness of this popular nanoparticle characterization technique